Studies On The Evaluation Of Chilling Tolerance And Physiology Mechanism Of Chilling Adaptation Of Pepper(Capsicum Annuum L.)

Chilling stress during winter and early spring usually causes flower abscission and other injuries of pepper (Capsicum annuum L.), and then has a significant negative effect on year-round production of this crop. So it is important to study the physiology mechanism and cultivation techniques of pepper under low temperature conditions. In this paper, 10 varieties with different cold tolerance were selected, and the effect of low temperature on the pollination, fertilization, carbohydrate metabolization, membrane injury peroxidation and endogenous hormones of pepper were investigated, and the effect of exogenous regulators on the pepper production during cold season was studied. Furthermore, galactinol synthase, a cold induced gene, was cloned and the exprerssion pattern of this gene under chilling stress was studied. The results provided some beneficial clues for pepper cold tolerant breeding and cultivation. The main results showed as follows:The chilling stress inhibited the vegetation growth and field formation of pepper significantly. Among the ten varieties, SCH and SJ-5 has the lowest and highest cold tolerance, respectively. The correlation analysis among vegetative- chilling- tolerant index, yield- formation- chilling- tolerant index, germination index and seedling chilling injury index indicated that the seedling chilling injury index and the germination index at 15℃were feasible to identify the chilling tolerance of pepper varieties.The chilling sensitivity of stamen, pistil and fertilization of pepper at different stages was studied. According to the investigation of fruit-set, seeds number per fruit, at alabastrum stage the stamen were more sensitive than the pistil to chilling stress, while at anthesis, the pistil and fertilization were more susceptible than the stamen.With the development of pepper fruit, the content of starch, total soluble sugars and sucrose in mesophyll, internode, pulp and root were all improved, and the content of glucose and fructose of mesophyll, internode and pulp were highest in swelling time of fruit. AI and NI activity showed a low-high-low trend and SPS activity increased is similarly with sucrose. Because of chilling stress, the content of starch and sucrose in different organs were significantly decreased, while the content of total soluble sugars, glucose and fructose in leaf were increased. Low temperature enhanced AI and NI activity and reduced SPS activity.Pro content, POD activity and MDA content in leaves increased significantly under cold stress. The content of USFA was adding and that of SFA was decreasing continually with the falling of temperature. Under chilling stress, A new POD isozyme band (Rf =0.3145) in leaves of pepper just were the production of chilling stress.Chilling stress increased the level of Put, Spd, Spm and ABA and reduced the level of GA₃ and IAA in leaves. Changes of Put and ABA might be an emergency response of plant to low temperature because their contents would come back to the control level as soon as the chilling stress stopped. While the changes of Spm and IAA may be an adaptitude response because they can not restored to the normal level until days after normal temperature condition begin.1 mmol·L^-1 Put and 150 mg·L^-1ABA applied at seedling stage with six or seven leaves were helpful to increase fruit-set and yield, while 200 mg·L^-1Pro and 100 mg·L^-1ABA had the best effect at anthesis. Exogenous ABA application can relievd the chilling injury of pepper remarkably by enhancing Pn, Gs and Ci in leaves and improving assimilation rate and N, P and K utilization.Full length cDNA sequence of a galactinol synthase gene (GS) (GenBank locus: EF566470) was cloned from cold-stressed pepper (Capsicum annuum L.'SCH') leaves using RT-PCR and rapid amplification of cDNA ends (RACE). The gene consists of 1444 bp encoding a protein of 336 amino acids. Phylogenetic analysis revealed that pepper GS is high homologous to reported GS of other plants. RT-PCR analysis showed that GS mRNA was induced in pepper leaves after 4℃or 10℃cold- stress for 6 h, but not accumulated in cold -stressed stems and roots, no GS mRNA can be detected in pepper tissues under normal temperature. Southern blot analysis indicated that there may be several GS copies in the pepper genome.