Abstract
The production of mannanase, a cell-wall-degrading carbohydrase, can be manipulated in isolated lettuce (Lactuca sativa cv Grand Rapids) endosperms by changes in the volume of buffer in which they are incubated. The enzyme is produced when endosperms are incubated in a large volume, but not when incubated in a small volume, which is suggestive that an endogenous, diffusible inhibitor of mannanase production is being lost from the endosperms in a large volume (JD Bewley, P Halmer 1980/1981 Israel J Bot 29: 118-132). We have investigated the possibility that the phytohormone abscisic acid (ABA) is involved in this regulation of mannanase production in isolated lettuce endosperms. We find several correlations between the presence of the endogenous inhibitor and of ABA, i.e. (a) a ;leachate' prepared from isolated lettuce endosperms induces synthesis of ABA-specific proteins in barley aleurone layers, indicating that incubation of endosperms in a large volume results in the diffusion of ABA therefrom into the surrounding medium; (b) fractionation of the components of a leachate by either polyvinylpyrrolidone-chromatography of C(18) reversed-phase high performance liquid chromatography fails to separate the endogenous inhibitor from authentic ABA; and (c) changes in the incubation volume of endosperms result in changes in the amount of extractable ABA in the endosperms, as detected by ELISA. These results are consistent with a role for endogenous ABA in the regulation of mannanase production in isolated lettuce endosperms.