Effect of water stress and subsequent re-watering on K+ and water flows in sunflower roots. A possible mechanism to tolerate water stress

• The effect of water stress on plant growth was different among sunflower cultivars.
• Water stress stimulated the water flow in excised roots in all cultivars.
• The higher the susceptibility to water stress, the greater the potassium transport in the root.

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 in excised roots as well as the relationship of these flows with water stress tolerance was 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 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 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.