Abstract
Direct and indirect roles of vitamin B6 in leaf acclimation to supplementary UV-B radiation are shown in vitamin B6 deficient Arabidopsis thaliana mutant rsr4-1 and C24 wild type. Responses to 4 days of 3.9 kJ m−2 d−1 biologically effective UV-B dose were compared in terms of leaf photochemistry, vitamer content, and antioxidant enzyme activities; complemented with a comprehensive study of vitamer ROS scavenging capacities. Under UV-B, rsr4-1 leaves lost more (34%) photochemical yield than C24 plants (24%). In the absence of UV-B, rsr4-1 leaves contained markedly less pyridoxal-5′-phosphate (PLP) than C24 ones, but levels increased up to the C24 contents in response to UV-B. Activities of class-III ascorbate and glutathione peroxidases increased in C24 leaves upon the UV-B treatment but not in the rsr4-1 mutant. SOD activities remained the same in C24 but decreased by more than 50% in rsr4-1 under UV-B. Although PLP was shown to be an excellent antioxidant in vitro, our results suggest that the UV-B protective role of B6 vitamers is realized indirectly, via supporting peroxidase defence rather than by direct ROS scavenging. We hypothesize that the two defence pathways are linked through the PLP-dependent biosynthesis of cystein and heme, affecting peroxidases.
Highlights
Direct and indirect roles of vitamin B6 in leaf acclimation to supplementary UV-B radiation are shown in vitamin B6 deficient Arabidopsis thaliana mutant rsr[] and C24 wild type
UV-B is generally sensed by plants through the UV RESISTANCE LOCUS 8 (UVR8) photoreceptor and its downstream signaling components[19] which in turn regulate over 100 genes
One of the more non-specific modes of action of UV-B on plants is the formation of ROS28 and the UV-B-induced increase in vitamin B6 content in plants most likely is a result of increased oxidative pressure
Summary
Direct and indirect roles of vitamin B6 in leaf acclimation to supplementary UV-B radiation are shown in vitamin B6 deficient Arabidopsis thaliana mutant rsr[] and C24 wild type. Based on the UV sensitivity of the pdx1.3 mutant[7], we hypothesized that rsr[] plants (i) will either be more sensitive to supplementary UV-B doses than the C24 wild type, (ii) or compensate for presumably less efficient non-enzymatic ROS scavenging by higher antioxidant enzyme activities.
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