Little is known about the physiological mechanisms underlying plant responses and their ability to recover
from water stress, especially responses that concern the root system. The effect of water stress on K+
and water flows inexcised roots as well as the relationship of these flows with water stress tolerance was studied in six sunflower (Helianthus annuusL.) cultivars. Plants growing in a growth chamber were subjected to
water stress by deficitirrigation for 15 days. After this period, the plants were re-irrigated and the exudates
from the excised roots were collected. Water stress reduced the shoot growth of all plants, although
differences were observed among the cultivars. While water stress stimulated the water flow in the excised roots of all cultivars, K+(Rb+) uptake by the root and its discharge into the xylem was promoted only in those
cultivars that were more susceptible to water stress. The same effect was observed when plants were
subjected to water stress using polyethylene glycol (PEG)6000.The promotion of bothK+ and water
flows could be considered as a mechanism to tolerate water stress, through which the plant restores cell
turgidity, shoot water status and plant growth after a water stress period