| Wheat is one of the important food crops in China,and its high and stable yield is very important for the food security of China.Photosynthesis is the only energy source of plant,and improving photosynthetic performance is the fundamental way to improve crop yield.Therefore,people did a lot of related research on wheat photosynthesis,and have achieved fruitful results.Through the breeding of plant type and leaf type,the harvest index of wheat and the population structure of wheat canopy were improved which lead to the yield of wheat greatly improving.In recent years,through the breeding of the plant type and leaf type to improve the yield of wheat encountered a bottleneck.But the study of wheat ear photosynthesis research has become a new hot issue.However,the study of the photosynthetic characteristics of wheat and the contribution of wheat photosynthesis to grain yield is very limited.This paper systematically studied the photosynthetic capacity of wheat ear and the effect of wheat ear photosynthesis on grain yield.The main results obtained are as follows:(1)In order to elucidate the photosynthetic capacity of wheat,we compared the photosynthetic rate and photosynthetic rate per unit area of the ear and different parts of it and the flag leaf.The net photosynthetic rate of ear per unit area was only about 25% of that of flag leaf,while the total photosynthetic rate of the ear per unit area was only about 55% of that of flag leaf.However,when the photosynthesis of wheat and flag leaves was compared with the unit organ,the net photosynthetic rate of wheat ear could account for about 70% of the net photosynthetic rate of flag leaf,and the total photosynthetic rate of one ear was even more than that of one flag leaf.This is mainly due to the fact that wheat has a large photosynthetic area and a higher respiration rate.(2)Chlorophyll is an important constituent of photosynthetic apparatus,and its content is closely related to photosynthetic capacity.In order to explore the relationship between chlorophyll content and wheat ear photosynthetic capacity,we selected Zhengmai 7698(a high chlorophyll content of the ear)and Xian 8(a low chlorophyll content of the ear),and compared the photosynthetic capacity of the ear in the two cultivars.The results showed that the total photosynthetic rate of the ear per unit area of glume and lemma in Zhengmai 7698 were significantly higher than that of glume and lemma in Xian 8.But there is no significant difference between the total photosynthetic rate of the ear per unit chlorophyll of glume and lemma in Zhengmai 7698 and in Xian 8.This indicated that the photosynthetic capacity of ear was positively correlated with chlorophyll content.(3)The flag leaf and the ear were located in different CO2 environment and light environment.To explore the adaptation mechanism of the ear and the flag leaf to the different CO2 environment and light environment,the response of flag leaf and ear and its parts to CO2 concentrations and light intensities were determined.The results of the response of flag leaf and ear and its parts to CO2 concentrations showed that the CO2 saturation of ear and its parts was significantly higher than that of flag leaf.This suggests that ear has adapted to the higher CO2 environment and can take advantage of higher CO2 concentrations.The results of the response of flag leaf and ear and its parts to light intensities showed that the light saturation point of the ear was similar to that of the flag leaves,while the light saturation points of the glumes,lemma and grains were significantly lower than that of the flag leaves.Those results suggests that the whole wheat leaves showed sun-type characteristics,but its glumes,lemma and grain due to long-term located in low light environment,so show a certain shade-type characteristics.The utilization ability of each part of ear is weak for strong light,but the whole ear which has multi-layer bract structure can take advantage of strong light effectively.(4)One of the most important differences between the C3 photosynthetic pathway and the C4 photosynthetic pathway is that the size of the photorespiration is different.C4 plants almost have no photorespiration,but C3 plants have a high photorespiration.In order to explore whether C4 pathways present in wheat ear,the wheat and the flag leaves were compared by measuring the oxygen sensitivity and the post-illumimation CO2 burst(PIB),which reflect the size of the photorespiration.The results showed that the oxygen sensitivity of flag leaf was significantly higher than that of ear and its parts,and the oxygen sensitivity of glumes and lemma was similar in each part of ear,and the oxygen sensitivity of grain was significantly lower than that of glumes and lemma.However,even the oxygen sensitivity of grain is also about 12%,which is significantly higher than that of typical C4 plants.The results showed that the post-illumimation bursting of CO2 of the ear was significantly stronger than that of flag leaf,and the PIB of ear was 2.5 times higher than that of flag leaf.This also shows that ear is a typical C3 photosynthetic pathway.(5)The PSII reaction center is one of the most sensitive parts of the photosynthetic electron transport chain,while the maximum photochemical efficiency Fv/Fm of PSII reflects the maximum activity of the PSII reaction center.By comparing the change of PSII activity under different dehydration conditions,to explore the resistance level of ear and flag leaf to water stress and its causes.The results showed that during the same dehydration time the maximum photochemical efficiency Fv/Fm of ear decreased faster than that of flag leaf,but relative water content(RWC)of flag leaves was faster than that of the ear.This indicates that the water retention capacity of ear is stronger than that of flag leaf.Further,under the same relative water content,the PSII maximum photochemical efficiency of the flag leaf was significantly higher than that of the ear.This result indicates that the resistance of the PSII response center of flag leaf to water stress is stronger than that of ear.Based on the previous studies and the results of this experiment,we suggested that the ability of ear to maintain good photosynthetic performance under water stress could be related to the different water supply capacity of root to the ear and flag leaf,and the dehydration tolerance of wheat ear photosynthetic structure itself was not significantly higher than flag leaf,even lower than flag leaf.(6)It is known that the wheat ear is an important photosynthetic organ.However,the effects of photosynthetic capacity of the ear and flag leaf on wheat grain filling in field conditions are not well known.In this study,six representative winter wheat cultivars in the Huang-huai-hai area of China were selected as study materials.The photosynthetic capacity of the ear and flag leaves was studied in situ with a specially designed chamber which did not change the position of the ear and the flag leaf.The light energy interception and the effects of shade treatments of ears and flag leaves,respectively,on grain filling and grain yield in field conditions were also studied.The results showed that the photosynthetic capacity of the wheat ear generally equaled that of the flag leaf,and the photosynthetic duration of ears in some cultivars was longer than that of flag leaves.In one day,a layer of wheat ears could intercept 45-58% of the total photosynthetic photon flux density.In general,the total photosynthetic assimilation of a single ear in a day equaled that of a flag leaf or exceeded it.The effect of ear photosynthesis on grain filling and grain yield was greater than that of the flag leaf,and the contribution of photosynthesis of the ear to the final grain yield reached 38%-68%.In conclusion,the wheat ear has a strong photosynthetic capacity and a better light environment;photosynthesis of the wheat ear contributes greatly to grain yield.Therefore,in the selection of high-yielding wheat varieties,one should consider not only the photosynthetic capacity of the flag leaf but also the photosynthetic capacity of the wheat ear. |
PDF Full Text Request