Plant desiccation tolerance: from physiology of seeds to the molecular mechanism of vegetative tissues

• Main Authors: Mao-Sen Liu, 劉茂森
• Other Authors: Tsan-Piao Lin
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/51845133691446026643

博士 === 國立臺灣大學 === 植物科學研究所 === 96 === Membrane phospholipids play an important role in acclimation of seeds to desiccation stresses. The compositions of phospholipids in embryonic axes of several recalcitrant seeds and orthodox seeds were studied. The ratio of phosphatidyl ethanolamine to phosphatidylcholine in embryonic axes of recalcitrant seeds and orthodox seeds was overlapping in the range. Percentage of saturated fatty acids of phospholipid (stearic acid, C18:0, and palmitic acid, C16:0) was significantly different between orthodox seeds (in the range of 16% to 27%) and recalcitrant seeds (32% to 36%), and this difference also reflected in the lower phase transition temperature of orthodox seeds. The proportion of unsaturated fatty acids (C18:2 and C18:3) of phospholipids was overlapping in both seed types. Using imbibed soybean seedlings as a model system for recalcitrance, the ratio of phosphatidyl ethanolamine over phosphatidylcholine of embryonic axes increased in early imbibition and decreased later on. The percentage of saturated fatty acids in phospholipids of soybean seedlings excluding cotyledon was significantly higher than that in dry embryonic axis. This agrees with the results from the comparison of recalcitrant and orthodox seeds. Increases in saturated fatty acids were not correlated with lower transition temperature of extracted phospholipids of seedling indicating linolenic acids (C18:3) might play a role on Tm value. In conclusion, both recalcitrant seeds and imbibed seedlings while sharing recalcitrance, exhibited a similar trend in fatty acid saturation and higher percentage of linolenic acid in phospholipids, and higher phase transition temperature when compared with orthodox seeds and dry embryonic axes. Selaginella tamariscina, one of the most primitive vascular plants, can remain alive in a desiccated state and resurrect when water becomes available. To evaluate the nature of desiccation tolerance in this plant, we compared the composition of soluble sugars and saturation ratios of phospholipids (PLs) between hydrated and desiccated tissues of S. tamariscina using gas chromatography (GC). In this study, differences in protein dynamics, superoxide dismutase (SOD) activities, gene expressions and abscisic acid (ABA) contents were also analyzed during dehydration. The results revealed that trehalose (at > 130 mg g-1 dry weight) was the major soluble sugar, and low saturated fatty acid contents in PL (0.31) was maintained in both hydrated and desiccated tissues. Novel proteins and an inducible CuZnSOD activity were detected during dehydration. In addition, the ABA content of S. tamariscina increased 3 folds, and genes involved in ABA signaling and cellular protection were upregulated while photosystem-related genes were downregulated during dehydration. The biochemical and molecular findings suggest that both constitutive and inducible protective molecules contribute to desiccation tolerance of S. tamariscina. To study the function of StCaLB putatively encoding a calcium dependent lipid binding protein screened from differential display of Selaginella tamariscina during dehydration, the genomic sequence, putative protein domain and the response of this gene to different abiotic stresses were analyzed. Also, the transgenic plants of Arabidopsis that over-expressing StCaLB were generated. The results indicated the expression of StCaLB is induced by NaCl, 30% PEG, heat and abscisic acid, but not by cold treatment. The StCaLB is predicted to contain two N-terminal transmembrane domains and a central C2 domain. The StCaLB over-expressing Arabidopsis were obtained. However, further biochemistry and genetic research still need to be evaluated for the function of this gene.