Protection against salinity stress in black cumin involves karrikin and calcium by improving gas exchange attributes, ascorbate–glutathione cycle and fatty acid compositions

Abstract

The present study assessed the effect of karrikin (KAR) and calcium (CaCl2) to increase salt tolerance in black cumin. Salinity stress induced oxidative stress by enhancing electrolyte leakage (EL), malondialdehyde (MDA) and hydrogen peroxide (H2O2) content while having a negative effect on seed yield, fatty acid content and composition, total chlorophyll content, chlorophyll fluorescence and leaf gas exchange parameters of black cumin. The activity of antioxidant enzymes involved in the ascorbate–glutathione cycle was also affected by salt stress. Black cumin seed trimming with karrikin when followed with calcium foliar application mitigated the harmful effects of salinity by improving chlorophyll content, chlorophyll fluorescence and leaf gas exchange parameters while reducing the H2O2 generation, MDA accumulation and EL. Calcium application in karrikin pretreated seedlings also reversed salinity-induced changes by enhancing the activities of enzymes in the ascorbate–glutathione cycle, other antioxidants (superoxide dismutase, catalase) and osmoprotectant (proline). The ability of black cumin seedlings to cope with salt stress after pretreatment with KARs when followed by external application of calcium can be attributed to increased levels of polyunsaturated fatty acids and modification of enzymatic and nonenzymatic antioxidants as well as enhanced osmolyte accumulation.