Decreased growth-induced water potential. A primary cause of growth inhibition at low water potentials.

摘要

Cell enlargement depends on a growth-induced difference in water potential to move water into the cells. Water deficits decrease this potential difference and inhibit growth. To investigate whether the decrease causes the growth inhibition, pressurewas applied to the roots of soyabean cv. Williams seedlings and the growth and potential difference were monitored in the stems. In water-limited plants, the inhibition of stem growth increased when the roots were pressurized and it reverted to the previous rate when the pressure was released. The pressure around the roots was perceived as an increased turgor in the stem in small cells next to the xylem, but not in outlying cortical cells. This local effect implied that water transport was impeded by the small cells. The diffusivity for water was much less in the small cells than in the outlying cells. The small cells thus were a barrier that caused the growth-induced potential difference to be large during rapid growth, but to reverse locally duringthe early part of a water deficit. Such a barrier may be a frequent property of meristems. Because stem growth responded to the pressure-induced recovery of the potential difference across this barrier, it is concluded that a decrease in the growth-induced potential difference was a primary cause of the inhibition.