Physiological and biochemical responses of tomato microshoots to induced salinity stress with associated ethylene accumulation

Physiological and biochemical responses of open-pollinated 'Roma' and dwarf F1 hybrid 'Patio' tomato (Lycopersicon esculentum Mill.) cultivars to in vitro induced salinity were examined in light of the possible contribution of ethylene to these symptoms. Salinity was induced by incorporating 0 (control), 50, 100, 150, or 200 mM NaCl into shoot culture media. Elevated salinity treatments significantly enhanced ethylene accumulation in the headspace and were accompanied by increased leaf epinasty in both cultivars. Growth, leaf cell sap osmolarity, leaf tissue viability and shoot soluble protein content were generally depressed with elevated salinity treatments, whereas electrolyte leakage, membrane injury, raffinose, and total sugars were concomitantly increased. Macronutrients N, P, K, Ca, Mg, and S decreased with elevated salinity in both cultivars and were accompanied by a significant increase in Na content and a sharp decrease in K/Na ratio. Tissue micronutrients, Fe, B, Zn, Mn, and Cu were generally decreased with elevated salinity especially at 100 mM or more. Incorporating ethylene inhibitors CoCl₂ or NiCl₂ at 5.0 or 10.0 mg/l into media supplemented with 100 mM NaCl significantly reduced ethylene accumulation in the headspace and prevented epinasty, but did not eliminate the negative impacts on growth and other physiological parameters caused by salinity treatment in either cultivar. Our results indicate that the increase in ethylene under salinity stress is not the primary factor contributing to salinity's deleterious effect on tomato plant growth and physiology.