Study On Photosynthetic Functional Decline For Oilseed Rape (Brassica Napus L)

Five cultivars grown in the field were analysed to photosynthetic functional decline of leaves and photosynthesis characteristics and how extending the photosynthesis duration of silique in rapeseed (Brassica napus L) after anthesis. The results were as follow:After the flowering, different location of leaf have different course of photosynthetic functional decline. Lower part the leaf declines quickly compared to the middle leaf. The top of leaf belongs to newborn leaf, so it has longer photosynthesis duration. Photosynthesis duration of three type of leves most maintain 15~20d. Leaf is replaced by silique after 20d. SOD and CAT activity has the short rise and the stable stage in the top of leaf, MDA activity has stable stage too, and unanimous with photosynthetic rate. So there are inherent relations between photosynthesis function decline and fall of the Protective Enzyme System and accumulate of MDA.The photosynthesis duration of silique shows that 3 stages: First, photosynthetic rate rise stage of the silique, up to 15-20DAA, include the Nutrition body growth and grain preliminary formation in this stage. Second, photosynthetic rate drop stage, but the speed is slowly, and keep to 30DAA. Mainly is the grain grouting. The third stage shows that photosynthetic rate sharp fall phase and the grain only then few grouting after the 35DAA. Different cultivar have different duration in the three stage. Photosynthesis characteristics of silique in different location were researched, the result shows that caulis and ramus silique have not difference. In the different density, the top of silique have high phtotsynthetic rate than the lower, with the increase of density, the photosynthetic rate of lower leaf drop gradually, silique shows that three deloul curve in the diurnal variation of photosynthetic rate, the reason have not clear at present.The effects of single and mixed applications of Brassinolide (BR), Uniconazole(UN), 6-benzyl Aminopurine(6-BA) at 18DAA in the second stages. The results shows that photosynthesis duration were extended about 3d by combination with (BR+6-BA) or (UN+6-BA). Different phytohormones has different role to SOD CAT and MDA. In addition, The phytohormones may increase weight of grain, but the increased effect wasn't markedness.