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Philosophiae Doctor - PhD / 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. / National Research Foundation (NRF)

The aim of this study was to propose a non-destructive method for measuring Pinus sylvestris seedlings, to determine whether water stress would be evident in laboratory spectra of pines, to compare whether the response of pines would differ by ecotype, and to investigate whether two ecotypes of Pinus sylvestris could be distinguished using laboratory and image spectroscopy. For these purposes, hyperspectral images of seed orchards from August 2020 were processed and a three-month laboratory experiment was conducted, in which stress from water deficit was induced in two-year-old pine seedlings from the upland and hilly ecotypes. Spectral data were analysed using mixed statistical models, analysis of variance, principal component analysis, training of supervised pixel classifiers, vegetation indices, and linear regression. Based on the analyses, it was found that water stress can be detected in severely stressed Pinus sylvestris seedlings. The most sensitive spectral bands to water content were observed in the region between 1000-2500 nm. The initial response to water stress did not differ by ecotype, but a faster recovery was observed at the upland ecotype after the period of draught. The two Pinus sylvestris ecotypes were distinguished with high accuracy from both laboratory and image spectral...