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Effects of differential drying rates on viability retention of recalcitrant seeds of Ekebergia capensis

Published online by Cambridge University Press:  19 September 2008

N. W. Pammenter*
Affiliation:
Plant Cell Biology Research Unit, Department of Biology, University of Natal, Durban, 4041 South Africa
Valerie Greggains
Affiliation:
NERC Unit of Comparative Plant Ecology, Department of Animal and Plant Sciences, The University, Sheffield S10 2TN, UK
J. I. Kioko
Affiliation:
Plant Cell Biology Research Unit, Department of Biology, University of Natal, Durban, 4041 South Africa
J. Wesley-Smith
Affiliation:
Plant Cell Biology Research Unit, Department of Biology, University of Natal, Durban, 4041 South Africa
Patricia Berjak
Affiliation:
Plant Cell Biology Research Unit, Department of Biology, University of Natal, Durban, 4041 South Africa
W. E. Finch-Savage
Affiliation:
3Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK
*
*Fax: +27 31 260 2029 E-mail: pammente@biology.und.ac.za

Abstract

The drying rate of whole seeds of Ekebergia capensis (Meliaceae) was shown to influence the response to desiccation, with rapidly dried seeds surviving to lower water contents. Short-term rapid drying (to water contents higher than those leading to viability loss) actually increased the rate of germination. The form of the time course of decline of axis water content varied with drying rate; slow drying could be described by an exponential function, whereas with rapid drying initial water loss was faster than predicted by an exponential function. These observations suggest that slow drying brought about homogeneous dehydration and that the rapid drying was uneven across the tissue. This raised the possibility that the different responses to dehydration were a function of different distributions of water in the axis tissue under the two drying regimes. However, ultrastructural observations indicated that different deleterious processes may be occurring under the different drying treatments. It was tentatively concluded that a major cause of viability loss in slowly dried material was likely to be a consequence of aqueous-based processes leading to considerable membrane degradation. Uneven distribution of tissue water could not be rejected as a contributory cause of the survival of rapidly dried seeds to low bulk water contents. The differential response to dehydration at different drying rates implies that it is not possible to determine a ‘critical water content’ for viability loss by recalcitrant seeds.

Type
Physiology & Biochemistry
Copyright
Copyright © Cambridge University Press 1998

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