PLANT PHYSIOLOGY , Vol 101, Issue 3 773-779, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
An Osmotic Stress Protein of Cyanobacteria Is Immunologically Related to Plant Dehydrins
T. J. Close and P. J. Lammers
Department of Botany and Plant Sciences, University of California, Riverside, California 92521 (T.J.C.)
Dehydrins are a family of desiccation proteins that were identified
originally in plants (T.J. Close, A.A. Kortt, P.M. Chandler [1989] Plant
Mol Biol 13: 95-108; G. Galau, T.J. Close [1992] Plant Physiol 98:
1523-1525). Dehydrins are characterized by the consensus amino acid
sequence domain EKKGIMDKIKEKLPG found at or near the carboxy terminus; the
core of this domain (KIKEKLPG) may be repeated from one to many times
within the complete polypeptide. Dehydrins generally accumulate in plants
in response to dehydration stress, regardless of whether the stimulus is
evaporation, chilling, or a decrease in external osmotic potential.
Polyclonal antibodies highly specific to the consensus carboxy terminus of
plant dehydrins were used to search for dehydrins in cyanobacteria, many of
which are known to survive desiccation. A 40-kD osmoticstress-induced
protein was identified in Anabaena sp. strain PCC 7120. The 40-kD protein
was usually not detected in logarithmic cultures and was induced by
shifting the growth medium to higher solute concentrations. Several solutes
have inductive effects, including sucrose, sorbitol, and polyethylene
glycol (PEG). Measurements of osmotic potential suggest that a shift of
-0.5 MPa (sucrose and PEG) or -1.2 MPa (sorbitol) is sufficient to induce
synthesis of the 40-kD protein. Glycerol, which is highly permeable, was
not an inducer at -1.2 MPa (0.5 M), nor was the plant hormone abscisic
acid. Induction appears to be evoked by a shift in osmotic potential
approximately equal in absolute magnitude to the expected turgor pressure
of bacterial cells in logarithmic phase growth. A dehydrin-like polypeptide
was also identified among osmotically induced proteins from two other
filamentous, heterocyst-forming cyanobacteria. A 40-kD protein was observed
in Calothrix sp. strain PCC 7601, and in Nostoc sp. strain Mac-R2, an
osmotic-induced doublet at 39 and 40 kD was observed. From these data, it
appears that cyanobacteria produce a dehydrin-like protein under osmotic
stress.
