| Nine varieties with a potential ability of super high yield in heavy ear hybridrice,which were bred recently in China,and Shanyou 63 were used as materials in this study. The photosynthetic characteristics and assimilate's transportation of these varieties under different irradiance were studied by using 14C-isotope tracer techniques.Based on analyses of yield constituents and influential factors of photosynthetic production in these varieties, physiological ways of improving photosynthetic functions and physiological indexes of photosynthesis for super high yield in heavy ear hybrid rice were presented in this paper.The results were as follows.1 .The every grain yield of nine varieties of heavy ear hybrid rice in the field was totally higher than that of Shanyou 63.Among them,the every grain yield of three varieties,Eryou 162,Liangyoupeijiu and 65396,reached 10t/hm2 or more and was over 10% higher than that of Shanyou 63.The kernel number/spike and the valid kernel number/spike were more but the seed setting(%) was less in yield constituents of the nine varieties as compared with in Shanyou 63.Under the natural radiant condition,the total amount of photosynthetic production every plant or leaf in heavy ear hybrid rice during different phases of grain filling period was remarkably more than in Shanyou 63.At the 30th day after heading stage,the 14C-assimilate each plant of Diyou 68,Liangyoupeijiu and Eryou 162 in heavy ear hybrid ricewas as 1.87,1.66 and 1.53 times respectively as in Shanyou 63.The 14C- assimilate per unit weight of plant or leaf in heavy ear hybrid rice was also noticeably higher than in Shanyou 63.Furthermore,the active photosynthesis duration of flag leaf and the relative steady phase of chlorophyll in these varieties of heavy ear hybrid rice were as long as 42~49 days while that of Shanyou 63 was only 35 days.2. Under the photoinhibitory condition,photosynthetic production of the ten varieties reduced in different levels due to different varieties and different growth stages of plant.The photosynthetic capacities of all varieties in seedling stage reduced more than in heading stage under high light intensity and were considered as more sensitive to photoinhibition.Some of heavy ear hybrid rice, Such as Eryou 162 and Liangyoupeijiu,had a more stable ability of producing assimilate and their photosynthetic production reduced less and were considered as tolerance to photoinhibition under the stress of high light intensity.On the other hand,some of heavy ear hybrid rice, Such as Yueyou 938, and Shanyou 63 were more sensitive to reduction of photosynthetic production and their photosynthetic rate reduced sharply in high light intensity.The activities of oxygen radical scavenging enzyme,superoxide dismutase (SOD),and functions of the xanthophyll cycle in the varieties with tolerance to photoinhibition increased in a high level during photoinhibitory conditions.Especilly,their activities of phosphoenolpyruvate carboxylase (PEPC) were appeared to raise several times as compared with in normal light condition due to high light intensity.3.Under the shading conditions,the dry matter of plant,grain yield and MC-assimilate in the ten varieties decreased sharply in different levels as a result of different varieties.Some of heavy ear hybrid rice, such as Teyou 124, and Shanyou 63 had a more stable ability to produce assimilate.Their photosynthetic rate reduced slowly and reduced less than 50% of normal irradiance in 14 days shading condition and these varieties were identified as a shade tolerant variety type.On the opposite side,most of heavy ear hybrid rice,such as Eryou 162 and Liangyoupeijiu,were identified as a shade sensitive variety type.Their dry matter of plant and l4C-assimilate reduced sharply and only remained 30%~40% of normal irradance under 14 days shading treatment.The recovery abilities of photosynthetic rate in these varieties after shading treatments were much weaker than in the varieties with shade tolerance and their photosynthetic rates could not recover...
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