Plant physiology

About: Plant physiology is a research topic. Over the lifetime, 1537 publications have been published within this topic receiving 72038 citations.

Some aspects of aluminum toxicity in plants

Abstract: Aluminum toxicity is a major factor in limiting growth in plants in most strongly acid soils. Toxic effects on plant growth have been attributed to several physiological and biochemical pathways, although the precise mechanism is still not fully understood. In general, root elongation is hampered through reduced mitotic activity induced by Al, with subsequent increase in susceptibility to drought. The initial site of uptake is usually the root cap and the mucilaginous secretion covering the epidermal cells. Al ions bind very specifically to the mucilage by exchange adsorption on the polyuronic acid, complexing with the pectic substances and by the formation of polyhydroxy forms, increasing the number of Al atoms per positive charge. Toxicity has been suggested to be initiated at the sites of mucopolysaccharide synthesis. Al is absorbed on all Ca-binding sites on the cell surface. In the intact tissues, most of the Al is bound to the pectic substances of the cell wall and a part to the nucleic acids and cell membrane. Al is also reported to enter the plant by moving into meristematic cells via the cortex, bypassing the endodermal barrier. Being a polyvalent cation, it follows principally the apoplasmic pathway of transport through cortical cells, but may also enter the stele through the plasmalemma. Ultrastructural studies have shown the maximum accumulation to be in the epidermal and cortical cells. The interaction of Al with different systems follows different pathways. The plasma membrane at the outer boundary of the root cell is a potential target and its physical properties can be altered by Al through interaction with membrane-bound ATPase, lipids, carbohydrates and proteins. The Golgi apparatus has been suggested as the primary site of action, followed by damage to the plasmalemma. Aluminum interferes with the uptake, transport and use of several essential elements, including Cu, Zn, Ca, Mg, Mn, K, P and Fe. Excess of Al reduces the uptake of certain elements and increases that of others, the patterns being dependent on the element, the plant part and species involved. A major factor is the pH concentration. At an acid pH, below 5.5, the antagonism between Ca and Al is probably the most important factor affecting Ca uptake by plants. The molecular mechanism of tolerance of Al is as yet not clear. Tolerant plants reduce the absorption by the root or detoxify Al after absorption. Al tolerant plants may be grouped into those with higher Al concentrations in tops and those with less. In the latter, more Al is entrapped in roots. Uptake of Al may be reduced by binding to cell wall or to membrane lipid. Tolerance may be different in different species and seems to be controlled by one or more genes. Absorption of Al in non-metabolic conditions is affected only slightly by temperature. Anaerobic conditions, like the presence of nitrogen and metabolic inhibitors, damage the endodermal membrane barrier, increasing the uptake and enhancing injurious effects. Aluminum also causes morphological damage to plant parts. It affects photosynthesis by lowering chlorophyll content and reducing electron flow. Reduced respiratory activity might be due to reduced metabolic energy requirement. Protein synthesis is decreased probably due to effect on ribosome distribution at endoplasmic reticulum. Aluminum is known to bind to DNA and nuclei. However, its penetrance to DNA of mitotically active centers is slow. On accumulating in roots, it initially inhibits mitotic activity, possibly through affecting the integrated control function of the root meristem. Aluminum toxicity in acid soil is of special importance due to the destruction of components of forest ecosystems under specific conditions. It reduces biomass yield and tree growth and represses litter-degrading microflora. Further information is required on the factors affecting membrane permeability, distribution and accumulation of Al in different plant parts and different species. Al tolerance may be studied with relation to the presence of different ligands, nitrogen metabolism (nitrate reductase and protein accumulation), nitrogen tolerance in relation to pH change and metal ion activities, the role of Ca and P and interference with water relations and litter degradation.

Physiology of pollen

Abstract: Storage Introduction ........................................................................................................................................................ 326 Effect of Humidity and Temperature ................................................................................. 327 Influence of Gases and Pressure ............................................................................................. 331 Effects of Diluents .................................................................................................................................... 331 Bursting of Pollen as a Test of Viability ........................................................................ 332 Erratic Germination of Stored Pollen ................................................................................. 333 Nutritional Requirements of Stored Pollen and Causes of Loss of Viability .............................................................................................................................. 334 Correlation Between Viability of Pollen and Fruit Set ................................... 335 Longevity of Pollen and Taxonomic Relationship ................................................ 337

