Browsing by Author "Ludidi, Ndiko"
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Item 3,3'-diindolylmethane improves drought tolerance of Zea mays through enhancing antioxidant activity(University of the Western Cape, 2018) Basson, Gerhard Leroy; Ludidi, Ndiko; Keyster, Marshall; Gokul, ArunMaize is one of the most abundantly produced cereals and contributes to about 40% of the global cereal production. This figure will have to increase in order to feed the ever-growing human population. One of the major environmental constraints that impact maize production is drought. Plants use antioxidant defences to cope with drought stress. Understanding and improving these defence mechanisms will be important to improve overall drought tolerance. A previous study done by Gokul and authors in 2016 showed that 3,3’-diindolylmethane (DIM) improves both seed germination and seedling shoot growth in Brassica napus. Plants belonging to the Brassicaceae family have the metabolic machinery to synthesize glucosinolates such as DIM, which play vital roles in physiological and stress responses. These responses have not been investigated in plants such as maize, which lack the machinery to produce DIM. Therefore, this study investigated the effects of exogenously applied DIM on the physiological and biochemical responses of maize under drought stress. Physiological parameters such as relative water content, chlorophyll content and lipid peroxidation, were determined in order to understand how drought and DIM , as separate or combined treatments, affected the plants. Additionally, proline accumulation was also assessed because free proline plays a role as an osmoprotectant during stress. The accumulation of ROS, namely hydrogen peroxide, was measured using spectrophotometric assays to determine how the above treatments affect ROS accumulation in maize. As a result of changes in the ROS content in due to the treatments, it would only be natural to investigate the changes in antioxidants as well. Given that hydrogen peroxide was the ROS to be measured, we therefore investigated the antioxidant enzymatic activities responsible for hydrogen peroxide scavenging. Therefore, changes in Ascorbate peroxidase (APX) and catalase (CAT) were assessed. An improved drought response was observed in maize plants treated with DIM as these plants had better ability to maintain their water status than when no DIM was applied. This is indicated by water-deprived plants treated with DIM having a higher RWC than water-deprived plant without DIM.Item Assessment of genetic diversity in Tunisian populations of Medicago polymorpha based on SSR markers(Instituto de Investigaciones Agropecuarias, 2021) Haddoudi, Loua; Hdira, Sabrine; Ludidi, NdikoMedicago polymorpha L. is a herbaceous legume that can be a useful pasture crop, especially in Mediterranean climates. This study aimed to analyze the genetic variation in five populations of M. polymorpha collected from different ecogeographic regions in Tunisia using eight SSR markers. The transferability of 112 SSR markers distributed on the eight chromosomes of M. truncatula Gaertn. showed that 50 SSR markers could be amplified in M. polymorpha. Among these 50 SSR markers, eight (8) markers were polymorphous. A high level of polymorphism (126 polymorphic alleles with an average of 5.3 alleles per locus) and a moderate level of genetic diversity were found in all the studied populations, with observed and expected heterozygosities averaging between 0 and 0.69, respectively. Results from analysis of molecular variance (AMOVA) revealed that the most variation was found within populations (76%). Moderate levels of population differentiation (FST = 0.12 to 0.19) accompanied by a high rate of gene flow between populations (Nm = 1.08 to 1.83) were recorded. This molecular differentiation (FST) was not dependent on geographical distances (r = 0.395, p = 0.524), suggesting that studied populations are not geographically isolated. Our results showed that studied populations were clustered into three groups. A first group is formed by the populations of El Kef (TNP7) and Bulla Regia (TNP9), a second group of Enfidha (TNP1) and a third group of Soliman (TNP8) and Mateur (TNP11). Results obtained in our study could be helpful for breeders considering introduction of some lines of this species into M. polymorpha breeding programs.Item Association between antioxidant activities and drought responses of two contrasting sugar beet genotypes(University of the Western Cape, 2017) Majola, Anelisa; Ludidi, NdikoSugar beet (Beta vulgaris L), which belongs to the Amaranthaceae family is a biennial crop widely used as a source of domestic sugar in the