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Results for “Plant Physiological Phenomena”

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At least 19 recordsLinked to original sources
PubMedDate not supplied

Progress in space biology.

Over the past two decades there has arisen a new branch of biology--space biology. This short review is devoted to a discussion of its achievements. It considers the results of research in the area of gravitation biology, and an account is made of studies in those areas of radiobiology which have relevance to the study of the cosmos. There is a brief summary of the results of the search for the upper and lower limits of the biosphere, and information is presented regarding the measures employed to maintain planetary quarantine. A great deal of attention has been given to the search for extraterrestrial life, one of the most important of problems. The results obtained with the aid of the American Viking probes on Mars are given special attention. The review presents experimental data based both upon data obtained in experiments on biological specimens during space flights of satellites and space vehicles, and also upon the results of laboratory research.

Air Microbiology↗
PubMed1978

Toward the engineering of photosynthetic productivity.

This article is a review of progress towards a general quantitative theory of photosynthetic productivity or autotrophy in plants. It is not intended to be an exhaustive review, but rather a perspective of the autotrophic puzzle and current approaches to its solution. The review describes attempts to quantitatively describe a generalized plant based on theoretical expressions for its component parts. Particular emphasis has been placed on the source-transport-sink continuum. This continuum can be broken into five subsections: 1. Stomal mechanics and physiology 2. Photosynthesis (within chlorophyllous cells) 3. Mass and energy exchange between the leaf and environment 4. Phloem translocation 5. Sink metabolism models Progress towards the development of physiologically based models in each of the above areas is assessed, relying heavily on the approach and findings of the authors and their colleagues. The problems and possibilities inherent in attempting to couple these components into a generic model of productivity are discussed. Finally, the potential benefits and hazards of genetic engineering of plants are discussed, and weaknesses in the current approach are highlighted.

Biophysical Phenomena↗
PubMed1979

Pollen-pistil incompatibility in Petunia hybrida: changes in the pistil following compatible and incompatible intraspecific crosses.

The structural events in the stigma and transmitting tissue of Petunia hybrida pistils that accompany compatible and incompatible intraspecific pollinations have been investigated in detail, together with the changes in reserve levels that also take place at this time. Many of these phenomena may be explained in terms of 3 phases of secretion by the cells in the upper regions of the transmitting tissue. The first, independent of pollination, results in the deposition of an intercellular matrix, rich in protein and carbohydrate. The second, triggered by pollination, although independent of the compatibility of the pollen grain, involves synthesis of molecules believed to be specific to the S(incompatibility)-gene system. The third phase of secretion occurs only following a compatible mating, and involves the transfer of stylar reserves to support the growth of the pollen tubes. These observations are discussed in terms of current models of the incompatibility mechanism operating in Petunia.

Crosses, Genetic↗
PubMedDate not supplied

Metabolic factors and the utilization of phosphorus by plants.

The overall process of entry and transport of phosphate by plants has been separated into its component parts. Rapid esterification is involved but a small proportion of the total transport may occur by a non-metabolic route. Mannose alters the metabolism of phosphate in roots of cereals and thereby reduces the transport to the shoot by as much as 99% whereas dicotyledonous species are much less sensitive. The sequestration of phosphate as mannose 6-phosphate is reversible in some species depending on the extent of its conversion into fructose 6-phosphate and it is possible that in vivo controls of this type operate in whole plants. The factors involved in the control of distribution of inorganic phosphate between cellular organelles and throughout the plant are discussed. Enzymic hydrolysis of organic forms by roots and associated microorganisms may also be important in soils where available orthophosphate is limiting. Other inorganic nutrients, particularly boron, play an important role during the transport of phosphate across membranes. Major differences have been found in the capacities of different species to transport absorbed phosphate to the shoot. Peas and field beans absorb efficiently in the early weeks of growth but the rate of transport is about one thirtieth that of oats, barley, mung bean or sunflower. The relevance of the experimental findings to the wider problem of efficiency of fertilizer use and the possible selection of genotypes with high capacities for absorption and transport are discussed.

Absorption↗
PubMedDate not supplied

Physiological basis of salt tolerance in plants.

For most plants, and under most field conditions, osmotic effects of salinity greatly predominate in restricting growth and yields. In certain cases, however, specific ion effects may be decisive. These may involve either nutrition, as in calcium deficiency in some lettuce varieties, tomato, and bell peppers, or direct toxicity (chloride or sodium toxicity, or both) in tree and vine crops. Rootstocks, or varieties that restrict the uptake of toxic ions, increase the salt tolerance of some susceptible fruit crops. Salinity-induced nutritional imbalance can, in some cases, be corrected by selecting better adapted varieties and in others by the use of foliar nutrient sprays. Recent evidence indicates simple single-gene control over uptakes of chloride and sodium, but the more general osmotic effects appear to be complex and under multigenic control.

