Study On The Auxin-mediated Feedback Regulation Mechanism By Scion On Rootstock Potassium Uptake In Grafted Watermelon

Watermelon Zaojia‘ZJ’(Citrullus lanatus(Thunb.)Matsum.and Nakai,cv.Zaojia8424;sensitive to low potassium)an Yongshi‘YS’(Citrullus lanatus sp.tolerant to low potassium)are two different potassium-efficient genotype,by using seedlings grafted b y different scions and non-grafted seedlings treated by exogenous auxin(NAA)or auxin Polar transport inhibitors(NPA or TIBA)as material,the following aspects were studied:(a)Root morphological differences of two different potassium efficient watermelon genotypes in ZJ and YS under low potassium stress and the expression of auxin-related important transporter genes in respective root systems;(b)Effects of different watermelon scion on potassium uptake of roots under low potassium stress and the effect of different scion on auxin content changing in root;(c)Effects of exogenous auxin and auxin Polar transport inhibitors on K~+uptake of ZJ and Ys under low potassium stress.The results are showed as follows:1.The root morphological and gene expression results of ZJ and YS watermelon seedlings under low potassium stress showed that the ZJ and Ys watermelon seedlings growth were both inhibited after being treated with low potassium by 12 days,but the inhibitory degree of YS Watermelon was less by comparison.The potassium content of root and leaf of ZJ and YS both decreased under low potassium condition,but the potassium content of root and leaf of ZJ decreased more than that of YS,furthermore,the relative expression of high affinity potassium uptake gene Cla012760(HAK5)in YS was higher than that in ZJ.The expression of auxin transporter-related important genes Cla017975(AUX1)and Cla018455(PIN1)was higher in the root of YS plant.2.According to the results,the low potassium-tolerant watermelon YS as scion improved the low K~+tolerance of low potassium-sensitive watermelon ZJ under low potassium stress,the total root length,root volume,root surface area and root tip numbers of Y/Z combination watermelon seedlings were increased compared with Z/Z,furthermore,in grafted watermelon seedlings Y/Z,the potassium content of the leaves and roots increased significantly,and the auxin content of roots and leaves were also significantly higher,relative expression of genes Cla012760(HAK5),Cla017975(AUX1),Cla018455(PIN1),Cla01887(PIN2)was significantly increased,which showed that the tolerance of low potassium is closely related to the shoot.3.Effects of exogenous NAA、auxin transport inhibitors NPA and TIBA on root growth and potassium uptake of ZJ and YS were studied,the results showed that NAA can increase the potassium content of root and leaf of ZJ and YS under normal potassium conditions,but the effects of NAA on ZJ and YS under low potassium conditions have differences,From the results of root morphology and gene expression,YS is more sensitive to exogenous NAA or may be related to higher auxin content in itself.NPA and TIBA inhibited the growth of ZJ and YS under both normal and low potassium levels,furthermore,NPA and TIBA increased potassium content of root and decreased potassium content of leaves in ZJ and YS under low potassium.In conclusion,the results showed that scion can regulate grafted watermelon root growth and potassium uptake by auxin,but the precise mechanism requires further study.