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

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 w eight, size and oil content. Energy dispersive X-ray (EDX) analysis was car ried out on mineral nutrient storage globoids in developing Cucurbita cotyl edons from 4 to 9 weeks after pollination. Phosphorus peak-to-background (p /b) and potassium p/b ratios increased slightly after the fourth week, whil e magnesium p/b ratios remained unchanged. The calcium p/b ratio was statis tically 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 rat io was higher in globoids at 4 weeks than at 9 weeks. Traces of manganese w ere 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 mum i n diameter was the highest at 4 weeks and was zero at 9 weeks. The frequenc y 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-f old increase in the embryo phytic acid, which is the main component of glob oids. 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.