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Background and Aims: Leaf morphology, anatomy, degree of lignification, and tensile strength were studied during vegetative phase change in an inbred line of Zea mays (OH43 x W23) to determine factors that influence mechanical properties during development. Methods: Tensometer, light microscopy, histochemistry. Key results: Mature leaf length increased linearly with plant development, peaked at leaves 7 and 8 (corresponding to the onset of the adult phase) and then declined. Leaf width was stable for leaves 1 through 3, increased to leaf 7, remained stable to leaf 10, and then declined through leaf 13. Lamina thickness was highest for leaf 1 and decreased throughout development. Leaf failure load to width ratio and failure load to thickness ratio increased with development suggesting that changes in leaf morphology during development do not entirely account for increases in failure load. Histochemical analyses revealed that leaf tensile strength correlates with percent lignification and the onset of anatomical adult features at various developmental stages. Conclusions: These data demonstrate that in Zea mays lignification of the midrib parenchyma and epidermis may be directly correlated with increased tensile strength associated with phase change from juvenility to adulthood. Failure load and resultant tensile strength values are primarily determined by the percent tissue lignification and the appearance of leaf architectural characters that are associated with the transition from the juvenile to the adult phase. Increased mechanical stability that occurs during the phase transition from juvenility to adulthood may signify a fundamental change in strategy for an individual plant from rapid growth (survival) to reproduction.
The study concerned an evergreen herbal plant Waldsteinia trifolia Roch. This species can be found more and more often in garden plantings in Poland. The aim of the study was to estimate the content of photosynthetic pigments, anthocyanins and dry matter as well as the permeability of cytoplasmatic membranes of Waldsteinia leaves. Plants grew in an ornamental plant collection at the premises of the Faculty of Horticulture of the Agricultural University in Kraków. The study was conducted in 2006 and 2007 in the following months: March, May, June, September, October and November. The permeability of cytoplasmatic membranes was estimated based on electrolyte leakage from leaf discs at 20°C in relation to total electrolytes in the tissue after unfreezing. The fi rst days with temperature drops down to around 0°C in autumn resulted in a decrease in chlorophyll a, b and carotenoid content, but significantly increased anthocyanin content. The ratio of chlorophyll a to band the ratio of total chlorophylls to carotenoids did not change in particular months. In both years of study, similar changes in dry matter content of the Waldsteinia leaves were observed. Dry matter content signifi cantly increased in June and November and decreased in May and October. In June and in autumn, after first slight frosts, an increase of electrolyte leakage from the leaf discs was observed. However, high dry matter content (40.3%) was accompanied by lower permeability of the cytoplasmatic membranes of the leaves after winter during March. These results have shown good adaptation of Waldsteinia trifolia plants to the climatic conditions in Poland.
Seed priming is one of the potential physiological approaches to enhance the seed germination under the salinity stress. The present study examined the role of two seed priming molecules: salicylic acid (SA) and hydrogen peroxide (H2O2), in enhancing the salt tolerance of lentil seeds at germination stage. Salinity stress caused significant decrease in germination percentage and primary root elongation. This decrease was associated with significant increase in lipid peroxidation and total lipid (TL) contents in embryonic axis. The catalase (CAT), guaiacol peroxydase (GPOX) and superoxide dismutase (SOD) activities remained unchanged or decreased significantly under the influence of salt stress, in both embryonic axis and cotyledons. Starch mobilization was not affected by the salt stress. The two priming treatments effectively alleviated the negative effects of salinity stress. SA and H2O2 applications after dose optimization resulted in a significant enhancement of germination percentage and primary root elongation. No significant changes in starch, soluble sugars contents and SOD activity were detected following SA and H2O2 treatments. Seed priming treatments triggered the activities of GPOX and CAT and caused the reduction in lipid peroxidation, especially in embryonic axis. TL content and especially the fatty acid C18:3 increased after SA applications. Better performance under salt stress of primed lentil seeds was associated with lower lipid peroxidation, and activation of enzymatic antioxidative defense system. Obtained results confirm the potential for using SA and H2O2 to improve germination and plant growth under salt stress conditions.
Potato plants grown in vitro were subjected to different salt stresses by providing the salts NaCl, Na₂SO₄, MgCl₂ and MgSO₄ in different concentrations up to 300 mM. Salinity greatly affected the survival and the rooting of the plants. Shoot and root growth decreased with increasing salt concentrations. Under mild stress conditions, i.e. in conditions where the plant is able to adapt to the stress, the observed decrease was dependent upon the salt used. Under severe stress conditions, however, the decrease of the shoot and root growth was independent of the nature of the ions.
