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

Abstract

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.