Response Of Function,Antioxidative Capacity And Ultrastructure Of Chloroplast In Two Wucai Genotypes Against Chilling Stress

Wucai(Brassica campestris L.ssp.chinensis var.rosularis Tsen et Lee.)is a biennial herbaceous plant of cruciferous.It grows well in cool climate,but can be caused decline of economic yield and quality in lower temperatures.As the cultivation area and market needs of wucai are on the increase,it is vital to evaluate its chilling tolerance systematically and further explore its chilling tolerance mechanisms.In this study,two wucai genotypes,WS-1(chilling-tolerant genotype)and Ta2(chilling-sensitive genotype)were selected as experiment material with different sensitivity to low temperature.Growth parameters,photosynthetic and fluorescence characteristics,oxidative damage and antioxidant capacity of chloroplast in two wucai genotypes were evaluated.The main results are as follows.1.Chilling stress caused shoot fresh weight,shoot dry weight;leaf relative water content and membrane stability index were gradually decreased in wucai seedlings.Obviously,the declines of these indicators in the chilling-sensitive genotype Ta2 were higher than in the chilling-tolerant genotype WS-1.2.Under chilling treatment,PN,Gs and Tr of wucai seedlings were significantly decreased,and photosynthetic parameters exhibited lower level in Ta2 than in WS-1.Moreover,the rapid chlorophyll fluorescence dynamics curve(OJIP)showed the J-step of two wucai genotypes showed a rise,and Ta2 was significantly higher than WS-1.These data indicated that photosynthesis and photochemical activity were more serious in the chilling-sensitive genotype Ta2 than in the chilling-tolerant genotype WS-1.3.Chilling stress resulted in the decrease of ATPase activity and ATP level,the ATP level of WS-1 was always higher than that of Ta2 before and after chilling stress.It was beneficial to reduce the damage to chloroplast by chilling stress.4.Chilling stress inhibited the carboxylation process Calvin cycle of wucai seedlings,reducing the key enzymes of Calvin cycle,such as Rubisco,s FBPase?GAPDH and Aldolase.And inhibition to the chilling-tolerant genotype WS-1 was lower than the chilling-sensitive genotype Ta2.5.Chilling stress resulted in the degradation of chlorophyll and the increase of carotenoid synthesis.The chloroplast ultramicrographic section showed that chloroplast structure of the chilling-sensitive genotype Ta2 was more severely damaged than the chilling-tolerant genotype WS-1 during chilling stress.6.In chloroplast of two genotypes,Ta2 showed higher degree of membrane lipid peroxidation under chilling stress,compared to WS-1.As the stress time increased,the antioxidant capacity of As A-GSH cycle in WS-1 chloroplast was retained higher activity than Ta2,against oxidative stress caused by chilling temperatures.