Abstract
It is known that the sink organ is not just a reservoir of carbon, but must also acquire water in appropriate proportion as the organ grows. In this study, the dynamics of tuber growth rate in sweet potato plants (Ipomoea batatas Lam.) was analyzed with reference to water relations using a newly developed system for on-line measurement of tuber volume. Tuber growth rate in the dark was higher than in the light, and the growth rate was almost parallel to the change in leaf water potential. Furthermore, transient responses of tuber growth rate were found just after rapid changes in evaporative demand, i.e. tuber growth rate drastically increased in 1 h after turning off the light, increasing humidity or excising all leaves, and the growth rate drastically decreased 1 h after turning on the light or decreasing humidity. Thus, the tuber growth rate was higher under higher leaf water potential, and it appeared to be affected by leaf transpiration through the whole plant water balance.