European countries, United States, China and Japan. However, in South Africa, sugar cane is the sole source of natural sugar and therefore sugar beet is a potential source of bioethanol since it would not be in direct competition with a food crop for sugar production. Thus, sugar beet can be utilized as a renewable source of energy, reducing the need and use of fossil fuels (such as petrol) that produce greenhouse gases and consequently cause global warming and climate change. Nonetheless, drought stress is one of the major factors limiting the growth of sugar beet, resulting in sugar beet yield reductions worldwide.Item Capacity to control oxidative stress-induced caspase-like activity determines the level of tolerance to salt stress in two contrasting maize genotypes(Springer, 2013) Keyster, Marshall; Klein, Ashwil; Du Plessis, Morné; Jacobs, Alex; Kappo, Abidemi; Kocsy, Gábor; Galiba, Gábor; Ludidi, NdikoThe response of two maize (Zea mays L.) genotypes, named GR (salt-tolerant) and SK (salt-sensitive), to salt stress (150 mM NaCl) was investigated under controlled environmental growth conditions. Genotype SK experienced more oxidative damage than the GR genotype when subjected to salt stress, which corresponded to higher O2- production rate and H2O2 content in the SK genotype than the GR genotype. Induction of caspase-like activity in response to salt stress was stronger in the SK genotype than in the GR genotype. On the other hand, induction of antioxidant enzyme activity to scavenge O2- and H2O2 in response to salt stress was weaker in the SK genotype than in the GR genotype. Consequently, the higher level of oxidative damage in the SK genotype in response to salt stress was manifested as more extensive cell death and biomass reduction in the SK genotype than it was in the GR genotype. Our results suggest that a direct relationship exists between salt stress-induced oxidative damage and cell death-inducing caspase-like activity, with tolerance to the salt stress being controlled by the efficiency of the plantantioxidant enzymes in limiting salt stress-induced oxidative damage and thus limiting cell death-inducing caspase-like activity.Item Characterisation of a novel soybean candidate glutathione peroxidase/thioredoxin-dependent peroxidase in soybean exposed to osmotic/drought stress(University of the Western Cape, 2012) Phillips, Kyle; Ludidi, Ndiko; Keyster, MarshallDrought stress is a major contributor to reduced soybean crop yield and quality, this can however be mitigated by the plant’s antioxidant defence mechanisms. One group of antioxidant enzymes that are active in these defence mechanisms are glutathione peroxidases (GPXs). GPXs are antioxidant proteins which are able to reduce H2O2, a toxic reactive oxygen species which accumulates under stress conditions. This study aims at isolating the protein encoded by Glyma01g42840 and determining if it has Phospholipid hydroperoxidase glutathione peroxidase (PHGPX) and/or Thioredoxin dependent peroxidase (TRX-PX) activity as well as assaying the effect of Drought stress on the expression of this putative GPX . This will be accomplished by molecular cloning, sequencing as well as the expression of the isolated protein to assay it enzymatic activity. It was found that the enzyme encoded by Glyma01g42840 is able to use glutathione and thioredoxin as electron donors for the detoxification peroxides, however enzymatic activity is more efficient when using glutathione as an electron donor. In conclusion it was found that glyma01g42840 encodes an enzyme which is able to utilise more than one electron donor and as glutathione produces the greatest amount of enzymatic activity it can be said that glyma01g42840 encodes a GPX.Item Characterization of the role of a cycloartenol synthase gene (ZMCAS494) in Zea mays responses to drought stress(University of the Western Cape, 2016) Kolo, Zintle; Ludidi, NdikoPlant Sterols are an important part of the membrane and their role is to control cell membrane fluidity and permeability. Several studies have indicated that plants that are mutant for genes that play a role in the sterol biosynthetic pathway show increased sensitivity to drought stress. Even though the exact molecular mechanism is unknown, such studies suggest that sterols do play a role in plant drought stress responses. To elucidate the mechanism through which sterols regulate Zea mays responses to water deficit, the effect of drought stress on phytosterol content and on expression of a cycloartenol synthase-like gene (ZMCAS494) was investigated. The effect of inhibition of sterol biosynthesis, using terbinafine, on maize reactive oxygen species production and on activity of the superoxide