ABA regulated stomatal control and photosynthetic water use efficiency of potato ( Solanum tuberosum L.) during progressive soil drying

Abstract

Glasshouse experiments at two developmental stages (tuber initiation and tuber bulking) of potatoes ( Solanum tuberosum L.) were conducted to investigate plant water relation and leaf gas exchange characteristics during progressive soil drying. Leaf relative water content (RWC), leaf water potential ( Ψ l), root water potential ( Ψ r), stomatal conductance ( g s), photosynthesis ( A), and xylem sap abscisic acid (ABA) concentration ([ABA] xylem) were determined in well-watered (WW) and drought-stressed (DS) plants. At both stages, RWC and Ψ l were hardly affected, significant decreases of the two parameters occurred only at severe soil water deficits; however, g s decreased much early at 2 and 1 days after imposition of stress (DAIS) at tuber initiation and tuber bulking, respectively, and coincided with decrease of Ψ r and increase of [ABA] xylem; while A decreased 2 days later than g s at each stage. Analyses of the pooled data of the two stages showed that g s was linearly correlated with [ABA] xylem at mild soil water deficits (i.e. Ψ r > −0.3 MPa); photosynthetic water use efficiency, viz. A/ g s, increased linearly with decreasing g s until the latter reached 0.2 mol m −2 s −1, below this point, it decreased sharply. The results suggest that at mild soil water deficits, g s of potato is seemingly controlled by xylem-borne ABA. As a consequence of A being less sensitive than g s to soil drying, photosynthetic water use efficiency, i.e. A/ g s, is increased at mild soil water deficits.