WATER STATUS OF CALLUS FROM HEVEA-BRASILIENSIS DURING INDUCTION OF SOMATIC EMBRYOGENESIS

To improve somatic embryogenesis in Hevea brasiliensis, the water and plant growth regulator status of the culture medium was studied. Induction of embryogenic tissue from the internal integument of immature seeds was clearly favored by stabilizing the water potential of the culture medium at -0.7 MPa, by using low and decreasing concentrations of 3,4-dichlorophenoxyacetic acid and benzyladenine or by incorporating 10(-7) M abscisic acid in the medium. Each of these changes in the medium favored a specific water status in the callus, namely a high relative water content (93 to 95%) and an elevated water potential (-0.9 MPa). These characteristics were apparently important for initiating somatic embryogenesis, and their decrease corresponded to the loss of embryogenic potential in the callus. Thus, the relative water content and water potential of callus appear to be good markers of its embryogenic state.