| Wheat (Triticum) is the third crop planted in our country. Yield of winter wheat is about90%of the total wheat yield of our country. Wheat production occupies an important place inour national economy. Recently, heat stress caused by global warming has become morefrequent and severe, which can bring risks to food security. Non-foliar green organs, such asears have photosynthesis performance still in an adverse condition. No-foliar green organscan supply the deficiencies of grain-filling due to green leaves area reducing during latergrowth. Tapping the photosynthesis potential of non-foliar can become a good way forpushing yield limitation and realizing high yield and tolerance-resistance. Studying thephotosynthetic performance and contributions to yield of wheat non-foliar in adverseconditions is very important and can give theories on population structure regulating for ahigh and more stable yield.Four different heat-resistance winter wheat varieties-Jimai22(JM22), Xinmai26(XM26),056852series(056852) and Gaocheng8901(GC8901) were selected as plantmaterials. Effect of high temperature on different green organs and yield formation in wheatduring grain-filling was systematically studied. Photosynthetic performance, heat resistanceperformance of different green organs and contributions to grain yield were preliminarilyclarified. The main results were as follows.1. Studies on contributions of different green organs to grain yieldBy clipping leaves, wrapping ears and wrapping stems and sheaths, the contributions ofdifferent green organs to grain yield were studied at anthesis. The results showed that ears hadthe largest contribution to grain yield with a contribution ratio of41.15%-47.36%. The secondlarger contributor were leaves, with35.98%-43.89%ratio; then were the storage matter instems and sheath; the contributions of exposed peduncle and flag leaf sheath photosyntheticproduct were still small in last place. We also found that different heat-resistance varietiesshowed consistent trend on contribution of different green organs to grain yield.Wheat flag leaves and ears were respectively fed with13C. The results showed that theratio of13C to total C in ears was the highest, either the fed objects were ears or flag leaves;secondly was in stems and sheaths; thirdly was in leaves and the last was in glumes.Comparing the results between treatments of ears fed and of flag leaves fed, we found thatphotosynthesis products in glumes, kernels and leaves from13C fed to ears were more thanthose fed to flag leaves. That is to say, photosynthetic efficiency of ears was higher than thatof flag leaves. 2. Studies on effect of high temperature to yield formation of different heat–resistancevarieties in wheatHigh temperature stress caused different heat-resistance varieties changed at differentlevels in plant morphology. Changes of NDVI valve could reflect the changes of wheat plantmorphology. There were no significant difference in JM22and056852series after hightemperature stress. Yet significant difference happened in NDVI values of XM26and GC8901after stress. As growth times went on, the both latter have more notable difference comparedwith their respective contrasts. High temperature stress accelerated the process of wheatsenescence.The grain-filling duration of different heat resistant varieties was shortened under hightemperature stress and the largest grain-filling ratio was advanced. Heat stress also decreasedthe largest grain-filling ratio of different heat-resistance varieties. The smallest reduction ofgrain-filling ratio was that of056852series, and the second was that of JM22, and the thirdwas that of GC8901, and the largest was that of XM26.High temperature decreased the1000-kernel weight of wheat, which resulted in thedecrease of grain yield. The order of1000-kernel weight change after high temperature wasXM26>GC8901>056852series>JM22by size. Grain yield change was consistent with1000-kernel weight change. The yield reductions of XM26and GC8901were more, reducing11.43%and10.05%compared with their respective contrast. While JM22and056852serieshad less yield reduction, with6.41%and6.93%, respectively.3. Effects of high temperature on photosynthesis enzymes of different green organs inwheat.RuBPCase activates of all different green organs decreased after high temperature stress.Among of the green organs, RuBPCase activities of flag leaves decreased the most. Thedifference between stress treatments and contrasts continued to increase after heat stressending. RuBPCase activities of stressed leaves were significantly lower than those ofcontrasts until to the days after high temperature stress ending. Changes of RuBPCaseactivities in flag leaf sheaths decreased relatively more and had same trend with that of in flagleaves. RuBPCase activities in ears changed the