Physiological Mechanism Of Salt Tolerance For Two Different Genotypes Banana And Ca²⁺Changes Under Salt Stress

Banana (Musa spp.) is salt-sensitive plant. One of the most serious problems limiting the extension of banana plantation in the world is soil salinization. Therfore, to extend banana cultivation, one method is to improve banana tolerance of salt by cultivation techniques and the other is to cultivate new salt-tolerant crop varieties. Two different genotypes of banana seedling those were Brazil banana (Musa. AAA cavendish var. Brazil) and Fenjiao (Musa. ABB Pisang awak), were threatened under different concentration of NaCl(30mmol/L、60mmol/L、90mmol/L). After treated for0、2、4and6days, the changes in two varieties of banana seedling related salt tolerance physiological characters under different salt stress conditions were determined. And these characters were analysed by principal component analysis and subject function analysis. After being enhanced or blocked Ca2+·CaM signal transduction by treated with exogenous calcium and calmodulin antagonists, indexes of leaves and roots of Brazil banana and fenjiao seedling under salt stress were studied, including the relative water content and the membrane permeability et al. With scan-ningion-selective electrode technique, the effects of salt shock on transient Ca2+and K+kinetics at apical regions of banana seedling were studied. The purpose of this study was to provide a theoretical basis for salt tolerant breeding and cultivation of banana. And provide a theoretical basis for calcuim signaling system in regluting physiological.The study results as follow.1. As stress levels increase, the membrane permeability and MDA content of Brazil banana and fenjiao leaves were increased significantly compared to their control. And the membrane permeability and MDA content in their roots were aslo increased significantly.2. with prolonged time and increased concentration of salt, chlorophyll content, leaves relative water content of Brazil banana and fenjiao were decreased significantly compared to their control.3. The root vigor of two varieties bananas under salt stress were significantly decreased. On the6days, as NaCl stress increasing, root vigor of Brazil banana was decreased significantly by32.26%,42.38%,57.85%, respectively; while feijiao was decreased significantly by12.64%,39.30%,41.36%, respectively, compared to its control. The root vigor of Brazil banana is decreased more than fenjiaos, which mean that Brazil banana roots is more sensitive to salt stress, suffered more damage.4. Proline content and soluble sugar content in leaves and roots of Brazil banana and fenjiao, were significantly increased under NaCl stress. Soluble protein content of leaves in two varieties banana showed a significant increasing under salt stress, and as stress levels increasing, amplitude of variation of their contents decreased gradually. On the2days, the soluble protein content of Fenjiao reached the maximum, while Brazil banana reached maximum on the4days.5. The SOD activity in leaves and roots of Brazilian banana and fenjiao seedlings were significant increased under salt stress. When under90mmolL-1NaCl stress, the activity of SOD of two varieties of banana seedlings was increased18.42%and91.29%, respectively. POD activity of roots in two varieties of banana under three salt stress levels showed the same trend to leaves under salt stress. As concentration of NaCl increase, their activities increased gradually.6. The20characters were analysed by applicating principal component analysis. And the characters which had a large eigenvectors were take up, including:MDA content of leaves, soluble sugar content of leaves, MDA content of roots, SOD activityof roots, soluble sugar content of roots, proline content of roots, soluble protein content of roots, SOD activity of leaves, membrane permeability of roots. Those characters were summed up the majority information of the20characters and were the important indicators to evaluate the salt tolerance of banana.7. Application for subjectional function, Brazil banana and fenjiao of salt tolerance were comprehensively evaluated.The salt tolerance of Fenjiao(ABB) was better than Brazil banana(A AA). It was found in these two varieties of banana that the more B genome was, the more stronger salt tolerance of banana was. It suggested that genome types and salt tolerance was a sort of relevance.8. K+efflux of Brazil banana under salt stress was increased rapidly, then it was decreased rapidly, after4.5minute it reached to its original balance, it suggested that, Brazil banana can be achieved K+balance regulation under salt stress to some extent60mmol/L NaCl salt shock on transient Ca+efflux at apical regions of Brizal banana increased rapidly, then the Ca2+efflux of Brizal banana of salt-induced gradually weakened, and after about5minute reached to new balance; while Ca2+of fenjiao from influx transformed into efflux, then Ca2+efflux gradually weakened, and it needed10minute to restore new balance, It was showed that Ca2+flux of banana were varieties of different genotypes, and Brazil banana roots Ca2+efflux is lager than fenjiao’s under salt stress. when treated with calmodulin antagonists EGTA and TFP, the Ca2+influx under salt stress were significantly decreased, compared to salt control. Which was to further proved that salt shock on transient Ca2+efflux at apical regions of banana come into being calcium signal.9. As concentration of salt increases, the leaf in the middle spongy tissue gap of banana becomes larger, and some symptoms were appeared, such as the lower epidermis of leaves disintegrate gradually. The result showed that, after treatment with calmodulin antagonists EGTA, TFP and LaCl3, the relative water content and content of Chl in leaves of Brazil banana and fenjiao seedling under salt stress were significantly decreased, while the membrane permeability in their leaves were significantly increased, which made leaf anatomical structure of banana suffered more damage. And the damages of salt stress to banana seedling can be mitigated in a certain degree by applying adequate concentration of calcium. It suggested that salt tolerance and Calcium signal was a sort of relevance.