UV-B priming enhances specific secondary metabolites in Oryza sativa (L.) empowering to encounter diverse abiotic stress
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ORIGINAL PAPER
UV‑B priming enhances specific secondary metabolites in Oryza sativa (L.) empowering to encounter diverse abiotic stresses T. T. D. Thomas1 · Jos T. Puthur1 Received: 10 December 2019 / Accepted: 16 May 2020 © Springer Nature B.V. 2020
Abstract Plants are exposed to various abiotic stresses and there exists sophisticated mechanisms within them for tolerating these stresses. The present study clearly revealed the efficacy of UV-B priming at both seed and seedling stage in tolerant (Kanchana) and sensitive (Aiswarya) rice varieties, to tolerate UV-B stress, polyethylene glycol-6000 (PEG) and NaCl stresses. Increase in UV stress specific characters such as accumulation of UV absorbing compounds [flavonoids (242–368%) and anthocyanin (367–386%) content],increased activity of phenylalanine ammonia lyase (116–210%) and increased leaf cuticular wax content (382–403%) was observed in UV-B primed seedlings of rice subjected to UV-B, NaCl and PEG stresses. The increase in the levels shown as percent increase were highest in seedlings subjected to UV-B stress followed by NaCl and PEG stresses. The influence of priming imprints was more effective in seeds and seedlings of the tolerant rice variety (Kanchana) than the sensitive variety (Aiswarya). Functional groups variation in wax content was more prominent in PEG stress conditions than UV-B and NaCl stresses and it was mainly observed in Aiswarya than in Kanchana. Additionally our results suggests the UV-priming mediated enhancement of the stress tolerance potential of a tolerant variety seems to be more successful than the sensitive variety. Keywords UV-B · Cuticular wax · Phenylalanine ammonia lyase · Seed priming · UV absorbing compounds
Introduction UV-B radiations have significant impact on growth, development, biomass accumulation, yield and metabolism of plants. Mechanisms to counter UV-B irradiations in plants are increased leaf thickness, alterations in cuticle and increased production of UV-B protective pigments (Shaukat et al. 2013; Kreslavski et al. 2020). Plants have inbuilt mechanisms to counter the UV-B stress situation of which the production of secondary metabolites (e.g., flavonoids, epicuticular wax) is considered as a prominent one (Qaderi et al. 2010). Flavonoids act as antioxidant agents by scavenging ROS and have a key role in encountering stress situations. The anthocyanins are a group of flavonoids and the production of anthocyanins in plants is affected by various stresses through * Jos T. Puthur [email protected] 1
Plant Physiology and Biochemistry Division, Department of Botany, University of Calicut, C.U. Campus P.O., Kerala 673635, India
the inhibitory action on the synthesis process of transcription factors involved in its synthesis (Shaki et al. 2018; Fu et al. 2019; Wang et al. 2019). Phenylalanine ammonia lease (PAL) is an important enzyme in regulating flavonoid biosynthesis and is transcriptionally induced by UV-radiation. Increased PAL activity stimulates the synthesis of flavonoid and anthocyanins (Ravindran et al
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