CHANGES IN THE HYDROXAMIC ACID CONTENT OF MAIZE LEAVES WITH TIME AND AFTER ARTIFICIAL DAMAGE - IMPLICATIONS FOR INSECT ATTACK

The dynamics of hydroxamic acids (Hx) in maize plants were examined, along with the effects on this process of artificial leaf damage. The concentration of Hx in maize (cv. LG11) leaves declined rapidly with age, although young emerging tissue did have relatively high levels. The decline was not entirely due to a growth dilution effect, as the total Hx content in leaves also decreased with age. This effect was less pronounced in isolated leaves. The plant hormone abscisic acid (ABA) accelerated the decline in Hx in isolated maize leaves, while indole acetic acid (IAA) had no apparent effect. Artificial leaf damage on growing plants produced a significant increase in the concentration of Hx relative to undamaged controls. The difference was greatest (about 18%) two days after damage, but seemed to be largely due to a slower rate of decline relative to controls. Isolated maize leaves generally showed a much higher level of increase (20 - 40%). The results are generally consistent with the theory that Hx functions as a defence against insect attack.