Moulin M, Deleu C, Larher F, Bouchereau A
Plant Metabolism, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
Plant Physiol Biochem. 2006 Jul-Sep;44(7-9):474-82. doi: 10.1016/j.plaphy.2006.08.005. Epub 2006 Aug 23.
Higher plant responses to abiotic stresses are associated with physiological and biochemical changes triggering a number of metabolic adjustments. We focused on L-lysine catabolism, and have previously demonstrated that degradation of this amino acid is osmo-regulated at the level of lysine-ketoglutarate reductase (LKR, EC 1.5.1.8) and saccharopine dehydrogenase (SDH, EC 1.5.1.9) in Brassica napus. LKR and SDH activities are enhanced by decreasing osmotic potential and decrease when the upshock osmotic treatment is followed by a downshock osmotic one. Moreover we have shown that the B. napus LKR/SDH gene is up-regulated in osmotically-stressed tissues. The LKR/SDH activity produces alpha-aminoadipate semialdehyde which could be further converted into alpha-aminoadipate and acetyl CoA. Alternatively alpha-aminoadipate could behave as a precursor for pipecolic acid. Pipecolic acid is described as an osmoprotectant in bacteria and is co-accumulated with proline in halophytic plants. We suggest that osmo-induction of the LKR/SDH activity could be partly responsible for pipecolic acid accumulation. This proposal has been assessed in this study through pipecolic acid amounts determination in rape leaf discs subjected to various upshift and downshift osmotic treatments. Changes in pipecolic acid level actually behave as those observed for LKR and SDH activities, since it increases or decreases in rape leaf discs treated under hyper- or hypo-osmotic conditions, respectively. In addition we show that pipecolic acid level is positively correlated with the external osmotic potential as well as with the duration of the applied treatment. On the other hand pipecolic acid level is related to the availability of L-lysine and not to that of D-lysine. Collectively the results obtained demonstrate that lysine catabolism through LKR/SDH activity is involved in osmo-induced synthesis of pipecolic acid.
高等植物对非生物胁迫的响应与引发一系列代谢调节的生理和生化变化相关。我们聚焦于L-赖氨酸分解代谢，并且之前已经证明，在甘蓝型油菜中，这种氨基酸的降解在赖氨酸-酮戊二酸还原酶（LKR，EC 1.5.1.8）和酵母氨酸脱氢酶（SDH，EC 1.5.1.9）水平受到渗透调节。降低渗透势会增强LKR和SDH的活性，而在渗透上冲处理后接着进行渗透下冲处理时，其活性会降低。此外，我们已经表明，甘蓝型油菜LKR/SDH基因在渗透胁迫组织中上调。LKR/SDH活性产生α-氨基己二酸半醛，其可进一步转化为α-氨基己二酸和乙酰辅酶A。或者，α-氨基己二酸可作为哌啶酸的前体。哌啶酸在细菌中被描述为一种渗透保护剂，并且在盐生植物中与脯氨酸共同积累。我们认为，LKR/SDH活性的渗透诱导可能部分导致了哌啶酸的积累。在本研究中，通过测定经受各种上冲和下冲渗透处理的油菜叶圆片中的哌啶酸含量，对这一推测进行了评估。哌啶酸水平的变化实际上与LKR和SDH活性的变化一致，因为在高渗或低渗条件下处理的油菜叶圆片中，哌啶酸水平分别升高或降低。此外，我们表明，哌啶酸水平与外部渗透势以及处理持续时间呈正相关。另一方面，哌啶酸水平与L-赖氨酸的可用性有关，而与D-赖氨酸的可用性无关。总体而言，所获得的结果表明，通过LKR/SDH活性的赖氨酸分解代谢参与了渗透诱导的哌啶酸合成。
