Calcium Distribution in Globoid Crystals of Cucurbita Cotyledon Protein Bodies

Abstract

Protein bodies in seeds are important for seedling growth because they provide necessary nitrogenous compounds. It is often overlooked that protein bodies also function as the subcellular location of much of a seed's reserves of macronutrients such as P, K, Ca, and Mg. Structural investigations of storage tissue from several cucurbit seeds have revealed that protein bodies often consist of proteinaceous matrix, protein crystalloid, soft globoid, and globoid crystal regions (2, 8, 9). The protein reserves are thought to be located primarily in the proteinaceous matrix and protein crystalloid regions. The mineral reserves usually occur in the electron-dense globoid crystals and are generally considered to be largely phytin, a cation (K, Mg, Ca) salt of inositol hexaphosphoric acid (3,4,(11)(12)(13).Recently, Lott et al. (7) published results of an energy-dispersive x-ray analysis study of globoid crystal composition in 10 different regions of Cucurbita maxima embryos. Although P, K, and Mg were commonly found in globoid crystals in all squash embryo regions, the Ca distribution showed definite differences between embryo regions. Ca was common in globoid crystals of the radicle and stem regions. In the cotyledon, Ca levels were on average much lower than those of the root-shoot regions. Most globoid crystals from spongy or palisade mesophyll cells lacked any detectable Ca. The bulk of the Ca values for the cotyledon samples thus came from a fraction of the globoid crystals present. In this paper we report the results of EDX2 analysis studies designed to discover where globoid crystals with relatively high Ca levels are located within Cucurbita cotyledons.

Mineral Reserves in Castor Beans: The Dry Seed

“…There were no major differences between the cultivars with regard to the distribution of elements in globoid crystals, as studied with EDX analysis. These castor bean findings differ from studies of a series of Cucurbita species with different seed sizes, in which a difference in the Ca distribution pattern was observed (11,12). However, Cucurbita is an exalbuminous seed, while Ricinus is an albuminous seed.…”

“…Subsequent studies of globoid crystals isolated from whole seeds indicated that phytin was predominantly a K and Mg salt of phytic acid with small amounts of Ca (19). In these later studies, it was not determined whether the Ca was uniformly distributed or not, a feature worthy of investigation, since in some other seeds Ca-containing globoid crystals are concentrated in specific cell types or embryo regions (9,11,13 Fixation and Embedding. Testas were removed from dry seeds, and small pieces of endosperm, cotyledon, radicle, and stem regions were fixed according to the procedure of Lott (6).…”

“…In Cucurbita maxima cotyledons, Ca-containing globoid crystals are often found in protodermal cells, provascular cells, and cells next to the provascular regions, yet are absent from most of the mesophyll cells (11). In wheat grains, there is a distinct distribution pattern for Mncontaining globoid crystals.…”

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.…”

Localization of Phosphorus and Cation Reserves in Lilium longiflorum Pollen

“…Characteristically, the EDX spectra of seed globoids show large P and cation (most notably Mg, Ca, K) signals relative to those signals generated from surrounding cytosolic regions (13)(14)(15)(16)(17)(18). The elemental composition of globoids is indicative of the presence of phytin which is composed of salts of myo-inositol hexakisphosphate (14,15).…”