Betalains and expression of antioxidant enzymes during development andabiotic stress in Rivina humilis L. berries

Abstract

This work investigated the betalains profile and associated molecular changes during Rivina humilis L. berry development and 1 month after inducing stress through elicitors such as salicylic acid (SA, 0.05-0.5 mM) and chitosan (CH, 0.1%-1.0%). The results showed that, during berry development, diphenol oxidase activity of tyrosinase increased, which was reflected in an exponential increase in betalains accumulation. Expression levels of a putative Rivina humilis betanidin-5-O-glucosyltransferase 2 (RhBGT2) remained unchanged, while that of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) decreased. Treatment with SA (0.1 mM) and CH (0.5%) enhanced betalains accumulation. The pattern of betalains accumulation during berry development and after elicitor treatment suggested that, probably, both betacyanins and betaxanthins are synthesized from the same pool of betalamic acid. There was no significant change in expression levels of RhBGT2, SOD, and CAT following elicitor stress. However, treatment with CH (1.0%) produced morphological changes (shrinking) in the berries and expression of SOD was significantly suppressed. This is the first report that shows enhancement of betalains accumulation in intact berries through elicitor treatment.

Plant betalains: Chemistry and biochemistry

“…Consequent to the changes in enzyme activity, chloroplast changes to chromoplast wherein carotenoids begin to accumulate (Looney and Patterson, 1967;Khan et al, 2011). Vacuolar pigments like anthocyanins and betalains too start accumulation in fruits and leaves, which are green in the initial stages of ontogeny, with concomitant drop in chlorophyll content (Tucker and Grierson, 1987;Khan et al, 2014;Khan and Giridhar, 2014b). Sometimes the green chlorophyll pigments mask the colour of these metabolites in fresh leaves and fruits.…”

“…In another study, triacontanol was applied through soil, chitosan and salicylic acid through floral spray to R. humilis plants. Triacontanol (upto 20 lM) did not affect the biochemical contents of fruit juice including pigments, whereas chitosan (0.5%) and salicylic acid (100 lM) could enhance pigment content significantly (Khan et al, 2014). Jasmonic acid (JA), SA, H 2 O 2 , and ethylene are endogenously produced signalling molecules.…”

Physiological and biochemical responses of sugar beet (Beta vulgaris L) to ultraviolet-B radiation

“…This reduction reached 10–20% (Fig. 1) and was thus significantly milder than the reduction in leaf area by 77% described previously (Khan, Kumar & Giridhar, 2016). In line with our findings, growth reduction under UV-B has also been reported in Arabidopsis thaliana (Morales et al, 2013) and Capsicum annuum (Rodriguez-Calzada et al, 2018).…”

“…One of the betalain producing plants is sugar beet ( Beta vulgaris ) which, because of its ability to accumulate a large quantity of sugar in storage roots, provides about 40% of the world’s sugar production. However, environmental factors can reduce sugar production potential by affecting sugar beet plant productivity (Khan, Kumar & Giridhar, 2016). There have been many investigations on response of sugar beet plants to abiotic stresses including drought, heat, cold and UV radiation.…”

“…However, given the importance of sugar beet for agriculture in Iran, more data are needed about the tolerance of this crop to UV. Since the previous detailed analysis of UV stress in sugar beet used high doses of UV-B, which led to a 77% reduction in leaf area (Khan, Kumar & Giridhar, 2016), data from treatments corresponding to the more physiological doses of UV-B radiation are needed. In the present work we evaluated a widely grown Iranian multigerm cultivar of sugar beet BR1 for its physiological and biochemical responses to three different UV-B radiations to evaluate its potential as an efficient crop in the areas with different doses of UV-B.…”