Studies On The Photosynthetic Characters Of High-yielding Hybrid Rice 'Liangyoupeijiu'

Rice(Oryza Sativa L.) is one of the most important food crops in China,its planting area accounts for 30%of all the food crop planting area and its yield accounts for 40%of the total food yield.Therefore,rice production plays a very important part in the grain reserves and economic development of the country.Presently,high yield and good quality in rice production is still our main research goal.The successful breeding of super hybrid rice has greatly increased the output of rice.In order to get higher yield, promoting photosynthetic rate is one of the main measures.It is of significance for increasing rice yield to study the photosynthesis mechanism of high yielding rice.This study was designed to explore the photosynthetic characters of the flag leaf blade and its sheath of high-yielding hybrid rice 'Liangyoupeijiu'(LYP9),using 'Liangyoupeijiu','9311','Peiai 64S'(PA64S) and 'Shanyou 63'(SY63) as the experimental materials;adopting the techniques of an artificial reaction system for photosynthetic membrane,isotopic labeling,¹⁴C radio-autography and so on;using sophisticated instruments such as photosynthesis system,liquid scintillation counter, inductively coupled plasma emission spectrometer and transmission electron microscope(TEM).The results are as follows:1.The photosynthetic capacities of the flag leaf blade and its sheath of Liangyoupeijiu were higher than the others.The means of Pn,the incipient carboxylation activities,total carboxylation activities and activation percentage of Rubisco of the flag leaf blade and its sheaths for Liangyoupeijiu were all higher than those for Shanyou 63,and these reached significant level at most stages;under the same planting density in the field,the LT at the middle positions of the flag leaf sheaths and at the middle positions of the penultimate leaf sheaths from the tops were 1.54 and 1.51 times higher than those of Shanyou 63,respectively;The assimilate transport in the sheaths of Liangyoupeijiu was quicker than that of Shanyou 63,and its assimilate transporting to its spikes were also higher than those of Shanyou 63.The photosynthetic capacities of the flag leaf blades and its sheaths of Liangyoupeijiu were of mean potence at most stages,and sometimes heterobeltiosis in comparison with those of its parents. The photosynthates produced by rice sheaths were mainly transported to the spikes and blades,some were stored in sheaths,few was transported to the roots.The contribution of rice sheaths to yields was usually between 9%and 19%.The high photosynthetic capacities of both its blade and sheathe in Liangyoupeijiu is an important base of its high yields.2.The characters of the photosynthetic apparatus of the flag leaf blade and its sheath of Liangyoupeijiu were better than the others.The chloroplast number of each mesophyllous cell in the flag leaf blade and its sheath of Liangyoupeijiu were higher than those of Shanyou 63,which indicated that the chlorophyll molecules of Liangyoupeijiu were distributed over more chloroplasts than those of Shanyou 63.This expanded the light area of the chlorophyll molecules in Liangyoupeijiu;The chlorophyll contents(SPAD) in the chloroplasts of the flag leaf blade and its sheath of Liangyoupeijiu were 4.55 and 0.56 higher than those of Shanyou 63.Compared with Shanyou 63,the senescence of the chloroplasts and the decomposition of the chlorophyll of the flag leaf blade and its sheath of Liangyoupeijiu was slower than those of Shanyou 63;the photosynthetic period of its mesophyllous cells was longer.Mg²⁺ content of the chlorophyll liquid of the flag leaf blade and its sheath of Liangyoupeijiu were higher than those of Shanyou 63,which indicated that there were more Mg²⁺ around its chloroplasts.This was favorable to the photosynthesis of Liangyoupeijiu. The TEM observation showed that the periphery of the vascular bundle sheath of the principal vein in the flag leaf blade of Liangyoupeijiu had a layer of transfer cells.This indicated that the photosynthate transport in Liangyoupeijiu was faster than that of Shanyou 63.The characters of photosynthetic apparatus in the flag leaf blade and its sheath of Liangyoupeijiu were of mean potence or heterobeltiosis in comparison with those of its parents.Liangyoupeijiu presented hybrid characters.The absorption spectrums of the chlorophyll in flag leaf sheaths were found to be very similar among the four varieties.The statistical results showed that the profuse filling stage i.e.the third stage of the flag leaf of rice was a turning point of the mesophyllous cells, chloroplasts and chlorophyll of the blade and sheath beginning to senesce and decomposite,was also a key period to prevent the blade and sheath of rice from quick senescent in cultivation.3.The anti-overoxidation of the membrane lipid of the flag leaf blade and its sheath of Liangyaopeijiu were stronger and the photosynthetic period were longer than the others.SOD activity and Vc content of the anti-overoxidation of the membrane lipid of the flag leaf blade and its sheath of Liangyoupeijiu were higher than those of Shanyou 63,respectively;the V_E content of the sheath were also higher than those of Shanyou 63,and the means of the V_E content of the flag leaf blade and its sheath at grain filling peak stage were 2.77 and 1.10μg·mL^-1 higher,respectively.MDA content and the electric conductivities of the tissue exosmosis of overoxidation of the membrane lipid of the flag leaf blade and its sheath of Liangyoupeijiu were lower than those of Shanyou 63,respectively.Correlative analysis showed that the anti-overoxidation of the membrane lipid of the flag leaf blades and sheaths of the four varieties/combinations was very significantly and negatively correlated with the overoxidation.The anti-overoxidation and overoxidation of the membrane lipid of the sheaths were significantly and positively correlated with those of the flag leaf blades.The above results proved that compared with Shanyou 63,the abilities of the anti-overoxidation of the membrane lipid of the flag leaf blade and its sheath of Liangyoupeijiu were stronger; the senescence of the flag leaf blade and its sheath of Liangyoupeijiu were slower at the later stage,the functional period of the flag leaf blade and its sheath were longer than those of Shanyou 63,Liangyoupeijiu had significant antisenescence ability.The flag leaf blade and its sheath of Liangyoupeijiu was of significant mean potence or heterobeltiosis in the respect of anti-overoxidation of the membrane lipid compared with its parents.The test also showed that at the peak of grain filling stage,the overoxidation of the membrane lipid of the flag leaf blades and sheaths of the four varieties/combinations formed a turning point which determined the flag leaf blades and sheaths to senesce quickly or slowly at the late stage,was also the key period to prevent the flag leaf blades and sheaths of rice from presenility at the late stage in cultivation.4.The assimilatory power of the photosystem in the flag leaf blade and its sheath of Liangyoupeijiu were higher than the others.PSâ… reducing power and PSâ…¡oxygen evolution activities of the flag leaf blades and sheaths of Liangyoupeijiu were higher than those of Shanyou 63,respectively,and at most stages these difference reached significant level;the extracted calcium contents in the flag leaf blades and sheaths of Liangyoupeijiu were significantly higher than those of Shanyou 63;Mg²⁺-ATPase activities on the chloroplast membranes of the flag leaf blades and sheaths of Liangyoupeijiu were significantly higher than those of Shanyou 63 at most stages;The means of the cyclic and noncyclic photophosphorylation activities of the flag leaf blades and sheaths of Liangyoupeijiu were also higher than those of Shanyou 63,respectively, and significantly higher at nearly half of all stages;the photochemical avtivities of the flag leaf blades and sheaths of Liangyoupeijiu were significantly higher than those of its parents at most stages,and were of mean potence or heterobeltiosis.High assimilatory power in both the flag leaf blade and sheath of Liangyoupeijiu is one another important base of its high yield.