J. L. Hall

Quantitative ion localization within Suaeda maritima leaf mesophyll cells

Grown under saline conditions, Suaeda maritima accumulates Na+ and Cl- into its leaves, where individual mesophyll cells behave differently in their compartmentation of these ions. Measurements of ion concentrations within selected subcellular compartments show that freeze-substitution with dry sectioning is a valuable preparative technique for analytical electron microscopy of highly vacuolate plant material. Using this approach, absolute estimates were made of Na+, K+ and Cl- concentrations in the cytoplasm, cell walls, chloroplasts and vacuoles of leaf mesophyll cells.

The effect of salt on protein synthesis in the halophyte Suaeda maritima

SummaryAn amino acid-incorporating microsomal fraction has been isolated from the leaves of the halophyte Suaeda maritima and the characteristics of the incorporation described. There were no differences in the properties of the microsomes isolated from plants grown in saline and non-saline conditions. The incorporation was severely inhibited by high concentrations of sodium or potassium ions. The results are discussed in relation to the mechanism of salt tolerance in halophytes and the localization of salt in the cells.

Evidence for the cytoplasmic localization of betaine in leaf cells of Suaeda maritima

An attempt has been made to localize glycinebetaine in shoots of Suaeda maritima L. Dum. using a technique based on the formation of an iodoplatinate precipitate. Deposits were largely restricted to the cytoplasm of salt-grown plants and were analysed by transmission analytical electron microscopy. The results are considered to support the hypothesis that glycinebetaine acts as a cytoplasmic osmoticum to balance high vacuolar salt levels in certain halophytes.

The use of freeze-substitution in the preparation of plant tissue for ion localization studies

A method, utilizing freeze substitution, is described for the preparation of plant tissue for analytical electron microscopy. The fine structure of the cytoplasm was adequately preserved after freezing leaf tissue in 2‐methylbutane at −170°C. Furthermore, following substitution in ether, losses of sodium and potassium from the tissue were less than 4% of the original ion content and the loss of chloride was less than 1%. The merits of the procedure as a means of tissue preparation for ion localization studies are discussed.

Cytochemical localization of peroxidase activity in root cells.

SummaryThe distribution of peroxidase in the apical 3 mm of pea roots has been investigated using the histochemical method employing 3,3-diaminobenzidine as a substrate. At the tissue level the enzyme is localized predominately in the root cap, epidermis, inner cortical cells, endodermis, phloem and maturing xylem. At the subcellular level peroxidase is found mainly in the intercellular regions of the cortex cell walls and in the cytoplasm and vacuoles of the steler cells. Root microbodies, unlike those of leaves, do not appear to be able to oxidize this substrate. The significance of these observations is discussed in relation to the validity of the technique and the proposed roles of the enzyme in cellular metabolism.

The effect of cytochalasin B on the rate of growth and ultrastructure of wheat coleoptiles and maize roots

Cytochalasin B (CB) inhibits the elongation growth of maize roots, and that of wheat coleoptile segments incubated in indolyl-3-acetic acid, by over 30% after a lag period of about 60 min. This long lag is not due to poor tissue penetration by the inhibitor, but seems to reflect a property of the process inhibited by CB. The only visible ultrastructural change accompanying growth inhibition is the accumulation of secretory vesicles in the vicinity of dictyosomes, which occurs between 90 and 300 min. However, a massive accumulation of vesicles is seen after 120 min in root cap cells which possess very active dictyosomes. The results indicate that CB does not inhibit elongation growth by interfering with cytoplasmic streaming. Instead, they indicate that the drug acts to inhibit the secretion of cell wall components at some stage after vesicle production, but prior to their transport.

The role of the epidermis in auxin-induced and fusicoccin-induced elongation of Pisum sativum stem segments.

The effects of peeling and wounding on the indole-3-acetic acid (IAA) and fusicoccin (FC) growth response of etiolated Pisum sativum L. cv. Alaska stem tissue were examined. Over a 5 h growth period, peeling was found to virtually eliminate the IAA response, but about 30% of the FC response remained. In contrast, unpeeled segments wounded with six vertical slits exhibited significant responses to both IAA and FC, indicating that peeling does not act by damaging the tissue. Microscopy showed that the epidermis was removed intact and that the underlying tissue was essentially undamaged. Neither the addition of 2% sucrose to the incubation medium nor the use of a range of IAA concentrations down to 10-8 M restored IAA-induced growth in peeled segments, suggesting that lack of osmotic solutes and supra-optimal uptake of IAA were not important factors over this time period. It is concluded that, although the possibility remains that peeling merely allows leakage of hydrogen ions into the medium, it seems more likely that peeling off the epidermis removes the auxin responsive tissue.

Cytochemical localization of ATP‐ase activity in plant root cells

ATP‐ase activity in root‐tip cells of Zea mays has been localized by using a lead phosphate precipitation procedure. Activity is associated with the plasmalemma, nucleus, mitochondria, Golgi bodies, vacuoles and endoplasmic reticulum al though the relativeactivities vary in different regions of the root. The localization of surface ATP‐ase is compared with that of surface β‐glycerophosphatase and the results discussed in relation to the possible role of ATP‐ase in ion transport.

Regulation of swelling of etiolated-wheat-leaf protoplasts by phytochrome and gibberellic acid

The effect of light on the size of intact protoplasts isolated from the primary leaves of etiolated Triticum aestivum was studied. A 2-min red-light irradiation in the presence of 1 mM KCl was sufficient to cause a swelling of protoplasts compared with those maintained in darkness. The effect was photoreversible by far-red light over two light cycles, indicating the involvement of phytochrome. At 4°C, escape from reversibility occurred between 2 and 5 min after the exposure to red light. In exposure-response experiments, 20 s red light at 27 μmol m-2s-1 was sufficient to saturate the response. Exogenous gibberellic acid added in darkness in the presence of KCl also induced protoplast swelling. Gibberellins may act as an intermediate in the phytochrome-induced swelling of protoplasts.

Localization of cell surface adenosine triphosphatase activity in maize roots

In recent years a close linkage has been established between the transport of cations across animal cell membranes and adenosine triphos phatase (ATP-ase) activity bound to these membranes (Post and Sen, 1965). Although no such association has been shown in plant cells, ATP-ase activity has been demonstrated at the surface of intact, excised roots (Chang and Bandurski, 1964) and salt stimulated ATP-ase activity has been demonstrated in cell wall preparations from a variety of plants (Dodds and Ellis, 1966; Atkinson and Polya, 1967). How ever, the precise location of this activity in higher plant cells has not been established; the enzyme might be associated with the cell wall proper or with the outer cell membrane. In a previous study of phos phatase activity with the electron microscope (Poux, 1966), no clear distinction between these possible sites was made. This work involves the fine structural localization of surface ATP-ase activity and demon strates its close association with the outer cell membrane and plasma desmata of maize root cells.