Effect Of Low Temperature And Light Intensity Stress On Photosynthetic Characteristics Of Cucumber Seedling

The adaptation difference of photosynthesis in different cucumber varities to suboptimal temperature and low light intensity were studied with'SARIG HA-454'(Europe variety),'Cuiliü'(South China variety) and'Jinyou No.3'(Nouth China variety) as materials. Effects of low light intensity, suboptimal temperature, suboptimal temperature and low light intensity, low temperature and light intensity on growth and photosynthesis of cucumber seedlings were studied. And the mechanism of calcium affects phoatosynthetic function of cucumber under suboptimal temperature and low light intensity was studied with'Jinyou No.3'as material. The results showed as follows.1.'SARIG HA-454'had the largest leaf area,'Cuiliü'had the least one under control condition. However, the dry mater of'Jinyou No.3'was more than those of'SARIG HA-454'and'Cuiliü'. During 7d suboptimal temperature and low light intensity stress,'Jinyou No.3'showed the largest, while'SARIG HA-454'was the least in increasement per day of leaf area and dry mater.2. The photosynthetic rate (Pn), carboxylation efficiency (CE) and actual photochemical efficiency of PSâ…¡(ΦPSâ…¡) of the experimental varieties decreased, but no significant changes in maximum photochemical efficiency of PSâ…¡(Fv/Fm) had been observed. Although chlorophyll content increased, lower the ratio of Chl a/b. Comparison among different varieties, the Pn and CE of'Jinyou No.3'were the highest, while those of'SARIG HA-454'were the lowest. Before imposed in stress condition,'SARIG HA-454'was the highest and'Jinyou No.3'was the lowest inΦPSâ…¡, however, that of'SARIG HA-454'decreased,'Jinyou No.3'and'Cuiliü'changed little after stress. So we suggested that the adaptability of'Jinyou No.3'to suboptimal temperature and low light intensity was higher than that of'SARIG HA-454'and'Cuiliü'. It was the important basis that keeping higher efficiency for solar energy conversion and activity of carbon assimilation enzymes on developing adaptability to suboptimal temperature and low light intensity.3. Low light, suboptimal temperature, suboptimal temperature and low light intensity, low temperature and light intensity stress all led to decrease in net photosynthetic rate (Pn), that was mainly attributed to non-stomatal limitation, besides of suboptimal temperature, suboptimal temperature and low light stress, which had something to do with stomatal limitation. Temperature plays a primary role to Pn under suboptimal temperature and low light intensity.4. During 10d low light or suboptimal temperature and low light, the light compensation point declined, while theΦPSâ…¡increased, therefore the adaptation enhanced. The light compensation point of stress seedlings in suboptimal temperature also decreased, and theΦPSâ…¡and Fv/Fm decreased, but changes in Fo had not been observed. Low temperature and light intensity led to increase in light compensation point obviously, and yet resluted in decrease inΦPSâ…¡and Fv/Fm and accompanied by increase in Fo. This indicates that cucumber seedlings can auto-accommodate low light environment by decreasing the light compensation point and developing photochemical efficiency under low light intensity or suboptimal temperature and low light intensity. Suboptimal temperature or low temperature and light intensity stress are likely to induced PSâ…¡photoinhibition, and furthermore, low temperature and light intensity stress probably resulted in irreversible injury to PSâ…¡reaction centers.5. Treated with 10mmol/L CaCl2 before imposed to suboptimal temperature and low light intensity stress condition, the Pn, CE, photochemical quench (qP),ΦPSâ…¡, electron transport rate (ETR), Ribulose 1,5-Bisphosphate carboxylase(RuBPase) and Ca²⁺-ATPase activity et al. all elevated in diverse level, in compare with that pretreated by H2O. However, the results which pretreated with LaCl3,EGTA and CPZ was in contrary. It indicated that Ca²⁺ took an important part in regulating the photosynthesis of cucumber seedlings. It alleviated the effects of suboptimal temperature and low light intensity by propelling the opening proportion of PSâ…¡reaction centres, maintaining higher photosynthetic electron transfer and the efficiency for solar energy transformation, and heightening RuBPase and Ca²⁺-ATPase activity...