| Non-hydraulic root-source signals(n HRS)and hydraulic root-source signals(HRS)are important responses of plants to drought stress.They are important for plant plasticity,biomass accumulation,transportation and distribution,water use,source-sink regulation,and yield formation in dryland wheat.However,its evolutionary laws and regulatory mechanisms are still not very clear.Therefore,based on the theory of root-shoot communication,14 wheat varieties with genetic relationship and different degrees of domestication along the evolutionary route were selected as the experimental materials.The pot experiment and field experiment were used to combine the method of setting different water gradient(In the potted water control experiment,three water conditions were set:adequate water supply,moderate drought stress and severe drought stress;in the field experiment,two water conditions were set:adequate water supply and drought stress).The gas exchange parameters,plant type,yield and yield component factors,water use efficiency,biomass accumulation,transportation and distribution,source-sink relationship and other indexes of wheat were measured.The characteristics and differences of plant type plasticity,yield formation,biomass allocation mode,water use efficiency,biomass accumulation,transport and distribution characteristics,and sink source relationship of different wheat materials under the regulation of root signal were analyzed and compared,and their response mechanisms were studied and discussed,the main research results obtained are as follows:1.Response of different ploidy wheat plant types to root signal regulation(water control experiment in pot)1)The relative water content(LRWC)and stomatal conductance(GS)of wheat were measured under three water gradients i.e.adequate water supply(CK,80%FC),moderate drought stress(50%FC)and severe drought stress(30%FC).The results showed thatthe LRWC of wheat did not change significantly under 50%FC,but the Gs was significantly reduced compared with adequate water supply(CK,80%FC),indicating that plants initiate non-hydraulic root signals in response to drought stress.Under 30%FC conditions,both LRWC and Gs of wheat were significantly reduced,indicating that the plant initiates hydraulic root signals as a kind of response to deeper drought stress.2)The plant type structure of wheat is changed under the regulation of root signal.Under the regulation of n HRS,all ploidy wheat leaf area,plant height,node length,the node diameter,the ratio of under-spike node length to total node length,tiller number,ear length,grain number per plant and root weight decreased slightly,with the increase of basal angle,opening angle,root-to-shoot ratio,canopy biomass density and leaf length/width ratio,wheat leaves become"slender";under the control of HRS.The above plant type indicators of wheat are greatly changed.Different ploidy wheats have different responses to root signal regulation.The reduction in leaf area,effective tiller number,spikelet number,grain number per spike,spike length,and root weight of high-ploid wheat was less than that of diploid wheat,while the root-shoot ratio was highly increased than that of diploid wheat.2.Response of yield formation,water use efficiency and biomass allocation of different ploidy wheat to root signal regulation(water control experiment in pot).3)The yield and formation factors of all ploidy wheat were decreased under the root signal regulation,but there were differences in the extent of reduction.Under the control of HRS,the reduction rates of grain yield of diploid,tetraploid and hexaploid wheat were 45%,40%and 36%,respectively.While,the reduction rates of aboveground biomass was 40%,36%and 35%;harvest index was 9.6%,5.0%and4.8%;grain number per plant were 51%,36%and 33%;ear weight per plant were47%,38%and 35%;spikelet number per plant were 36%,33%and 31%,respectively in diploid,tetraploid and hexaploid of wheat.Under the control of HRS,the grain yield of diploid,tetraploid and hexaploid wheat decreased by 69%,65%and 65%;The biomass by 65%in all ploides;The harvest index by 16%,23%and 22%;The grain number per plant by 68%,72%and 71%,and ear weight per plant by 69%,71%and 70%,respectively.The number of spikelets per plant decreased by 68%,66%and65%,respectively.It could be concluded that the decrease of grain yield,yield components and harvest index of tetraploid and hexaploid wheat under n HRS regulation was lower than that of diploid wheat.Under the regulation of HRS,there is no difference in the decrease rate of the three ploidy.and the decrease rate of the three ploidies are basically the same wheat under HRS regulation.Therefore,under the regulation of n HRS,the drought tolerance of artificially selected tetrahexaploid wheat is greater than that of naturally selected diploid wheat,and when wheat starts HRS,it has exceeded the