least. Small changes happened in earsRuBPCase from the stress ending day to5thday after stress ending. There were nosignificance between stress treatments and contrasts. Change trends of RuBPCase activities inexposed peduncles were fundamentally same as those in ears. Unlike with those in ears,RuBPCase activities in exposed peduncles were still higher on10thday after stress ending.RuBPCase activities differed not only among different green organs but also between varieties. Drop of RuBPCase activities in XM26green organs was more than that in JM22,which was one of the reasons that caused photosynthetic ability decrease more than that ofJM22.PEPCase activities in different green organs of wheat differed. PEPCase activities inexposed peduncles and in ears were highest; the second highest PEPCase activities were inflag leaf sheaths. PEPCase activities in flag leaves were the lowest, with only50%of those inexposed peduncles and in ears. PEPCase activities increased after high temperature stress.PEPCase activities in all green organs were higher than those in contrasts at stress ending day.But PEPCase activities in contrasts were more than those in stress treatments at5thday and10thday after stress ending. High temperature stress had the smallest effect on PEPCaseactivities in exposed peduncles which changed moderately during the whole experience.There were most drastic changes in flag leaves PEPCase activities: it increased slightly at thestress ending day and then dramatically reduced at5thday after stress ending. There were verylow PEPCase activities in peduncles at10thday after stress ending day. Change extent ofPEPCase activities in ears and in sheaths was in between that of flag leaves and of exposedpeduncles.PEPCase activities not decreased but increase in the conditions of this experiment, whichproved that PEPCase activity increased with temperature rising within certain temperaturelimition.4. Effect of high temperature on photosynthetic rate of different green organsThe general trend in the Pn response to high temperature stress was similar between bothcultivars, while it differed between cultivars in the magnitude of change. Under non-stressedconditions, the Pn in the flag leaves of both cultivars declined steadily from DAS to DES. Incontrast, the Pn in the stressed leaves of both cultivars decreased linearly over time and thedifferences between cultivars were more pronounced under conditions of high temperaturestress. Compared with their respective non-stressed treatments, the Pn of JM22had decreasedby about6.6%at DES and59%at10DAS; however, for the heat-sensitive cultivar XM26,the Pn declined by12.8%at DES and69.9%at10DAS. These results indicate that hightemperature stress accelerated the decline process, showing an inhibition of photosynthesis byhigh temperatures. Conversely, heat stress significantly increased Gs by7.09%for JM22and23.67%for XM26, compared with their respective controls. Nevertheless, Gs declined afterDES. At10DAS, the stomatal conductance for flag leaves of XM26was significantly lowerthan that at DBS. Transpiration showed the same tendency as stomatal conductance. Hightemperature stress had a minor effect on Ci that was associated with the decline in Pn and the drastic changes in Gs and Tr. No obvious changes in Ci were measured during theexperimental period. Except at10DAS, the Ci of leaves was much higher for XM26understress than that without stress due to the acceleration of senescence by high temperaturestress.From the analysis of gas exchange parameters, we concluded that the inhibition ofhigh temperature stress on Pn was not the result of stomata closing, but rather non-stomatallimitation. Furthermore, the decline in Pn from high temperature stress wascultivar-dependent, which was exemplified by the larger variation of Pn in XM26comparedto JM22.Photosynthetic performance of ears in all varieties declined with different degrees. Therewas little difference on photosynthetic ability of ears in056852series between stresstreatments and contrasts. Photosynthetic rate decreased a little between stress and contrast.There were significant differences on photosynthetic rate of XM26and GC8901, comparedwith their respective contrasts. Differences of photosynthetic rate between stresses andcontrasts in the four varieties became more significant at5thday after high temperature stressending. The turn of photosynthetic rate in the four varieties wasXM26>GC8901>JM22>056852by order of difference size.5. Effect of high temperature on fluorescence characteristic of different green organs inwheat.F0of both varieties were significantly enhanced by high temperature. Response of F0tohigh temperature in different green organs and in varieties was consistent. Increase extent ofF0in ears was the most, then in flag leaf sheaths, and then in flag