Effects of Inhibitors of Protein and Nucleic Acid Synthesis on the Development of Ion Uptake Mechanisms in Beetroot Slices (Beta vulgaris)

Mechanisms for the uptake of K+, Na+ and Cl‐ develop sequentially in thin slices of beetroot tissue washed under aerobic conditions. Actinomycin D inhibited or prevented the development of K+, Na+ and Cl‐ uptake mechanisms when added to freshly cut slices, but had no effect on net ion uptake when added after the development of the ion uptake mechanisms. The use of puromycin as a specific inhibitor of protein synthesis was unsatisfactory as it caused leakage of pigments and excessive loss of ions from the disks. Cycloheximide prevented the development of ion uptake mechanisms when added at the start of the experiment, but when added after the development of ion uptake mechanisms its inhibitory effect did not become apparent until after a certain time interval which varied from 3 hours for Cl‐ to 25 hours for K+ uptake in the same experiment. p‐Fluorophenylalanine caused an appreciable shortening of the time required for the development of Na+ and K+ uptake capabilities, while it completely prevented the development of a Cl‐ uptake mechanism. p‐Fluorophenylalanine‐induced early uptake of Na+ and K+, however, was followed by periods of net leakage of these ions. It is suggested that the development of ion uptake mechanisms depends on the production of m‐RNA, which appears to be relatively stable after its synthesis. The synthesis and decay characteristics of specific proteins required for the ion uptake mechanisms appear to differ for each ion species. Copyrigh

Evidence for structural units in chloroplast thylakoids

When tissue preparation for electron microscopy includes staining with aqueous uranyl acetate overnight at 60 °C prior to the dehydration process, regular repeating elements are revealed within the loculi of chloroplast thylakoids. This region of the chloroplast usually appears to be featureless when conventional techniques of specimen preparation are used. The apparent difference in structure is discussed with reference to changes occurring during the dehydration process

Effect of protein synthesis inhibitors on the formation of crystalloid inclusions in the endoplasmic reticulum of beetroot cells

Thin slices of beetroot tissue develop long ER lamellae during a period of aerated washing. After 2-3 days crystalloid bodies begin to appear within the ER cisternae and these were shown to consist largely of protein. The effect of inhibitors of RNA and protein synthesis on the formation of ER lamellae and crystals was studied, and results indicate that protein synthesis, but not synthesis of m-RNA, is essential for both processes. It is also suggested that the protein-synthesizing system associated with the ER is more stable than the cytoplasmic polyribosome system, which may require the continued production of m-RNA after slicing

Inhibition of the Development of a Cation Accuniulatory System and of Tris‐induced Uptake in Storage Tissues by N6‐benzyladenine and Kinetin

The effect of N6‐benzyladenine (BA) and kinetin on cation uptake in disks of beetroot (Beta vulgaris L.) and swede (Brassica napobrassica Mill.) tissue was measured in aerated solutions, containing 1 mM NaCl or 1 mM KCl, and in the presence or absence of trishydroxymethyl ammo methane (tris) buffer at pH 8. This investigation followed a suggestion that the immediate activation of cation uptake in freshly sliced beetroot disks by tris (the tris‐effect) may depend on stimulation of hexokinase activity. BA, a competitive inhibitor of hexokinase, caused a complete inhibition of tris stimulated cation uptake in beetroot disks, but the effect was delayed and preceded by a 3–4 hour period of promoted cation uptake. Generally, the effects of BA and kinetin were identical. Use of 14C‐kinetin indicated a rapid incorporation of kinetin into the tissue. BA and kinetin also prevented the development of a cation uptake capability during the aging of the beetroot disks. Swede disks which do not show a tris‐effcct and no lag phase in development of cation uptake capability were not affected by BA and kinetin treatments. Mechanisms of tris induced cation uptake are discussed with emphasis on its role as a proton acceptor. Copyrigh

Glucosamine-induced starch degradation in leaf tissue: An EM autoradiographical study

Electron microscope autoradiographical studies have been undertaken in order to investigate further the aggregation of particles and the associated starch grain degradation induced by treatment of cereal leaf segments with D-glucosamine in the light. It has been found that label from D-glucosamine-6-H3 is located predominantly in the chloroplasts and that, within the chloroplasts, the silver grains are largely concentrated over the particles and semidigested starch grains

Ultrastructural observationof lemon fruit abscission

Ultrastructural changes in the abscission zone between ovary wall and floral disc were followed during abscission of young lemon (Citrus limon (L.) Burm. f. cultivar 'Villafranca') fruit explants. Although some cell breakage was observed by light and scanning electron microscopy as well as cell wall dissolution, only middle lamella dissolution was observed by transmission electron microscopy, strongly suggesting that pectic substance dissolution is the primary cause of cell separation. Prior to cell separation the middle lamella of the cell wall stained deeply, the amount of rough endoplasmic reticulum (ER) profiles increased, and the number of Golgi bodies also increased. However no change in mitochondria or chloroplast structure was observed before cell separations, and no microbodies were observed. In Ethephon (2-chloroethylphosphonic acid)-treated explants, essentially similar cytoplasmic and cell wall changes occurred during the course of abscission, but the changes were more rapid

Rapid action of abscisic acid on photosynthesis and stomatal resistance

(RS)-Abscisic acid, a natural plant hormone, has been found to inhibit photosynthesis in both detached and attached primary wheat leaves. The action occurs rapidly and is accompanied by large increases in stomatal diffusive resistance

Starch associated particles in D-glucosamine-treated leaf tissue

Light incubation of barley and wheat leaf segments with 20 mM D-glucosamine at pH 6.0 or pH 8.0 results in the formation of clusters of particles (150-225 Å) closely associated with chloroplast starch grains which appear to break down at the periphery. Thes ultrastructural changes are apparent after 6 hours treatment. Only relatively minor changes can be detected in the dark. D-mannosamine has a similar though much less pronounced effect but no ultrastructural changes are observed with either D-galactosamine or N-acetyl D-glucosamine. When leaf segments are treated in the light with both D-glucosamine and tris (hydroxymethyl) aminomethane in equimolar concentrations, the different ultrastructural changes induced by each substance can be observed in the same chloroplast. The glucosamine-induced particles appear to contain protein

The ultrastructure of wheat leaves II. The effects of kinetin and ABA on detached leaves incubated in the light

Incubation of detached wheat leaves in water in the light results in a temporary accumulation of starch in the chloroplasts. This accumulation is prevented by treatment with ABA. On the other hand, treatment of the detached leaves with kinetin causes a large increase in the size and number of starch grains