Photosynthetic capacity of canola (Brassica napus L.) plants as affected by glycinebetaine under salt stress

Salinity causes reduction in growth and severe losses of crop productivity by affecting various biochemical and physiological processes including photosynthesis. Plants sense and adapt to salt stress by modulating different physiological processes including accumulation of osmoprotectants. Glycinebetaine (GB) is an important osmoprotectant and found to have ameliorative effects on the growth of plants by altering ion homeostasis, photosynthetic and antioxidant capacity. In this study, it was attempted to reveal how GB improves photosynthetic activity and salt tolerance of two canola cultivars which differ in degree of salt tolerance. Two cultivars (Dunkled and Cyclone) of canola (Brassica napus L.) were grown under non-saline or saline (150 mM NaCl) conditions. Glycinebetaine (100 mM) was foliarly applied to both non-stressed and salt stressed plants of both canola cultivars at the vegetative growth stage. Salt stress reduced growth of both canola cultivars, however, cv. Dunkled was superior to cv. Cyclone. Foliar application of GB improved leaf relative water contents (RWC), osmotic potential and proline accumulation in salt stressed plants. The chlorophyll fluorescence transient (CFT) remained unchanged at O and J phase while at I and P phase it was affected by salt stress in both cultivars that was ameliorated by GB application. The positive values of K band after 1000 mu s under salt stress revealed the reduced efficiency of oxygen evolving complex (OEC). The GB application enhanced electron transport chain and decreased heat dissipation under salt stress. This effect was more in cultivar Cyclone as compared to Dunkled. Furthermore, a considerable proteomic variation was noted in canola cultivars after application of GB under both saline and non-saline condition. The results suggested that exogenous foliar application of GB ameliorated the adverse effects of salt stress on both cultivars of canola by osmotic adjustment, growth improvement, increased light absorption by reaction centers, efficient energy trapping and enhanced electron transport chain in both cultivars of canola.