TREHALOSE-INDUCED IMPROVEMENT IN GROWTH, PHOTOSYNTHETIC CHARACTERISTICS AND LEVELS OF SOME KEY OSMOPROTECTANTS IN SUNFLOWER (HELIANTHUS ANNUUS L.) UNDER DROUGHT STRESS

Accumulation of trehalose, a sugar rarely found in plants, is believed to be involved in improving drought stress tolerance in different plant species. To assess the influence of trehalose on regulation of different gas exchange attributes, chlorophyll contents and osmoprotectants of sunflower (Helianthus annuus L.) plants, an experiment was conducted under drought stress conditions. Fifteen day-old seedlings of two sunflower cultivars i.e. Hysun 33 and FH 598 were exposed to non-stress (100% field capacity) and water limited stress (60% field capacity). After 30 days of drought stress treatments, four levels of trehalose (0, 10, 20 and 30 mM) were applied to the plant leaves of both sunflower cultivars. Water deficit conditions suppressed shoot and root fresh and dry weights, chlorophyll a and b contents, photosynthetic rate (A), transpiration rate (E), stomatal conductance (g(s)), sub-stomatal CO2 concentration (C-i), and C-i/C-a ratio of both sunflower cultivars while it significantly enhanced the WUE as well as accumulation of proline and glycinebetaine (GB)contents in both sunflower cultivars. Foliar-applied different levels of trehalose significantly improved shoot fresh and dry weights, root dry weight, chlorophyll a and b, A, E, g(s), C-i, C-i/C-a, WUE, proline and GB contents under water stress conditions. Of both sunflower cultivars, cv. Hysun 33 was superior in shoot and root fresh and dry weights, A, E, g(s), C-i, C-i/C-a, under water limited conditions, whereas cv. FH 598 in WUE. Of all trehalose levels used, 20mM and 30mMwere more effective for improving shoot fresh weight, chlorophyll b, g(s), C-i, and C-i/C-a in both sunflower cultivars. Overall, exogenous application of trehalose was effective in enhancing drought stress tolerance in sunflower plants by improving osmoprotection and gas exchange characteristics.