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
waterflows in excised roots aswell as the relationship of theseflows withwater stress tolerancewas studied
in six sunflower (Helianthus annuus L.) cultivars. Plants growing in a growth chamber were subjected to
water stress by deficit irrigation 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
differenceswere observed among the cultivars.Whilewater stress stimulated thewaterflow in the excised
roots of all cultivars, K+ (Rb+
) uptake by the root and its discharge into the xylemwas 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 both K+ 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.