drought tolerance threshold of wheat,so there is no difference between the three ploidy.4)The water use efficiency of wheat is reduced under the regulation of root signal.Under the control of n HRS,the WUE of aboveground biomass of diploid,tetraploid and hexaploid wheat was decreased by 2.4%,2.1%and 1.8%,respectively,while the WUE of grain yield was decreased by 8.0%,3.2%and 2.8%,respectively.Under the regulation of HRS,the WUE reduction rates of aboveground biomass of diploid,tetraploid and hexaploid wheat were 13.9%,16.2%,and 17.7%,respectively,while the WUE reduction rates of grain yield were 26.0%,31.9%and 33.0%,respectively.Under the regulation of n HRS,the high ploidy wheat with artificial selection trace could maintain high water use efficiency and strong drought tolerance,while under the regulation of HRS,drought tolerance of high-ploidy wheat would decrease,resulting in a significant decrease in water use efficiency.5)Root-shoot ratio of wheat increases under the regulation of root signal and the root-shoot ratio of tetraploid and hexaploid wheat was significantly lower than that of diploid wheat.According to allometry analysis,the allometric exponent(?)of Maboveground vs Mroot decrease of diploid,tetraploid and hexaploid wheat under CK condition were 1.31,0.68 and 0.69,respectively.It was observed that tetraploid and hexaploid wheat?<1,diploid wheat?>1;The allometric exponent between Mear vs Mvegetative of diploid,tetraploid and hexaploid wheat were 1.48,1.75 and 1.91,respectively,showing an increasing trend.Under the control of n HRS,the?values between Maboveground vs Mroot of tetraploid and hexaploid wheat were 0.89 and0.76,?<1;Under the control of HRS,the?between Mear vs Mvegetative of hexaploid wheat was 1.35,?>1.The results show that as the degree of domestication increases,high-ploid wheat will allocate more biomass to the above-ground parts and reproductive organs.High-ploid wheat can still maintain this biomass distribution pattern under the control of root signals.3.Responses of biomass accumulation,transportation and distribution of different ploidy wheat to root signal regulation(water control experiment in pot)6)The regulation of root signal decreased the capacity of assimilate accumulation pre-anthesis and post-anthesis,but increased the capacity of assimilate transport of pre-anthesis and its contribution rate to grain formation.Under the control of n HRS,the decreasing rates of pre-anthesis assimilate accumulation in diploid,tetraploid and hexaploid wheat were 28%,23%and 19%,respectively.The reduction rates of assimilate accumulation of post-anthesis were 46%,44%and 34%,respectively.The increase rates of post-anthesis transportation of pre-anthesis assimilate in diploid,tetraploid and hexaploid wheat were 6%,15%and 31%,respectively.Post-anthesis transport rate of pre-anthesis assimilate increased by 46%,53%and 57%in diploid,tetraploid and hexaploid,respectively.The contribution rate of pre-anthesis assimilate to grain yield increased by 32%,34%and 37%,respectively.Under the control of HRS,the reduction rates of pre-anthesis assimilate accumulation were 35%,29%and 28%and in assimilate accumulation of post-anthesis were 78%,63%and 52%in diploid,tetraploid and hexaploid,respectively.The increase rates of post-anthesis transportation of pre-anthesis assimilate were 10%,19%and 34%,respectively.The post-anthesis transport rate of pre-anthesis assimilate increased by70%,77%and 84%,respectively.The contribution rate of pre-anthesis assimilate to grain yield increased by 57%,62%and 65%,respectively.The results showed that with the increase of ploidy,the reduction rate of pre-anthesis and post-anthesis assimilates accumulation of high-ploid wheat was lower than that of diploid wheat,and the capacity of transportation of pre-anthesis and the contribution rate of pre-anthesis assimilates to grain is higher than that of diploid wheat,indicating that high ploid wheat has a greater ability to compensate grain yield under adversity than diploid wheat,so high ploid wheat can still maintain a higher yield under the regulation of root signals.7)The root signal regulation changed the allocation ratio of biomass accumulation in different vegetative organs of wheat.Under the regulation of n HRS,the allocation ratio of rachis and glumes in tetraploid and hexaploid wheat was significantly reduced,and the allocation ratio in stems increased significantly,and there was no significant difference in the allocation ratio of grains.Under the control of HRS,the allocation ratio of grains in tetraploid and hexaploid wheat decreased.Under the regulation of n HRS,the drought tolerance of artificially selected tetraploid and hexaploid wheat is greater than that of naturally selected diploid wheat,and can carry out active defense strategies to maintain the grains formation,and when wheat starts