Department of Biotechnology

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Browsing by Subject "Abscisic acid"

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    Characterization of the role of Zea mays burp domain-containing genes in maize drought responses
    (University of the Western Cape, 2016) Phillips, Kyle; Ludidi, Ndiko
    Global 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.
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    Involvement of abscisic acid and H2O2 in antioxidant enzyme activities mediated by nitric oxide synthase-like activity in maize
    (University of the Western Cape, 2018) Hlatshwayo, Siphiwe Gift; Ludidi, Ndomelele Ndiko; Phillips, Kyle
    In recent years, nitric oxide (NO) has emerged as an important endogenous plant signalling molecule that mediates many developmental and physiological processes. NO regulates the activity of antioxidant enzymes in response to droughtinduced stress by controlling the expression of the genes that encode these enzymes. Antioxidant enzymes function in scavenging reactive oxygen species like superoxide ion (O2 -) and hydrogen peroxide (H2O2) that are generated in response to drought-induced stress and other abiotic stresses. Abscisic acid, a phytohormone that acts as a stress-related hormone in plants, also stimulates production of H2O2, thus further triggering the antioxidant enzyme activity in order to scavenge the excess H2O2. Accumulated data indicate that NO interacts with reactive oxygen species, notably hydrogen peroxide and superoxide. This study was aimed at clarifying the role of NO derived from nitric oxide synthase-like (NOS-like) enzymatic activity in scavenging of H2O2 and to establish if this is dependent or independent of ABA signaling. This was achieved by using Nω-Nitro-L-Arginine methyl ester (L-NAME), an inhibitor of NOS to control the amount of NO in maize tissue. The study investigated the effect of L-NAME on the accumulation of superoxide, which is scavenged by superoxide dismutase. Furthermore, the study determined the role of NOS-like activity in ABA-mediated production of H2O2. Lastly, the effect of L-NAME on H2O2 accumulation and antioxidant enzyme activity was also investigated. Application of L-NAME altered the enzymatic activity of superoxide dismutase, ascorbate peroxidase and catalase. These changes in enzymatic activity were coupled with altered levels of O2 - and H2O2 in leaves and roots. Treatments with ABA in combination with L-NAME resulted in reversal of H2O2 content to basal levels. These results suggest that nitric oxide, produced by nitric oxide synthase-like activity, is important in regulation of antioxidant enzyme activity and cross-talks with ABA.
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    Plant biomarkers as early detection tools in stress management in food crops: a review
    (Springer Science and Business Media Deutschland GmbH, 2024) Aina, Omolola; Bakare, Olalekan O.; Fadaka, Adewale O.
    Main conclusion: Plant biomarkers are objective indicators of a plant’s cellular state in response to abiotic and biotic stress factors. They can be explored in crop breeding and engineering to produce stress-tolerant crop species. Abstract: Global food production safely and sustainably remains a top priority to feed the ever-growing human population, expected to reach 10 billion by 2050. However, abiotic and biotic stress factors negatively impact food production systems, causing between 70 and 100% reduction in crop yield. Understanding the plant stress responses is critical for developing novel crops that can adapt better to various adverse environmental conditions. Using plant biomarkers as measurable indicators of a plant’s cellular response to external stimuli could serve as early warning signals to detect stresses before severe damage occurs. Plant biomarkers have received considerable attention in the last decade as pre-stress indicators for various economically important food crops. This review discusses some biomarkers associated with abiotic and biotic stress conditions and highlights their importance in developing stress-resilient crops. In addition, we highlighted some factors influencing the expression of biomarkers in crop plants under stress. The information presented in this review would educate plant researchers, breeders, and agronomists on the significance of plant biomarkers in stress biology research, which is essential for improving plant growth and yield toward sustainable food production.