CHANGES INDUCED BY SALINITY, DEMARCATING SPECIFIC ION RATIO (Na/Cl) AND OSMOLALITY IN ION AND PROLINE ACCUMULATION, NITRATE REDUCTASE ACTIVITY, AND GROWTH PERFORMANCE OF LETTUCE

Abstract

In order to differentiate the effects of sodium (Na), chloride (Cl), NaCl, and concentrated macronutrients on ion and proline accumulation, nitrate reductase activity (NRA), and growth performance of lettuce (Lactuca sativa L.), plants were grown in eight different nutrient solutions. The nutrient solution was prepared by increasing the salt concentration of a basic nutrient solution by providing 40 mM NaCl, and on the basis of 40 mM NaCl five Na/Cl ratios (100/0, 75/25, 50/50, 25/75, and 0/100), and 2.75 times the macronutrients. The osmolality of the basic nutrient solution was 53 m OS mol, and that of the other seven nutrient solutions was around 100 m OS mol. Fresh and dry weights of the lettuce were not influenced by any of the treatments. Accumulation of proline in plant tissue was enhanced by increasing the osmolality of nutrient solution. Increasing Cl in nutrient solution also increased proline accumulation. The macronutrients and increasing Cl in nutrient solution decreased, albeit not significantly, the NRA in lettuce. Oxalic acid, total nitrogen (N), and NO₃-N contents of lettuce were decreased by decreasing Na/Cl ratio but increased by macronutrients, NaCl, and Na treatments. Plant potassium (K) concentration and K/Na ratio were decreased by NaCl and, increasing Na in nutrient solution. Phosphorus concentrations showed increases with Na in nutrient solution. Regardless of the source, increased osmolality caused decreases in calcium (Ca) concentration of plant tissue. The macronutrients and increasing Cl in nutrient solution seemed to increase the Ca concentration of plants. It was concluded that lettuce plant performance under different treatments was affected both by ionic and osmotic effects.

ACKNOWLEDGMENTS

The authors would like to express their appreciation to Prof. Oktay Karatan (Faculty of Medicine, Ankara University) and his colleagues for their assistance in the determinations of the osmolality of the nutrient solutions with Micro Osmometer (Model 3300).