Systemic feedback regulation of K+ uptake in cotton at seedling stage.

This hydroponic split-root experiment was conducted to elucidate the long-distance systemic regulation of K+uptake in cotton(Gossypium hirsutum L.)seedlings with two cotton cultivars CCRI41 and Liaomian17 as materials.Inverted Y grafting(one scion/two rootstocks,hypocotyl-to-hypocotyl)was used to establish split-root plants.The K+-uptake characteristics of cotton seedlings were measured by depletion method and described by kinetic parameters,Imax(the maximum rate of uptake),Km(the external concentration at which the uptake rate is 0.5 Imax)and Cmin(the external concentration at which no net flux occurs).In relative to the sufficient K+control(both root halves supplied with 2.50 mmol L–1K+),the root half supplied with 2.50 mmol L–1 K+for six days showed 79% to 92% more Imax owing to the induction of K+-demand signal derived from the root half starved with K+.Compared with the K+starvation control(both root halves supplied with 0.01 mmol L–1K+),Imax of root half supplied with 0.01 mmol L–1K+for six days decreased by 27% to 40% due to the suppression of K+-supply signal initiated by the root half grown in sufficient K+.When the root half starved with K+in CCRI41 was removed after three days of split-root treatment,the remained root half incessantly supplied with 2.50 mmol L–1K+for six days had less Imax relative to the whole split-root plants,which is likely attributed to the loss of K+-demand signal from the other root half during last three days.This systemic feedback regulation of K+uptake in cotton seedlings was independent of K+content of either root or shoot.