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Changes in the element composition of globoids and whole embryos in developing seeds of Cucurbita maxima

Published online by Cambridge University Press:  22 February 2007

Irene Ockenden
Affiliation:
Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
Marcia West
Affiliation:
Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
Jon Domingues
Affiliation:
Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
John N.A. Lott*
Affiliation:
Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
*
*Correspondence Tel: (905) 525-9140 ext. 24589 Fax: (905) 522-6066 Email: lott@mcmaster.ca
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Abstract

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Cucurbita maxima Duch. cv. Warted Hubbard, which produces large fruits with many seeds, was used as a test system to study changes in several mineral nutrients during seed formation. Developing embryos increased markedly in weight, size and oil content. Energy dispersive X-ray (EDX) analysis was carried out on mineral nutrient storage globoids in developing Cucurbita cotyledons from 4 to 9 weeks after pollination. Phosphorus peak-to-background (p/b) and potassium p/b ratios increased slightly after the fourth week, while magnesium p/b ratios remained unchanged. The calcium p/b ratio was statistically higher at 4 weeks than in the subsequent weeks. Traces of iron and zinc were found in most of the globoids at all fruit ages. The zinc p/b ratio was higher in globoids at 4 weeks than at 9 weeks. Traces of manganese were detectable in only 18% of the globoids at 4 weeks and not detectable in any globoids at 9 weeks. The frequency of the small globoids of 0.25 μm in diameter was the highest at 4 weeks and was zero at 9 weeks. The frequency of the larger globoids increased progressively from 4 to 9 weeks. As the spherical globoids increased in size and hence in volume, there was a 6.4-fold increase in the embryo phytic acid, which is the main component of globoids. On a whole embryo basis, P content increased 4.5-fold, K 3.3-fold, Mg 5.4-fold and Ca 3.2-fold from the fourth to the ninth week.

Information

Type
Research Article
Copyright
Copyright © Cambridge University Press 2001