| Temperature and Radiation are main ecological factors affecting formation of wheat yield and quality. Elucidating the physiological mechanism for the effects of high temperature and deficient radiation intensity on grain yield and quality formation in wheat is of great importance for understanding grain quality physiology and guiding cultural management in wheat. Two wheat cultivars differing in protein content including Yangmai 9 with low protein content and Yumai 34 with high protein content were grown under varied temperature and radiation intensity conditions including 32℃/24, 24℃/16℃and 500μmol·m-2·s-1,200μmol·m-2·s-1 during grain filling. The quality formation, photosynthetic characters, senescence, C/N assimilates translocation were investigated, and the physiological regulatory mechanisms of high temperature and deficient radiation intensity on wheat yield and quality formation was elucidated. The main results were as follows:High temperature promoted the synthesis of protein and starch at the first time of grain filling stage, increased markedly the gliadin contents, that led to protein content increased observably. Deficient radiation mainly affected the synthesis of protein and starch at the late time of grain filling stage, increased the glutenin contents, restrained the synthesis of amployectin, that also led to protein content increased. High temperature and deficient radiation intensity increased HMW-GS content in the beginning of grain filling and advanced the rapid accumulation period. Deficient radiation intensity also significantly enhanced the HMW-GS accumulation during late grain filling of Yumai 34, but for Yangmai 9 that was opposite. So continuance high temperature was bad for the synthesis of protein and starch, while deficient radiation was good for the synthesis of protein and bad for starch. The component content of protein and HMW-GS of Yumai34 was more sensitive to temperature and radiation intensity than Yangmai9, while the synthesis of starch of Yangmai9 was more sensitive to temperature and radiation intensity than Yumai34.The chlorophyll content reduced later to photosynthetic rate under high temperature indicated that the photosynthetic rate decreased early was not because of the chlorophyll. At deficient radiation, the chlorophyll content and photosynthetic rate didn't reduced, but the stoma was low and the stoma open degree was low, so stoma restrained was the main reason of the photosynthetic production synthesization decreased. The Fv/Fm and FPSⅡdecreased under high temperature and deficient radiation intensity. The FPSⅡwas markedly lower under deficient radiation intensity than high temperature. This indicated that there was different with energy utilization efficiency under high temperature and deficient radiation intensity. Deficient radiation intensity reduced the energy utilization efficiency ably in the center of PSⅡ.The content of MDA, the SOD activity in flag leaves was higher under high temperature than under deficient radiation intensity. It showed that alive oxygen could be cleared by SOD, photosynthetic institution was protected and the senescence rate was stayed under deficient radiation intensity. Under the continued high temperature, the MDA content increased and the SOD activity decreased made the photosynthetic institution destroyed and the senescence rate accelerated. High temperature improved the endonpeptidases activity and decreased the content of soluble protein, which led to the protein decompose and senescence accelerated. The endonpeptidases activity was low and the content of soluble protein were increased under the condition of deficient radiation intensity, which led to the protein decompose and senescence accelerated slowed. High temperature and deficient radiation intensity improved endonpeptidases activity and increased the content of free amino acid, which were of benefit of the synthesis of protein in grain. The cultivars with high protein content of Yumai 34 had higher endonpeptidases activity and lower protein content than Yangmai 9, which indicated proteinases activity in flag was relation with protein content in grain.High temperature reduced soluble sugar content and the ratio of C/N in vegetative organs and kernels whole grain filling, shortened the grain filling time, so that the post-anthesis assimilates reduced observably. The soluble sugar content and the ratio of C/N reduced slowly in deficient radiation than in high temperature treatment so that the post-anthesis assimilation effected lightly than in high temperature treatment. High temperature and deficient radiation both enhanced free amino acid content in flag leaf, but because of the shorten grain filling time under high temperature treatment that the post-anthesis assimilation nitrogen decreased significantly. Deficient radiation increased post-anthesis assimilation significantly, which resulted the protein content increased relatively, although the remobilization nitrogen amount pre-anthesis was low. The action of high temperature and deficient radiation was remarkable, which decreased pre and post-anthesis accumulation and translation of C and N assimilate. The accumulation and translation of C and N assimilates of cultivar Yangmai 9 was affected lightly by deficient than the cultivar Yumai 34.In summary, high temperature enhanced post-anthesis nitrogen assimilation and translation, but reduced photosynthesis rate in flag leaf, decreased photosynthesis production quantity, advanced the course of senescence. Deficient radiation intensity reduced greatly post-anthesis nitrogen translation, but enhanced evidently post-anthesis nitrogen assimilation and delayed the course of senescence. So the synthetically effect of photosynthesis production, nitrogen assimilation and translation, and the course of the senescence result the difference of the protein and starch quality formation between temperature and radiation. |