dismutase, ascorbate peroxidase and glutathione peroxidase enzymes was also investigated. Quantitative polymerase chain reaction (qPCR) analysis of the expression of ZMCAS494 indicated a change in gene expression in response to drought. Inhibition of phytosterols synthesis resulted in altered ascorbate peroxidase activity, glutathione peroxidase activity as well as superoxide dismutase activity in roots and leaves of maize. The ROS content of maize leaves was increased by inhibition of phytosterols synthesis. Data obtained in this study suggests a relationship between sterol biosynthesis, sterol content and reactive oxygen species signalling.Item Characterization of the role of single domain soybean cystatins in regulating drought responses in soybean(University of the Western Cape, 2015) Karriem, Zaheer; Ludidi, NdikoThis study investigated the effects that drought stress imposed on the growth and development of soybean plants. Soybeans were initially observed at the whole-plant level in order to identify the physical changes that had taken place in response to drought. Further investigation of the effects of drought stress on Soybean plants were quantified at the molecular level. Physical changes of soybeans in response to drought stress were typified by the change in leaf morphology and pigmentation. At the molecular level, it was observed that drought stress resulted in the accumulation of hydrogen peroxide in soybean leaves, which was met by elevated levels of lipid peroxidation. The effects of drought on the modulation of (and interplay between cystatins) cysteine protease (caspase-like) activity and programmed cell death (PCD) were also investigated. Total caspase-like activity and cell death were enhanced in response to water deficit despite the up-regulation in gene expression of the cystatin Glyma14g04250. The cystatin Glyma18g12240 was not expressed in soybean leaves, whilst the gene expression of the cystatin Glyma20g08800 remained unchanged in response to drought. This study was aimed at the characterization of two single domain soybean cystatins, namely, Glyma14g04250 and Glyma20g08800 which could potentially be overexpressed in transgenic soybean plants in an attempt to alleviate the effects of drought stress.Item Characterization of the role of Zea mays burp domain-containing genes in maize drought responses(University of the Western Cape, 2016) Phillips, Kyle; Ludidi, NdikoGlobal climate change has resulted in altered rainfall patterns, causing annual losses in maize crop yield due to water deficit stress. Therefore, it is important to produce maize cultivars which are more drought-tolerant. This not an easily accomplished task as plants have a plethora of physical and biochemical adaptation methods. One such mechanism is the drought-induced expression of enzymatic and non-enzymatic proteins which assist plants to resist the effects of water deficit stress. The RD22-like protein subfamily is expressed in response to water deficit stress. Members of the RD22-like subfamily include AtRD22, GmRd22 and BnBDC1 which have been identified in Arabidopsis thaliana, Glycine max and Brassica napus respectively. This study aims at characterising two putative maize RD22-like proteins (designated ZmRd22A and ZmRd22B) by identifying sequence/domain features shared with characterised RD22-like proteins. Semi-quantitative and quantitative PCR techniques were used to examine the spatial and temporal expression patterns of the two putative maize Rd22-like proteins in response to, water deficit stress and exogenously applied abscisic acid in the roots and 2nd youngest leaves of maize seedlings. Using an in silico approach, sequence homology of the two putative maize Rd22- like proteins with AtRD22, GmRD22 and BnBDC1 has been analysed. Online bioinformatic tools were used to compare the characteristics of these Rd22-like proteins with those of the two maize proteins. It was shown that the putative maize RD22-like proteins share domain organisation with the characterised proteins, these common features include a N-terminal hydrophobic signal peptide, followed by a region with a conserved amino acid sequence, a region containing several TxV (x is any amino acid) repeat units and a C-terminal BURP domain-containing the conserved X₅-CH-X₁₀-CH-X₂₃-₂₇-CH-X₂₃-₂₆-CH-X₈-W motif. The putative maize Rd22-like protein appears to be localized in the apoplast, similarly to AtRD22, GmRD22 and BnBDC1. Analysis of the gene's promotor regions reveals cis-acting elements suggestive of induction of gene expression by water deficit stress and abscisic acid (ABA). Semi-quantitative and quantitative real time PCR analysis of the putative maize RD22-like gene