芥菜型油菜黄化突变体叶片叶绿素合成代谢变化

Changes of Chlorophyll Synthesis Metabolism in Chlorophyll-deficient Mutant in Brassica juncea

以芥菜型油菜黄化突变体(L638-y)及其野生型(L638-g)为材料,测定了叶片叶绿素(Chl)、类胡萝卜素(Caro)、Chl合成代谢中间产物含量变化,及叶绿素分解代谢的关键酶叶绿素酶(Chlase)和叶绿素合成代谢相关的氨基乙酰脱氢酶(ALAD)、胆色素原脱氨酶(PBGD)、粪卟啉原Ⅲ氧化酶(CPOX)和原卟啉原Ⅸ氧化酶(PPOX)的活性变化,以揭示芥菜型油菜黄化突变体L638-y叶片缺绿的生化机制。结果显示:(1)从油菜苗期到现蕾期,L638-y叶片总Chl和Caro含量均显著低于L638-g,且Chl b含量降低程度大于Chl a,总Chl含量降低程度大于Caro;(2)L638-y叶片Chlase活性在3～5叶期显著低于L638-g,其它各生长时期二者Chlase活性均无显著差异;(3)L638-y叶片叶绿素合成代谢中间产物氨基乙酰丙酸(ALA)、胆色素原(BPG)、尿卟啉原Ⅲ(UrogenⅢ)和粪卟啉原Ⅲ(CoprogenⅢ)含量均显著大于L638-g,而原卟啉Ⅸ(ProtoⅨ)、镁原卟啉(Mg-Proto)、原脱植基叶绿素(Pchlide)的含量却显著低于L638-g;与L638-g相比,L638-y叶片ALAD活性无显著差异,BPGD活性显著增加,而COPX和PPOX活性却显著降低。研究表明,L638-y叶片叶绿素缺乏的主要原因是叶绿素合成代谢受阻,而并非其叶绿素降解所致,受阻位点在由CoprogenⅢ-ProtoⅨ的反应。这是一种不同于前人报道的新型缺绿突变体。

The chlorophyll-deficient mutant L638-y and wild-type L638-g of Brassica juncea were used as the materials to detect the content of chlorophyll,carotene,and the intermediates of chlorophyll synthesis metabolism.In addition,the activities of chlorophyllase,a key enzyme in chlorophyll catabolism and 4 key enzymes involved in chlorophyll synthesis metabolism,i.e.Aminolevulinate dehydrogenase（ALAD）,PBG deaminase（PBGD）,coproporphyrinogen Ⅲ oxidase（CPOX） and Protoporphyrinogen Ⅸ oxidase（PPOX） were measured.The purpose of the present study is to reveal the biochemical mechanisms of chlorophyll deficient in the leaves of chlorophyll-deficient mutant L638-y in B.juncea.The results showed that the contents of total Chl and Caro in L638-y leaves were much lower than those in L638-g from seedling to budding period,Chl b decreased much more than Chla,and total Chl reduced more than Caro.The activity of leaf chlorophyllase in L638-y was significant lower than that in L638-g in 3～5 leaves stage,while there were no significant difference in leaf chlorophyllase activities between L638-y and L638-g in other development stages.The contents of four intermediates for chlorophyll synthesis ALA,BPG,Urogen Ⅲ and Coprogen Ⅲ in L638-y were significantly higher than those in L638-g,but the contents of the other three intermediates Proto Ⅸ,Mg-Proto and Pchlide were significantly lower.In addition,the activity of ALAD between L638-y and L638-g had no difference.The activity of BPGD in L638-y was significantly higher than that in L638-g and the activity of COPX and PPOX in L638-y was much lower than that in L638-g.All these results indicated that chlorophyll deficient in L638-y was caused by blocking of chlorophyll synthesis pathway at the reaction from Coprogen Ⅲ to Proto Ⅸ,rather than chlorophyll degradation.L638-y is a new type of chlorophyll-deficient mutant different from the previous report.