Effects Of Light And Temperature Stress On The Growth And Development Of Cauliflower (Brassica Oleracea Var. Botrytis L.)

Cauliflower (Brassica oleracea var. botrytis L.) belongs to green vernalization plant and is strict to growth condition. In this paper, the effects of variety and seeding date on the growth and development in the early cauliflower were studied; the physiological and biochemical changes of the early cauliflower leaves, as well as flower buds and flower stems under different temperatures and lights were investigated. The main results were as follows:1) Varieties had obviously influence in growth increment when curd appearance. No. of leaves, leaf length, leaf width and plant height of common varieties 'Bai-Long-Shan 50-day' and 'Rui-Xue-Te-Da 50-day' were lower than those of hybrid seeds. Growth duration of the variety 'Rui-Xue-Te-Da 50-day' was later than other varieties, and the percentage of abnormal curds was higher than other varieties as well. The seeding date affected the growth and development of cauliflower, but the effects varied with varieties. The later the seeding date was, the more the plant growth amounts (leaf length, leaf width, and plant height) were, and the fewer the number of leaves was .Days to curd appearance and curd maturity had significant affected by seeding date. The experiment results verified that the seeding date was very important in the early cauliflower cultivation.2) Heat stress inhibited the growth of curd and significantly decreased its fresh weight, dry weight, dry matter and starch contents, while increased sucrose, reduced sugar and total soluble sugar contents. Under high temperature condition, the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoid decreased by more than 25 percent as compared with the control. The intrinsic photochemical efficiency (Fv/Fm), quantum yield of PSII (PSH) and photochemical quenching (qP) decreased as well by high temperature stress. On the other hand, SOD, APX, GPX, CAT activities and ascorbate (AsA, DAsA) content, glutathione (GSH, GSSG) content increased under high temperature stress. After heat stress SOD, CAT ,APX and GPX activities significantly increased, while ascorbate contents decreased in flower buds; In flower stems SOD, CAT ,APX activities andascorbate contents significantly increased, but GPX activity decreased under heat stress.This is because ascorbate contents in flower buds and GPX activity were sensitive to high temperature. MDA content indicated greatly elevation in leaves, flower buds and stems under heat stress, furthermore showed higher in flower buds than in flower stems.3) Chlorophyll a, chlorophyll b, total chlorophyll, carotenoid and protein contents as well as Chl a/ Chl b and Car / Chl significantly decreased with the decrease of light intensity; Under' shade condition, width diameter, length diameter, fresh weight and sucrose, reduced sugar, total soluble sugar, protein contents of curds significantly decreased, but starch content apparently increased. Except GPX activity, which was obviously increased, other antioxidant enzyme activities and antioxidant contents obviously decreased in early cauliflower leaves under shade condition. This is probably because GPX lies in the peroxisome and is closely related with senescence. Under shade condition only DHAR activity apparently decreased in the flower buds and flower stems, other enzymes activities had a little change. Shade culture caused As A and GSH contents increase in flower buds, but decrease in flower stems. This is probably because AsA and GSH are related with organize and organize tenderness.