revealed that the genes are not expressed in the roots. Exposure to water deficit stress resulted in an increase of ZmRD22A transcript accumulation in the 2nd youngest leaves of maize seedlings. ZmRD22A was shown to be non-responsive to exogenous ABA application. ZmRD22B was highly responsive to exogenous ABA application and responded to water deficit stress to a lesser degree. Transcript accumulation studies in three regions of the 2nd youngest leaves in response to water deficit stress showed that ZmRd22A transcripts accumulate mainly at the base and tips of the leaves. A restricted increase in ZmRD22A transcript accumulation in the middle of the leaves was observed. ZmRD22B showed a similar, but weaker transcript accumulation pattern in response to water deficit stress. However, ZmRD22B showed increased transcript accumulation in the middle region of the leaves. In response to exogenous ABA application, ZmRd22B exhibited high transcript accumulation at the base of the 2nd youngest leaves, with the middle showing higher transcript accumulation than the tip of the leaves. It was concluded that ZmRD22A and ZmRD22B share the domain organisation of characterised RD22-like proteins as well as being responsive to water deficit stress, although only ZmRD22B was shown to be responsive to exogenous ABA application.Item Common bean as a potential crop for future food security: an overview of past, current and future contributions in genomics, transcriptomics, transgenics and proteomics(Taylor & Francis Open Access, 2021) Nadeem, Muhammad Azhar; Yeken, Mehmet Zahit; Ludidi, NdikoCommon bean is an important legume crop having high quality protein, micronutrients, vitamins and antioxidants, which makes it a “grain of hope” for poor communities. Hence, a good number of breeding activities have been performed on the improvement of various key traits for years. However, recent advancements in molecular markers, sequencing technologies and the completion of the common bean genome sequence have opened numerous opportunities for fine mapping and gene characterization. The availability of these tools together with investigations of quantitative trait loci (QTL) and candidate genes for key traits such as morpho-agronomic, iron and zinc contents, cooking and quality traits, antioxidant activity, biotic and abiotic stresses pave the way to the development of new strategies for common bean genetic improvement. As a food source, it can contribute to the reduction of food scarcity worldwide in the coming years. Therefore, it is very important to take synergic efforts to integrate common bean genetic and genomic resources in breeding activities to ensure food security and contribute significantly to improved livelihoods in developing countries. Moreover, Kompetitive allele specific PCR (KASP) and CRISPR-Cas9 should be used to develop climate resilience common bean varieties. Here, we provide an overview of the evolution of common bean research by highlighting the past and recent advances in genomics, transgenics, transcriptomics and proteomics and also critically discuss the future prospects for further genetic improvement and better expansion of this crop.Item Comparative analysis of responses to field salinity stress in contrasting soybean accessions highlights NaCl exclusion in leaves as a key mechanism for salinity stress tolerance.(JOURNAL OF OASIS AGRICULTURE AND SUSTAINABLE DEVELOPMENT, 2021) Akanbi, Musa; Egbichi, Ifeanyi; Ludidi, NdikoSalinity is one of the main limitations to legume productivity in many regions of the world and it is estimated that 50% of all arable land will become affected by salinity by 2050. The impact of field salinity on soybean performance was assessed using two soybean accessions (KCW and HMC) cultivated in salt- treated soil and non-salt treated soil. We used a 30 cm deep field system layered with 0.4 kg/m2 NaCl for the salt-treated experiment while the control field received no salt treatment. The results show that salinity reduces soybean growth and yield as evident from the reduction in the plant shoot length, stem diameter, number of branches, number of pods and seed weight. However, the reduction in these growth parameters was less pronounced in the HMC accession than the KCW accession. Furthermore, Na+ content in leaves of the HMC accession was lower than that of the KCW accession. This proved that salinity has a damaging effect on soybean growth and yield and the relative tolerance of the HMC accession is attributed in part to its ability to restrict Na+ transport to the leaves. While the study emphasizes salt exclusion as a potentially useful mechanism for salinity tolerance in soybean, it provides evidence that