Photon flux density and light quality induce changes in growth, stomatal development, photosynthesis and transpiration of Withania Somnifera (L.) Dunal. plantlets

Abstract: The aim of the study was to establish whether the quantity and the quality of light affect growth and development of Withania somnifera plantlets. We have studied growth and histo-physiological parameters [stomatal characteristics, chloroplastic pigments concentrations, photosynthesis, and transpiration (E)] of W. somnifera plantlets regenerated under various light intensities, or monochromatic light or under a mixture of two colors of light in tissue culture conditions. Plantlets grown under a photon flux density (PFD) of 30 μmol m-2 s-1 showed greater growth and development than those raised under other PFDs. Chlorophylls and carotenoids, numbers of stomata, rate of photosynthesis (PN) and transpiration (E), stomatal conductance (gs), and water use efficiency (WUE) increased with increasing the PFD up to 60 μmol m-2 s-1. Light quality also affected plantlets growth and physiology. Highest growth was observed under fluorescent and in a mixture of blue and red light. Very few stomata were developed in any of the monochromatic light but under fluorescent or under a mixture of two colors stomatal numbers increased. Similarly, gs, E, PN, and WUE were also higher under fluorescent light and under a mixture of red and blue light. Regressional analysis showed a linear relationship between PN (r2 = 70) and gs and between E (r2 = 0.95) and gs. In conclusion, both the quality and the quantity of light affect growth of plantlets, development of stomata and physiological responses differently depending on the intensity and the wavelength of light.

Changes in the composition of phenolic compounds and antioxidant properties of grapevine roots and leaves (Vitis vinifera L.) under continuous of long-term drought stress

Abstract: Grapevine seedlings Vitis vinifera L. were grown in a greenhouse under optimum conditions (soil moisture ca 70 %) and under drought stress (soil moisture ca 30 %). Drought stress caused reduction in total phenolic compounds in grapevine leaves and roots, where were identified tree phenolic acids: caffeic acid, p-coumaric acid and ferulic acid. All acids found in leaves and roots occurred in the ester-bound form. Only caffeic acid in leaves appeared in the free and ester-bound form. Caffeic acid was present in the highest concentrations. The content of ferulic acid was the lowest in both tissues. The levels of all phenolic acids in leaves and roots decreased significantly under the drought stress. All the extracts from grapevine leaves and roots had antioxidative properties, but the antiradical activity of the extracts obtained from roots subjected to drought stress was lower to the control. The results of the analysis revealed that long-term drought stress caused a decrease in selected elements of secondary metabolism in such a different plant tissues that are the leaves and roots of the grapevine.

Cell wall-bound invertase limits sucrose export and is involved in symptom development and inhibition of photosynthesis during compatible interaction between tomato and Xanthomonas campestris pv vesicatoria

Abstract: Cell wall-bound invertase (cw-Inv) plays an important role in carbohydrate partitioning and regulation of sink-source interaction. There is increasing evidence that pathogens interfere with sink-source interaction, and induction of cw-Inv activity has frequently been shown in response to pathogen infection. To investigate the role of cw-Inv, transgenic tomato (Solanum lycopersicum) plants silenced for the major leaf cw-Inv isoforms were generated and analyzed during normal growth and during the compatible interaction with Xanthomonas campestris pv vesicatoria. Under normal growth conditions, activities of sucrolytic enzymes as well as photosynthesis and respiration were unaltered in the transgenic plants compared with wild-type plants. However, starch levels of source leaves were strongly reduced, which was most likely caused by an enhanced sucrose exudation rate. Following X. campestris pv vesicatoria infection, cw-Inv-silenced plants showed an increased sucrose to hexose ratio in the apoplast of leaves. Symptom development, inhibition of photosynthesis, and expression of photosynthetic genes were clearly delayed in transgenic plants compared with wild-type plants. In addition, induction of senescence-associated and pathogenesis-related genes observed in infected wild-type plants was abolished in cw-Inv-silenced tomato lines. These changes were not associated with decreased bacterial growth. In conclusion, cw-Inv restricts carbon export from source leaves and regulates the sucrose to hexose ratio in the apoplast. Furthermore, an increased apoplastic hexose to sucrose ratio can be linked to inhibition of photosynthesis and induction of pathogenesis-related gene expression but does not significantly influence bacterial growth. Indirectly, bacteria may benefit from low invertase activity, since the longevity of host cells is raised and basal defense might be dampened.