The Regulation Of Radiation Utilization During Post Anthesis In Response To The Interaction Between Exogenous 6-BA And Nitrogen Of Two Different Stay-green Wheat Cultivars

Wheat(Triticum astivum L.) is one of the main food crops in China. To further improve the yield of wheat is one of the means which can ensure the total production and protect food security. At present, under the guidance of the high yield cultivation theory that ensure enough population and strong individual plant in wheat cultivation, one of the main limiting factors to further achieve higher yield is that individual productivity of wheat during grain filling stage and leaf photosynthetic productivity are poor. Therefore, the purpose of this experiment was to investigate the effects of exogenous cytokinin(6-BA) and nitrogen application with varied rates on photosynthetic characteristics of wheat post anthesis and provide a theoretical basis for enhancing photosynthetic productivity of wheat. A stay-green wheat(Wennong 6) and a non-stay-green wheat(Jimai 20) were selected in this experiment.The experiment was conducted with three nitrogen rates, namely, N0(0), N1(240kg/ha) and N2(360kg/ha). Exogenous 6-benzyladenine(6-BA)(25mg/L) and Lovastatin(300mg/L)were sprayed to the leaves at a rate of 100 mL/m2 for 3 days after anthesis(DAA). The main results were as follows.(1) The regulation of fluorescence characteristics during post anthesis in response to the interaction between exogenous 6-BA and nitrogen of two different stay-green wheat cultivarsFoliar application of exogenous 6-BA significantly raised the max photochemical efficiency(Fv/Fm), actual photochemical efficiency(?PSII), photosynthetic electron transport rate(ETR) and photochemical quenching coefficient(qP) of flag leaves of two wheat cultivars in different growth stages post anthesis. Those chlorophyll fluorescent parameters were significantly decreased by spraying lovastatin. It was showed that under N0 treatment, spraying exogenous 6-BA increased ?PSII of flag leaves of Jimai 20 by 12.08%,6-BA combined with N1 treatment and N2 treatment increased ?PSII by 14.21% and 9.43%,respectively. ?PSII of flag leaves of Wennong 6 was increased by 12.44%, 14.84% and11.58%, respectively, under above three treatments. In addition, under N0 treatment, spraying exogenous 6-BA enhanced photosynthetic electron transport rate(ETR) of flag leaves in Jimai 20 by 16.57%, 6-BA combined with N1 treatment and N2 treatment enhanced ETR by25.81% and 18.83%, respectively. ETR of flag leaves of Wennong 6 was increased by13.88%, 23.58% and 22.80%, respectively under above three treatments. Other indicators of flag leaves in both wheat cultivars showed the following rule that under 6-BA combined with N1 treatment, fluorescence parameters of flag leaves were increased more than 6-BA combined with N0 treatment or 6-BA combined with N2 treatment. Meanwhile, the cultivar,nitrogen fertilizer, single hormone effect, hormone combined with nitrogen fertilizer affected?PSII, ETR and qP significantly. In addition, Fv/Fm was affected significantly by cultivar,hormone but not affected by combined application of nitrogen fertilizer and hormone significantly. Besides, under N0 treatment, foliar application of the inhibitor of cytokinin lovastatin reduced ETR of flag leaves of Jimai 20 by 22.71%, lovastatin combined with N1 treatment and N2 treatment decreased ETR by 12.06% and 11.92%, respectively. Other fluorescence parameters including Fv/Fm, ?PSII and qP of two cultivars showed a downward trend. Increasing nitrogen application rate could slow down the decrease of fluorescence parameters of both wheat cultivars caused by the reduction of the synthesis of cytokinin.Exogenous 6-BA had significant effects on the content of endogenous hormones in two cultivars of wheat.(2) The regulation of function of wheat leaves during post anthesis in response to the interaction between exogenous 6-BA and nitrogen of two different stay-green wheat cultivarsExogenous 6-BA had significant effects on the content of endogenous hormones in two cultivars of wheat. Spraying exogenous 6-BA significantly increased the zeatin riboside(ZR)content and the auxin(IAA) content of flag leaves post anthesis in both cultivars. The gibberellins(GA3) content was significantly increased at 21-28 DAA. On the contrary,abscisic acid(ABA) was significantly decreased after spraying exogenous 6-BA. After spraying exogenous lovastatin, changes of endogenous hormones contents were on the contrary with above results. With the increase of nitrogen application rate, the ZR and IAA content was enhanced at 21-28 DAA. The overall trend of the ABA content was decreased with the increase of nitrogen rate. Under N1 treatment, the GA3 content was higher than thatunder the other two