the HMC accession is a good genetic resource for breeding soybean varieties with improved salinity stress tolerance.Item Comparative molecular, physiological and proteomic analyses of maize and sorghum subjected to water deficit stress(University of the Western Cape, 2019) Ali, Ali Elnaeim Elbasheir; Ludidi, Ndiko; Husselmann, Lizex; Tabb, DavidDrought is a major abiotic stress which causes not only differences between the mean yield and the potential yield but also yield variation from year to year. Although selection for genotypes with improved productivity under drought environments has been a central goal of numerous plant breeding programs, the molecular basis for plant tolerance towards drought stress is still poorly understood. Exposure of plants to this abiotic stress is known to trigger excessive formation of reactive oxygen species (ROS), which induce cell death and reduce growth. Part of the mechanism of plant responses to drought involves alterations in the expression of antioxidant enzymes and biosynthesis of different compatible solutes such as proline. Sorghum is regarded as generally more drought tolerant than maize, and it is a potential key model system for investigating the physiological and molecular mechanisms conferring drought tolerance. Comparative studies in crop plants to decipher differences in drought tolerance are essential for crop improvement to sustain a higher level of production, which in turn will improve food security, under severe drought conditions resulting from climate change. On this basis, the aim of this study is to determine molecular differences between Zea mays and Sorghum bicolor in response to drought stress in an attempt to identify novel biomarkers for drought tolerance. The physiological and molecular responses of maize and sorghum were studied for changes in growth, chlorophyll content, relative water content, ROS content, lipid peroxidation level, proline content, and antioxidant enzyme activity. Spectral Count Label-free Quantitation analysis was conducted to reveal the changes in protein profiles under drought in attempt to identify drought-responsive molecular mechanisms in the leaves of the two plant species. In this study, water deficit triggered mechanisms that resulted in overproduction of ROS in both Zea mays and Sorghum bicolor. However, Sorghum bicolor showed less oxidative damage under water stress compared to Zea mays. Drought-induced proline accumulation in the roots of Sorghum bicolor was associated with enhanced water retention. Significant changes were identified in the antioxidant enzyme activity between the two plant species in response to drought conditions. Proteomics results showed differing patterns for drought-responsive proteins in the two species. Together with the physiological, biochemical and proteomic profiling results between Zea mays and Sorghum bicolor, potential proteins and/or metabolic pathways underlying drought tolerance were identified. The findings obtained through this study provide insight towards understanding the molecular basis of crop drought tolerance.Item Deciphering the determinants of molecular physiological responses to drought and heat stress in sorghum lines contrasting in stress tolerance via a proteomics approach(University of the Western Cape, 2022) Ali, Ali Elnaeim Elbasheir; Ludidi, NdikoSorghum is an important crop in Sub-Saharan Africa and South Asia. The predicted rise in global temperatures will increase the probability of exposing sorghum to heat waves in combination with drought. Thus, production and availability of sorghum and its products will be negatively affected. Although much progress has been made in identifying molecular processes involved in some crop responses to drought or heat stress, knowledge on such responses in sorghum is limited and in fact does not exist for combined drought and heat stress in sorghum lines that respond differently to these stresses.Item Diversity of Frankia associated with Morella species of the Cape floristic region of Southern Africa(University of the Western Cape, 2016) Wilcox, Dale Adrian; Cowan, A; Ludidi, NdikoFrankia is one of two partners in the globally distributed N2-fixing actinorhizal symbiosis between this filamentous soil-dwelling actinomycete and almost 300 species of host plants from eight diverse angiosperm families. The actinorhizal symbiosis is a major contributor to nitrogen reservoirs in terrestrial ecosystems, and allows actinorhizal plants to perform the role of pioneers in newly formed and nitrogen-poor soils. Frankia are differentiated into four main host-infection groups (1: Alnus/Comptonia/Myrica-infective, 2: Rosaceae/Datisca/Coriaria-infective, 3: