Mesophyll cell ultrastructure of wheat leaves etiolated by lead and selenium.

The ultrastructure of mesophyll cells was studied in leaves of the Triticum aestivum L. cv. "Trizo" seedlings after two weeks of growth on soil contaminated by Pb and/or Se. The soil treatments: control; (Pb1) 50mgkg-1; (Pb2) 100mgkg-1; (Se1) 0.4mgkg-1; (Se2) 0.8mgkg-1; (Pb1+Se1); (Pb1+Se2); (P2+Se1); and (Pb2+Se2) were used. Light and other conditions were optimal for plant growth. The (Se1)-plants showed enhanced growth and biomass production; (Pb1+Se1)-plants did not lag behind the controls, though O2 evolution decreased; chlorophyll content did not differ statistically in these treatments. Other treatments led to statistically significant growth suppression, chlorophyll content reduction, inhibition of photosynthesis, stress development tested by H2O2 and leaf etiolation at the end of 14-days experiment. The tops of etiolated leaves remained green, while the main leaf parts were visually white. Plastids in mesophyll cells of etiolated parts of leaves were mainly represented by etioplasts and an insignificant amount of degraded chloroplasts. Other cellular organelles remained intact in most mesophyll cells of the plants, except (Pb2+Se2)-plants. Ruptured tonoplast and etioplast envelope, swelled cytoplasm and mitochondria, and electron transparent matrix of gialoplasm were observed in the mesophyll cells at (Pb2+Se2)-treatment, that caused maximal inhibition of plant growth. The results indicate that Pb and Se effects on growth of wheat leaves are likely to target meristem in which the development of proplastids to chloroplasts under the light is determined by chlorophyll biosynthesis. Antagonistic effect of low concentration of Se and Pb in combination may retard etiolation process.

Biochemistry and cell ultrastructure changes during senescence of Beta vulgaris L. leaf.

The comparative study of biochemical and ultrastructure features in senescing sugar beet (Beta vulgaris L.) leaves was carried out. One group of plants was grown under normal conditions in washed river sand and poured in turn with nitrate-containing mineral solution or water (N plants). Another group of plants, after 1 month of normal growth, was further grown with nitrate omitted in the nutritive solution (defN plants). The starting point of normal leaf senescence in N plants was identified by the maximal content of soluble protein. Soluble carbohydrate pools were statistically constant in senescing N plants, whereas glucose pools varied noticeably. A decrease in the contents of soluble protein and chlorophyll (a + b) in the course of senescing was typical for N plant leaves. The cell membrane in N plant leaves remained mostly intact; the central vacuoles in the leaf cells were large, and their membranes remained intact. The chloroplasts and mitochondria in senescing N plant leaves became swollen. The vesicles that were present in the cytoplasm of N plant leaves were especially large in the oldest leaves. It was concluded that senescing of sugar beet leaves at sufficient nitrate nutrition occurs according to a "vacuolar" scenario. In the case of nitrate deficiency, the content of soluble carbohydrates in defN leaves first reached maximum and then decreased in older leaves; the protein and chlorophyll (a + b) contents were totally lower than those in normal leaves and continuously decreased during the experiments. Chloroplasts in mesophyll cells of defN plant leaves became more rounded; starch grains in chloroplasts degraded and the number and size of lipid globules increased. The multitude of membrane impairments and lots of large vesicles-"crystals" appeared during the experiment. The results showed the controlling action of nitrogen nutrition in the senescing of sugar beet leaves.

Untangling metabolic and spatial interactions of stress tolerance in plants. 1. Patterns of carbon metabolism within leaves.

The localization of the key photoreductive and oxidative processes and some stress-protective reactions within leaves of mesophytic C(3) plants were investigated. The role of light in determining the profile of Rubisco, glutamate oxaloacetate transaminase, catalase, fumarase, and cytochrome-c-oxidase across spinach leaves was examined by exposing leaves to illumination on either the adaxial or abaxial leaf surfaces. Oxygen evolution in fresh paradermal leaf sections and CO(2) gas exchange in whole leaves under adaxial or abaxial illumination was also examined. The results showed that the palisade mesophyll is responsible for the midday depression of photosynthesis in spinach leaves. The photosynthetic apparatus was more sensitive to the light environment than the respiratory apparatus. Additionally, examination of the paradermal leaf sections by optical microscopy allowed us to describe two new types of parenchyma in spinach-pirum mesophyll and pillow spongy mesophyll. A hypothesis that oxaloacetate may protect the upper leaf tissue from the destructive influence of active oxygen is presented. The application of mathematical modeling shows that the pattern of enzymatic distribution across leaves abides by the principle of maximal ecological utility. Light regulation of carbon metabolism across leaves is discussed.

Structural features of the salt glands of the leaf of Distichlis spicata 'Yensen 4a' (Poaceae).

The epidermal salt glands of the leaf of Distichlis spicata 'Yensen 4a' (Poaceae) have a direct contact with one or two water-storing parenchyma cells, which act as collecting cells. A vacuole occupying almost the whole volume of the collecting cell has a direct exit into the extracellular space (apoplast) through the invaginations of the parietal layer of the cytoplasm, which is interrupted in some areas so that the vacuolar-apoplastic continuum is separated only by a single thin membrane, which looks as a valve. On the basis of ultrastructural morphological data (two shapes of the extracellular channels, narrow and extended, are found in basal cells), the hypothesis on the mechanical nature of the salt pump in the basal cell of Distichlis leaf salt gland is proposed. According to the hypothesis, a driving force giving ordered motion to salt solution from the vacuole of the collecting cell through the basal cell of the salt gland to cap cell arises from the impulses of a mechanical compression-expansion of plasma membrane, which penetrates the basal cell in the form of extracellular channels. The acts of compression-expansion of these extracellular channels can be realized by numerous microtubules present in the basal cell cytoplasm.