Embryo-endosperm interactions in the hydrolysis of lettuce seed reserves.

Abstract

Red light- and gibberellin-induced seeds of lettuce ( Lactuca sativa L., cv. Grand Rapids) produce copious amounts of endo-β-mannanase after germination is completed. This enzyme is produced and secreted by the endosperm itself and participates in the hydrolysis of its cell walls, which are largely mannans. The resulting oligomannans are further hydrolysed by β-mannosidase, an enzyme produced within the cotyledons. Degradation of the endosperm is completed prior to mobilization of the main storage reserves within the cotyledons. Isolated endosperms produce and release mannanase. This can be prevented by placing the endosperms in a small incubation volume, probably due to insufficient dilution of endogenous leachable inhibitor(s). The inhibition is lifted during germination: it also can be relieved by benzyladenine and gibberellic acid when the cotyledons are present. Abscisic acid can prevent mannanase production by isolated endosperms and it may contribute to the endogenous inhibitory regulation of this enzyme. By using dissection experiments it has been demonstrated that mannanase production by the endosperm is under the control of the embryo, and that both the axis and cotyledons play a role. The cotyledons are capable of lifting the inhibition, but depend upon an axial event early in germination, apparently involving the transmission of diffusible substances.