Elaeagnaceae/Gymnostoma-infective and 4: Casuarina-infective), and there is a large degree of phylogenetic clustering within these HIGs. Of these host lineages, species from the genus Morella, from the family Myricaceae, are notable as they have the ability to establish effective partnerships with Frankia from more than one host-infection group. Africa houses 16 of the world’s 33 currently accepted Morella species, and Morella is the continents only genus containing endemic actinorhizal species. Despite this, the diversity of Frankia in symbiosis with African Morella has never been explored. To address this lack of knowledge I investigated Frankia in root nodules of six Morella species from the Cape flora of Southern Africa, as well as in rhizosphere soils from selected hosts. Partial nif H gene fragments recovered from 202 root nodules yielded 26 unique sequences, which phylogenetic analysis assigned to Frankia Cluster I (the Alnus host infection group) and Frankia Cluster III (the Elaeagnus host infection group)1. Nineteen nif H sequences were assigned to three sub-clusters within Frankia Cluster III (CC-3, CC-4 and CC-5), and the remaining seven sequences to two sub-clusters within Cluster I (CC-1 and CC-2), one of which (CC-1) is novel to the current study. Identical sequences were recovered from nodules collected at geographically distant locations, suggesting a cosmopolitan distribution within the region for some subgroups from both clusters, but more localized distribution (or tighter host-specificity) for others. Soil pH correlated with strain presence in nodules, with Cluster I sequences being associated with hosts growing in acidic soils exclusively. Furthermore, three Morella species from the Cape flora of southern Africa are promiscuous in their natural habitats, with host infection group influenced by habitat edaphic conditions. In order to explore the correlation between soil characteristics and Frankia presence in nodules, nif H soil libraries were created from selected host rhizospheres. While Cluster III sequences from these libraries corresponded closely to sequences found in nodules from the same sites, the dominant Cape Cluster I group (CC-1) was absent from all six libraries, even when present in nodules recovered from the same soils. Whether this was due to low abundance of -but strong selection for- these strains by hosts under particular conditions, or due to the absence in soil of hyphal forms of these strains could not be determined. Cluster III strains are known to be better able to persist saprophytically than their relatives from other host-infection groups. A second group of Cluster I strains, detected at only one sampling site, was present in that site's corresponding soil library. An Alnus-infective subgroup, cluster AI, which has been detected in soils collected on five continents, was also detected in the of the Cape soil libraries but never in nodules, raising questions as to this group’s ability to persist in soil in the absence of known suitable hosts. Ten Frankia strains representing all three of the numerically dominant subgroups (CC-1, CC-3 and CC-4, found in 186 of 202 root nodules) were isolated from four Morella species. These isolates represent six of the most abundant unique nodular nif H sequences found in the field survey, and display morphological and cultural characteristics typical of Frankia. Phylogenetic analysis confirmed their identity as Frankia, and multilocus analysis revealed that the isolates belong to three genospecies. Two of these genospecies fall into existing groups within the Elaeagnus-infective Cluster III, while the remaining genospecies is a novel addition to the otherwise well-described Alnus-infective Cluster I. Whole genome sequencing of a representative from each of the Cape genospecies allowed for basic annotation and genome descriptions, which agreed in each case with what has been previously found for strains from the Elaeagnus and Alnus host-infection groups, respectively. Similarly, the organization of nitrogenase gene clusters in each of the sequenced strains mirrors that found in other strains from their respective host-infection groups, indicating that this gene cluster is highly conserved in different Frankia lineages. For the first time the diversity of Frankia nodulating endemic African Morella, and present in root-associated soils of these species, has been explored. This is also the first study to report isolation and description of Frankia strains from actinorhizal plants endemic to Africa.Item Drought and exogenous abscisic acid alter hydrogen peroxide accumulation and diferentially regulate the expression of two maize RD22-like genes(Nature Research, 