Chilling Shock-induced Chilling Tolerance And Its Physiological Mechanism In Jatropha Curcas Seedlings

Jatropha curcas, origining form tropical and subtropical area, belongs to the tribe Jatropheae in the Euphorbiaceae family, is a chilling-sensitive plant that is sensitive to low temperature. Low temperature not only is one of the major environmental factors that affect metabolism, growth, development, geographical distribution, and even survival of chilling-sensitive plants J. curcas, but also a main bottleneck that limits industrial development of J. curcas. In addition, J. curcas is considered as a sustainable energy plants with great potential for biodiesel production due to the fact that its seed contains high oil content. Therefore, finding methods that improve chilling tolerance of J. curcas and understanding its physiological mechanism is of great theoretical and practical significance. However, whether short-term chilling shock can improve chilling tolerance of J. curcas seedlings, and its mechanisms of the acquisition of chilling tolerance induced by shorter-term chilling shock are not completely clear. In this dissertation, based on the present research progress, using J. curcas as experimental materials, the following contents were investigated and the results were as follows:(1) Effect of different seed disinfectants and seed priming agents on seed germination of J. curcas. The results show that Cu SO4 not only had a good disinfection effect, but also improved germination rate, germination index, lipase activity of the seeds. Inversely, other disinfectants weakened germination rate, germination index, lipase activity and the growth of seedlings in J. curcas, indicating that Cu SO4 was a better surface disinfectant for J. curcas seeds. In addition, pretreatment of J. curcas seeds with H2O2 and H2 S greatly improved germination percentage of seeds, and H2 S might be a downstream signal molecule of H2O2 in germination of J. curcas seeds.(2) Effect of different time of chilling shock and recovery on chilling tolerance of J. curcas seedlings. Short-term chilling shock(5 for 4 h) followed by recovery(26for 4 h) could significantly improve survival percentage of 12-day-old J. curcas seedlings under chilling stress at 1 for 5 d. In addition, a 4-h chilling shock without 4-h recovery could not induce the acquisition of chilling tolerance of seedlings. These results suggest that chilling shock could improve chilling tolerance of J. curcas V seedlings, and recovery after chilling shock plays a key role in the acquisition of chilling tolerance induced by chilling shock.(3) Effect of short-term chilling shock, recovery and chilling stress on antioxidant defense system activity in J. curcas seedlings. Short-term chilling shock and recovery obviously enhanced antioxidant enzymes superoxide dismutase(SOD), ascorbate peroxidase(APX), catalase(CAT) and glutathione reductase(GR) activities and expression level of corresponding enzyme genes, as well as the levels of antioxidants ascorbic acid(As A) and glutathione(GSH); and alleviated a decrease in activities of SOD, APX, CAT, GR and guaiacol peroxidase(GPX), As A and GSH contents, and the ratio of the reduced antioxidants to total antioxidants [As A/(As A+DHA) and GSH/(GSH +GSSG)] in leaves of J. curcas seedlings under chilling stress. These data illustrate that antioxidant defense system, including antioxidant enzymes and antioxidants, exerts a very important role in the acquisition of chilling tolerance induced by chilling shock followed by recovery in J. curcas seedlings.(4) Effect of short-term chilling shock, recovery and chilling stress on osmolyte in J. curcas seedlings. Short-term chilling shock and recovery markedly increased the contents of osmolytes proline(Pro), betaine(BT), total soluble sugar(TSS) and trehalose(TRE), as well as gene expression of corresponding enzymes(1-pyrroline-5-carboxylate synthetase(P5CS), ornithine aminotransferase(OAT), proline dehydrogenase(Pro DH), betaine dehydrogenase(BADH), trehalose-6-phosphate phosphatase(TPP)) involved in osmolyte synthesis in leaves of seedlings of J. curcas compared with the control without chilling shock. Under chilling stress, chilling-shock seedlings maintained higher Pro, BT, TSS and TRE contents in leaves of seedlings of J. curcas from beginning to end compared with the control. These results indicate that osmolytes play a very important role in chilling tolerance induced by chilling shock followed by recovery in J. curcas seedlings.(5) Change in lipidomic in leaves of J. curcas seedlings during the course of short-term chilling shock, recovery and long-term chill hardening(12 for 1 and 2 d) was analyzed using liquid chromatography-electrospray ionization-mass spectrometry(LC-ESI-MS) approach. The results show that short-term chilling shock, recovery and long-term chill hardening triggered significant change in the relative abundances of nine classes and 71 species of membrane lipids, including six classes(phosphatidylethanolamine(PE), phosphatidylcholine(PC), phosphatidylglycerol(PG), phosphatidylinositol(PI), lysophosphatidylcholine(lyso PC) and lysophosphatidylglycerol(lyso PG) and 45 species of phospholipids; two classes(digalactosyldiacylglycerol(DGDG) and monogalactosyldiacylglycerol(MGDG)) and 20 species of glycolipids; and one class(sulfoquinovosyldiacylglycerol(SQDG)) and six species of sulfolipids in leaves of J. curcas seedlings. In addition, short-term chilling shock, recovery and long-term chill hardening increased obviously the relative abundances of total phospholipids, PE, PI, phosphatidylinositol-4-monophosphate(PIP), lyso PC, lyso PG, DGDG and SQDG. Also, during the process of short-term chilling shock, recovery and long-term chill hardening, the relative abundances of six PEs(36:2-, 36:3-,38:3-, 38:4-, 38:5- and 38:6-), three PCs(34:1-, 36:1- and 36:4-), two PGs(34:2- and 34:4-), three SQDGs(32:0, 34:2- and 34:3-), 34:1-PI, 34:5-DGDG and 34:2-MGDG, as well as the degree of unsaturation of membrane lipids significantly improved, while the chain length of membrane lipids obviously reduced. Inaddition to these, further study show that the expression levels of fatty acid desaturase 2(Jc FAD2), fatty acid desaturase 3(Jc FAD3), fatty acid desaturase 5(Jc FAD5), fatty acid desaturase 7(Jc FAD7), fatty acid desaturase 6(Jc FAD6) and stearoyl-acyl carrier protein desaturase 3(SAD3) in leaves of J. curcas seedlings were upregulated to some extent during chilling shock and recovery. These results illustrate that maintaining and rebuilding of biomembrane integrality and fluidity was achieved by increasing the contents of membrane lipids(especially phosphalipids), the the degree of unsaturation of membrane lipids and decreasing the chain length of membrane lipids induced by short-term chilling shock, recovery and long-term chill hardening, which might be common physiological basis of hort-term chilling shock- and long-term chill hardening-induced chilling tolerance of J. curcas seedlings.