Abscisic Acid Concentration in Leaf and Xylem Sap, Leaf Water Potential, and Stomatal Conductance in Maize

Genetic variation of and the relationships among abscisic acid (ABA) concentration in the bulk‐leaf tissue (L‐ABA) and xylem sap (X‐ABA), bulk‐leaf water potential (Ψ), and stomatal conductance were investigated in eight early‐maturity and seven medium‐maturity maize ( Zea mays L.) lines grown under drought conditions in the field. Data were collected in two samplings, 1 wk apart, during flowering. From the first to the second sampling, L‐ABA and X‐ABA increased 34.4 and 71.5%, respectively, Ψ declined 10.5%, whereas SC did not change appreciably. Significant differences ( P < 0.05) among lines were found at both samplings for L‐ABA (from 229 to 1025 ng ABA g −1 dry wt.), Ψ, and SC. Significant differences (P < 0.05) for X‐ABA (from 10.3 to 41.1 nmol ABA L −1 ) were present only among mediummaturity lines at the first sampling. Correlation coefficients computed on a single‐plot and variety‐mean basis (r p and r v , respectively) were generally similar. L‐ABA and X‐ABA were positively correlated. On a variety‐mean basis, SC was more strongly correlated with X‐ABA than with L‐ABA at the first and second samplings (r v of − 0.60* vs. −0.40 and −0.71** vs. −0.19, respectively). The association between Ψ and SC changed markedly from the first to the second sampling (r p from −0.46** to 0.66**; r v from −0.37 to 0.31). An analogous trend was found for the correlations computed on a single‐plant basis within each line: all of the 13 lines characterized by negative correlations in the first sampling showed positive coefficients 1 wk later. The negative relationship between Ψ and SC at the first sampling suggests that SC was controlling Ψ.