2017) Phillips, Kyle; Ludidi, NdikoIncreased biosynthesis of abscisic acid (ABA) occurs in plants in response to water defcit, which is mediated by changes in the levels of reactive oxygen species such as H2O2. Water defcit and ABA induce expression of some RD22-like proteins. This study aimed to evaluate the efect of water defcit and exogenous ABA (50µM ABA applied every 24hours for a total of 72hours) on H2O2 content in Zea mays (maize) and to characterise genes encoding two putative maize RD22-like proteins (designated ZmRD22A and ZmRD22B). The expression profles of the two putative maize RD22-like genes in response to water defcit and treatment with ABA were examined in leaves. In silico analyses showed that the maize RD22-like proteins share domain organisation with previously characterized RD22-like proteins. Both water defcit and exogenous ABA resulted in increased H2O2 content in leaves but the increase was more pronounced in response to water defcit than to exogenous ABA. Lignin content was not afected by exogenous ABA, whereas it was decreased by water defcit. Expression of both RD22- like genes was up-regulated by drought but the ZmRD22A gene was not infuenced by exogenous ABA, whereas ZmRD22B was highly responsive to exogenous ABA.Item Effects of nitric oxide and hydrogen peroxide on antioxidant enzyme activity in zea mays subjected to drought(University of Western Cape, 2021) Kopana, Nolusindiso; Ludidi, NdikoAgricultural practices are significantly affected by drought. Drought is one of the most important plant stresses, causing several physiological, morphological, biochemical, and molecular changes in plants. Drought stress is of great challenge for crop growth, development and yield. Zea mays (maize) is one of the important crops worldwide due to the nutritional profile and other uses such as human consumption, manufacturing and animal feed. Under unfavorable conditions, plants produce high amounts of reactive oxygen species (ROS). Excessive formation of ROS is harmful for plant survival and can induce cell death. Defense mechanisms activated in response to drought in plants include antioxidant enzyme activity and proline accumulation. There is evidence of the use of nitric oxide (NO) donors and hydrogen peroxide (H2O2) at low concentrations to enhance the activity of antioxidant enzymes in stressed plants. Hence, the aim of the study is to examine the role of NO and H2O2 in regulation of antioxidant enzyme activity in maize subjected to water deficit.Item The effects of nitric oxide on soybean superoxide dismutase activity during osmotic stress(University of the Western Cape, 2012) Jack, Babalwa Unice; Ludidi, NdikoNitric oxide (NO) is a signaling molecule involved in mediating plant responses to various biotic and abiotic stresses. Major abiotic stresses (drought, salinity, cold) induce common cellular responses, causing osmotic stress in plants. This results in oxidative stress due to increased production of reactive oxygen species (ROS). The increased ROS levels simultaneously induce the antioxidative system (including antioxidant enzymes such as superoxide dismutase) that regulates ROS toxicity and enhance stress tolerance in plants. It is suggested that the scavenging of ROS by antioxidant enzymes can be controlled by NO. The aim of this study was to evaluate the role of exogenously applied NO on soybean (Glycine max L. Merr.) during osmotic stress, with the purpose of determining the effects of NO on the superoxide dismutase (SOD) activity in response to osmotic stress. This study also aimed at identifying and characterising SOD isoforms induced in soybean in response to osmotic stress and exogenous NO. To achieve these aims, soybean plants were treated with sorbitol (to induce osmotic stress), an NO donor [2,2'-(hydroxynitrosohydrazono)bis-ethanimine, DETA/NO] and its respective control (Diethylenetriamine, DETA). The results showed that exogenous NO alleviated osmotic stress-induced damage by reducing the superoxide radical content, lipid peroxidation levels and also maintaining cell viability in soybean leaves, nodules and roots. Only two SOD isoforms i.e. manganese SOD (MnSOD) and copper/zinc SOD (CuZnSOD) were identified and characterised in soybean leaves and roots, iron SOD (FeSOD) was not induced. The isoforms identified exhibited low SOD activity in response to osmotic stress, with the exception of a few isoforms that had increased activity. The SOD activity was regulated by exogenously applied NO. The enzymatic activity of SOD isoforms was up-regulated by exogenous NO, except for a few SOD isoforms that were not responsive to NO. The results also showed that the increased SOD activity was associated with