The Photosynthetic Mechanism Responsible For Delay Sensecence In 'Stay-green' Wheat Cultivars

As the most important food crop worldwide, compared before, although the wheat yield has improved, the yield was limited by photosynthesis competence itself. As 70% of wheat yield was derived from the photosynthesis assimilation after anthesis, prolonging the photosynthesis competence after anthesis play a key role in improvement of yield. Studying the new trait related photosynthesis competence after anthesis is not only important significance of photosynthesis and yield in physiological and genetic research field, but also is the foundation of wheat high yield breeding. We chose two stay-green wheat cultivars, Chuannong12 (CN12) and Chuannong18 (CN18), harboring the wheat-rye 1BL/1RS translocated chromosome and MY11, the agronomical parent of both CN12 and CN18, which was used as the control as material. We investigated the content of fatty acid constituent in thylakoid membrane, the content of H2O2 by means of a new nano technique, called quantum dot (QD) fluorescence and the yield trait in three of them during the whole senescence stage. Meanwhile, we used the photosynthetic apparatus LI-6400 to detect the change of values for net photosynthetic rate, stomatal conductance, Intercellular CO2 concentration, Maximum photochemical efficiency of PSⅡ, photochemical quenching of PSⅡ,The efficiency of excitation capture by open PSⅡreaction centers,ΦPSⅡ,ETR to elucidate the photosynthetic mechanism responsible for delay senescence in stay-green wheat cultivars.1 At the whole senescence stage, stay-green wheat cultivars CN12, CN18 have a higher net photosynthetic rate and photosynthesis competence than that of in MY11, it showed that CN12,CN18 have the ability to prolong the photosynthesis2 At the whole senescence stage, compared with the control MY11, the reasonable change of the stomatal conductance in stay-green wheat cultivars CN12, CN18 play a key role in prolonging the photosynthesis competence.3 The analysis of chlorophyll fluorescence parameter showed stay-green wheat cultivars CN12, CN18 have a better activity and integration of photosynthetic apparatus in thylakoid membrane than MY11, which exhibited the electron transport chain was maintained well during the whole senescence stage.4 At the whole senescence stage, stay-green wheat cultivars CN12, CN18 have a stronger mechanism of thermal dissipation than MY11,which had been started to dissipate excess light energy, and protect the leaf from photo-oxidation and the competence photosynthetic apparatus in thylakoid membrane was retained.5 Stay-green wheat cultivars CN12,CN18 have a higher level of unsaturated fatty acid than that in MY11,and also maintained a high level in the whole senescence stage. This act have a positive effect for electron absorbing, transporting and transforming in thylakoid membrane.6 Compared with MY11,stay-green wheat cultivars CN12,CN18 not only decrease the content of H2O2, regarding as the promoting factor for senescence, to protect the photosynthetic apparatus in thylakoid membrane, but also decrease the content of H2O2 to modulate the stomatal open and close for increasing the net photosynthetic rate.7 The persistent high photosynthetic activity formed a sustained and efficient 'source'and harmonious proportion of 'source' to 'sink' in stay-green wheat cultivars CN12, CN18. this mechanism could transport directly the fixation into'sink', which showed the yield of CN12, CN18 is higher than that of MY11.Above all, in the whole senescence stage, the high level of unsaturated fatty acid provide a biochemical foundation for integration of thylakoid membrane to maintain a efficient electron absorbing, transporting and transforming, meanwhile the persistent antioxidant defend the H2O2 to delay senescence,thus, these condition maintain a high photosynthetic activity to make the fixation transport into 'sink' to improve the yield.