Effects of sodium chloride on prevention of thermodormancy, ethylene and protein synthesis and respiration in Grand Rapids lettuce seeds

Grand Rapids lettuce (Lactuca saliva L.) seeds entered into a state of secondary dormancy (thermodormancy) when they were imbibed at 40°C for 72 h. The effect of 40°C in inducing thermodormancy was largely reduced by imbibing seeds at 40°C in solutions of polyethylene glycol (PEG), mannitol and NaCl. Despite similar water potentials of solutions, NaCl pretreatment was more effective. Subsequent germination in the dark at 25°C of saline, high-temperature-pretreated seeds required only gibberellic acid (GA3), as was the case with nonthermodormant seeds. Thermodormancy reduced total respiratory capacity (VT) and increased the ratio of alternate pathway (Valt) to cytochrome pathway (Vcyt) respiration. This was prevented by saline pretreatment. Ethylene production and protein synthesis were depressed in thermodormant seeds, and this was partly alleviated by saline pretreatment. The patterns of protein synthesis in saline- and nonsaline-freated seeds at 40°C were similar, differing only in that the saline treated seeds produced in addition a 78 kDa polypeptide. The pattern of protein synthesis at 40°C differed significantly from that at 25°C.