PLANT PHYSIOLOGY , Vol 111, Issue 2 403-412, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Characterization of Membrane Properties in Desiccation-Tolerant and -Intolerant Carrot Somatic Embryos
FAA. Tetteroo, A. Y. de Bruijn, RNM. Henselmans, W. F. Wolkers, A. C. van Aelst and F. A. Hoekstra
Departments of Plant Physiology (F.A.A.T., R.N.M.H., W.F.W., F.A.H.) and Plant Cytology and Morphology (A.Y.d.B., A.C.v.A.), Wageningen Agricultural University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands
In previous studies, we have shown that carrot (Daucus carota L.) somatic
embryos acquire complete desiccation tolerance when they are treated with
abscisic acid during culture and subsequently dried slowly. With this
manipulable system at hand, we have assessed damage associated with
desiccation intolerance. Fast drying caused loss of viability, and all K+
and carbohydrates leached from the somatic embryos within 5 min of
imbibition. The phospholipid content decreased by about 20%, and the free
fatty acid content increased, which was not observed after slow drying.
However, the extent of acyl chain unsaturation was unaltered, irrespective
of the drying rate. These results indicate that, during rapid drying,
irreversible changes occur in the membranes that are associated with
extensive leakage and loss of germinability. The status of membranes after
2 h of imbibition was analyzed in a freeze-fracture study and by Fourier
transform infrared spectroscopy. Rapidly dried somatic embryos had clusters
of intramembraneous particles in their plasma membranes, and the transition
temperature of isolated membranes was above room temperature. Membrane
proteins were irreversibly aggregated in an extended [beta]-sheet
conformation and had a reduced proportion of [alpha]-helical structures. In
contrast, the slowly dried somatic embryos had irregularly distributed, but
non-clustered, intramembraneous particles, the transition temperature was
below room temperature, and the membrane proteins were not aggregated in a
[beta]-sheet conformation. We suggest that desiccation sensitivity of
rapidly dried carrot somatic embryos is indirectly caused by an
irreversible phase separation in the membranes due to de-esterification of
phospholipids and accumulation of free fatty acids.
