Ultraviolet‐B‐Radiation‐Induced Changes in Nicotinamide and Glutathione Metabolism and Gene Expression in Plants

Abstract

Pea (Pisum sativum L. cv. Greenfeast) plants were exposed to supplementary ultraviolet‐B (UV‐B) radiation (biologically effective dose rates normalised to 300 nm, UV‐BBE300: 0.18, 0.32 or 1.4 W m−2). Leaf nicotinamide, trigonelline, GSHtot (total glutathione) and GSSG (oxidised glutathione) levels remained unchanged after exposure to the lowest dose rates. 1.4 W m−2 UV‐BBE,300: gave rise to 60‐fold and 4.5‐fold increases in GSSG and GSHtot, respectively. 3.5‐fold and 9.5‐fold increases were found in nicotinamide and trigonelline, respectively, cab (Chlorophyll‐a/b‐binding protein) transcript levels decreased and CHS (chalcone synthase) and PAL (phenylalanine ammonia‐lyase) mRNA increased after shorter UV‐B exposures (hours) to the higher dose rate of UV‐B, and after exposure to the intermediate dose rate. CHS and PAL mRNAs also increased after prolonged exposure to the lowest dose rate. cah transcripts completely disappeared, whereas CHS and PAL mRNA levels rose by 60‐fold and 17‐fold, respectively, after 12 h exposure at the highest dose rate and 12 h of development. Our results indicate that nicotinamide or trigonelline do not function as signalling compounds for CHS and PAL gene expression. Elevated nicotinamide and trigonelline levels occur in response to UV‐B, but only at UV‐B doses high enough to cause oxidative stress.

The role of the pyridoxine (vitamin B6) biosynthesis enzyme PDX1 in ultraviolet-B radiation responses in plants

“…Recently, Wagner et al [20] concluded that both genes probably have overlapping functions, and both are required to act synergistically to establish pyridoxine homeostasis. Also, comparable basal levels of vitamin B 6 were detected in both the pdx1.3 mutant and in the Col-0 ecotype. After exposure to UV-B, significantly increased vitamin B 6 levels were found in Col-0 wild type (Fig.…”

“…Increased activities of anti-oxidative enzymes have been demonstrated, in addition to decreased content of antioxidants [6]. Also, changes in expression of ROS-dependent genes, such as PR-1 and PR-5, indicate that ROS is involved in at least high level or long-term UV-B responses [7,32,34].…”

“…Labeling of probes and hybridization were performed according to Sävenstrand et al [25]. Control of RNA loading and transfer was accomplished by hybridization with a radiolabelled 18S ribosomal cDNA probe [6] to the same membrane after stripping. …”

“…The deleterious effects include DNA damage [1], damage to the photosynthetic apparatus [2], and alteration of the structural integrity of membranes [3]. As one response to the perception of UV-B radiation, plants show altered expression of genes encoding components of different protective pathways, such as detoxification of reactive oxygen species [4], and production of UV-Babsorbing pigments [5,6]. In addition, increased expression Q1 of pathogenesis-related genes, such as PR-5 [7], occurs.…”

Assessment of impact of solar UV components on growth and antioxidant enzyme activity in cotton plant

“…Plants respond to UV-B stress by activating antioxidant enzymes like Superoxide dismutase, Ascorbic acid peroxidase, Glutathione reductase (Takeuchi et al 1995;Rao et al 1996;Teckchandani and Guruprasad 1998;Jain et al 2003;Kataria et al 2007). Plants also respond to UV-B by enhancing the endogenous level of ascorbic acid (Rao et al 1996;Sharma et al 1998;Jain et al 2004a, b) and glutathione (Takeuchi et al 1996;Kalbin et al 1997). In addition to this synthesis of UV absorbing substances like flavonoids and other phenolic compounds are enhanced in response to supplemental UV-B (Searles et al 2001;Day and Neale 2002).…”