The mechanism of high yield of winter wheat in the field at late growth period was investigated by measuring the photosynthetic characteristics of photosystem Ⅱ （PSⅡ） and xanthophylls cycle, which could provide physiological reference for breeding. Weimai 8 （W8）, a super high yield cultivar, and Lumai 14 （L14）, a control cultivar were object. The photosynthetic rate （Pn）, parameters of chlorophyll fluorescence and chlorophyll content were measured. The Pn, maximum photochemical efficiency of PSII （Fv/Fm）, quantum yield of PSII electron transport （ΦPSⅡ）, efficiency of excitation energy capture by open PSII reaction centers （Fv＇/Fm＇）, and photochemical quenching coefficient （qP） were higher in Weimai 8 compared to that in Lumai 14, a commercial high yield cultivar. Furthermore, Weirnai 8 showed a lower non- photochemical quenching coefficient and a lower de-epoxidized ratio of the xanthophyll cycle pigments than of Lumai 14 at late growth period. At mature stage, chlorophyll content of different leaves decreased both in Weimai 8 and Lumai 14. Chlorophyll content in flag, second and third leaf from the top of plant decreased more in Lumai 14 than in Weimai 8. These results suggested that Weimai 8 had more antenna pigments to absorb light energy, and had higher photosynthetic capability and photochemical efficiency of PSⅡ. The yield of Weimai 8 was also higher than that of Lumai 14.
SUI NaLI MengMENG Qing-weiTIAN Ji-chunZHAO Shi-jie
An endoplasmic reticulum-localized tomato ω-3 fatty acid desaturase gene （LeFAD3） was isolated. The antisense tomato plants were obtained under the control of the cauliflower mosaic virus 35S promoter （35S-CaMV）. Northern blot analysis confirmed that the expression of LeFAD3 was inhibited in the tomato genome. Levels of 18：3 decreased and correspondingly levels of 18：2 increased in total lipids of leaves and roots. After heat stress, the fresh weight of the aerial parts of antisense transgenic plants was higher than that of the wild type （WT） plants. The membrane system ultrastructure of chloroplasts in leaf cells and all of the subcellular organelles in the root tips of transgenic plants remained more intact than those of WT. Relative electric conductivity increased less in transgenic plants than in WT. Under heat stress, the maximal photochemical efficiency of photosystem Ⅱ （Fv/Fm） and the O2 evolution rate decreased more in WT than in transgenic plants. These results suggested that the depletion of LeFAD3 increased the saturation of fatty acids and alleviated high temperature stress.