nitrogen rates at 7-14 DAA. Meanwhile, the ZR content was significantly affected by the cultivar, nitrogen fertilizer, single hormone effect, combined application of nitrogen fertilizer and hormone. The chlorophyll content in Wennong 6 was significantly higher than that in Jimai 20. Exogenous 6-BA remarkably increased chlorophyll content of flag leaf in two cultivars. It was increased by 10.70% to 19.70% compared to the control.However, spraying exogenous lovastatin decreased chlorophyll content notably. Chlorophyll content was enhanced with the increase of nitogen rate. Under N0 treatment, exogenous 6-BA enhanced chlorophyll content by 13.2%, while 6-BA increased it by 19.7% and 15.2% under N1 treatment and N2 treatment in Jimai 20, respectively. In addition, exogenous 6-BA resulted in 18.82%, 20.79% and 13.45% increase chlorophyll content under N0 treatment, N1 and N2 treatment, respectively. The same law was in antioxidant enzyme activity. It was that under 6-BA combined with N1 treatment, chlorophyll content and antioxidant enzyme system activity of flag leaves were increased more than 6-BA combined with N0 treatment or 6-BA combined with N2 treatment. Combined application of nitrogen fertilizer and hormone had significant effects on chlorophyll content and antioxidant enzyme system activity. Lovastatin combined with N0 treatment reduced chlorophyll content and antioxidant enzymes activity more than that lovastatin combined with N1 and N2 treatment. This shows that increasing nitrogen fertilizer application could mitigate the senescence of the photosynthetic structure.(3) The regulation of grain filling during post anthesis in response to the interaction between exogenous 6-BA and nitrogen of two different stay-green wheat cultivarsExogenous 6-BA increased the max grain filling rate, the average grain filling rate, active growth stage and actual grain filling final stage in Wennong 6,while enhanced active growth stage and actual grain filling final stage in Jimai 20. Compare grain filling parameters with different nitrogen levels, the results showed that the max grain filling rate and the average grain filling rate obtained from the N2 treatment in Jimai 20 were higher that those from N1 treatment and N0 treatment. Under N1 treatment, the active growth stage was longer than that under N2 treatment and N1 treatment. The max grain filling rate, the average grain filling rate and active growth stage in the N1 treatment were higher than those in N2 treatment and N0 treatment. The results showed that appropriate nitrogen rate could effectively enhance grain filling rate and extend grain filling stage and finally increased 1000-grain weight in twocultivars. However, grain filling rateand 1000-grain weight were reduced under nitrogen deficiency treatment. Excessive nitrogen application, not only caused the waste of nitrogen,but also was not conducive to the increase of grain weight.(4) The regulation of dry matter accumulation and distribution and yield in response to the interaction between exogenous 6-BA and nitrogen of two different stay-green wheat cultivarsAfter spraying exogenous 6-BA, the amount and distribution of dry matter in the grain at mature period were higher than those in the control treatment of two cultivars, but the amount and distribution of dry matter in the sheath, spike-stalk and glume and leaves were lower than those in the control treatment.The results indicated that the improvement of endogenous cytokinin was beneficial to the transport of dry matter to grains. In addition, the amount and distribution of dry matter in the grain at mature period from N1 treatment was the highest,while it was the lowest from N0 treatment. Exogenous 6-BA increased contribution rate of storage and assimilation before anthesis to grain in Jimai 20, but Wennong 6 enhanced the contribution rate of storage and assimilation after anthesis. Undet different nitrogen levels,the contribution rate of storage and assimilation before anthesis to grain in Jimai 20 was N1>N2>N0 and the contribution rate of storage and assimilation afetr anthesis to grain in Wennong 6 was N1>N2>N0.Variety had a significant effect on the spike number, grain number and 1000-grain weight.Spraying exogenous 6-BA significantly affected the grain weight and yield(P<0.01), while had no significant effects on the spike number and grain number were observed. Nitrogen affected significantly yield and yield componets. Interaction between nitrogen fertilizer and exogenous 6-BA had a significant effect on the number of spike, grain number per spike,1000 grain weight and yield. In a word, significantly higher yields were obtained from interaction treatment between exogenous 6-BA and N1 compared to spraying 6-BA and interaction treatment between exogenous 6-BA and N2.