Salvucci Michael E, DeRidder Benjamin P, Portis Archie R
USDA-ARS, Arid-Land Agricultural Research Center, Maricopa, AZ 85239, USA.
J Exp Bot. 2006;57(14):3793-9. doi: 10.1093/jxb/erl140. Epub 2006 Sep 22.
Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activation decreases under moderate heat stress. This decrease is caused by an impairment of activase function, which is exacerbated by faster rates of Rubisco deactivation at elevated temperatures. To determine if stromal oxidation causes inhibition of activase, transgenic Arabidopsis plants expressing suboptimal amounts of either the redox-regulated 46 kDa alpha- or non-redox regulated 43 kDa beta-isoform of activase were examined. Photosynthesis, as measured by gas exchange and chlorophyll fluorescence, and Rubisco activation were inhibited to a much greater extent by moderately high temperatures in the two transgenic lines expressing suboptimal levels of the individual isoforms of activase compared with wild-type plants or transgenic plants expressing levels of the beta-isoform sufficient for wild-type rates of photosynthesis. Net photosynthesis and Rubisco activation in transgenic plants expressing suboptimal amounts of the beta-isoform of activase from the Antarctic hairgrass were even more sensitive to inhibition by moderate heat stress than in the transgenic plants containing Arabidopsis activase. The results demonstrate that photosynthesis exhibits a similar sensitivity to inhibition by moderately high temperature in plants expressing either of the two different isoforms of activase. Thus, impairment of activase function under heat stress is not caused by oxidation of the redox-sensitive sulphydryls of the alpha-isoform of activase. Instead, the results are consistent with thermal denaturation of activase under moderate heat stress, the effects of which on Rubisco activation would be enhanced when activase levels are suboptimal for photosynthesis.
在适度热胁迫下，1,5 - 二磷酸核酮糖羧化酶/加氧酶（Rubisco）的激活作用会降低。这种降低是由激活酶功能受损引起的，而在高温下Rubisco失活速度加快会加剧这种损害。为了确定基质氧化是否会导致激活酶受到抑制，研究人员检测了表达激活酶的氧化还原调节型46 kDaα亚基或非氧化还原调节型43 kDaβ亚基数量不足的转基因拟南芥植株。与野生型植株或表达足以支持野生型光合速率的β亚基水平的转基因植株相比，在表达激活酶各亚基水平不足的两个转基因株系中，通过气体交换和叶绿素荧光测量的光合作用以及Rubisco激活受到适度高温的抑制程度要大得多。与含有拟南芥激活酶的转基因植株相比，表达南极发草中激活酶β亚基数量不足的转基因植株的净光合作用和Rubisco激活对适度热胁迫抑制更为敏感。结果表明，在表达两种不同激活酶亚基的植物中，光合作用对适度高温抑制表现出相似的敏感性。因此，热胁迫下激活酶功能的损害并非由激活酶α亚基中对氧化还原敏感的巯基氧化所致。相反，这些结果与适度热胁迫下激活酶的热变性一致，当激活酶水平对光合作用而言次优时，热变性对Rubisco激活的影响会增强。
