Cotton ovules cultured in an insufficiency of boron (10 micromolar), showed inhibition of fiber growth by the ninth day in culture. Averaging data from eight to eleven days of culture under these conditions, total incorporation of 16-4Clorotic acid into fiber was inhibited by 59%. Inhibition was evident in all radioactively labeled pools, indicating that the effect may be at the membrane transport level or at an early stage of orotic acid metabolism. On a per cent basis, incorporation into RNA under boron deficiency was higher than under sufficiency. The effect is greater on the eighth day of culture, with a decreasing difference from controls up to the eleventh day. Conversely, the per cent incorporation into UDP-glucose was lower under boron deficiency than in controls, having a more or less constant value from 8 to 11 days of culture. Thus, a prinary event of boron deficiency in cotton fiber culture is an alteration in the flow of metabolites through the pyrimidine synthesis pathway.A possible primary event of boron deficiency is the influence of boron on pyrimidine metabolism. A Robertson and Loughman (18,19) for Vicia roots where elongation was being inhibited but had not ceased. In recent studies, Chapman and Jackson (6, 13), working with Phaseolus root tips, showed both early and late effects. There was an early (6-10 h) increased uptake of ["C]-uridine or [32Plinorganic phosphate into RNA at a time when the RNA levels were unchanged. RNA levels fell only after root elongation ceased (100 h) concurrently with manifestation of other boron deficiency symptoms. Increased ribonuclease activity may accompany the decrease in RNA in boron-deficient tissues (6,25).Information about the influence of boron on nucleotide levels is very sparse (4,5,28). Robertson and Loughman (18,19) Working with the in vitro-cultured cotton fiber system, Birnbaum et al. (21) found that the OMP'-decarboxylase inhibitor, 6-azauracil gave symptoms resembling those caused by boron deficiency (3). The correlation was further strengthened by the finding that low uracil concentrations partially overcame both boron deficiency and 6-azauracil effects, presumably by utilization of the uracil salvage pathway.In the present study, we sought to establish more directly whether boron regulates the pyrimidine pathway in some way. Our experimental tissue was fiber from the cotton ovule culture system. We studied the incorporation of [14CJOA into intermediates of the pyrimidine pathway. A factor which had to be taken into account was the possible effect of boron deficiency on OA uptake by the tissue itself.A defmitive study on the interaction of boron with ion transport mechanisms has been done by Loughman's group (14, 16-19), using mainly V. faba seedlings at a stage where root elongation was inhibited by boron deficiency but had not totally ceased. They discovered that the reduced uptake of [32P]phosphate and other inorganic ions caused by boron deficiency, actually involves several components including translocation, metabolism, inter...

Cells of the marine alga Coccolithus pelagicus (Wal‐lich)J. Schiller grown in axenic cultures were homogenized and fractionated. The distribution of organelle markers was assessed enzymatically after centrifugation through zonal, density, and flotation gradients made with sucrose, sorbitol, or Percoll. Mitochondria (1.19 g·cm‐3) and chloroplasts (1.15 g·cm‐3) were recovered in sucrose gradients at densities similar to those observed for higher plants and most algae. The position of endoplasmic reticulum and plasma membrane in the gradients was monitored by NADPH cytochrome c reductase and vanadate‐sensitive Mg2+‐ATPase, respectively. Higher plant Golgi markers, latent undine diphosphatase (UDPase) and glucan synthase I, were colocalized at a density range including two peaks of activity at 1.13–1.15 g·cm‐3. Bound calcium was associated with high density (1.15 g·cm‐3) membranes. Ca2+‐stimulated ATPase was found at high levels on membranes that did not coisolate with the latent UDPase‐containing membranes. The Ca2+‐stimulated ATPase, a possible participant during calcification, was associated with a chloroplast‐enriched fraction in all the organelle separation systems. However, about 30% of the total activity was separated from both the chloroplasts and Golgi on 0–70% Percoll gradients containing 0.4 M sucrose. The possible relationship of the Golgi and the high‐density organelle exhibiting Ca2+‐stimulated ATPase to coccolithogenesis and the process of calcification and crystal formation is discussed.

The properties of the microbody malate debydrogenase (EC 1.1.1.37) (MDH) isozyme from cotyledons of Cucumus sativus L. were compared during development. It is conduded that the isozyme remains unaltered, despite the transition from glyoxysomal to peroxisomal function that occurs during greening of the cotyledons. This condusion is based on electrophoretic behavior, chromatographic elution from DEAE-cellulose, molecular weight, kinetic behavior, and immunological identity. In most cases, the distinct properties of the other MDH isozymes in the tissue during development provide additional support for an unchanging microbody isozyme. A method for assaying specifically the microbody isozyme was developed; a diluted preparation was assayed spectrophotometrically before and after complete immunological precipitation. The turnover of the microbody MDH isozyme was investigated by a radioactive labeling study. There is incorporation into both glyoxysomal and peroxisomal MDH. Degradation rates do not correspond with either decline of glyoxysomal activity or the continuation of peroxisomal activity. Apparently, the microbody MDH isozyme is continually turned over throughout cotyledon development.The transition, during the development of epigeal cotyledons, from a primary function of fat metabolism (nongreen cotyledons) to one of photosynthesis (green cotyledons) has been correlated with a parallel transition in microbody function. In particular, the development of microbodies in cucumber cotyledons has been well documented by electron microscopy (14).This work has substantiated earlier findings on sunflower cotyledons (4, 10) that the microbodies are first associated with the lipid bodies (for lipid catabolism), whereas later they are associated with chloroplasts and contain peroxisomal enzymes (functioning in photorespiration) (13). A previous study on catalase indicated that during the transition, the three-band isozyme pattern on electrophoresis is supplemented by an additional nine bands (3). By contrast, evidence is presented here that the microbody MDH isozyme is not altered during the transition in microbody function. The isozyme is organelle-specific rather than being adapted to the particular metabolic pathway in which it is involved. In addition, radioactive labeling experiments have given some insight into the turnover (synthesis and degradation) of the isozyme during glyoxysomal and peroxisomal function. This work is more fully detailed in a thesis dissertation (15). MATERIALS AND METHODSPlant Material and Preparation of the Homogenates. Seeds of a Burpee hybrid and the Straight Eight variety (6033-5) of cucumber (Cucumis sativus L.) were grown in vermiculite in a dark chamber (30 C) for the first 4 days and then transferred to a growth chamber with a 12-hr light/dark regime, with corresponding temperatures of 26.5 C and 15.5 C, respectively.The washed cotyledons were homogenized in 2 volumes of cold grinding medium (0.1 M tris or K phosphate at pH 7.5, containing 1 mM EDTA and 1 mm DTF) at 4 C, either ...

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