Browsing by Author "Ludidi, Ndomelele Ndiko"

Now showing 1 - 6 of 6
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    Characterization of two Arabidopsis thaliana genes with roles in plant homeostasis
    (University of the Western Cape, 2004) Ludidi, Ndomelele Ndiko; Gehring, C. A.
    Plants are continuously exposed to varying conditions in their environment, to which they have to adapt by manipulating various cellular processes. Environmental (abiotic) and pathogen (biotic) stress are challenges against which plants have to defend themselves. Many plant responses to stress stimuli are a result of cellular processes that can be divided into three sequential steps; namely signal perception, signal transduction m1d execution of a response. Stress signal perception is, in most of these cases, facilitated by cell surface or intracellular receptors that act to recognize molecules presented to the cell. In several cases, hormones are synthesized in response to stress signals and in turn these hormones are perceived by cellular receptors that trigger signal transduction cascades. Propagation of signal transduction cascades is a complex process that results from activation of various signaling molecules within the cell. Second messengers like calcium (Ca2+) and guanosine 3', 5'-cyclic monophosphate (cGMP) play a vital role in mediating many signal transduction processes. The result of these signal transduction cascades is, in most instances, expression of genes that contribute to the plant's ability to cope with the challenges presented to it. Plant natriuretic peptides (PNPs) are novel plant hormones that regulate water and salt homeostasis via cGMP-dependent signaling pathways that involve deployment of Ca2+. The aim of this study is to partially characterize a PNP and a guanylyl cyclase, both from Arabidopsis thaliana. Guanylyl cyclases synthesize cGMP from the hydrolysis of guanosine 5' -triphosphate (GTP) in the cell. The study also aims to investigate the effect of drought and salinity on cGMP levels in plants, using sorbitol to mimic the osmolarity/dehydration effect of drought and NaCl as a source of salinity stress and thus link NaCl and sorbitol responses to both AtPNP-A and cGMP up-regulation.
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    Influence of a selected endophyte consortium on salinity responses in Medicago sativa
    (University of Western Cape, 2022) Keyster, Eden; Ludidi, Ndomelele Ndiko
    Salinity is one of the major limiting factors to crop production, which consequently contributes to the risk of reduced food security. Among other factors, food security depends on availability of sufficient and nutritious food for humans. Livestock such as cattle and sheep are fed with various plant-based feeds; with Medicago sativa (commonly known as alfalfa or lucerne) being a very important forage/feed crop, so much that it is regarded as the queen of forage crops. However, alfalfa is severely affected by high soil salinity and thus its growth and yield are drastically reduced in soils with high NaCl content. Among the various alfalfa genotypes/varieties examined in this study, Agsalfa was identified as salt tolerant because it performed better under salt treatment compared to Magna601.
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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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    Modulation of soybean and maize antioxidant activities by caffeic acid and nitric oxide under salt stress
    (University of Western Cape, 2012) Klein, Ashwil Johan; Ludidi, Ndomelele Ndiko; Keyster, Marshall
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    Modulation of soybean and maize antioxidant activities by Caffeic acid and nitric oxide under salt stress
    (University of the Western Cape, 2012) Klein, Ashwil Johan; Ludidi, Ndomelele Ndiko; Keyster, Marshall
    This study explores the roles of exogenously applied nitric oxide, exogenously applied caffeic acid and salt stress on the ontioxidant system in cereal (exemplified by maize) and legume (using soybean as an example) plants together with their influence on membrane integrity and cell death. This study investigates changes in H₂O₂ content, root lipid peroxidation, root cell death and antioxidant enzymatic activity in maize roots in response to exogenously applied nitric oxide (NO) and salt stress. This part of the study is based on the partially understood interaction between NO and reactive oxygen species (ROS) such as H₂O₂ and the role of antioxidant enzymes in plant salt stress responses. The results show that application of salt (NaCl) results in elevated levels of H₂O₂ and an increase in lipid peroxidation, consequently leading to increased cell death. The study also shows that by regulating the production and detoxification of ROS through modulation of antioxidant enzymatic activities, NO plays a pivotal role in maize responses to salt stress. The study argues for NO as a regulator of redox homeostasis that prevents excessive ROS accumulation during exposure of maize to salinity stress that would otherwise be deleterious to maize. This study extends the role of exogenously applied NO to improve salt stress tolerance in cereals crops (maize) further to its role in enhancing salt stress tolerance in legumes. The effect of long-term exposure of soybean to NO and salt stress on root nodule antioxidant activity was investigated to demonstrate the role of NO in salt stress tolerance. The results show that ROS scavenging antioxidative enzymes like SOD, GPX and GR are differentially regulated in response to exogenous application of NO and salt stress. It remains to be determined if the NO induced changes in antioxidant enzyme activity under salt stress are sufficient to efficiently reduce ROS accumulation in soybean root nodules to levels close to those of unstressed soybean root nodules. Furthermore, this study investigates the effect of long-term exposure of soybean to exogenous caffeic acid (CA) and salt stress, on the basis of the established role of CA as an antioxidant and the involvement of antioxidant enzymes in plant salt stress responses. The effect of CA on soybean nodule number, biomass (determined on the basis of nodule dry weight, root dry weight and shoot dry weight), nodule NO content, and nodule cyclic guanosine monophosphate (cGMP) content in response to salt stress was investigated. Additionally, CA-induced changes in nodule ROS content, cell viability, lipid peroxidation and antioxidant enzyme activity as well as some genes that encode antioxidant enzymes were investigated in the presence or absence of salt stress. The study shows that long-term exposure of soybean to salt stress results in reduced biomass associated with accumulation of ROS, elevated levels of lipid peroxidation and elevated levels of cell death. However, exogenously applied CA reversed the negative effects of salt stress on soybean biomass, lipid peroxidation and cell death. CA reduced the salt stress-induced accumulation of ROS by mediating changes in root nodule antioxidant enzyme activity and gene expression. These CA-responsive antioxidant enzymes were found to be superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and glutathione reductase (GR), which contributed to the scavenging of ROS in soybean nodules under salt stress. The work reported in Chapter 2 has been published in a peer-reviewed journal [Keyster M, Klein A, Ludidi N (2012) Caspase-like enzymatic activity and the ascorbate-glutathione cycle participate in salt stress tolerance of maize conferred by exogenously applied nitric oxide. Plant Signaling and Behavior 7: 349-360]. My contribution to the published paper was all the work that is presented in Chapter 2, whereas the rest of the work in the paper (which is not included in Chapter 2) was contributed by Dr Marshall Keyster.
