Abstract
Xanthine dehydrogenase (XDH) is an important enzyme in purine metabolism. It is involved in regulation of the normal growth and non-biological stress-induced ageing processes in plants. The present study investigated XDH’s role in regulating rice leaf senescence. We measured physical characteristics, chlorophyll content and fluorescence parameters, active oxygen metabolism, and purine metabolism in wild-type Kitaake rice (Oryza sativa L.), an OsXDH over-expression transgenic line (OE9), and an OsXDH RNA interference line (Ri3) during different growth stages. The expression patterns of the OsXDH gene confirmed that XDH was involved in the regulation of normal and abiotic stress-induced ageing processes in rice. There was no significant difference between the phenotypes of transgenic lines and wild type at the seedling stage, but differences were observed at the full heading and maturation stages. The OE9 plants were taller, with higher chlorophyll content, and their photosystems had stronger light energy absorption, transmission, dissipation, and distribution capacity, which ultimately improved the seed setting rate and 1000-seed weight. The opposite effect was found in the Ri3 plants. The OE9 line had a strong ability to remove reactive oxygen species, with increased accumulation of allantoin and alantoate. Experimental spraying of allantoin on leaves showed that it could alleviate chlorophyll degradation and decrease the content of H2O2 and malonaldehyde (MDA) in rice leaves after the full heading stage. The urate oxidase gene (UO) expression levels in the interference line were significantly lower than those in the over-expression line and wild-type lines. The allantoinase (ALN) and allantoate amidinohydrolase (AAH) genes had significantly higher expression in the Ri3 plants than the in OE9 or wild-type plants, with OE9 plants showing the lowest levels. The senescence-related genes ACD1, WRKY23, WRKY53, SGR, XERO1, and GH27 in Ri3 plants had the highest expression levels, followed by those in the wild-type plants, with OE9 plants showing the lowest levels. These results suggest that enhanced activity of XDH can regulate the synthesis of urea-related substances, improve plant antioxidant capacity, effectively delay the ageing process in rice leaves, and increase rice yield.
Highlights
Rice (Oryza sativa L.) is subject to premature senility during its late growth period, manifesting as premature deterioration of metabolic function, which seriously hinders the improvement of rice yield (Großkinsky et al.2018)
Expression Pattern Analysis for OsXDH In order to determine the response of OsXDH gene expression to ageing and stress factors, qPCR was used to analyse the OsXDH gene expression level in leaves, roots, stems and leaves of rice at different growth stages under different stress conditions
Plant Height and Chlorophyll Content at Different Growth Stages Xanthine dehydrogenase (XDH) interference (Ri3, Ri5, and Ri6) and over-expression (OE1, OE3, and OE9) transgenic lines were constructed for explore the function of OsXDH
Summary
Rice (Oryza sativa L.) is subject to premature senility during its late growth period, manifesting as premature deterioration of metabolic function, which seriously hinders the improvement of rice yield (Großkinsky et al.2018). Given these findings, improvement in photosynthetic activity in rice leaves could be key to reaching high or even super-high yields. Leaf senescence is found to be a complex physiological process affected by, for example, low chlorophyll (Buchanan-Wollaston 1997; Peng and Peng 2000), high malondialdehyde (MDA) content (Rajinder et al 1981), reduced free radical and reactive oxygen scavenging enzyme activity, decomposition of nucleic acids, proteins and other macromolecules (Park et al 2007), and nutrient reuse (Simpson and Dalling 1981)
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