Biological Transport↗
PubMed1975

Preformed mRNA and the programming of early embryo development.

A significant feature of the early development of fertilized echinoderm and amphibian eggs and germinating seed embryos is the utilization of genetic information that has been previously transcribed during oogenesis and seed ripening. When RNA synthesis is suppressed in the early developing embryos by actinomycin D, cordycepin, or alpha-amanitin, there is no effect on the translation of the "preformed mRNA", only a limited number have been thus far identified; microtubule and histone proteins in the fertilized sea urchin egg and carboxypeptidase and isocritric lyase in germinating cottonseed. Data obtained on the protein synthetic pattern at different times after the onset of development suggest that preformed mRNAs are made available to the translational system in a gradual process, thereby providing a molecular basis for the regulation of development. The possibility is considered that polyadenylation of mRNA, a reaction known to occur early after sea urchin fertilization, is responsible for regulating the release of preformed mRNA. It is shown that this reaction (polyadenylation) can be completely suppressed with little effect on the function of preformed mRNA. Finally, it is suggested, at least for the seed embryo system, that the formation of ATP may be a prerequisite for the activation of protein synthesis.

Amanitins↗
PubMed1992

Cellulase and polygalacturonase involvement in the abscission of leaf and fruit explants of peach.

Ethylene-induced abscission in leaf and fruit explants of peach involves different enzymes. In leaves abscission is accompanied by increased occurrence of cellulase forms differing in isoelectric point (pI 6.5 and 9.5). A polypeptide with a molecular mass of 51 kDa gives in a western blot a strong cross-reaction with an antibody raised against a maturation cellulase from avocado fruit. Cellulase activity is also found in abscising fruit explants but the amount is very low compared to that of the leaf explants. A northern analysis with a cellulase clone from avocado reveals the presence of two hybridizing mRNAs with a size of 2.2 kb and 1.8 kb, respectively. The steady-state level of the 2.2 kb mRNA is significantly increased by treatment with ethylene. Polygalacturonases are not detected in abscising leaves, but are strongly induced by ethylene in fruit explants. Of the three forms found, two are exopolygalacturonases while the third is an endoenzyme. Ethylene activates preferentially the endoenzyme and the basic exoenzyme but depresses the acid exopolygalacturonases. A northern analysis carried out with a cDNA coding for tomato endopolygalacturonase shows hybridization only with one endopolygalacturonase mRNA form in the fruit abscission zone. Treatment with ethylene causes an increase in the steady-state level of this mRNA. The differences in the enzyme patterns observed in fruit and leaf abscission zones and a differential enzyme induction suggest the feasibility to regulate fruit abscission in peach with the aid of antisense RNA genes.

Blotting, Northern↗
PubMed1992

Ubiquitin genes are differentially regulated in protoplast-derived cultures of Nicotiana sylvestris and in response to various stresses.

Four ubiquitin mRNA size classes were found to be differentially regulated in mesophyll protoplast-derived cultures of Nicotiana sylvestris. Three mRNA families of 1.9, 1.6 and 1.35 kb were expressed as soon as protoplasts were isolated. The 1.9 and 1.6 kb size classes were transiently expressed during the first hours of culture, whereas the level of expression of the 1.35 kb size class was maintained as long as cells kept dividing. A 0.7 kb mRNA size class started to be expressed just before the first divisions were observed. cDNAs corresponding to each of these families were isolated from a 6-h-old protoplast cDNA library and characterized. The 1.9, 1.6 and 1.35 kb mRNAs thus encode 7- or more, 6- and 5-mers, respectively, of ubiquitin whereas the 0.7 kb mRNAs encode a monomer of ubiquitin fused to a carboxyl extension protein of 52 amino acids. The expression of ubiquitin genes was studied, using probes specific for each of these transcript families, during protoplast culture and, for comparison, after various stresses including heat shock, HgCl2 treatment, a viral infection giving rise to a hypersensitive reaction, and an Agrobacterium tumefaciens infection which resulted in tumour formation. The 1.9 and 1.6 kb mRNA size classes were found to be stress-regulated, the 0.7 kb mRNA size class developmentally regulated and the 1.35 kb size class both stress- and developmentally regulated.

Amino Acid Sequence↗