MODULATION IN GROWTH, PHOTOSYNTHETIC PIGMENTS, GAS EXCHANGE ATTRIBUTES AND INORGANIC IONS IN SUNFLOWER (HELIANTHUS ANNUUS L.) BY STRIGOLACTONES (GR24) ACHENE PRIMING UNDER SALINE CONDITIONS

Plants respond to various abiotic stresses in a complex way, depending upon their severity through cellular, morphological and physiological modifications. Phytohormones are signaling molecules which mediate plant growth and development. They modulate plant physiological responses to acclimatize stress like salinity. Phytohormones interact with each other to alleviate abiotic stress. Striglactones are relatively newly discovered phytohormones and are proposed to have their role in stress responses like those of salinity. A synthetic analogue of strigolactones GR24 was used to explore its role to ameliorate adverse effects of salt stress on sunflower plants. Achenes of two sunflower hybrids (FH-593 and FH-596) were primed with four concentrations of GR24 (water (0), 0.001, 0.01 and 0.1 mg L-1) and grown under two salt regimes i.e. non-saline and 120 mM NaCl in pots. Salt stress significantly decreased growth attributes while GR24 showed a positive effect to alleviate salt stress. Pre-sowing achene treatment with GR24 significantly enhanced plant biomass and shoot length. Salinity markedly decreased photosynthetic pigments and net CO2 assimilation, stomatal conductance and transpiration. Chlorophyll contents and gas exchange attributes of both sunflower hybrids showed a non-significant response to GR24 treatment. However, carotenoids contents increased with GR24 pre-sowing achene treatment. Salinity significantly raised the contents of Na+ contents but decreased that of Ca2+ and K+ ions in both shoot and root. The GR24 application enhanced the Na+, K+ and Ca2+ in shoots and roots.