Physiological Responses of Tomato Microshoot Cultures to in vitro Induced Salinity Stress

Microshoot cultures were used to evaluate salt stress responses in two (JO112 and JO992) tomato (Lycopersicon esculentum Mill.) genotypes. Microshoots were grown on media supplemented with 0, 50, 100, 150 and 200 mM NaCl and CaCl2 in equal molar ratios. Growth and physiological traits were determined. Most microshoots of the two genotypes did not develop roots when exposed to 150 mM or higher salt levels and negative response occurred in growth parameters (fresh weight, dry weight and shoot height). Na+, Cl¯ and Ca+² concentrations increased in the microshoots with increasing salinity in both genotypes. On the other hand, K+ content decreased with increasing salinity. Proline accumulation increased with increasing salinity in the microshoots. Induced salinity significantly reduced cell sap osmotic potential in the microshoots. The genotype JO992 generally had higher shoot fresh weight, dry weight, shoot height and cell sap osmotic potential than JO112. The salt induced polypeptides (18, 26 and 41 KDa) and depressed 33 KDa in tomato microshoots compared to the control. In this study, stress tolerance was probably achieved by physiological and biochemical mechanisms, as evidenced by strong root growth (length and number) and accumulation of inorganic ions, proline and protein