Mineral reserves in castor beans: the dry seed

Subcellular Localization and Characterization of Excessive Iron in the Nicotianamine-less Tomato Mutant chloronerva

To understand the function of the Fe2+-complexing compound nicotianamine (NA) in the iron metabolism of plants we have localized iron and other elements in the NA-containing tomato wild type (Lycopersicon esculentum) and its NA-free mutant chloronerva by quantitative x-ray microanalysis. Comparison of element composition of the rhizodermal cell walls indicated that the wild type accumulated considerable amounts of iron and phosphorus in the cell wall, whereas in the mutant iron and phosphorus were detected in the cytoplasm and vacuoles of the rhizodermis. In mutant leaves containing high iron concentrations in the symplast, electron-dense inclusions were detected in chloroplasts and phloem. Such particles, consisting mainly of iron and phosphorus, were never found in the wild type and were very rarely detected in young chlorotic mutant leaves or after treatment of the mutant with NA. For further characterization the electron-dense inclusions in mutant leaves were isolated and compared by sodium dodecyl sulfate-gel electrophoresis and immunoblotting to ferritin from iron-loaded Phaseolus vulgaris leaves. Antibodies raised against purified Phaseolus leaf ferritin were used. Neither in mutant nor in wild type (iron loaded and control) was ferritin protein detected. These results suggest that the electron-dense inclusions in mutant leaves are not identical with ferritin. It is concluded that NA is necessary to complex ferrous iron in a soluble and available form within the cells. In the absence of NA the precipitation of excessive iron in the form of insoluble ferric phosphate compounds could protect the cells from iron overload.

Complementary analysis of freeze-dried and frozen-hydrated plant tissue by electron-probe X-ray microanalysis: Spectral resolution and analysis of calcium

Automated methods of peak determination including peak location, background determination and peak deconvolution are presented. Special attention is given to the problem of severely overlapped peaks, such as the primary calcium peak (Caka) and the secondary potassium peak (Kkβ). A method, based on the principle of electronic transitional probabilities, is presented for estimating Ca in the presence of a high background of K, and limitations of resolution are discussed. Minimally detectable concentrations of elements in prepared frozen-hydrated standards are estimated empirically by analysis of the relative variance. Minimally detectable Ca is estimated in both frozen-hydrated and freeze-dried tissue standards. Using our instrumentation and procedures P, S, Cl and K are detectable down to 24 mM, while Na and Mg are only detectable down to 38 mM in frozen-hydrated tissue. In the presence of 100 mM K, detection of calcium is possible down to 22 and 2 mM in frozen-hydrated and freeze-dried tissue, respectively. As an example, total Ca is shown not to conform to the radial gradient of K across the lettuce (Lactuca sativa L.) taproot.

Identification of phosphate granules occurring in seedling tissue of two palm species (Phoenix dactylifera and Washingtonia filifera)

Haustoria of two palm species, Phoenix dactylifera L. (date) and Washingtonia filifera (Lindl.) Wendl were carefully dissected from seeds, and the ultrastructural characteristics of the large, electron-opaque granules present in the cells of this tissue were compared using standard aldehyde and OsO4 fixations. In Washingtonia, the granules were smaller than those in date and were more variable in size and presence of non-opaque inclusions. All granules appeared to be membrane bounded although they often filled the bounded space. No protein, lipid, carbohydrate or tannins were found in the granules by standard staining procedures. The granules stained positively with two different metallic-phosphate stains which contained either bismuth or lead. Energy dispersive X-ray microprobe analysis, done on aldehyde-fixed granules and those stained with both phosphate stains, confirmed the fact that phosphorus and calcium were present in the granules. The granules also bound the metallic stains as expected. All procedures consistently confirmed the presence of phosphate in the granules. The data are most consistent with the hypothesis that the granules are composed of polyphosphate.

Pyruvate Decarboxylase from Zea mays L. : I. Purification and Partial Characterization from Mature Kernels and Anaerobically Treated Roots

Pyruvate decarboxylase (PDC) was purified from mature, dry maize kernels and from roots of anaerobically treated maize seedlings and partially characterized. PDC was purified to a specific activity of 96 units per milligram protein from kernels and to 41 units per milligram protein from root. The subunit molecular masses were estimated to be 61,000 and 60,000 for kernel PDC and 59,000 and 58,000 for root PDC. The pH optimum for each enzyme was 5.8. Since the pH optimum is nearly one pH unit below the value reported for the cytoplasm of anaerobically metabolizing maize roots (pH 6.7 +/- 0.2), we investigated the effects of pH 5.8 and 6.6 on the cooperative kinetics observed for PDC from each source. The maximum Hill coefficients (n(H)) were much greater at each pH for the kernel PDC (pH 5.8, n(H) = 2.5 and pH 6.6, n(H) = 3.2) than for the root PDC (pH 5.8, n(H) = 1.4 and pH 6.6, n(H) = 1.8). The cooperative kinetics observed with respect to pyruvate were asymmetric. Potassium inhibited maize PDC and was competitive with pyruvate (root PDC K(i) = 16 millimolar and kernel PDC K(i) = 10 millimolar).

Subcellular distribution of phytin in the endosperm of developing castor bean: a possibility for its synthesis in the cytoplasm prior to deposition within protein bodies

Studies using light and electron microscopy, and energy-dispersive X-ray analysis have allowed us to identify phytin particles within the cytoplasm of the developing endosperm of castor bean (Ricinus communis L.). These particles are present at the time of the formation of globoid particles within the protein bodies, but they are absent from mature tissue with fully formed protein bodies. We suggest that phytin is formed initially in the cytoplasm (perhaps in association with the cisternal endoplasmic reticulum) before being transported to the protein bodies, wherein it condenses to form the globoid.