Physiological, biochemical and root proteome responses of maize seedlings to drought stress
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Date
2022
Authors
Moloi, Lerato
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Publisher
University of the Free State
Abstract
A primary limiting factor for maize during its growing period is drought stress. With the decrease in yield and biomass triggered by drought stress in maize, drought has become a critical issue that must be considered due to the changing climate conditions. This study aimed to comparatively analyse the morpho-physiological, biochemical and root proteome changes of two maize varieties in response to drought stress. In this study, two maize varieties CN07/8-224 and CN07/8-292 with unknown drought phenotypes were used. The plant growth experiments were conducted in a growth chamber for mild stress with ~ 54% and ~48% of soil moisture content and a greenhouse for severe stress with ~51% and ~43% soil moisture content. In both growth experiments, 7-day-old maize seedlings were exposed to a 14-day drought stress treatment, while continuing to water the controls every other day. Thereafter, a range of morpho-physiological parameters such as shoot and root length/weight, leaf relative water content, chlorophyll and carotenoid content were measured. In addition, biochemical parameters such as the level of lipid peroxidation and hydrogen peroxide, as well as the activities of superoxide dismutase (SOD), and ascorbate peroxide (APX) were measured. The root proteome was analysed using the isobaric tags for absolute and relative quantitation (iTRAQ) method coupled with liquid chromatography- tandem mass spectrometry to identify differentially expressed proteins in response to drought stress. To annotate the proteins, bioinformatics studies were carried out by using the UniProt and InterPro databases. The Gene Ontology (GO) annotation and protein families were allocated to each protein that showed differential expression in response to the drought stress. Then, the proteins were functionally categorized using a modified version of the Bevan classification scheme. The results of the study showed some significant differences between the drought treated plants and control plants of CN07/8-224 and CN07/8-292, as well as between the maize varieties. Results indicated that both maize varieties experienced reductions in chlorophyll a, b, and carotenoids during drought stress. In addition, there were differences in the amounts of chlorophyll that accumulated in the various varieties. These reductions may be attributed to a reduced water supply observed in soil moisture content, which reduced the synthesis of photosynthetic pigments in maize plants. However, only the drought-stressed CN07/8-224 maize variety lengthened its roots to adapt to limited water supply. Higher lipid peroxidation and hydrogen peroxide levels correlated with increased antioxidant activities of CN07/8-292 drought-stressed roots as compared to control plants. This could be because there was more significant ROS detoxification under drought stress, which led to higher activities of SOD and APX in comparison to control plants. The root samples of CN07/8-224 and CN07/8-292 maize varieties were used to conduct iTRAQ analysis. A total of 1 232 and 1 558 proteins were positively identified in CN07/8-224 and CN07/8-292 varieties, respectively in response to mild drought stress conditions. A total of 116 and 146 of these proteins were responsive to the mild stress. The CN07/8-224 and CN07/8-292 varieties shared seven drought-responsive proteins, while the rest were unique to each variety. Collectively, the drought responsive proteins of both maize varieties were involved in primary/secondary metabolism, disease defence, and protein synthesis, all of which are involved in the response of maize varieties to drought. However, the expression of drought responsive proteins varied across the maize varieties. Overall, physiological and biochemical results have shown how the CN07/8-224 and CN07/8-292 maize varieties responded to drought stress using a range of mechanisms. In addition, strong root system architecture, as shown by higher root length and fresh root weight in CN07/8-224 variety under drought stress, could be responsible for the improved growth and greater stress tolerance. On the other hand, CN07/8-292 variety might happen to be sensitive to drought stress relative to CN07/8-224 based on the observed results. The obtained results would help researchers to find solutions on the impact of gene expression under drought.
Description
Dissertation (M.Sc.(Botany))--University of the Free State, 2022