College of Resources and Environment, Southwest University, Chongqing, 400716, China.
Vegetable and Flower Institute of Chongqing Academy of Agricultural Sciences, Chongqing, 401329, China.
BMC Plant Biol. 2020 Jun 22;20(1):286. doi: 10.1186/s12870-020-02481-6.
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 and 0.5 mmol L K).
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.
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.
在之前的研究中，我们研究了嫁接对低钾胁迫下根系钾吸收和烟草生长抑制的缓解作用。然而，嫁接对整个植株水平的烟草低钾胁迫感知和应对机制的影响尚不清楚。为了清楚地了解嫁接对烟草钾亏缺响应机制的影响，我们在两种烟草品种（‘武丰 2 号’和‘云烟 87’）不同钾供应水平（5mmol·L 和 0.5mmol·L K）下进行了互嫁接实验。
结果表明，与自根苗相比，嫁接显著增加了云烟 87 的全株钾含量（正常钾和低钾条件下分别增加了 97.57%和 189.74%），且增加幅度更大。全株 K 含量分布和烟草下胚轴净 K 流的数据表明，钾胁迫使植物更倾向于将 K 维持在地上部分而不是根部。此外，当发生 K 缺乏时，嫁接可以减少烟草下胚轴净 K 流下降到稳定水平所需的时间。根净 K 流的结果表明，K 通道蛋白和转运体在两种砧木中对钾耐性发挥不同的作用。转录水平分析表明，烟草中地上部和地下部之间 K 循环效率的提高是适应低钾胁迫的一种手段。
嫁接可以激活烟草‘云烟 87’中更多的 K 通道，这意味着更活跃的 K 循环、更高的地上部钾含量和更快的对嫁接烟草低钾胁迫信号的响应。此外，嫁接还可以改变烟草根系的 K 吸收模式，从以 HATS 为主导转变为 HATS 和 LATS 共同负责，在低钾胁迫下大大提高了根表面 K 跨膜转运的能力。这些无疑是嫁接烟草在应对低钾胁迫时表现更好的原因。
