TRANSIENT REDUCTION IN SECRETED 32 KD CHITINASE PREVENTS SOMATIC EMBRYOGENESIS IN THE CARROT (DAUCUS-CAROTA L) VARIANT TS11

At the nonpermissive temperature, somatic embryos of the temperature-s ensitive (ts) carrot (Daucus carota L.) cell variant ts11 only proceed beyond the globular embryo stage in the presence of medium conditione d by wild-type cells. The causative component in the conditioned mediu m has been identified as an acidic 32 kD endochitinase. An antiserum r aised against the 32 kD chitinase detected this protein in culture med ium from ts11 embryo cultures grown at the permissive temperature as w ell as at the nonpermissive temperature. No difference in biochemical characteristics or in effect on ts11 embryo development could be detec ted between the 32 kD chitinase purified from wild-type cultures and t he chitinase from ts11 cultures grown at the permissive or at the nonp ermissive temperature. Compared to the amount present in a ts11 embryo culture at the permissive temperature, a reduction in the amount of 3 2 kD chitinase was observed during the temperature-sensitive period at the nonpermissive temperature. These results imply that the arrested embryo phenotype of ts11 is not the result of a structural difference in its 32 kD chitinase, but is the result of a transient decrease in t he amount of 32 kD chitinase present. Morphological observations indic ate that the ts11 phenotype is pleiotropic and also affects the cell w all of nonembryogenic cells. (C) 1995 Wiley-Liss, Inc.