Induction of anthocyanin accumulation and status of protective system in winter rape plants treated with 5-aminolevulinic acid

Abstract

Effects of exogenous 5-aminolevulinic acid (ALA) on development and certain biochemical parameters of winter rape plants (Brassica napus L.) were studied. Plant growing on 50–200 mg/L ALA solutions for 7 days resulted in an accumulation of anthocyanins in cotyledonous leaves and changed in leaf color from green to violet. An application of 200 mg/L ALA under a stronger illumination (66.2 instead of 40.5 μmol photons/(m2 s)) elevated the anthocyanin content 1.8 times in cotyledons (up to 3.15 ± 0.37 mmol/g dry wt) and 1.3 times in hypocotyls (up to 2.71 ± 0.36 mmol/g dry wt). In the plants enriched with anthocyanins, the hypocotyl linear growth was significantly suppressed (63% of control) and the far stronger suppression of the root growth (46% of control) took place. In the treated plants, chlorophylls a and b accumulated much slower than in the control during vegetation. For both pigments, the corresponding values were 44 and 38% by the fourth day of development, 37 and 27% by the fifth day, 31 and 27% by the sixth day, and 24 and 21% by the seventh day. Thus, the difference between the treated and untreated plants progressively diminished. Levels of carotenoids obeyed a similar pattern. In 7-day-old seedlings treated with 200 mg/L ALA, the activity of the key enzyme of anthocyanin biosynthesis—dihydroflavonol-4-reductase (DFR)—was 1.8 times as high as the control. Simultaneously, the content of proline was 2.2-fold higher; the level of heme noncovalently bound to protein, as well as levels of hydrogen peroxide and reactive oxygen species, exceeded the control level 60, 30, and 25%, respectively. Meanwhile, amounts of lipid peroxidation products and those of superoxide radical were as low as 29 and 62% of the control. In anthocyanin-enriched cotyledons, antiradical and total antioxidant activities were, respectively, 38 and 42% higher than in the control. Therefore, the set of metabolic rearrangements was revealed in the protective and energy systems of winter rape plants in response to exogenous ALA. The reduction in uptake of exogenous ALA by the system synthesizing tetrapyrroles of chlorophyllic nature and decrease in their production were found. Induction of accumulation of anthocyanin antioxidants as a consequence of almost twofold activation of DFR was shown. Simultaneously, the increased contents of heme and proline, together with the rise in antioxidant and antiradical activities, were found. Overall, this reduced the superoxide-generating capacity and lipid peroxidation in intracellular membranes but slightly elevated ROS and H2O2 levels above the control.