Composition of Globoid Crystals from Embryo Protein Bodies in Five Species of Cucurbita

Abstract

Previous energy-dispersive x-ray analysis studies of globoid crystal composition in seed protein bodies gave an indication that there might be a correlation between seed size and the type of elements stored in globoid crystals. This possibility was tested by conducting energy-dispersive x-ray analysis studies of P, K, Mg, and Ca levels in gioboid crystals of four embryo regions (radicle, stem, cotyledon center palisade mesophyll, cotyledon center spongy mesophyli) in each of five different Cucurbita species (C. mixts, C. mschats, C. foeddissim, C. pepo, and C.). The species were chosen to provide a range of seed size and weight. Globoid crystals from all embryo regions in all five species contained P, K, and Mg.Some variations in the levels of these elements did occur but there was no consistent pattern with regard to area of the seed or with regard to seed size. Calcium distribution showed significant variations. In species with large seeds (C. mrita, C. mosehata) Ca was mainly found in globoid crystals in the radicle. Globoid crystals in species with small seeds (C. foetidissima, C. pepo, C.) contained Ca in all embryo regions tested. The results of this study support the concept that Ca distribution in globoid crystals can be correlated with seed weight.The protein bodies in seeds of most plant species contain mineral reserves in addition to proteins. These mineral reserves are generally thought to occur mainly as phytin, a cation (K, Mg, Ca) salt of inositol hexaphosphoric acid (see review in 6). In many species the phytin reserves are concentrated into electron-dense regions called globoid crystals (6,9,10,12). The bulk of a seed's available reserves of several important macronutrients are thus found in globoid crystals inside protein bodies.Lott et al. (8) carried out the first studies in which elemental composition of globoid crystals from different parts of a dicot embryo was studied with energy-dispersive x-ray analysis. Globoid crystals from all embryo regions of Cucurbita maxima were found to contain P, K, and Mg. The distribution of Ca was of particular interest since there was a definite spatial arrangement.Globoid crystals of the radicle and stem regions contained considerable Ca while globoid crystals in much of the cotyledon contained little, if any, Ca.Globoid crystals of protein bodies in the main storage organ of various oil seeds have been studied with EDX2 analysis (2, 3, 6, 7). Lott and Buttrose (6) observed that where Ca distribution was concerned there seemed to be an effect not only due to area of the embryo in question but also due to seed size. Globoid crystals from large cotyledons (sunflower, cashew, pistachio, walnut, hazel nut, jojoba) were found to contain either no Ca or only traces of

X-ray Analysis Studies of Elements Stored in Protein Body Globoid Crystals of Triticum Grains

“…That specific deposition patterns for certain minerals can occur in some species is evident from previous work on Cucurbita (19,21,22) and tomato seeds (39 (48). Although the pericarp was not investigated in this study, the autoradiographic results presented in Tanaka et at.…”

“…Using such procedures, it has been possible to document major extraction of elements from globoid crystals due to use of OS04 (18). Fixativebased loss of a readily soluble K compound from legume seed protein bodies has also been shown (15,22 66,1980 tative study such as this one, it is differential element extraction that is of greatest concern. The tendency of K to be somewhat more easily removed than other elements in globoid crystals has also been reported for Cucurbita maxima (19).…”

“…Freeze-dried tissue powders were used to check for possible extraction of elements from globoid crystals during fixation, dehydration, and embedding. Selected portions of wheat grains were carefully dissected out, then frozen in liquid N2, fractured while frozen, and low temperature freezedried using the procedure of Lott and Vollmer (22). The resulting freeze-dried powders were dusted or pressed onto Formvar and carbon-coated grids.…”

“…Although Mg and K are the most commonly occurring cations found in globoid crystals, a range of other cations, including Ba, Ca, Fe, Mn, and Na, have been demonstrated (5,9,17,19,22,37,47).…”

Mineral Reserves in Castor Beans: The Dry Seed

“…In extremely rare instances, Fe was detected in globoid crystals. Ca-containing (2,4,8,9,12,15,22). The protein bodies of castor bean endosperm have been studied previously (18,23,26) …”