Ladas N P, Papageorgiou G C
Institute of Biology, National Center for Scientific Research Demokritos, Athens, Greece, 153 10.
Photosynth Res. 2000;65(2):155-64. doi: 10.1023/A:1006423221150.
We employed chlorophyll a fluorometry in order to measure the evolution of turgor threshold (intracellular osmolality) during the adaptation of two genetic transformants of the freshwater cyanobacterium Synechococcus sp. PCC7942 to unfavorable external salinity: PAMCOD cells which oxidize imported choline and accumulate approx. 0.06-0.08 M glycine betaine; and PAM cells which do not oxidize choline [Deshnium et al. (1995a) Plant Mol Biol 29: 897-909]. Turgor thresholds increased linearly (a) with the NaCl concentration in the culture, and (b) with the molar sucrose/chlorophyll a ratio in the cell. PAMCOD cells could proliferate in culture medium containing 0.4 M NaCl (external osmolality, 0.815 Osm kg(-1)), after a lag period, during which intracellular sucrose rose to 10 mol (mol Chl a)(-1), or more, and turgor threshold (cytoplasmic osmolality) exceeded 1 Osm kg(-1). At comparative conditions, PAM cells accumulated approx. half as much sucrose, and attained approx. half as high turgor thresholds as the PAMCOD cells, but they did not proliferate. These results indicate that glycine betaine improved the salinity tolerance of the PAMCOD cells synergistically, by means of two effects that implicate sucrose, the main organic osmolyte of Synechocccus: enhancement of sucrose biosynthesis, and/or alleviation of sucrose toxicity.
我们采用叶绿素a荧光测定法来测量淡水蓝藻聚球藻属PCC7942的两个遗传转化体在适应不利的外部盐度过程中膨压阈值（细胞内渗透压）的变化：PAMCOD细胞可氧化导入的胆碱并积累约0.06 - 0.08 M的甘氨酸甜菜碱；以及不氧化胆碱的PAM细胞[德什纽姆等人（1995a）《植物分子生物学》29：897 - 909]。膨压阈值呈线性增加：（a）随着培养基中NaCl浓度的增加，以及（b）随着细胞中蔗糖/叶绿素a的摩尔比增加。PAMCOD细胞在含有0.4 M NaCl（外部渗透压，0.815 Osm kg⁻¹）的培养基中经过一段滞后期后能够增殖，在此期间细胞内蔗糖升至10 mol（mol Chl a）⁻¹或更高，并且膨压阈值（细胞质渗透压）超过1 Osm kg⁻¹。在比较条件下，PAM细胞积累的蔗糖约为PAMCOD细胞的一半，达到的膨压阈值约为PAMCOD细胞的一半，但它们不增殖。这些结果表明，甘氨酸甜菜碱通过涉及聚球藻主要有机渗透剂蔗糖的两种效应协同提高了PAMCOD细胞的耐盐性：增强蔗糖生物合成和/或减轻蔗糖毒性。
