Analysis of growth during light-induced hook opening in cress

Abstract. Growth in various regions of the hypocotyls of dark-grown cress seedlings before and after exposure lo continuous white light has been analysed by time-lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle.     

The adaptive significance of amphistomatic leaves

Abstract A clear correlation between the presence of stomata on both surfaces and factors such as habitat, growth form, and physiology has yet to emerge in the literature. However, certain loose trends with these factors are evident, and these are reviewed along with evidence for hypostomaty as the primitive form. It is proposed that the effect of developing stomata on the upper surface as well as the lower is to increase maximum leaf conductance to CO₂. Plants with a high photosynthetic capacity, living in full-sun environments, and experiencing rapidly fluctuating or continuously available soil water (as opposed to seasonal or long-term soil water depletion), are identified as deriving an adaptive advantage from a high maximum leaf conductance. The correlation between groups of plants fitting the above conditions and those noted to be amphistomatic is remarkable. Plants not fitting the conditions are found to be largely hypostomatic.     

Fatty Acid and Chlorophyll Levels of Coastal Bermudagrass during the Day and during Maturation

Lipids were extracted from fresh, field-grown coastal bermudagrass (Cynodon dactylon (L.) Pers.) and the fatty acids determined by gas chromatography. Total fatty acid levels (dry weight basis) increased during the day and reached a single maximum at sunset in 2-week-old grass; whereas, in older grass, the fluctuations in fatty acid levels showed two maxima. The first maximum occurred 4 h after sunrise and the second maximum occurred at sunset. Total fatty acid levels, based on dry weight, decreased during the first 6 weeks of growth and changed very little after an additional 4 weeks' growth in bermudagrass leaf blades. Chlorophyll levels (dry weight basis) continuously decreased during the entire growth period (10 weeks). Chlorophyll alb ratios increased at sunset in 2- and 6-week-old grass, but this ratio did not change during the day in subsequent growth stages. The results of these experiments show that stages of maturity affected fatty acid fluctuations during the day as well as total fatty acid and chlorophyll levels in Coastal bermudagrass leaf blades. Chlorophyll alb ratios varied independently of fatty acid levels.     

The Electrical Potential Difference Across the Tonoplast of Root Cells

Changes in electrical potential, measured as a microelectrodewas advanced into epidermal cells and from cell to cell in rootsof Lolium multiflorum and Zea mays, are described. The recordingssuggest that the electrical potential difference between thecytoplasm and vacuole, E_vc is of the order of a few millivolts,the vacuole tending to be the more positive. E_vc appeared tobe approximately the same for epidermal, cortical, endodermal,and pericycle cells.     

Role of the Vegetal Body in the Regulation of Development in Bithynia tentaculata (Prosobranchia, Gastropoda)

In the first polar lobe of the egg of Bithyma tentaculata thereis a cup-shaped mass of small vesicles rich in RNA, called thevegetal body. It is passed to the CD blastomere with the polarlobe and then its contents are distributed to C and D. Whenthe polar lobe is removed, embryos form neither mesentoblastnor mesoderm bands. They fail to establish bilateral symmetryor to form eyes, foot, operculum and shell. AB half embryosdevelop only the structures found in lobeless embryos, whileCD halves develop lobe dependent adult structures such as eyes,foot and shell. AD- and BC-2/4-embryos develop similarly andboth have lobe dependent structures. Three quarter embryos developas in other molluscs except that ABD (–C) develops poorlyand ABC (–D) develops all lobe-dependent structures. Thus,all evidence available indicates that C receives cytoplasm usuallyrestricted to D in molluscs and therefore has the capacity toexert a similar morphogenetic influence on development.     

Ultrastructure of the Invasion of Eimeria magna Sporozoites into Cultured Cells*†‡

SYNOPSIS. Monolayers of bovine kidney cells were overlaid with Eimeria magna sporozoites and observed with phase-contrast optics until penetration of the cells by the parasites had begun. Cells and penetrating parasites were fixed with glutaraldehyde and OsO₄-containing ruthenium red, dehydrated, and embedded in situ. Cells being penetrated were selected for study in the electron microscope. The lack of intracellular staining with ruthenium red and intact plasmalemmas of cells being penetrated, was accepted as evidence that the sporozoites did not disrupt the plasma membranes. The sporozoite caused invagination of the host cell plasmalemma until the parasite was entirely within the cell, after which the invagination was sealed off by short pseudopodia enclosing the sporozoite within a membrane-lined vacuole inside the cell. Often myelin-forms, apparently of host cell origin, were seen in the space between the sporozoite and the cell.     

Effect of the Antiphagocytic Agent Cytochalasin B on Macrophage Invasion by Leishmania mexicana Promastigotes and Trypanosoma cruzi Epimastigotes*

Unstimulated mouse peritoneal exudate cells were cultured on coverslips in Medium 199 containing 10% (v/v) calf serum. Cytochalasin B dissolved in dimethyl sulphoxide (DMSO) and diluted in Medium 199 was added to cultures to give final concentrations of 1, 5 and 10 μg/ml. Equal numbers of Leishmania mexicana promastigotes, Trypanosoma cruzi epimastigotes and sheep red cells were added to 24 hr cultures incubated at 37 C. The macrophage monolayers were fixed and stained at various time intervals. L. mexicana promastigotes and sheep red blood cells were found to attach to macrophages in the presence of the drug but did not enter the cells. When the medium containing the Cytochalasin was replaced with normal medium phagocytosis of the adherent parasites and red cells followed rapidly. T. cruzi epimastigotes were found inside macrophages in both drug-treated and drug-free cultures although the number found to be intracellular in the latter was significantly greater. This study suggests that L. mexicana promastigotes enter macrophages by being phagocytosed, whereas T. cruzi epimastigotes can actively penetrate these cells.     

On the Origin of Thymic Lymphocytes

In the leopard frog (Rana pipiens), thymic lymphocytes do notoriginate from blood-borne stem cells that migrate into thethymus anlage; rather they arise in situ from elements in thethymic rudiment itself. After thymic differentiation, the lymphocytes(or their descendants) leave the thymus and extensively seedthe peripheral lymphoid organs. Indeed, virtually all the lymphocytesin the spleen, kidney, and bone marrow are ontogenically derivedfrom thymic cells. In postmetamorphic life, the thymus representsan organ in which lymphopoiesis is genuinely self-sustaining.Throughout the juvenile life of the frog, there is no indicationof an inward afferent stream of cells entering the intact thymus.     

The Distribution of Na+, K+ and Glycinebetaine in Salicornia bigelovii

Stems of young actively growing Salicornia bigelovii were dissectedinto the three major tissue layers: vascular, spongy mesophylland palisade. Each layer was analysed for chlorophyll, ash (salt),protein and glycinebetaine content. When glycinebetaine contentwas based on protein content, the vascular and spongy mesophylllayers had nearly identical values. Correction for probableRuBP carboxylase content in the palisade layer gave a glycinebetaine/proteinratio similar to that of the other tissues. All three tissuelayers were found to contain significant amounts of salt. Key words: Salicornia bigelovii, Salt distribution