HRS,tetraploid and hexaploid wheat have adopted a passive defense strategy to reduce grain yield.4.Response of source-sink characteristics of different ploidy wheat under the control of non-hydraulic root signals(field experiment)8)The dry weight of leaf,sheath and stem,effective spikelet number per plant,ear weight per plant,grain number per plant and grain weight per grain were decreased by non-hydraulic root signal regulation,and the source-sink ratio of wheat was changed,and the source-sink regulation was affected.Under the control of non-hydraulic root signals,the accumulation of assimilates of post-anthesis decreases,while the post-anthesis transportation and post-anthesis transport rate of pre-anthesis assimilate and contribution rate of pre-anthesis assimilate to grain yield increases.pre-anthesis assimilation can buffer the contradiction between source supply and sink demand,and high-ploid wheat has a strong buffering capacity,so it can maintain a higher grain yield,which verifies the conclusion of the potted water control experiment.9)Under the regulation of n HRS,with the increase of ploidy,the dry weight of leaves,sheaths and stems under the treatment of defoliated and de-grained showed a trend of first increased and then decreased,and the dry weight of leaves,sheaths and stems of diploid,tetraploid and hexaploid wheat under the treatment of defoliated decreased,and the loss rates of leaves of diploid,tetraploid and hexaploid wheat were18.5%,13.6%and 23.4%,respectively.The loss rates of sheaths in three ploidies wheat were 11.3%,5.3%and 22.3%,respectively.The loss rates of stems in three ploidies wheat were 15.0%,8.4%and 19.8%,respectively.All showed a trend of decreasing first and then increasing with the increase of ploidy,and the decrease rate of hexaploid wheat was the largest.The dry weight of leaves,sheaths and stems increased under the treatment of de-grained.And the increase rates of leaves of diploid,tetraploid and hexaploid wheat were respectively were 12.4%,28.6%,7.2%,the increase rates of sheaths of diploid,tetraploid and hexaploid wheat 10.1%,33.7%,3.9%and the increase rates of stems of diploid,tetraploid and hexaploid wheat were11.1%,25.9%,6.4%,all of which showed a trend of first increasing and then decreasing with the increase of ploidy,and the increase of hexaploid wheat the smallest.The results showed that in the process of domestication from diploid to hexaploid,the source-sink ratio of wheat first increased and then decreased,showing a form of first increasing source and then expanding sink.The source-sink ratio of hexaploid wheat was the lowest.10)Under the regulation of n HRS,the treatment of defoliated and de-grained reduced the yield of wheat,and the decline under the treatment de-grained was greater than that of the treatment of defoliated.The de-grained treatment removed half of the ears.The reduction rate of the number of tetraploid spikelets under the de-grained treatment was greater than 50%,the reduction rate of diploid and hexaploid was less than 50%,and the reduction rate of diploid was more than hexaploid wheat.It shows that tetraploid wheat has a certain sink imitation,while diploid and hexaploid wheat have certain source imitation,and the source limitation of hexaploid wheat is greater than that of diploid wheat.The defoliated treatment reduced the thousand-grain weight,and the decline showed a trend of first decrease and then increase with the increase of ploidy;the de-grained treatment increased the thousand-grain weight,but did not increase to twice that of the control,which indicated that different ploidy wheat had different degree of source limitation and sink limitation.Therefore,in order to improve the yield in future breeding,it is necessary to further increase the sink capacity while expanding the source,so as to reduce the limit of yield improvement.Based on the response of different ploidy wheat plant types,yield formation,water use,biomass accumulation,transportation and distribution,and sink-source relationships to root-source signals.It is concluded that under the regulation of non-hydraulic root-source signals,wheat takes a proactive approach in response to mild drought stress,under the regulation of hydraulic root signals,a passive defense strategy is adopted to deal with deeper drought stress,and high ploidy wheat can still maintain better plant structure and yield formation under the regulation of root signals.In this study,we systematically studied the response mechanism of yield formation and plant type plasticity under the regulation of root signals.The results of this study not only provide theoretical basis for drought resistance and water saving breeding and cultivation techniques,but also provide new data support for the current crop ecology and system evolution field. |
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