The Differential Responses of Chlorophyll Fluorescence Parameters and Lipid Metabolism to Low Temperature between Cycas Bifida and C. panzhihuaensis

Abstract

Background: Our previous work showed that freezing tolerance of Cycas panzhihuaensis was higher than that of C. bifida. However, the mechanisms underlying the differential freezing tolerance of the two species is not clear. Photosynthesis is one of the most temperature-sensitive processes. Lipids play important roles in membrane structure, signal transduction and energy storage which are closely related to stress response of plants. Hence, the chlorophyll fluorescence parameters and lipid profiles of the two species were characterized to explore the dynamic changes of photosynthetic activity and lipid metabolism following low temperature and subsequent recovery. Results: The photosynthetic activity decreased significantly with the decrease of temperatures in C. bifida, reaching to zero after recovery, which however, was little affected in C. panzhihuaensis. Lipid composition of C. bifida was more affected by cold and freezing treatments than C. panzhihuaensis. Compared to the control, the proportions of all the lipid categories recovered to the original level for C. panzhihuaensis but those of most lipid categories changed significantly for C. bifida after 3 d of recovery. Particularly, the glycerophospholipids and prenol lipids of C. bifida degraded severely during recovery period for C. bifida. The changes of acyl chain length and double bond index (DBI) occurred in more lipid classes immediately after low temperatures in C. panzhihuaensis than those in C. bifida. DBI of the total main membrane lipids of C. panzhihuaensis was significantly higher than that of C. bifida following all the treatments. Conclusions: The results of chlorophyll fluorescence parameters confirmed that the freezing tolerance of C. panzhihuaensis was higher than that of C. bifida. The lipid metabolism of the two species had differential responses to low temperatures. The homeostasis and plastic adjustment of lipid metabolism and the higher level of DBI of the main membrane lipids might contribute to the higher tolerance of C. panzhihuaensis to low temperature.