Abscisic Acid Accumulation in Lines of Maize Differing in Drought Resistance: A Comparison of Intact and Detached Leaves

Abstract

Maize lines were grown in field and growth chamber experiments to compare the effects of drought stress on abscisic acid (ABA) accumulation in intact plants with ABA accumulation in a detached-leaf test (DLT). Three pairs of lines, differing within each pair in drought resistance on the basis of visual assessment of plant survival, were compared. The three pairs represented early, medium, and late maturity groupings. In a field experiment, plants were sampled several times on one day, and in a pot experiment plants were stressed by withholding water, and sampled daily once the stress had begun. Although stress was mild in the field experiment, one line (Polj 17) had consistently higher ABA levels than any of the others (79ng g FW−1 compared with 35–45ng g FW−1 for the others), despite similar water potentials (ΨL). However, in the pot experiment line ZPBL 1304 had a significantly steeper regression slope for the relationship between ABA and ΨL(1980 ng g DW−1 MPa−1) than the other five (1190–1460ng g DW−1 MPa−1). In the pot experiment the water relations of the six lines varied little, with zero turgor (ΨL) estimated to be reached at similar ΨL for most lines (ca. −1.4 to −1.5MPa). However, ΨL and ΨP declined much more rapidly in line F-2. In general the early lines became stressed more quickly than the later maturing ones. In the detached-leaf test, leaves from well-watered plants were stressed by partial dehydration and then incubated for five hours to allow ABA to accumulate. In this test none of the six lines differed in ABA accumulation (125–147ng g initial FW−1). However, one of four additional lines (L-155), which were examined only in the detached-leaf test, had significantly more ABA (365 ng g initial FW−1). Non-stressed levels of ABA in this test were similar for all lines. In both the intact-plant experiments and the DLT, the lines that accumulated the most ABA were assessed to be drought resistant lines. The line that became stressed most rapidly in the pot experiment (line F-2) was a drought susceptible one. The pattern of ABA present in the lines differed markedly between the DLT, pot and field experiments and possible explanations for this are discussed.