Study On Physiological Effect And Regulatory Mechanism Of Polyamines On Drought Resistance In Banana Plantlets

Banana belongs to Musa of Musaceae, is one of the world’s important economic crops and an important fruit tree in the southern China. Because of large leaf area, shallow root distribution, banana requires high water. Drought affects the output and quality of banana severely. Polyamines are a class of ubiquitous biologically active low-molecular aliphatic nitrogen bases, and closely related to the stress resistance of plant. However, the studies on physiological effect and regulatory mechanism of polyamines on drought resistance in banana had not been carried. Therefore, the studies of the relationships between polyamines and banana drought resistance had great significance. The purpose of the studies was to provide a theoretical basis for banana drought resistant chemical control, to lay a theoretical foundation for the further research of physiological mechanism about polyamines on enhancing drought resistance in banana. The experiment was conducted with the plantlets of Baxi banana which is one of main cultivars grown. First, foliar sprayed of banana plantlets with Put, Spd, Spm, polyamine biosynthesis inhibitors D-Arg and CHA, then treated under PEG-6000 solution of water culture to simulate drought stress, studied the changes of physiological and biochemical indexes in banana plantlet leaves about drought resistance. The results showed that:1. The pretreatment with suitable concentrations of exogenous Put, Spd and Spm increased the relative water content of the banana plantlet leaves under drought stress, reduced the relative conductivity, promoted the accumulation of proline and soluble proteins, improved the activity of SOD and POD, decreased the rate of O2- production and the accumulation of MDA, thereby enhanced the drought tolerance of banana plantlets.2. By applicating the fuzzy subject function, exogenous Put, Spd, Spm promotive effects on drought resistance of banana plantlets were comprehensively evaluated. The optimum concentrations of the three kinds of polyamines were found to be 1.25 mmol·L-1 Put,1.00 mmol·L-1 Spd,0.75 mmol·L-1 Spm. The effects were Spm＞Spd＞Put.3. At 0 to 72 h under drought stress, the content of endogenous Put, Spd and Spm in leaves of banana plantlets increased and then decreased. The pretreatment with exogenous 0.75 mmol·L-1 Spm,1.00 mmol·L-1 Spd and 1.25 mmol·L-1 Put all improved the content of endogenous Put, Spd and Spm in leaves of banana plantlets under drought stress; The pretreatment with exogenous 1.00 mmol·L-1 D-Arg reduced the content of endogenous Put, Spd and Spm in leaves of banana plantlets under drought stress; The pretreatment with exogenous 1.00 mmol·L-1 CHA reduced the content of endogenous Spd and Spm in leaves of banana plantlets under drought stress, while increased the content of endogenous Put.4. At 0 to 72 h under drought stress, the Pn, Tr and Gs showed a downward trend while the Ci showed a slow upward trend in leaves of banana plantlets. The pretreatment with 0.75 mmol·L-1 Spm,1.00 mmol·L-1 Spd and 1.25 mmol·L-1 Put improved the Pn in leaves of banana plantlets under drought stress, reduced the Tr, Gs and Ci, enhanced the drought resistance of banana plantlets; The pretreatment with 1.00 mmol·L-1 D-Arg and 1.00 mmol·L-1 CHA reduced the Pn in leaves of banana plantlets under drought stress, improved the Tr, Gs and Ci, reduced the drought resistance of banana plantlets.5. At 0 to 72 h under drought stress, the soluble proteins content, SOD activity and POD activity in leaves of banana plantlets increased and then decreased, the MDA content and the rate of O2- production always improved. The pretreatment with 0.75 mmol·L-1 Spm,1.00 mmol·L-1 Spd and 1.25 mmol·L-1 Put all improved the soluble proteins content, SOD activity and POD activity in leaves of banana plantlets under drought stress, decreased the rate of O2-production and the MDA content, enhanced the drought resistance of banana plantlets; The pretreatment with 1.00 mmol·L-1 D-Arg reduced the soluble proteins content, SOD activity and POD activity in leaves of banana plantlets under drought stress, increased the rate of O2-production and the MDA content, reduced the drought resistance of banana plantlets; The pretreatment with 1.00 mmol·L-1 CHA reduced the soluble proteins content, SOD activity and POD activity in leaves of banana plantlets under drought stress, increased the rate of O2-production, while did not increase the MDA content.6. The correlativities of banana plantlets between endogenous polyamines and physiological indexes under drought stress were analysised. The correlation coefficient of (Spd+Spm)/Put ratio and Pn was 0.49516, checked for an extreme significant positive correlation; The correlation coefficients of endogenous Put content, Spd content, Spm content, total three kinds of polyamines with soluble proteins content were 0.54671,0.58966,0.82409, and 0.77520, checked for an extreme significant positive correlation; The correlation coefficients of endogenous Put content, Spd content, Spm content, total three kinds of polyamines with antioxidase activity checked for an extreme significant positive correlation. The correlation coefficients of endogenous Put content, Spd content, Spm content, total three kinds of polyamines with SOD activity were 0.60625,0.71633,0.88251 and 0.85937, with POD activity were 0.58950,0.68036,0.85164 and 0.82825. Under drought stress, the higher ratio of (Spd+Spm) to Put contributed to improve the photosynthesis of banana plantlets,the higher content of endogenous polyamines contributed to promote the accumulation of soluble proteins and improve the activity of antioxidant enzymes, thus enhanced the drought resistance of banana plantlets.