Physiological Response of Rice Plants Growing under Osmotic Stress in Hydroponics

Osmotic stress is a common consequence of drought and salinity. These kinds of abiotic stresses induce a series of morphological, physiological, biochemical and molecular changes that negatively affect plant growth and productivity. In this study, two agents that produce osmotic stress (100 mM NaCl and 10% polyethylene glycol -PEG-) and the control (without osmotic stress) were evaluated on the growth of four Mexican rice cultivars: 'Cotaxtla', 'Temporalero', 'Huimanguillo' and 'Tres Rios'; the last one classified as susceptible to drought. The evaluation was performed during the vegetative stage (tillering). Twelve days after germination, plants were maintained under hydroponic conditions in greenhouse for 45 days, using the universal Steiner nutrient solution at 50%. A factorial experiment 4x3 in a completely randomized design was utilized and the plants were treated with osmotic agents (either NaCl or PEG) during 15 days. Results indicate that height of plant, weight of fresh and dry matter of shoot and roots were significantly reduced in the four cultivars under study. However, the root/shoot ratio was increased in the cultivars 'Cotaxtla' and 'Temporalero'. The NaCl significantly reduced the chlorophyll concentration; while PEG had no negative effects on this variable. Both NaCl and PEG increased total amino acid concentration in leaves, except in 'Tres Rios', which was only affected by salinity. Furthermore, NaCl substantially increased proline concentration, 5- to 25-fold more than the control. This indicates that a drought tolerant cultivar is not necessary tolerant to salinity, Cotaxtla being the most tolerant cultivar to salinity and drought.