Response of grafting tobacco to low potassium stress

Background: In the previous study, we investigated the alleviation effect of grafting on potassium uptake in roots and tobacco growth inhibition under low potassium stress. However, the effect of grafting on the low potassium stress perception and coping mechanism of tobacco at the whole plant level is not clear now. In order to clearly understand the impact of grafting on potassium deficit responding mechanism in tobacco, a mutual grafting experiment has been conducted in two varieties of tobacco ('Wufeng No.2' and 'Yunyan 87') in different K supply level (5 mmol L^{- 1} and 0.5 mmol L^{- 1} K).

Results: The results show that compared with the self-rooted seedlings, grafting significantly increased the potassium content of the whole plant of Yunyan 87 (97.57 and 189.74% under normal potassium and low potassium conditions, respectively), and the increase in shoots was greater. The data of whole plant K content distribution and tobacco hypocotyls net K⁺ flux demonstrates that potassium stress makes plants more inclined to maintain K⁺ in the shoot rather than root. In addition, when K deficiency occurs, grafting could reduce the time required for downward net K⁺ flux in tobacco hypocotyl to decrease to stable levels. The results of net K⁺ flux in the roots indicated that K channel proteins and transporters play different roles in two rootstocks in terms of potassium tolerance. Transcription level analysis suggested that the increased circulating efficiency of K⁺ between the shoots and roots in tobacco constitutes one means to low potassium stress adaptation.

Conclusions: Grafting can activate more K⁺ channels in tobacco 'Yunyan 87', this means a more active K⁺ cycle, higher potassium content in shoot and faster response to low potassium stress signals in grafting tobacco. In addition, grafting can also change the K⁺ absorption mode of tobacco root from being dominated by HATS to being jointly responsible by HATS and LATS, greatly improving the ability of K⁺ transmembrane transportation on root surface under low potassium stress. These are undoubtedly the reasons why grafting tobacco performs better in coping with low potassium stress.

Keywords: Grafting; K+ channel current; Net K+ flux; Potassium stress; Tobacco.