Changes in 1-(malonylamino)cyclopropane-1-carboxylic acid content in wilted wheat leaves in relation to their ethylene production rates and 1-aminocyclopropane-1-carboxylic acid content.

In excised wheat (Triticum aestivum L.) leaves, water-deficit stress resulted in a rapid increase, followed by a decrease, in ethylene production rates and in the levels of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene. However, the level of N-malonyl-ACC (MACC), the major metabolite of ACC, increased gradually, then leveled off. This increase in MACC was much greater than the decrease in ACC level. The MACC levels were positively correlated with severity of water stress. Once established, the MACC levels did not decrease even after the stressed tissues were rehydrated. Administration of labeled ACC and MACC showed that the conjugation of ACC to MACC was essentially irreversible. Repeated wilting treatments following the first wilting and rehydration cycle resulted in no further increase in ethylene production and in the levels of ACC and MACC. However, when benzyladenine was supplied during the preceding rehydration process, subsequent wilting treatment resulted in a rise in MACC level and a rapid rise followed by a decline in ethylene production rates and in the level of ACC. The magnitude of these increases was, however, smaller in these rewilted tissues than that observed in the first wilting treatment. Since MACC accumulates with water stress and is not appreciably metabolized, the MACC level is a good indicator of the stress history in the detached leaves used.