Growth and Physiologic Effects of Brazil Banana Seedlings under Salinity Stress and Alleviatory Effect of Calcium
|Keywords||Brazil banana Salinity stress Calcium Growth Physiology|
Banana (Musa spp.) is one of the most important economic crops in tropical and subtropical regions of the world. Its production, however, presents some limitations in areas with dry and salt-affected soils, while the mechanism of salt tolerance of banana, and the relation of calcium and salinity-tolerance controlling were not so clear so far. In this paper, Musa AAA Cavendish var. Brazil was treated by different concentration of NaCl, different concentration and different kind of exogenous calcium, EGTA and TFP by solution culture. Those experiments aimed to provide fundamental studies about the mechanism of salt tolerance of banana. The results were as follows:1. Growth of Brazil banana seedling was promoted by 5～2O mmol/L NaCl, while those treatments whose NaCl concentrations were higher than 20 mmol/L showed inhibition of growth. The aerial part was more sensitive than roots. Brazil banana was thought to be a salt-sensitive plant, and its threshold salinity value was about 20～30 mmol/L NaCl.2. The relative water content of Brazil banana seedling leaves were decreased under salinity stress, along with declines in Gs, Tr, chlorophyll content and photosynthesis, and increased Ci, indicating that decrease of Brazil banana leaves photosynthesis under salinity stress was mainly caused by the non-stomatal factor.3. As the concentration of NaCl increased, the content of Na+ increased in Brazil banana seedling, roots and pseudostem increased more than leaves; K+ content increased in pseudostem and leaves, increased and then decreased in the root; Ca2+ content decreased significantly along with a significantly decline in K+/Na+ and Ca2+/Na+ ratio, while leaves dropped least. Therefore, the salt exclusion mechanism of Brazil banana might be:root and pseudostem accumulated Na+ to restrict its movement to the leaves, while roots transport K+ to the aerial part, ensuring a higher K+/Na+ and Ca2+/Na+ ratio in leaves, reduced symptom expression and reduced damage to the leaf lamina.4. The root activities of Brazil banana seedling dropped under salinity stress, and the proline, soluble sugar and soluble protein content in leaves and roots increased; MDA content and membrane permeability both increased significantly, while POD, SOD activity increased. Indicated that the reactive oxygen species were accumulated in Brazil banana seedlings under salinity stress, caused great damage in plasma membrane, affected the cell metabolism of soluble solute.5.148,100,52,41,39,34,32,28 and 25 kilodaltons proteins were expressed in Brazil banana seedling leaves whether it had been under tress, while 140 and 124 kilodaltons proteins were induced, but just expressed 2 and/or 6 days after treatments by high concentration of NaCl.6. The symptom of Brazil banana seedlings of salinity stress could be alleviated by adequate concentration exogenous calcium treatment, in the contrary, high concentrations treatment aggravated the salt injury. It was suggested that 5 mmol/L was the optimal concentration of Ca2+, CaCl2 and Ca(NO3)2 were better than Ca(AC)2.7. After treatment of adequate concentration of Ca2+, membrane permeability of Brazil banana seedlings under salinity stress was reduced, lipid peroxidation was reduced, cell membranes were protected, proline content and osmotic potential were increased, at the same time, water content of leaves was increased, damage of chlorophyll was relief, so that a normal photosynthesis could be maintained, so as to the ion balance of plant, and the salt damage was relief. However, such remission was blocked by the treatment with Ca2+ chelator EGTA and the CaM antagonist TFP. These two treatments significantly increased the membrane permeability, inhibited antioxidant enzymes activities, increased membrane lipid peroxidation, limited the proline accumulation, reduced water content of leaf and accelerated the degradation of chlorophyll, inhibited leaf photosynthesis, reduced K-1/Na+ and Ca2+/Na+ ratio. It was indicated that the calcium signaling system was involved in controlling salinity stress resistance of Brazil banana.