Salt Stress Effects On Crops And Exogenous Calcium Mitigation Role

The salt stress causes damage to plants in many aspects: concluding the drought stress caused by low osmotic potential, mineral nutrition-stress caused by the competition between the Na⁺ and nutrient ions, imbalance of ions in cells all of which have a strong impact on normal growth of plants. This study applied the solution culture and glass microelectrode technique to monitor the effects of NaCl on plants concluding the uptake rate of ions, growth of plants and membrane potential of root cells. We also observed the possible abilities of calcium in ameliorating salt-stress and maintaining the stability of transmembrane potential. The main results were as follows:1. The salt-stress affected the absorptions of the two main nutrient elements(K⁺,NO₃^-) of two maize varieties, but different salt-tolerant maize varieties had different responses: the salt-tolerant maize variety(Denghai 11) at normal condition had smaller uptake rate of Na⁺, NO₃^-, K⁺ than the common maize variety(Yangnuo 1), which meant that the salt-tolerant variety might have higher utilization efficiency of nutrients. On the other hand, under salt stress the uptake rate of nutrients of the the salt-tolerant variety was less decreased and could still keep the similar or even higher uptake rate of nutrients (especially for NO₃^-) than the common maize variety, that is to say, the salt-tolerant maize variety could maintain the balance of nutrients in plants and consequently improving its tolerance to salt stress.2. The Na⁺ uptake rate of wheat increased with the increasing of NaCl concentration, while K⁺ and NO₃^- uptake rate decreased with the increasing of NaCl concentration. It indicated that the Na⁺ accumulated and nutrient ions would be scarce with the increasing of NaCl concentration.3. Under salt stress the growth of roots, plant height, root vitality, biomass of maize decreased and the cell membrane permeability increased. 4. Under the 100mmol L-1NaCl stress, the addition of CaSO4 had some ameliorative effects; while under the 200mmol L-1NaCl stress, the addition of CaSO4 even aggravated the salinity injury.5. Under salt stress the growth of roots, biomass of wheat decreased and the cell membrane permeability, the proline content increased. The calcium could ameliorate the salt stress to some extent, but no significant effect. There were no significant differences between different Ca2⁺ concentrations.6. NaCl could lead to depolarization of maize and wheat root cell membrane. The response time of depolarization was shortened with the increasing of NaCl concentration. The extent of depolarization was positive correlation with NaCl concentration and increased with the increasing of NaCl concentration. Calcium could postpone the response time of depolarization caused by NaCl and decreased the mean value of depolarization.7. Effects of 8mmol L-1NaCl on membrane potential of root cells varied with different tested crops: The extent of depolarization of maize root cells was smaller than that of wheat root cells and that of soybean root cells was the biggest. The response time of depolarization of maize roots was shorter than that of wheat and it was also shorter than that of soybean.8. There was a close relationship between the extent of depolarization of maize and wheat root cell membrane and the uptake rate of Na⁺ and K⁺: The extent of depolarization increased with the increasing of NaCl concentration, the Na⁺ uptake rate also increased with the increasing of NaCl concentration while the K⁺ uptake rate decreased. The results indicated that NaCl might affect the K⁺ transmembrane uptake by changing the membrane potential of root cells.