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Results for “Plant Physiological Phenomena”

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At least 19 recordsLinked to original sources
PubMed1982

Semiconductor properties of natural melanins.

Basic semiconductor characteristics of natural melanins isolated from bovine eye, human dark hair, and banana peel were obtained by means of the dc dark conductivity experiments and optical absorption measurements. The results were compared with results obtained for synthetic melanin. Specific conductivity in natural melanins is of the order 10(-11) omega -1 cm-1 and in synthetic melanin 10(-8) omega -1 cm-1. Thermal activation energies in the range 298-333 degrees K are eye melanin, 0.93 eV; hair melanin, 1.01 eV; banana melanin, 1.04 eV; whereas synthetic melanin has two values of activation energy: up to 311 degrees K, 0.1 eV; above 313 degrees K, 0.78 eV. Optical gaps are: in eye melanin, 1.73 eV; in hair melanin, 1.35 eV; in banana melanin, 1.55 eV; and in synthetic melanin, 1.40 eV. The observed differences between natural melanins and the synthetic one could be explained by either the presence of protein residues in natural melanins or the influence of the isolation method on their electrical properties.

Animals↗
PubMed2005

From semi-conductors to the rhythms of sensitive plants: the research of J.C. Bose.

J.C. Bose (1858-1937) was one of the world's first biophysicists. He was the first person to use a semi conducting crystal to detect radio waves, and the ingenious inventor of a portable apparatus for generating and detecting microwaves (approximately 1 cm to 5 mm radio waves, frequency 12-60 GHz), as well as inventing many instruments now routinely used in microwave technology. Bose extended his specialist knowledge of the physics of electromagnetic radiation into insightful experiments on the life-processes of plants. He became a controversial figure in the west. He invented unique, delicate instruments for simultaneously measuring bioelectric potentials and for quantifying very small movements in plants. He worked with touch-sensitive plants, including Mimosa pudica, with plants that perform spontaneous movements, including the Indian telegraph plant Desmodium, and with plants and trees that did not make obvious rapid movements. Bose concluded that plants and animals have essentially the same fundamental physiological mechanisms. All plants co-ordinate their movements and responses to the environment through electrical signalling. All plants are sensitive explorers of their world, responding to it through a fundamental, pulsatile, motif involving coupled oscillations in electric potential, turgor pressure, contractility, and growth. His overall conclusion that plants have an electromechanical pulse, a nervous system, a form of intelligence, and are capable of remembering and learning, was not well received in its time. A hundred years later, concepts of plant intelligence, learning, and long-distance electrical signalling in plants have entered the mainstream literature.

Biomechanical Phenomena↗
PubMed2001

Allelopathic bacteria and their impact on higher plants.

The impact of allelopathic, nonpathogenic bacteria on plant growth in natural and agricultural ecosystems is discussed. In some natural ecosystems, evidence supports the view that in the vicinity of some allelopathically active perennials (e.g., Adenostoma fasciculatum, California), in addition to allelochemicals leached from the shrub's canopy, accumulation of phytotoxic bacteria or other allelopathic microorganisms amplify retardation of annuals. In agricultural ecosystems allelopathic bacteria may evolve in areas where a single crop is grown successively, and the resulting yield decline cannot be restored by application of minerals. Transfer of soils from areas where crop suppression had been recorded into an unaffected area induced crop retardation without readily apparent symptoms of plant disease. Susceptibility of higher plants to deleterious rhizobacteria is often manifested in sandy or so-called skeletal soils. Evaluation of phytotoxic activity under controlled conditions, as well as ways to apply allelopathic bacteria in the field, is approached. The allelopathic effect may occur directly through the release of allelochemicals by a bacterium that affects susceptible plant(s) or indirectly through the suppression of an essential symbiont. The process is affected by nutritional and other environmental conditions, some may control bacterial density and the rate of production of allelochemicals. Allelopathic nonpathogenic bacteria include a wide range of genera and secrete a diverse group of plant growth-mediating allelochemicals. Although a limited number of plant growth-promoting bacterial allelochemicals have been identified, a considerable number of highly diversified growth-inhibiting allelochemicals have been isolated and characterized. Some species may produce more than one allelochemical; for example, three different phyotoxins, geldanamycin, nigericin, and hydanthocidin, were isolated from Streptomyces hygroscopicus. Efforts to introduce naturally produced allelochemicals as plant growth-regulating agents in agriculture have yielded two commercial herbicides, phosphinothricin, a product of Streptomyces viridochromogenes, and bialaphos from S. hygroscopicus. Many species of allelopathic bacteria that affect growth of higher plants are not plant specific, but some do exhibit specificity; for example, dicotyledonous plants were more susceptible to Pseudomonas putida than were monocotyledons. Differential susceptibility of higher plants to allelopathic bacteria was noted also in much lower taxonomical categories, at the subspecies level, in different cultivars of wheat, or of lettuce. Therefore, when test plants are employed to evaluate bacterial allelopathy, final evaluation must include those species that are assumed to be suppressed in nature. The release of allelochemicals from plant residues in plots of 'continuous crop cultivation' or from allelopathic living plants may induce the development of specific allelopathic bacteria. Both the rate by which a bacterium gains from its allelopathic activity through utilizing plant excretions, and the reasons for the developing of allelopathic bacteria in such habitats, are important goals for further research.

Bacterial Physiological Phenomena↗
PubMed2000

[Review on research of plant nutrient use efficiency].

The concept of nutrient use efficiency is the central to the understanding of ecosystem function. We reviewed the concept of nutrient use efficiency and resorption, its expression and calculation, affecting factors and biochemical basis, we also analyzed the current problems in the studies of nutrient use efficiency, and pointed out the directions for future research work of this field.

Absorption↗