Response of Root Development and Auxin in Tea Plants to Different Nitrogen Forms
Tea plants(Camellia sinensis)prefer NH4+as the dominant nitrogen(N)source.Although it has been proven that the use of mixed nitrate(NO3-)and ammonium(NH4+)as a N source can improve plant growth,whether genotypic difference in response to mixed nutrition exists in different tea plants remains obscure.Two tea cultivars(Camellia sinensis cv.Xinyang 10 and Zhongcha 108)were grown at three ratios of NH4+/NO3-(4∶0,3∶1 and 0∶4)to elucidate how the ratio of NH4+/NO3-modulate the architecture of the root system by investigating root growth,N content and auxin content as well as the expression of related genes.Xinyang 10 had the highest root and shoot dry matter and root N content under mixed nutrition(3∶1).And Xinyang 10 had the longer adventitious roots under mixed nutrition relative to sole NH4+,but no difference was observed in growth of lateral root between sole NH4+andmixed nutrition treatments.IAA content was significantly increased in the roots of Xinyang 10,but significantly decreased in its leaves.Response of Zhongcha 108 to ratios of NH4+/NO3-was different from Xinyang 10.Shoot biomass and N content of root and shoot in Zhongcha 108 were significantly reduced under mixed nutrition relative to sole NH4+,while length of adventitious root increased,but not reaching statistical significance.Compared with sole NH4+,mixed nutrition increased length of lateral root but decreased the number and density of lateral roots in Zhongcha 108.And the IAA content in roots of Zhongcha 108 was significantly reduced under mixed nutrition relative to sole NH4+,but not in its leaves.The results of qRT-PCR showed that auxin synthetic genes CsTSA,CsNIT1,transportation genes CsPIN3a,CsPIN3b and response genes CsARF3,CsIAA27 in roots of Xinyang 10 were significantly up-regulated under mixed nutrition compared with sole NH4+;however,auxin synthetic genes CsNIT1,CsNIT2,transportation CsABCB4 and response genes CsARF1,CsARF3,CsARF5,CsARF6 in roots of Zhongcha 108 were significantly down-regulated under mixed nutrition compared with sole NH4+.In conclusion,Xinyang 10 and Zhongcha 108 have genotypic differences when responding to N forms.The former is tolerant to NO3-and suitable for growth at the ratio of NH4+/NO3-as 3∶1,while the latter is sensitive to NO3-and suitable for growth under sole NH4+nutrition.Under the ratio of NH4+/NO3-at 3∶1,auxin transport to roots of Xinyang 10 increases but to those of Zhongcha 108 decreases,which may be one of the physiological mechanisms conferring different response of different tea roots to N forms.
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