Study On NaCl Induced Adaption To Low Temperature And Low Light Intensity Of Cucumber Seedlings

The effect of NaCl pretreatment on osmotic regulation system, reactive oxygenscavenging system and photosynthesis under low temperature and low light intensity, with‘Jinyou3’ cucumber seedlings were investigated. The objective is to verify the mechanism ofNaCl induced cross adaptation to low temperature stress in cucumber (Cucumis sativa L)seedlings. The main results were as follows:1. The appropriate pretreatment concentration of NaCl was screened, and that was100mmol·L-1. It was showed the optimum inducing effect that cucumber seedlings werepretreated for three days and recovered for two days.2. Pretreated with100mmol·L-1NaCl led to an increase in leaf area and dry matter weight,while a decrease in chilling injury index, compared with the control. This revealed that NaClpretreatment alleviated the injury of low temperature and low light intensity to cucumberseedlings.3. Pretreated with NaCl before exposure to stress condition, cucumber seedlings showed asignificant lower decrease degree in relative water content, water potential and osmoticpotential, while a higher increase degree in contents of proline, soluble sugar and solubleprotein, in comparison to the control. These data indicated that the adaptation to lowtemperature and low light intensity was related to the higher osmotic adjustment ability.4. Low temperature and low light intensity caused an obvious increase in electrolyteleakage (EL), and contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA), aswell as the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) andglutathione reductase (GR), and the contents of acetylsalicylic acid (AsA) and glutathione(GSH). NaCl pretreatment declined the increase degree of EL, and the contents of H2O2andMDA, and enhanced the increase degree of the activities of SOD, CAT, POD and GR, and thecontents of GSH and AsA in the cucumber seedlings under low temperature and low lightintensity. This suggested that NaCl pretreatment diminished the level of lipid peroxidationcaused by low temperature and low light intensity stresss compared to the control.5. Photosynthetic rate (Pn), the rate of transpiration (Tr), stomatal conductance (Gs),carboxylation efficiency (CE), actual photochemical efficiency of PS Ⅱ(ΦPS Ⅱ), maximalphotochemical efficiency of PS Ⅱ indarkness (Fv/Fm) of cucumber seedlings all decreased under low temperature and low light intensity, but the intercellular CO2concentration (Ci) andinitial fluorescence yield (Fo) increased. These suggested that non-stomatal limitation is themain cause of the decrease of Pn in cucumber seedlings during stress period. The Pn, Gs, CE,Tr, ΦPS Ⅱ and Fv/Fmwere higher in leaves of pretreated seedlings than those in the controlleaves. These data revealed that NaCl pretreatment alleviated the damage of low temperatureand low light intensity to photosynthetic apparatus.