Ethylene Biosynthesis inPoa pratensisLeaves in Response to Injury or Infection byBipolaris sorokiniana

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Abstract
Research was initiated to evaluate 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity. ACC content, and endogenous ethylene of Poa pratensis leaf blades subjected to wounding or infection by Bipolaris sorokiniana. Wounding stimulated ACC synthase activity, endogenous ethylene, and ACC content of leaf blades. ACC synthase activity peaked 1 hr after wounding followed by a peak in ethylene production 2 hr after wounding that slowly declined. ACC content increased rapidly and peaked 3 hr after wounding. Infection of leaf blades by B. sorokiniana resulted in peak ethylene production 36 hr after inoculation followed by peak ACC synthase activity at 72 hr. Endogenous ethylene produced in response to infection was somewhat greater than that produced in response to wounding and peak ACC synthase activity was more than five times greater in response to infection than to wounding. Infection resulted in an accumulation of ACC in leaf blades 96 hr after inoculation that did not occur in response to wounding. The results are discussed relative to the source of ethylene and ACC in infected leaf blades.