Study On The Chlorophyll Biosynthesis Of A Chlorophyll B-deficient Oilseed Rape Mutant (Brassica Napus L.) Cr3529

Chl b-deficient mutant have been reported in a lot of plants, and widely used in the research on photosynthesis mechanism and its process. Chlorophyll is the most abundant porphyrin in plant cell, it absorb light, transfer light energy and electron to the other molecule during photosynthesis. Hence, study on the chlorophyll biosynthesis of a chlorophyll b-deficient oilseed rape mutant (Brassica napus L.) Cr3529 can help us to get a better understand on the disfigurement mechanism of chlorophyll biosynthesis.We take 10-day old cotyledon both from wild type (WT) and mutant type (MT) as material to study the characteristic of the chlorophyll biosynthesis of a chlorophyll b-deficient oilseed rape mutant (Brassica napus L.). The contents of chlorophyll (Chl) biosynthetic main precursors in a Chl b-deficient oilseed rape mutant Cr3529 were determined. The results showed that the content of the first precursor in Chl biosynthesis,δ-Aminolevulinic acid (ALA), is nearly comparable to the wild type. ALA feeding led to the increasing of ALA content both in Cr3529 and its wild type, the increasing extent and absolute content were nearly the same in the two types, indicating that Chl biosynthesis in the mutant oilseed rape was not blocked at ALA formation. Of the subsequent precursors, the content of porphobilinogen was not decreased in mutant, but that of uroporphyrinogenⅢin mutant leaves was only one-half of that in the wild type, and only raise to 82％after ALA feeding. The contents of the following precursors, including coproporphyrinogenⅢ, protoporphyrinⅨ, Mg-protoporphyrinⅨand protochlorophyllide, were all decreased, even after feeded with ALA, suggesting that the biosynthesis of Chl in Cr3529 was blocked at the step of converting porphobilinogen to uroporphyrinogenⅢ. Different from most of the Chl b-deficient mutants in which the accumulation of ProtoⅨand the decreased synthesis of Mg-ProtoⅨwere caused by the decreased activity of Mg-chelatase, Chl b-deficient oilseed rape mutant Cr3529 has its specific mutation mechanism in Chl biosynthesis and the resulted different accumulation pattern of precursors.When the development of chloroplasts were inhibited by lincomycin, an inhibitor of chloroplast protein synthesis, the cotyledons of both WT and MT were perform yellow instead of green, and 1 can hardly examined the content of Chl. The contents of chlorophyll (Chl) biosynthetic main precursors ProtoⅨ, Mg-ProtoⅨand Pchlide in a Chl b-deficient oilseed rape mutant Cr3529 were determined. The results showed that the content of the three precursors perform a trend-first go up then get down, and lincomycin treated gives the same result. The absolute contents of the three precursors were all increased, but the extents were different, Mg-ProtoⅨis much higher than ProtoⅨand Pchlide.