PLANT PHYSIOLOGY , Vol 115, Issue 1 71-77, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Purification and in Vitro Chaperone Activity of a Class I Small Heat-Shock Protein Abundant in Recalcitrant Chestnut Seeds
C. Collada, L. Gomez, R. Casado and C. Aragoncillo
Departamento de Biotecnologia, Escuela Tecnica Superior de Ingenieros de Montes, Ciudad Universitaria, E-28040 Madrid, Spain
A 20-kD protein has been purified from cotyledons of recalcitrant
(desiccation-sensitive) chestnut (Castanea sativa) seeds, where it
accumulates at levels comparable to those of major seed storage proteins.
This protein, termed Cs smHSP 1, forms homododecameric complexes under
nondenaturing conditions and appears to be homologous to cytosolic class I
small heat-shock proteins (smHSPs) from plant sources. In vitro evidence
has been obtained that the isolated protein can function as a molecular
chaperone: it increases, at stoichiometric levels, the renaturation yields
of chemically denatured citrate synthase and also prevents the irreversible
thermal inactivation of this enzyme. Although a role in desiccation
tolerance has been hypothesized for seed smHSPs, this does not seem to be
the case for Cs smHSP 1. We have investigated the presence of
immunologically related proteins in orthodox and recalcitrant seeds of 13
woody species. Our results indicate that the presence of Cs smHSP 1-like
proteins, even at high levels, is not enough to confer desiccation
tolerance, and that the amount of these proteins does not furnish a
reliable criterion to identify desiccation-sensitive seeds. Additional
proteins or mechanisms appear necessary to keep the viability of orthodox
seeds upon shedding.
