PLANT PHYSIOLOGY , Vol 103, Issue 1 59-65, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Galactose-Specific Lectins Protect Isolated Thylakoids against Freeze-Thaw Damage
D. K. Hincha, I. Bakaltcheva and J. M. Schmitt
Institut fur Pflanzenphysiologie und Mikrobiologie, Freie Universitat, Konigin Luise-Strasse 12-16, W-1000 Berlin 33, Germany
We have measured freeze-thaw damage to isolated spinach (Spinacia oleracea
L.) chloroplast thylakoid membranes in the presence of different
galactose-specific seed lectins to determine whether the binding of
proteins to the membrane surface can lead to cryoprotection. Of the seven
lectins investigated, five were protective to different degrees and two
showed no measurable effect. Protection was afforded by a reduction of the
solute permeability of the membranes. This reduced the solute influx during
freezing and thereby osmotic rupture of the thylakoid vesicles during
thawing. Using model membranes and fluorescently labeled lectins, we could
show that the proteins bound exclusively to the digalactosyl lipids in the
membranes. Binding was a prerequisite for the protective effect, because
the presence of up to 5 mM galactose in the samples completely inhibited
both binding of the lectins to thylakoid and model membranes and
cryoprotection. The degree of binding was, in contrast, not related to the
cryoprotective efficiency of different lectins; cryoprotection was a
function of the hydrophobicity of the proteins.
