EFFECTS OF SODIUM SULFATE AND SODIUM BICARBONATE ON THE GROWTH OF LETTUCE Cloning and Expression Analysis of LsHsp70 from Lactuca sativa   Cloning and Expression Analysis of LsHsp70 from Lactuca sativa   In Vitro Shoot Differentiation from Cotyledon Explants of Lettuce Comprehensive Evaluation Analysis on Cultivation Effects of Lettuce under Different Nitrogen Levels Effects of NH4+-N/ NO3--N ratios on kinetics of nitrate uptake by two typical lettuce genotypes in hydroponics In Vitro Shoot Differentiation from Cotyledon Explants of Lettuce Effect of Nitrogen Forms on the Growth and Physiological Characteristics of Lactuca sativa L.Seedlings Studies on the Chemical Constituents of the Essential Oil in the Semen of Lactuca setiva L. and Its Diuretic Action