| Plants tend to generate non-hydraulic root signals (referred to as root-sourced signal) under drought stress. The signals would actively regulate stomatal opening, and induce an accumulative biosynthesis of drought induced proteins, thereby regulate plant growth and water use. Few of previous studies aimed to investigate differentiate expression of drought induced proteins and its eco-physiological effects. And the studies on this kind of differentiate performance and its evolutionary mechanism in wheat species with different ploidy has not been reported. In this study, six different ploidy wheat varieties with evolutionally genetic relations were chosen as trial materials, including two diploid (MO1 and MO4), two tetraploids (DM22 and DM31) and two hexaploids (Longchun 8275, L8275) and Monkhead. Pot culture experiments with soil medium were conducted to continuously track successive occurrence of non-hydraulic signal and hydraulic signal in wheat plants during progressive soil drying, and systematically measure the expression characteristics of drought induced protein bands and biomass changes in distribution patterns when the root-sourced signal operated. Furthermore, a few classic statistical analyses were made to compare the differences in above parameters among different ploidy wheats. A few major findings were achieved as follows:(1) A significant negative correlation was observed between threshold range of soil moisture when the root-sourced signal continuously operated and non-hydraulic stomatal sensitivity extent in wheat species of different ploidy. The threshold range of soil moisture during the operation of root signals had a similar performance in same wheat species, but with the increase of ploidy number, it became wider. The threshold of diploid MO1 and MO4 ranged from 50-43%, and that of tetraploid DM22 and DM31 was at the range of 56-40% and that of hexaploid L8275 and Monkhead was from 69-20% respectively. In addition, leaf stomatal conductance showed a similar decline trend as the above parameters during the continuous operation of root-sourced signal in all three wheat species, in which the decline rates of MO1 and MO4 were around 25.2, being significantly higher than that of tetraploid species (ranged from 15.7-15.9) and that of hexaploid species (from 13.3 to 14.6). Therefore, there existed a significant correlation between the soil moisture threshold range for the operation of root-sourced signal and non-hydraulic stomatal sensitivity.(2) In comparison with the treatment of sufficient water supply, biomass allocation pattern of various organs was changed significantly under the regulation of root-sourced signal in different ploidy wheat species, in which harvest index and grain to leaf ratio were increased significantly. Harvest index were significantly increased by 38.5%,28.9%,26.7%,18.8% and 16.8% in MO1, MO4, DM22, DM31 and Monkhead respectively, yet there was no significant change in L8275. Grain to leaf ratios were significantly increased by 102%,43.0%,85.4%,18.8% and 38.7% in MO1, MO4, DM22, L8275 and Monkhead respectively, yet there was no significant change in DM31. Furthermore, biomass maintenance rate showed a great diversity which varied from wheat variety and organs, in which maintenance rate of root biomass was the highest, the rate of spike being next and that of other organs the last.(3) Differentiate expressions of drought induced proteins were observed in different ploidy wheat species under the progressive operation of root-sourced signal, in which the molecular weight of specific proteins were around 41.5 KD and 17 KD respectively. The molecular weight of those specific protein bands whose relative content was changed significantly ranged from 25 to 61 KD. Of these specific proteins, the differences in relative contents for 61.0 KD,54.7 KD,33.3 KD and 29.7 KD particles were significant in different ploidy varieties. The relative content of the protein of 54.7 KD was significantly decreased by 31.5% as the non-hydraulic root signal started to operate in MO4, yet it was increased by 2.45% and 1.85% in DM31. The increase rate of the relative content in 61.0 KD protein increased significantly by 11.7% and 55.8% on the point of hydraulic root signal operation in MO1 and DM31 respectively. For the specific protein of 33.3 KD, its relative content on the point of hydraulic root signal operation rose by 11.7% in MO1, and the contents on the non-hydraulic and hydraulic root signal operations increased by 55.1% and 39.8% in DM31 respectively, and the content on non-hydraulic root signal increased by 330%, a highest value in L8275. The results suggest that the proteins of 61.0 KD,54.7 KD and 33.3 KD play a critical role in regulating drought adaptation in diploid and tetraploid wheat species.(4) Further analysis indicated that relative contents of specific protein of 29.7 KD on the point of non-hydraulic and hydraulic root signals were increased by 62.2% and 32.4%,40.4% and 37.8%,40.8% and 34.4% in DM22, DM31 and Monkhead respectively; however they were decreased by 21.0% and 20.8% in MO4 respectively. In addition, its increase rate on the point of non-hydraulic root signal operation reached up to 66.7%. It can be argued that the protein of 29.7 KD is endowed with evolutional conservation among different ploidy species, and is likely to act as a universal protein in response to drought stress in dryland wheat.(5) It can be concluded that the proteins of 61.0 KD,54.7 KD and 29.7KDwere closely related to plant growth and yield formation in droughted wheat under the regulation of root-sourced signal. The 33.3 KD and 26.8 KD proteins were found not to be significantly correlated with maximum plant height, leaf to aboveground ratio and harvest index. Therefore, these two proteins are probably related to endogenous regulation process, but not directly to external phenotype of wheat crop.On the basis of above results, it can be speculated that there exist an obvious phenomenon that drought induced proteins would be selectively expressed under drought stress in wheat. This kind of phenomenon is closely correlated with signaling cascade procedure at molecular and cellular levels during plant adapts to drying environment, which regulates differentiate biomass allocation in favor of individual survival and population reproduction.
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