Langenkämper G, McHale R, Gardner R C, MacRae E
School of Biological Sciences, University of Auckland, Private Bag, New Zealand.
Plant Mol Biol. 1998 Apr;36(6):857-69. doi: 10.1023/a:1005964812161.
Early during fruit ripening in kiwifruit (Actinidia deliciosa var. deliciosa [A. Chev.], C.F. Liang and A.R. Ferguson cv. Hayward), starch is broken down to sucrose and hexose sugars. Concomitantly, sucrose-phosphate synthase (SPS, EC 2.3.1.14) activity measured with saturating substrate increased, suggesting that SPS is induced in response to a higher requirement for sucrose synthesis. A 2584 bp long partial cDNA clone encoding SPS was isolated from ripening kiwifruit. cDNA fragments encoding the 5' end were isolated by PCR, and sequencing revealed at least four closely related (> 96% identity) mRNAs expressed early in kiwifruit ripening. Southern hybridisations in a diploid relative of kiwifruit, Actinidia chinensis (Planch.) var. chinensis, were consistent with the presence of a small gene family. Western analysis indicated a 125 kDa SPS protein present in all tissues of A. chitensis at all stages of development. Steady-state levels of SPS mRNA in A. chinensis increased near fruit maturity as net starch degradation began on the vine, and increased again during ethylene treatment of fruit after harvest. After removal from ethylene SPS transcript levels decreased, only to increase again as fruit moved into the climacteric and starch breakdown was completed. Exposure to low temperatures also caused an increase in SPS transcript level. These results indicate that SPS mRNA increases in kiwifruit in response to the presence of new substrate sourced from starch degradation, in response to ethylene and in response to low temperature.
在猕猴桃（美味猕猴桃中华变种[A. Chev.]，C.F. Liang和A.R. Ferguson品种海沃德）果实成熟早期，淀粉分解为蔗糖和己糖。与此同时，用饱和底物测得的蔗糖磷酸合酶（SPS，EC 2.3.1.14）活性增加，这表明SPS是因对蔗糖合成的更高需求而被诱导的。从成熟的猕猴桃中分离出一个编码SPS的2584 bp长的部分cDNA克隆。通过PCR分离出编码5'端的cDNA片段，测序显示在猕猴桃成熟早期至少有四种密切相关（> 96% 同一性）的mRNA表达。在猕猴桃的二倍体近缘种中华猕猴桃（Planch.）中华变种中进行的Southern杂交与一个小基因家族的存在一致。Western分析表明，在中华猕猴桃发育的所有阶段，所有组织中都存在一种125 kDa的SPS蛋白。在中华猕猴桃中，随着藤蔓上果实成熟时净淀粉降解开始，SPS mRNA的稳态水平增加，收获后对果实进行乙烯处理期间再次增加。从乙烯处理中移除后，SPS转录本水平下降，只是在果实进入呼吸跃变期且淀粉分解完成时再次增加。暴露于低温也会导致SPS转录本水平增加。这些结果表明，猕猴桃中SPS mRNA的增加是对淀粉降解产生的新底物的存在、乙烯以及低温的响应。
