Häusler R E, Rademacher T, Li J, Lipka V, Fischer K L, Schubert S, Kreuzaler F, Hirsch H J
Botanisches Institut der Universität zu Köln, Gyrhofstrasse 15, D-50931 Köln, Germany.
J Exp Bot. 2001 Sep;52(362):1785-803. doi: 10.1093/jexbot/52.362.1785.
To improve the efficiency of CO(2) fixation in C(3) photosynthesis, C(4)-cycle genes were overexpressed in potato and tobacco plants either individually or in combination. Overexpression of the phosphoenolpyruvate carboxylase (PEPC) gene (ppc) from Corynebacterium glutamicum (cppc) or from potato (stppc, deprived of the phosphorylation site) in potato resulted in a 3-6-fold induction of endogenous cytosolic NADP malic enzyme (ME) and an increase in the activities of NAD-ME (3-fold), NADP isocitrate dehydrogenase (ICDH), pyruvate kinase (PK), NADP glycerate-3-P dehydrogenase (NADP-GAPDH), and PEP phosphatase (PEPP). In double transformants overexpressing cppc and chloroplastic NADP-ME from Flaveria pringlei (fpMe1), cytosolic NADP-ME was less induced and pleiotropic effects were diminished. There were no changes in enzyme pattern in single fpMe1 overexpressors. In cppc overexpressors of tobacco, the increase in endogenous cytosolic NADP-ME activity was small and changes in other enzymes were less pronounced. Determinations of the CO(2) compensation point (Gamma*) as well as temperature and oxygen effects on photosynthesis produced variational data suggesting that the desired decline in photorespiration occurred only under certain experimental conditions. Double transformants of potato (cppc/fpMe1) exhibited the most consistent attenuating effect on photorespiration. In contrast, photorespiration in tobacco plants appeared to be diminished most in single cppc overexpressors rather than in double transformants (cppc/fpMe1). In tobacco, introduction of the PEP carboxykinase (PEPCK) gene from the bacterium Sinorhizobium meliloti (pck) had little effect on photosynthetic parameters in single (pck) and double transformants (cppc/pck). In transgenic potato plants, increased PEPC activities resulted in a decline in UV protectants (flavonoids) in single cppc or stppc transformants, but not in double transformants (cppc/fpMe1). PEP provision to the shikimate pathway inside the plastids, from which flavonoids derive, might be restricted only in single PEPC overexpressors.
为提高C₃光合作用中二氧化碳固定的效率，将C₄循环基因单独或组合在马铃薯和烟草植株中过表达。在马铃薯中过表达来自谷氨酸棒杆菌的磷酸烯醇式丙酮酸羧化酶（PEPC）基因（cppc）或来自马铃薯的（stppc，缺失磷酸化位点），导致内源性胞质NADP苹果酸酶（ME）诱导3至6倍，并使NAD-ME（3倍）、NADP异柠檬酸脱氢酶（ICDH）、丙酮酸激酶（PK）、NADP甘油酸-3-磷酸脱氢酶（NADP-GAPDH）和PEP磷酸酶（PEPP）的活性增加。在过表达cppc和来自普氏黄顶菊的叶绿体NADP-ME（fpMe1）的双转化体中，胞质NADP-ME的诱导较少，多效性效应减弱。单个fpMe1过表达体的酶模式没有变化。在烟草的cppc过表达体中，内源性胞质NADP-ME活性的增加很小，其他酶的变化也不太明显。对二氧化碳补偿点（Gamma*）以及温度和氧气对光合作用的影响的测定产生了变化的数据，表明仅在某些实验条件下才出现了预期的光呼吸下降。马铃薯的双转化体（cppc/fpMe1）对光呼吸表现出最一致的减弱作用。相比之下，烟草植株中的光呼吸在单个cppc过表达体中似乎比在双转化体（cppc/fpMe1）中减弱得更多。在烟草中，导入来自苜蓿中华根瘤菌的PEP羧激酶（PEPCK）基因（pck）对单转化体（pck）和双转化体（cppc/pck）的光合参数影响很小。在转基因马铃薯植株中，PEPC活性增加导致单个cppc或stppc转化体中紫外线保护剂（类黄酮）减少，但双转化体（cppc/fpMe1）中没有减少。向质体内部的莽草酸途径提供PEP，类黄酮由此产生，可能仅在单个PEPC过表达体中受到限制。