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    Modulation of soybean and maize antioxidant activities by Caffeic acid and nitric oxide under salt stress
    (University of the Western Cape, 2012) Klein, Ashwil Johan; Ludidi, Ndomelele Ndiko; Keyster, Marshall
    This study explores the roles of exogenously applied nitric oxide, exogenously applied caffeic acid and salt stress on the antioxidant system in cereal (exemplified by maize) and legume (using soybean as an example) plants together with their influence on membrane integrity and cell death.This study investigates changes in H2O2 content, root lipid peroxidation, root cell death and antioxidant enzymatic activity in maize roots in response to exogenously applied nitric oxide (NO) and salt stress. This part of the study is based on the partially understood interaction between NO and reactive oxygen species (ROS) such as H2O2 and the role of antioxidant enzymes in plant salt stress responses. The results show that application of salt (NaCl) results in elevated levels of H2O2 and an increase in lipid peroxidation, consequently leading to increased cell death. The study also shows that by regulating the production and detoxification of ROS through modulation of antioxidant enzymatic activities, NO plays a pivotal role in maize responses to salt stress. The study argues for NO as a regulator of redox homeostasis that prevents excessive ROS accumulation during exposure of maize to salinity stress that would otherwise be deleterious to maize. This study extends the role of exogenously applied NO to improve salt stress tolerance in cereals crops (maize) further to its role in enhancing salt stress tolerance in legumes. The effect of long-term exposure of soybean to NO and salt stress on root nodule antioxidant activity was investigated to demonstrate the role of NO in salt stress tolerance. The results show that ROS scavenging antioxidative enzymes like SOD, GPX and GR are differentially regulated in response to exogenous application of NO and salt stress. It remains to be determined if the NOinduced changes in antioxidant enzyme activity under salt stress are sufficient to efficiently reduce ROS accumulation in soybean root nodules to levels close to those of unstressed soybean root nodules. Furthermore, this study investigates the effect of long-term exposure of soybean to exogenous caffeic acid (CA) and salt stress, on the basis of the established role of CA as an antioxidant and the involvement of antioxidant enzymes in plant salt stress responses. The effect of CA on soybean nodule number, biomass (determined on the basis of nodule dry weight, root dry weight and shoot dry weight), nodule NO content, and nodule cyclic guanosine monophosphate (cGMP) content in response to salt stress was investigated. Additionally, CA-induced changes in nodule ROS content, cell viability, lipid peroxidation and antioxidant enzyme activity as well as some genes that encode antioxidant enzymes were investigated in the presence or absence of salt stress. The study shows that long-term exposure of soybean to salt stress results in reduced biomass associated with accumulation of ROS, elevated levels of lipid peroxidation and elevated levels of cell death. However, exogenously applied CA reversed the negative effects of salt stress on soybean biomass, lipid peroxidation and cell death. CA reduced the salt stress-induced accumulation of ROS by mediating changes in root nodule antioxidant enzyme activity and gene expression. These CA-responsive antioxidant enzymes were found to be superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione peroxidase (GPX), and glutathione reductase (GR), which contributed to the scavenging of ROS in soybean nodules under salt stress. The work reported in Chapter 2 has been published in a peer-reviewed journal [Keyster M, Klein A, Ludidi N (2012) Caspase-like enzymatic activity and the ascorbate-glutathione cycle participate in salt stress tolerance of maize conferred by exogenously applied nitric oxide. Plant Signaling and Behavior 7: 349-360]. My contribution to the published paper was all the work that is presented in Chapter 2,whereas the rest of the work in the paper (which is not included in Chapter 2) was contributed by Dr Marshall Keyster.