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) c oncentration in the bulk-leaf tissue (L-ABA) and xylem sap X-ABA), bul k-leaf water potential (psi), and stomatal conductance (SC) were inves tigated in eight early-maturity and seven medium-maturity maize (Zea m ays L.) lines grown under drought conditions in the held. Data were co llected 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%, res pectively, psi declined 10.5%, whereas SC did not change appreciably. Significant differences (P < 0.05) among lines were found at both samp lings for GABA (from 229 to 1025 ng ABA g(-1) dry wt.), psi, and SC. S ignificant differences (P < 0.05) for X-ABA (from 10.3 to 41.1 mmol AB A L(-1)) were present only among medium-maturity lines at the first sa mpling. Correlation coefficients computed on a single-plot and variety -mean basis (r(p) and r(v), respectively) were generally similar. L-AB A and X-ABA were positively correlated. On a variety-mean basis, SC wa s 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, res pectively). Tile association between psi and SC changed markedly from the first to the second sampling (r(p) from -0.46* to 0.66**; r(v) fr om -0.37 to 0.31). An analogous trend was found for the correlations c omputed on a single-plant basis within each line: all of the 13 lines characterized by negative correlations in the first sampling showed po sitive coefficients 1 wk later. The negative relationship between psi and SC at the first sampling suggests that SC was controlling psi.