Abstract:

Cold-induced stress memory，as a flexible behavior in response to environmental changes，plays an important role in plant acclimation to adverse conditions. To elucidate the regulating mechanism of cold circulation-induced stress memory on the environmental adaptability of photosynthesis in cucumber in solar greenhouse.‘Jinyou 35’cucumber plants were used as experimental materials，and were treated in an artificial climate chamber. There were four treatments： no cold induction treatment（C0R0），single cold induction（C1R1：24 h treatment at a day/night temperature of 8 ℃/8 ℃ followed by a recovery period of 48 h at 25 ℃/18 ℃），repeated cold circulation induction twice（C2R2：same conditions as C1R1，cycle twice），and repeated cold circulation induction three times（C3R3：same conditions as C1R1 treatment，cycle three times）. Subsequently，the seedlings were exposed to chilling stress condition（8 ℃/5 ℃）. The C0R0 treatment at normal temperature（25 ℃/18 ℃）was used as the control（CK）. The relevant indexes of photosynthesis were measured after 48-72 h of low temperature. The seedlings exhibiting the most favorable cold circulation-induced effect and C0R0 treatments were then selected and cultivated within a solar greenhouse to investigate the effect of cold-induce memory on the photosynthetic rate（P_n），photochemical efficiency，growth and yield. The results showed that C1R1-，C2R2- and C3R3-treated seedlings exhibited significantly higher P_n，stomatal conductance（G_s），transpiration rate（T_r），as well as activities and mRNA expressions of ribulose-1,5-bisphosphate carboxylase（RuBPCase）and Rubisco activase（RCA）. Additionally，the C1R1，C2R2 and C3R3 treatments revealed an increase in maximum photochemical efficiency of PSⅡ（F_v/F_m），actual photochemical effect of PSⅡ（Φ_PSII），electron transfer rate of PSⅡ[ETR(II)]，quantum efficiency of PSⅡ photochemistry[Y(Ⅱ)]，electron transfer rate of PSⅠ[ETR(Ⅰ)]and quantum efficiency of PSⅠ photochemistry[Y(Ⅰ)]. Whereas，there were either lower or no significant differences observed in intercellular CO₂ concentration（C_i），compared with the C0R0 treatment under chilling stress. Among the four treatments，C2R2-treated plants exhibited the greatest increase in P_n，G_s，T_r，F_v/F_m，Φ_PSⅡ，activity and mRNA expression of RuBPCase and RCA，and decrease in C_i，while C1R1 treated seedlings showed the least changes in these parameters. The P_n，F_v/F_m and Φ_PSⅡ of C2R2 treated cucumber grown in the solar greenhouse were significantly higher than those of the C0R0 at low temperatures. These findings indicate that the cold circulation induction maintain higher photosynthetic carbon assimilation capacity and photosystem activity，alleviate the damage to photosynthetic apparatus caused by chilling stress，thereby improve the growth and development of cucumber. The yield of C2R2 treatment was 10.25% higher than that of C0R0. The stress memory induced by two cycles of cold circulation in cucumber plants was between 20 and 30 days.

Key words: cucumber, cold circulation induction, stress memory, photosynthesis, yield