reduced lipid peroxidation levels. The results obtained from this study suggest that exogenous NO improves osmotic stress tolerance in soybean by regulating and increasing the SOD activity of only specific isoforms. The increased SOD activity maintains the redox homeostasis balance by detoxifying and controlling the superoxide radical levels, subsequently reducing lipid peroxidation and maintaining cell viability.Item Engineering Parageobacillus thermoglucosidans as a robust platform for bioethanol production(University of the Western Cape, 2018) van Zyl, Leonardo Joaquim; Trindade, Marla; Cowan, Donald; Ludidi, NdikoParageobacillus thermoglucosidans is a promising “platform” organism to use in the production ofa range of useful metabolites with demonstrated ability to produce ethanol, isobutanol and polylactic acid for bio-degradable plastics. Extensive work has been done in engineering the organism for enhanced ethanol production. However, an often used and highly effective alternative pathway (pyruvate decarboxylase mediated) for ethanol production has not yet been demonstrated in P. thermoglucosidans. We first characterize two novel bacterial pyruvate decarboxylase enzymes (PDC’s) then attempt to express the more thermostable of these enzymes from Gluconobacter oxydans in P. thermoglucosidans to improve ethanol yields. Initial expression was unsuccessful. Analysis of the codon usage pattern for the gene revealed that the codon usage was suboptimal in the heterologous host P. thermoglucosidans. After codon harmonization, we could demonstrate successful expression of the enzyme at 45°C, however not at the bacterium’s optimum growth temperature of 60°C. This was concomitant with enhanced ethanol production close to the theoretical yield possible (0.5g/l).Item Evaluation of agronomic and drought response traits in two cultivars of soybean for cultivation in the Transkei region of the Eastern Cape(University of Western Cape, 2020) Akanbi, Musa Oyebowale; Ludidi, NdikoDrought is a major stress that affects the productivity of plants across the globe. The consequences of drought are posed to continue reducing agricultural productivity as world climate changes. This makes it imperative to improve tolerance of staple food crops to drought. Under drought stress, reactive oxygen species (ROS) accumulate, which may lead to oxidative damage of DNA, proteins and lipids.Item Evaluation of the morpho-physiological, biochemical and molecular responses of contrasting medicago truncatula lines under water deficit stress(MPDI, 2021) Haddoudi, Loua; Hdira, Sabrine; Ludidi, NdikoMedicago truncatula is a forage crop of choice for farmers, and it is a model species for molecular research. The growth and development and subsequent yields are limited by water availability mainly in arid and semi-arid regions. Our study aims to evaluate the morpho-physiological, biochemical and molecular responses to water deficit stress in four lines (TN6.18, JA17, TN1.11 and A10) of M. truncatula. The results showed that the treatment factor explained the majority of the variation for the measured traits. It appeared that the line A10 was the most sensitive and therefore adversely affected by water deficit stress, which reduced its growth and yield parameters, whereas the tolerant line TN6.18 exhibited the highest root biomass production, a significantly higher increase in its total protein and soluble sugar contents, and lower levels of lipid peroxidation with greater cell membrane integrity. The expression analysis of the DREB1B gene using RT-qPCR revealed a tissue-differential expression in the four lines under osmotic stress, with a higher induction rate in roots of TN6.18 and JA17 than in A10 roots, suggesting a key role for DREB1B in water deficit tolerance in M. truncatula.Item Genetic variation in responses to salt stress in Tunisian populations of Medicago ciliaris(MDPI, 2022) Aloui, Meriem; Mahjoub, Asma; Ludidi, NdikoSoil salinity is one of the most serious environmental factors affecting crop productivity around the world. We used a morpho-physiological approach to investigate the salt responses of four Tunisian natural populations of Medicago ciliaris. Forty-six lines of M. ciliaris were grown under a control treatment and 100 mM NaCl. We measured 11 quantitative traits of shoot and root growth during harvest. An analysis of variance showed that the variations in salt response can be explained by the effects of the population, line, treatment, and interactions between the population and treatment and the line and treatment. Most of the measured traits showed significant differences between the studied populations under the control treatment and salt stress.