Supplemental potassium mediates antioxidant metabolism, physiological processes, and osmoregulation to confer salt stress tolerance in cabbage (Brassica oleracea L.)

Soil salinity is one of the severe threats of climate change that inflicts heavy losses to vegetable production. Potassium (K) has been considered essential approach against abiotic stresses in food crops, however, understanding of K regulated mechanisms for inducing tolerance to NaCl stress in cabbage (Brassica oleracea L.) plants is, still elusive. Here, we report the supplemental K effects on antioxidant defense system and physiological processes that may influence the cabbage production under saline conditions. Initially, cabbage varieties ('Stone Head', 'Golden Acre', '9j-940', 'Beauty Ball', 'Green Ball', 'Green Rise', 'Marco F-1') were tested under NaCl stress (50, 100, 150, and 200 mM) for their higher growth, vigor index and mineral contents. The identified cabbage var. salt-tolerant, cv. Beauty Ball (BB) and salt-sensitive cv. Green Ball (GB) were further exposed to foliar K (5 and 10 mM solutions of KNO3) under the same NaCl regimes. NaCl stress markedly inhibited photosynthetic efficiency, water status and chlorophyll pigments, thereby, resulted in reduced dry biomass of both varieties. Nevertheless, exogenous K spray at 10 mM caused positive gain in leaf water relations, chlorophyll contents in both cabbage varieties. The ameliorative impacts of K were more pronounced in salt-tolerant cv. BB as compared to salt-sensitive cv. GB in terms of higher accumulation of total soluble proteins, total free amino acids, proline contents, upregulated antioxidant activities and enhanced gas exchange characteristics. Hence, improvement in growth and K+/Na+ ratio of cabbage plants by foliar K application (10 mM) were related to up-regulation of physiological and biochemical mechanisms under saline conditions.