Physiological Effect Of5-aminolevulinic Acid On Cold Resistance Of Banana Seedlings

Banana is one of the most important economic crops in tropical and subtropical areas, it is also one of the staple fruit in southern China. However, in winter, banana is apt to suffer injury by cold wave, which has resulted in large economic losses.5-aminolevulinic acid(ALA) is considered to be a new plant growth regulator, which could promote the crop production, improveit’s cold resistance、salt tolerance and other various physiologic functions. So far, there is no report about the effect of ALA on cold-resistance of banana seedlings. In order to research cold-resistance mechanism of banana and offer theoretical basis on anti-cold cultivation of banana, the physiological effect of exogenous ALA on inducing cold resistance of banana seedlings was studied in this paper.In this study, banana (Musa AAA Group Cavendish cv. Brazil) seedlings were stressed in plant growth chamber under low temperature after being sprayed with ALA for several days.The effcet of different ALA spraying ways on cold tolerance of banana seedlings were studed by comparing the physiological indexes among the same concentration of different spraying ways and the same spraying way of different concentrations, by which the effective spraying way of ALA was explored; On this basis, physiological effects of ALA concentrations, spraying times, culture times on cold tolerance of banana seedlings were also studied to infer the best ALA concentration, spraying time and culture time on improving cold resistance of banana seedlings; Moreover, effect of ALA on photosynthetic characteristic and recovery capability of banana seedlings under low temperature stress were further studied. The results indicated as follows:1. Foliage spraying was better than root irrigation of ALA on alleviating cold injury in banana seedlings. Compared with the same concentration of root irrigation, the chlorophyll content was significantly increased, relative conductivity and MDA content were significantly reduced with treatment of foliar spraying, relative water contents SOD and POD activities of spraying5mg-L-1ALA treatment were increased by12.1%、64.5%and12.3%respectively.2. The best combination for enhancing banana cold-resistance ability were1mg-L"1ALA, spraying3times and culture for5days. That’s before5days of cold current coming, after being sprayed with1mg-L-1ALA at8:00and20:00for3times totally, cold resistance of banana seedlings could bring most effectively improved. 3. ALA could maintaine stress stability in banana seedling leaves under low temperature. At early period of cold stress (within24hour), there was no significantly difference between exogenous ALA treatment and low temperature control. After being stressed for36hour, proline,soluble protein content,SOD and POD activities of exogenous ALA treatment were increased by19.15%、47.3%、11.7%、58.4%respectively, generation rate of superoxide free radical(O2-)、relative conductivity、 MDA content were also decreased by85.3%、27.6%、37.1%respectively than low temperature control.So it implied that exogenous ALA could improve cold-resistant Physiological effeets of banana seedlings, enhance SOD and POD activities, reduce generation rate of superoxide free radical(O2-) and the membrane lipid peroxidation degree, as well as increase accumulation of proline and soluble protein.4. ALA could effectively enhance photosynthetic capability of banana seedlings under low temperature stress.The treatments with exogenous ALA could significantly raise the net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr) and stomatal limitation (Ls) of the leaves of banana seedlings. They were increased by121.3%、281.7%、335.9%and209.9%respectively.Water use efficiency(WUE)and intercellular CO2concentration (Ci) were also decreased by78.7%and37.4%respectively than low temperature control; decreased the minimal fluorescence (Fo) by23.8%; the PS Ⅱ maximal photochemical efficiency (Fv/Fm)、the ability of PS Ⅱ reaction center to trap energy from antenna pigment(1/Fo-1/Fm)、PS Ⅱ actual photochemical efficiency(ΦPS Ⅱ)、antenna transformation efficiency (Fv’/Fm ’)、photochemical quench (qP)、the non-photochemical quench(NPQ) and RuBPCase activity were increased by4.9%、38.1%、117.3%、24.7%、63.1%、93.3%and64.5%respectively than low temperature control, the difference have reached at significant or very significant level. So it implied that exogenous ALA could relieve chilling injury of banana seedlings by increasing photosynthetic capacity.5. Exogenous ALA could promote synthesis of endogenous ALA in banana leaves under low temperature stress, enhance the synthesis of chlorophyll.By spraying exogenous1mg·L-1ALA pretreatment could significantly increase endogenous ALA content in banana leaves under low temperature stress, and was a low temperature control1.372times; ALA-D activity of key enzymes of chlorophyll was increased by81.8%and chlorophyll content was increased by90.6%than low temperature control, differences have reached the significant level. So it implied that exogenous ALA could improve photosynthesis of banana seedlings by raising the chlorophyll content under low temperature stress.6. Exogenous ALA could enhance recovery capability of banana seedlings after chilling.1mg-L-1ALA could effectively restrain increase of the membrane permeability and accumulation of MDA content in banana seedlings during stress and recovery of low temperature, they were decreased44.4%and81.0%respectively than low temperature control; while the content of osmotic adjustment and the activities of SOD, POD were decreased under the normal conditions after low temperature stress prompting membrane damage back to the control levels.