The relationship between growth and some enzymes of carbohydrate metabolism in developing cotton fibre were studied. Two respiratory pathways of glucose oxidation i.e. oxidative pentose phosphate pathway (OPPP) and glycolysis operates in the elongating cotton fibres and the extent of their operation varies with the demand for respiratory products. In this respect, hexokinase, G-6-PDH, 6PGDH, and MDH show increased activities during the period of rapid cell elongation and decreased activities when rate slows down. The conversion of PEP to malate and/or via a transhydrogenase system consisting of enzymes PEPC, MDH and NADP-MDH(d) may play a significant role in carbohydrate compartmentation of developing cotton fibre. As the rate of fibre growth slows down, a decline in enzyme activities, points to a shift in metabolic priorities.
An expression of plants response to light availability is their shade tolerance which refers to the capacity of a given plant to tolerate low light levels. Survival in a shaded environment can determine phenotypic consequences at morphological and/or physiological levels and such changes may be crucial to survive in heterogeneous and variable conditions. However, the potential plastic response of a given plant trait may be large but the observed plasticity may be lowered by resource limitations or environmental stress factors. In this context, the aim of this research was to analyze morphological, anatomical and physiological leaf traits variations of Sesleria nitida Ten. growing in different light conditions. In particular, plants growing in open (PO) and shade (PU) conditions were analyzed. The results show a 35% higher specific leaf area (SLA) in PU than in PO due to a 94% larger leaf area (LA). The higher height and width of the central and the major lateral vascular bundle in PO than in PU contribute to a higher net photosynthesis (PN) in sun than in shade conditions. Moreover, the 33% higher ratio between respiration (RD) and PN (RD/PN) in PU than in PO highlights the greater proportion of the carbon consumed by RD in the shade population requiring a greater metabolic effort for growth and maintenance. S. nitida in the shaded environment might be favored by the soil pH being a neutro-basophilous species and the larger soil water content (SWC) and mineral content contributing to maintain a positive carbon balance in this limiting condition. The plasticity analysis for open vs. the understory plants (mean plasticity index = 0.32) highlights the leaf trait variations useful to maintain a positive carbon balance where light availability is the main limiting factor. Knowledge of the capacity of S. nitida to first colonize and then modify its phenotype in response to the shade condition can contribute to a better understanding of its ecology.
Voltage-gated potassium channels (Kv) are predominating and most widely studied ion channels in T lymphocytes (TL). Patch-clamp studies provide evidence that three different types of Kv channels, termed n, n' and l, are present in human in mouse TL. This review focuses on: 1) studies on biophysical properties of the three channel types, 2) role of Kv channels in TL cell function. Available data demonstrate that the activity of Kv channels in TL is required for: i. setting the TL resting membrane potential, ii. cell mitogenesis, iii. volume regulation. Blockade of Kv channels effectively blocks both mitogenesis and volume regulation of T cells, 3) changes of Kv channel expression in diseases. Results of patch-clamp studies provide evidence that expression of TL Kv channels is significantly altered in autoimmune diseases and in chronic renal failure. Autoimmune diseases are linked to an abnormally high expression of the l type Kv channels, which arises in parallel with the onset of autoimmunity, in mouse double-negative (DN-CD4-CD8-) TL. In chronic renal failure, a significant increase in the whole-cell potassium conductance (gKv), probably also due to altered channel expression, appears in human TL. The rise in the gKv value parallels the onset of the disease. Moreover, long-term therapy of uremic patients with recombinant human Erythropoietin is linked to a significant decrease in the gKv value towards the level of control TL. Altogether, the data demonstrate that patch-clamp studies on the Kv channels may provide a valuable tool delineating the role of the channels in TL cell-function and the pathogenesis of the diseases.
The establishment of certain morphological, physical and physiological criteria was considered and this might allow us to determine more precisely the maturation degree as well as the optimum harvest and sowing period of seeds. The criteria for assessing the maturation degree of seeds presented earlier (the completely formed embryo, the prominent endosperm with a normal consistency) can now be completed with a new criterion, namely the one referring to the slight tendency of the seesds tegument to get yellow. This is due to the fact that the seed completes its growing sooner than the pericarp. The fact was proved both by the greater decrease the fresh mass of the pericarp than that of the seed and by the greater decrease of the moisture content of the seed than that of the pericarp during the four examined ripening phases.
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