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Differential regulation of defence pathways in aromatic and non-aromatic indica rice cultivars towards fluoride toxicity

Banerjee, Aditya, Roychoudhury, Aryadeep
Plant cell reports 2019 v.38 no.10 pp. 1217-1233
Oryza sativa, abscisic acid, antioxidant activity, betaine, bioaccumulation, biosynthesis, cultivars, enzyme activity, fluorides, gene expression, genes, isozymes, lipoxygenases, peroxidase, phenylalanine ammonia-lyase, polyamines, proline, putrescine, rice, superoxide dismutase, toxicity, vigor, water content
KEY MESSAGE: Excessive bioaccumulation of fluoride in IR-64 caused low abscisic acid level, inhibition of polyamine biosynthesis and ascorbate–glutathione cycle but not in Gobindobhog which had higher antioxidant activity. The current study presents regulation of diverse metabolic and molecular defence pathways during fluoride stress in non-aromatic rice variety, IR-64 and aromatic rice variety, Gobindobhog (GB). Increasing concentration of fluoride affected fresh weight, dry weight, vigour index and relative water content to a lesser extent in GB compared to IR-64. GB exhibited lower methylglyoxal accumulation and lipoxygenase activity compared to IR-64 during stress. The level of osmolytes (proline, amino acids and glycine-betaine) increased in both the stressed varieties. The biosynthesis of higher polyamines was stimulated in stressed GB. IR-64 accumulated higher amount of putrescine due to degradation of higher polyamines as supported by gene expression analysis. Unlike IR-64, GB efficiently maintained the ascorbate–glutathione cycle due to much lower fluoride bioaccumulation, compared to IR-64. GB adapted to fluoride stress by strongly inducing guaiacol peroxidase, phenylalanine ammonia lyase and a novel isozyme of superoxide dismutase. While GB accumulated higher abscisic acid (ABA) level during stress, IR-64 exhibited slow ABA degradation which enabled induction of associated osmotic stress-responsive genes. Unlike GB, ABA-independent DREB2A was downregulated in stressed IR-64. The research illustrates varietal differences in the defence machinery of the susceptible variety, IR-64, and the well adapted cultivar, GB, on prolonged exposure to increasing concentrations of fluoride.