Chloroplast ultra structure, photosynthesis and enzyme activities in regenerated plants of Stevia rebaudiana (Bert.) Bertoni as influenced by copper sulphate in the medium.

Stevia rebaudiana (Bert.) Bertoni is an important medicinal plant used as noncaloric commercial sweetener. Plants regenerated with higher levels of copper sulphate in the medium exhibited enhanced activity of peroxidase and polyphenoloxidase (PPO) enzymes. Transmission electron microscopy (TEM) revealed increase in size and number of electron dense inclusions in the chloroplasts of plants regenerated at optimised level of copper sulphate (0.5µM) in the medium. There was decrease in chlorogenic acid (CGA) content. Chl-a-fluorescence transient pattern (OJIP) showed that the photosynthesis process was more efficient at 0.5µM CuSO4 in the medium. 

Ultrastructural changes and oxidative stress markers in wild and cultivar Sesamum orientale L. following Alternaria sesami (Kawamura) Mohanty and Behera inoculation.

Alternaria sesami causes leaf spot disease in Sesamum orientale. Conidium germination, inoculation, penetration and colonization of the pathogen on the plant surfaces were studied using scanning electron microscopy. Electron microscopy analysis revealed multiple germ tubes from conidium that spread in all direction across the leaf surfaces. Penetration in the plant surface occured, directly through the epidermis or via stomata with or without the appressoria formation. Hyphal penetration continued through the substomata cavity and some of hyphal branches grew in the intercellular space of mesophyll tissue. Hyphal toxin, caused cell and cell wall damages. Changes in different biochemical parameters in the diseased sesame plants (both in wild and cultivar) were compared to control. Transmission electron microscopy showed structural changes in the chloroplast of diseased plants. Isozyme pattern and assays of different enzymes, namely catalase, acid phosphatase and peroxidase expressed varied level of activities. Meanwhile, esterase, polyphenol oxidase and superoxide dismutase in diseased plants showed remarkable levels compared to control. Due to the infection, chlorophyll content, carbohydrates and total soluble protein decreased whereas free amino acid, proline, phenols and disease-related proteins increased in the host plants. Differential SDS-PAGE band profiling of total soluble proteins were also observed in plants due to the infection.

Analysis of chlorophyll fluorescence reveals stage specific patterns of chloroplast-containing cells during Arabidopsis embryogenesis

The basic body plan of a plant is established early in embryogenesis when cells differentiate, giving rise to the apical and basal regions of the embryo. Using chlorophyll fluorescence as a marker for chloroplasts, we have detected specific patterns of chloroplast-containing cells at specific stages of embryogenesis. Non-randomly distributed chloroplast-containing cells are seen as early as the globular stage of embryogenesis in Arabidopsis. In the heart stage of embryogenesis, chloroplast containing cells are detected in epidermal cells as well as a central region of the heart stage embryo, forming a triangular septum of chloroplast-containing cells that divides the embryo into three equal sectors. Torpedo stage embryos have chloroplast-containing epidermal cells and a central band of chloroplast-containing cells in the cortex layer, just below the shoot apical meristem. In the walking-stick stage of embryogenesis, chloroplasts are present in the epidermal, cortex and endodermal cells. The chloroplasts appear reduced or absent from the provascular and columella cells of walking-stick stage embryos. These results suggest that there is a tight regulation of plastid differentiation during embryogenesis that generates specific patterns of chloroplast-containing cells in specific cell layers at specific stages of embryogenesis.

Isolation and intracellular localization of insulin-like proteins from leaves of Bauhinia variegata

Evidence based on immunological cross-reactivity and anti-diabetic properties has suggested the presence of insulin-like peptides in plants. The objective of the present study was to investigate the presence of insulin-like proteins in the leaves of Bauhinia variegata ("pata-de-vaca", "mororó"), a plant widely utilized in popular medicine as an anti-diabetic agent. We show that an insulin-like protein was present in the leaves of this plant. A chloroplast protein with a molecular mass similar to that of bovine insulin was extracted from 2-mm thick 15 percent SDS-PAGE gels and fractionated with a 2 x 24 cm Sephadex G-50 column. The activity of this insulin-like protein (0.48 mg/mL) on serum glucose levels of four-week-old Swiss albino (CF1) diabetic mice was similar to that of commercial swine insulin used as control. Further characterization of this molecule by reverse-phase hydrophobic HPLC chromatographic analysis as well as its antidiabetic activity on alloxan-induced mice showed that it has insulin-like properties. Immunolocalization of the insulin-like protein in the leaves of B. variegata was performed by transmission electron microscopy using a polyclonal anti-insulin human antibody. Localization in the leaf blades revealed that the insulin-like protein is present mainly in chloroplasts where it is also found associated with crystals which may be calcium oxalate. The presence of an insulin-like protein in chloroplasts may indicate its involvement in carbohydrate metabolism. This finding has strengthened our previous results and suggests that insulin-signaling pathways have been conserved through evolution.

Fine structural study of the red seaweed Gymnogongrus torulosus (Phyllophoraceae, Rhodophyta)

The present study analyzed several characters of the red seaweed Gymnogongrus torulosus, such as cellular structure of the thallus, cuticle, pit plug and cell wall ultrastructure, and morphology of some organelles like plastids, Golgi bodies and mitochondria. Also, anomalous chloroplasts with thylakoid disorganization were found in medullary cells. The significance of this thylakoid disposition is still unclear. This is one of the first studies focused on the fine structure of a red alga recorded in Argentina.

Location of chloroplast membrane resonances in high resolution 13C-NMR spectrum of spinach leaves.

Spinach leaves were studied by high resolution 13C-NMR spectroscopy. The spectra obtained, though highly complex, showed some distinct resonances assignable to carbons of lipids of the chloroplast membranes, thereby offering a novel way for studying the chloroplast membranes in situ.

Studies on the powdery mildew fungus Sphaerotheca fuliginosa on squash in Egypt: ultrastructure and some physiological host responses

According to the criteria of conidia and cleistothecia, this study revealed that, the powdery mildew fungus which infects squash in Nile Delta, Egypt is Sphaerotheca fuliginea. This fungus was studied by light microscopy, scanning and transmission EM. The conidia are barrel or oval-shaped with wrinkled surface. The cleistothecia are spherical and contain one ellipsoid to spherical ascus with 4-8 ellipsoid ascospores. The host epidermal cell was penetrated by a penetration peg which, after penetration developed into haustorium consisting of a nucleated central body with several lobes, embedded in a matrix. The surrounding extrahaustorial membrane is an invagination of the plasmalemma of the host cell. As a defence mechanism, a collar was formed arround the penetration peg. Chloroplasts of infected leaf of squash showed a dramatic changes in their utltrastructure. The infection caused an alteration in the physiology of squash leaf. It is obvious that there wig a marked depletion in reducing sugars and sucrose which- accompanied by a simultaneous elevationn in polysaccharides of infected leaœ Also, the pigment content [chlorophyll. a,b and carotenoids] appeared geared to be reduced as a result of such infection. There was a massive decrease in the endogenous growth stimulants levels [auxins, gibberellins and cytokinins] with a concomitant increase in growth inhibitors in infected leaf of squash