5-aminolevulinic acid (ALA) regulates photosynthetic performance and nitrogen metabolism status in UV-B challenged Cajanus cajan L. seedlings

摘要

In the current study, the role of chlorophyll precursor, 5-aminolevulinic acid (ALA) and its effect on growth attributes, photosynthetic pigments, indices of chlorophyll a fluorescence, nitrogen metabolism, and contents of protein and carbohydrate in seedlings of pigeon pea varities BAHAR and KB-17 under the enhanced ultraviolet (UV-B; 2.2 kJ m(-2)d(-1)) radiations was investigated. Ultraviolet radiations (UV-B) adversely affected the fresh mass of shoot and root, shoot and root length, photosynthetic pigments content (Chl a + b and ratios of Chl a/b and Chl/Car), photosynthetic oxygen yield and chlorophyll a fluorescence parameters: i.e., F-v/F-m (Phi_P-0), psi(0) (Psi_0), phi E-0 (Phi_E-0) and performance index of PS II (PIABS) along with F-v/F-0 while increased the energy flux parameters, i.e., ABS/RC, TR0/RC, ET0/RC, and DI0/RC along with F-0/Fv and also consequently raised the dark respiratory rate in test seedlings; however, exogenous application with both the doses of ALA (low dose: ALA(1); 25 mu M and high dose: ALA(2); 100 mu M) through seed priming notably counteracted UV-B induced negative effects on growth attributes and other important growth-regulating processes. Additionally, inorganic nitrogen contents, i.e., nitrate (NO3-) and nitrite (NO2-) and the activities of nitrate assimilating enzymes, viz., nitrate reductase and nitrite reductase and ammonia assimilating enzymes, viz., glutamine synthetase and glutamate synthase (GOGAT) along with carbohydrate and protein contents were rigorously affected and declined under UV-B toxicity; while in present study, ammonium (NH4+) content and glutamate dehydrogenase (GDH) activity in both BAHAR and KB-17 varieties exhibited reverse trend. Furthermore, ALA priming induced significant alliveation against UV-B stress on these parameters except NH4+ content and GDH activity, which exhibited an apparent reduction under similar conditions. Our results suggest that ALA priming, particularly high dose (ALA(2)) more efficiently protects Cajanus cajan seedlings by attenuating UV-B toxicity in both the varieties (BAHAR and KB-17) by maintaining carbon and nitrogen status of seedlings through regulating photosynthesis and nitrogen metabolism.