Chilling stress accelerates degradation of seed storage protein and photosynthetic protein during cotton seed germination

Low temperature is one of the major abiotic stresses limiting the productivity and geographical distribution of many important crops. To gain a better understanding of chilling stress responses in cotton (Gossypium hirsutum L.), we carried out a comparative proteomic analysis. Cotyledon proteins of 1-week-old cotton seedlings treated with or without chilling treatment at 4 degrees C were extracted, separated by a two-dimensional gel electrophoresis and compared. Among 1500 protein spots reproducibly detected on each gel, 25 protein spots were down-regulated and 29 were up-regulated. Seven cotton proteins were identified by mass spectrometry analysis as beta-globulin A precursor fragments. One was identified as a Rubisco large subunit fragment, providing evidence of both seed storage protein and photosynthetic protein destruction by chilling stress. The related physiological and biochemical analysis showed that there was a significant increase in endopeptidase activity and activated oxygen generation rate, and an obvious decrease in carboxylation efficiency and maximum net photosynthetic rate of cotton seedlings under chilling stress. Based on the above results, the degradation mechanisms of beta-globulin and Rubisco under chilling stress were discussed. In conclusion, our study provides new insights into chilling-stress responses in cotton and demonstrates the advantages of proteomic analysis.