Elemental storage in Cucurbita embryos: X-ray microanalysis of magnesium, potassium, calcium, and phosphorus within globoid crystals

Abstract

Embryos of Cucurbita maxima, Cucurbita andreana, and their reciprocal hybrids store phosphorus, magnesium, potassium, and calcium in distinctive globoid crystals within protein bodies found in cotyledon mesophyll cells. Samples of cotyledon tissue from each of the four kinds of embryos were cryogenically prepared and analyzed by X-ray microanalysis in the frozen state in a scanning electron microscope. The relative proportions of phosphorus, magnesium, potassium, and calcium were expressed as peak to background ratios. Total concentrations of the four elements in whole cotyledons, as measured by neutron activation analysis, were similar to the trends shown by the peak to background ratios for the same elements. This supports the concept that the bulk of the elements P, K, Mg, and Ca in seed tissues is stored in globoid crystals.