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Australian Journal of Botany Australian Journal of Botany Society
Southern hemisphere botanical ecosystems
RESEARCH ARTICLE

Ultrastructure and anatomy of Macadamia (Proteaceae) kernels

David A. Walton A C , Helen M. Wallace A and Richard Webb B
+ Author Affiliations
- Author Affiliations

A Faculty of Science, Health and Education, University of the Sunshine Coast, Maroochydore DC, Qld 4558, Australia.

B Centre for Microscopy and Microanalysis, University of Queensland, St Lucia, Qld 4072, Australia.

C Corresponding author. Email: dwalton3@usc.edu.au

Australian Journal of Botany 60(4) 291-300 https://doi.org/10.1071/BT11148
Submitted: 10 June 2011  Accepted: 10 February 2012   Published: 11 April 2012

Abstract

Macadamia integrifolia Maiden & Betche and M. tetraphylla L.A.S.Johnson, and their hybrids, are cultivated for their edible kernels (mature embryos). Some kernels separate into halves (cotyledons) during post-harvest handling, and embryo cuticular characteristics may influence breakage. Some kernels have a gap between cotyledons before nut cracking, and this anatomical feature may be related to breakage. Kernels from cultivars producing high or low frequency of breakage were examined by transmission electron microscopy and scanning electron microscopy to identify differences in inner-cuticular wax. Whole seeds of each cultivar were opened without cracking to measure gaps between cotyledons and determine relationships between gaps and embryo breakage. Kernels from cultivars with low frequency of breakage had inner-epicuticular wax layers that were of the sculptured crust type whereas those of cultivars with high frequency of breakage were mainly of a wax-film type. Gap width and length of kernels separate at nut opening were more than twice those for intact kernels. There was a negative relationship between whole-kernel percentage and gap width between cotyledons.


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