CHARACTERIZATION OF MAIZE LINES DIFFERING IN LEAF ABSCISIC-ACID CONTENT IN THE FIELD .1. ABSCISIC-ACID PHYSIOLOGY

The inbred maize lines Polj17 and F-2 have previously been shown to di ffer by up to three-fold in leaf abscisic acid (ABA) concentration in the field. Lines from the cross Polj17 x F-2 differing in leaf ABA con centrations, and the parents, were studied in the field to characteriz e the differences amongst the lines in ABA concentrations during the s eason, during the day and in different parts of the plants. The water status of the plants was measured and leaves were heat girdled to get information on possible causes for the genetic variation amongst the l ines in ABA concentration. Leaf ABA concentrations of the high-ABA lin es increased markedly and consistently from flowering time onwards, wh ereas leaf ABA concentrations of the low-ABA lines gradually fell afte r flowering. Leaf water potentials of high-ABA and low-ABA lines were similar during this time. Leaf ABA concentrations varied little during the day, and heat girdling caused a rise in ABA concentrations, which was similar in both high-ABA and low-ABA lines, only after girdling f or at least 4 h. ABA concentrations were highest in the leaves and it was only in the leaves and developing kernels that substantial differe nces in ABA concentrations were found between the high-ABA and low-ABA classes. Although aerial brace roots also had high ABA concentrations , other roots and stem internodes had ABA concentrations which were co nsistently low and the same for both ABA classes. Differences between the ABA classes were unlikely to be due to differences in leaf water s tatus or in ABA export from the leaves. Other possible explanations fo r the genotypic differences in leaf ABA concentrations are discussed.