Does ABA in the Xylem Control the Rate of Leaf Growth in Soil-Dried Maize and Sunflower Plants?
Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were grown in large volumes of soil and leaf growth rate was monitored on a daily basis. Half the plants were given a soil drying treatment and when they showed a significant restriction of growth rate (compared to both their daily growth rate before drying and the average growth rate of well-watered plants on the same day), leaf water relations were measured and xylem sap was extracted using several techniques. There was a significant negative log-linear relationship between the rate of leaf growth and the concentration of ABA in the xylem for both species. There was no clear relationship between leaf growth rate and leaf water potential or turgor for either species. Assessment of different methods for sampling xylem sap suggests that exudates collected from stem stumps or samples collected by pressurizing the whole root system are suitable for estimating ABA concentration in xylem, at least with large plants of maize or