leaves, the least increaseextent in exposed peduncles. XM26showed sensitive to heat, for all of its green organs had alarger increase in F0than JM22.Qp, the closing degree of PSII reaction center, was expanded by high temperature. Thelargest closing degree of reaction center was in flag leaves, and then in flag leaf sheaths, andthen in ears, the smallest in exposed peduncles. Qp in XM26different green organs was largerthan that in each organs of JM22. High temperature decreased QY, the timely quantity yield,of different green organs. The largest effect of QYwas in ears, with a9.33%decrease inXM26and8.86%in JM22, and then in flag leaves and flag leaf sheaths, with a6%-7%decrease in XM26and5%-6%inJM22, the slightest effect of high temperature on F0inexposed peduncles, with a6.41%decrease in XM26and only3.75%in JM22. Fromcomparison between varieties, we concluded that larger decrease degree in QYand QPwasboth one of the reasons photosynthetic performance declined and a self-protection way that XM26avoided harm from excess light energy.6. Physiological mechanism on heat resistance of different green organs to hightemperature stress at grain-fillingHigh temperature accelerated the accumulation of MDA in different green organs.Heat-resistant variety and heat-sensitive variety showed a same trend, with different changedegree. The increase percent to contrast in flag leaves, ears, exposed peduncles and flag leafsheaths of JM22was5.44%,19.11%,3.00%and61.21%, respectively. The increase percentto contrast in corresponding organs was49.55%,15.17%,12.39%and70.46%, respectively.SOD activities and CAT activities in flag leaves increased after high temperature. Atstress ending day, Increase of SOD activities and CAT activities was15.55%and13.00%inJM22flag leaves,22.60%and34.40%in XM26, respectively. Yet high temperature decreasedSOD activities and CAT activities in ears, exposed peduncles and flag leaf sheaths. SODactivities and CAT activities in both varieties ears decreased significantly, with a decrease of12.67%SOD activities and30.09%CAT activities in JM22ears, with a decrease of23.00%SOD activities and30.09%CAT activities in XM26ears. Although there were decreases inpeduncle and flag leaf sheath SOD and CAT activities, there was no significance betweenstress and contrast.POD activities in all green organs declined significantly after high temperature stress,compared with the contrasts. Decreases percent of POD activities in flag leaves, ears, exposedpeduncles and flag leaf sheaths were21.41%,34.97%,36.17%and40.29%in JM22and28.73%,47.04%,46.89%and50.25%in XM26.High temperature had different effect on caroteinoid content in different green organs.Caroteinoid content in JM22flag leaves increased significantly, with a increase of9.28%.However, Caroteinoid content in XM26flag leaves decreased significantly, with a decrease of7.77%. High temperature increased caroteinoid of ears and exposed peduncles in bothvarieties.Caroteinoid content in JM22and XM26ears increased6.20%and7.27%, compared withtheir contrasts,3.46%and4.26%increase percent was in JM22and XM26exposed peduncles,respectively. High temperature stress decreased caroteinoid content in both varieties flag leafsheaths,4.20%decrease in JM22and8.99%decrease in XM26.Heat dissipation capability of different green organs depended on xantophyll cycleenhanced after high temperature. Heat dissipation capability of different green organs wasordered by (A+Z）/（V+A+Z）value, that was exposed peduncle＞ears＞flag leaf sheaths ＞flag leaves. Heat dissipation ability of JM22was greater than that of XM26.Non-photochemical heat dissipation capability was different in different greenphotosynthetic organs. Ears and exposed peduncles had better non-photochemical heatdissipation, while flag leaves and flag leaf sheaths had worse ones. Excessively light energyin different green organs decreased significantly after high temperature, compared withcontrasts. Differences order of different green organs between stress treatments and contrastswere ears, flag leaves, exposed peduncles and flag leaf sheaths.7. Effect of high temperature on ultra-structure of different green organsUltra-structures of different green organs were alerted by high temperature stress.Disruption of membrane structure was the most significant effect. Membranes of chlorophyll,mitochondria and nucleus changes visibly. From the comparison of chlorophyll changesamong awns, exposed peduncles and flag leaves, we found that high temperature stress hadlargest effect on awns chlorophyll structure, larger effect on exposed peduncle chlorophyllstructure and smallest effect on flag leaf chlorophyll structure. JM22showed better heatresistance than XM26, for injury level of JM22from high temperature stress was lesser thanthat of XM26. |
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