ALLEVIATION OF SALT-INDUCED ADVERSE EFFECTS BY EXOGENOUSLY APPLIED 5-AMINOLEVULINIC ACID IN SUNFLOWER (HELIANTHUS ANNUUS L.)

Abstract

Keeping in view the substantial role of a newly discovered plant growth regulator, aminolevulinic acid (ALA), in salinity tolerance, an initial experiment was carried-out to optimize ALA dose at which sunflower plants showed maximum response in terms of different gas exchange characteristics, chlorophyll pigments and growth under saline conditions. After fifteen days of seed germination, two sunflower cultivars (ORI-42B and ORI-48B), were subjected to 0 (control) or 150 mM NaCl. Ten varying levels of ALA (0, 10, 20, 30, 40, 50, 60, 70, 80 and 100 mg L -1 ) were applied as a foliar spray to 32-day old plants. Of all ALA levels, 20, 50 and 80 mg L -1 were relatively more effective in improving photosynthetic rate, chlorophyll a and b, a/b ratio, photosynthetic rate (A), water-use efficiency (WUE), transpiration rate (E) and stomatal conductance (gs) in both cultivars of sunflower under non-saline and saline conditions. Overall, ALA-induced growth improvement in salt stressed sunflower plants was positively correlated with A and chlorophyll pigments. The three levels (20, 50 and 80 mg L -1 ) of ALA found relatively more effective in the first experiment were used in the yield experiment to appraise the role of ALA in detail on growth, yield, seed oil contents and a variety of physio-biochemical attributes in two sunflower cultivars (Hysun-33 and S-278). The ALA treatments were applied as a foliar-spray after 21-day of salt (NaCl) treatments. Salt stress caused a significant suppression in gas exchange characteristics, chlorophyll contents, essential nutrients in addition to growth, yield, oil percentage and α-tocopherols of seed oils, while enhanced tissue Na + and Cl - , proline, GB, relative membrane permeability (RMP), H 2 O 2 , MDA and activities of CAT, POD and SOD in both sunflower cultivars. Of both sunflower cultivars, cv. S-278 was higher in growth, proline, SOD activity, while, cv. Hysun-33 in α-tocopherols under saline regimes. Foliar-applied different levels of ALA were effective in improving root fresh and dry weights, chlorophyll a, seed-oil α-tocopherols, water relation attributes, K + /Na + ratio and SOD activity and decreased seed oil contents under control and saline regimes. Overall, ALA was found to be effective in causing root fresh and dry weights improvement in sunflower plants which was found to be due to increased chlorophyll a, leaf K + /Na + ratio, seed-oil α-tocopherols, leaf SOD activity, and decreased leaf H 2 O 2 and RMP.