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PubMedDate not supplied

Influence of temperature on phytohormone interactions with monolayers obtained from phospholipids of wheat calli.

The effect of temperatures (15 and 5 degrees C) on adsorption parameters of phytohormones at monolayers prepared from a mixture of phospholipids extracted from non-embryogenic (NE) and embryogenic (E) winter wheat calli initiated from inflorescences (inf) and embryos (emb) was studied. The surface parameter values, i.e. limiting area and collapse pressure, were determined using the Langmuir method. Phytohormones 2,4-dichlorophenoxyacetic acid (2,4-D), indole-3-acetic acid (IAA), kinetin, zeatin and zearalenone were investigated. The phytohormones, at a concentration of 0.2 microg/ml dissolved in water, were injected into the subphase. Phospholipids, at the concentration of 2 mg/ml, were spread at the water surface and the monolayer was compressed. The anomalous temperature effect was observed, especially, in non-embryogenic systems. In monolayers obtained from E phospholipids, the temperature effect was dependent on the kind of tissue from which the callus was initiated. Among all the examined phytohormones, the greatest changes (monolayer expansion) were found for IAA and zearalenone. However, this activity depended strongly on the kind of tissue from which the phospholipid mixture was extracted.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2000

Enhancement of polygalacturonase activity during auxin induced para nodulation and endorhizosphere colonization of Azospirillum in rice roots.

Effect of different auxins, namely, 2,4-dichlorophenoxyacetic acid (2,4-D), naphthalene acetic acid (NAA) and indole acetic acid (IAA) and Azospirillum brasilense bioinoculation on the enhancement of polygalacturonase (PG) activity in rice roots during para nodulation and endorhizosphere colonization of Azospirillum was studied under in vitro condition. It was observed that Azospirillum bioinoculation could augment PG activity of rice roots to a lesser extent without any root morphogenesis whereas auxin application together with Azospirillum bioinoculation enhanced PG activity of rice roots to a higher level which resulted in better root morphogenesis (para nodule) and endorhizosphere colonisation of A. brasilense. Among the three auxins tested, 2,4-D, even at lower concentration (0.5 ppm) enhanced the rice root PG activity, root morphogenesis and endorhizosphere colonization of Azospirillum while it was 2.0 ppm with NAA and variable with IAA. It is concluded that there is a positive correlation existing among PG activity, degree of root morphogenesis and endorhizosphere colonization of Azospirillum brasilense in rice roots and the degree of correlation is determined by the chemical composition, concentration and mode of action of the auxin utilised.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1990

Calcium and plant hormone action.

Plant cells contain all the elements for a calcium-based messenger system that could couple the external stimuli of hormones to their physiological response. These include a highly regulated low cytoplasmic calcium level, plasma membrane and endomembrane calcium pumps and channels, and spatially controlled calcium-dependent regulatory proteins and kinases. However much of the evidence for calcium as a second messenger in plants is fragmentary and circumstantial. There is some evidence linking auxin to fluctuations in free calcium but most of the evidence points to auxin as a calcium antagonist or having little or no effect on calcium levels. The possibility that polar auxin transport is coupled to calcium transport in the opposite direction is strong. There are several recent reports that abscisic acid is a calcium agonists but the data are still preliminary and there are alternative reports that indicate that abscisic acid may actually lower calmodulin levels. There is a close link between gibberellic acid and increases in intracellular free calcium in the barley aleurone system. These studies need to be extended to other gibberellin-dependent physiological responses. The most convincing evidence that has accumulated correlates cytokinin-stimulation of several different responses with increases in intracellular calcium by activation of plasma membrane ion channels. There is also a need to recognize that we don't understand stimulus-response coupling yet in the simplest of plant systems and the higher plants present a daunting challenge to plant scientists. It is unlikely that all hormone effects on all plants will be explained by invoking calcium as a second messenger and we must recognize that the mechanism of action of plant hormones may be quite complex and diverse.

Abscisic Acid↗
PubMed1990

Phytohormones as specific inhibitors of Legionella pneumophila growth.

Legionellae have been found to be highly susceptible to a variety of biological products, which increases the difficulty of growing these microorganisms. We developed a hypotonic medium in which Legionella pneumophila and other legionellae grow well and multiply rapidly from small inocula. Several amino acids, mainly nonessential ones, inhibited the growth of legionellae at high concentrations (200-1,000 micrograms/ml). We describe a unique biological phenomenon of specific inhibition of growth of L. pneumophila by the plant growth hormone auxin (indole-3-acetic acid) and the closely related indole-3-propionic acid (IPA). The inhibition of growth was probably due to interference with the biosynthesis of L-tryptophan by the phytohormone or IPA. Other bacteria were found to be 50 to 100-fold more resistant to these agents. These findings may explain the peculiar ecology of legionellae. Bacterial susceptibility towards IPA (less than or equal to 5 micrograms/ml) may serve as a specific marker for the presence of legionellae.

Amino Acids↗
PubMed1990

Induction and superinduction of auxin-responsive mRNAs with auxin and protein synthesis inhibitors.

We have identified a class of small mRNAs (approximately 0.5 kilobases), referred to as small auxin-up RNAs (SAURs), that increases in abundance within minutes after auxin application to excised elongating hypocotyl sections of soybean. In this study, we present evidence that SAURs accumulate in the absence of auxin when protein synthesis is inhibited. Superinduction of SAURs occurs if the synthetic auxin 2,4-dichlorophenoxyacetic acid is added under conditions where protein synthesis is inhibited. Transcription run-on experiments with isolated nuclei show that, unlike 2,4-dichlorophenoxyacetic acid, protein synthesis inhibitors do not activate transcription of the SAUR genes. These results suggest that protein synthesis inhibitors act by stabilizing SAURs and that some labile protein(s) are involved in the rapid turnover of SAURs. This stabilization is not observed with GH3, another auxin-inducible mRNA. Whether induced with 2,4-dichlorophenoxyacetic acid or cycloheximide, SAURs are primarily expressed in epidermal and cortical cells of elongating hypocotyl sections, with little or no expression in vascular tissue. Unlike 2,4-dichlorophenoxyacetic acid-induced SAUR accumulation, the increase in abundance of SAURs induced by cycloheximide is transient, with a peak approximately 1 h after inhibitor addition. Complete inhibition of protein synthesis is not required for SAUR accumulation in the presence of protein synthesis inhibitors.

2,4-Dichlorophenoxyacetic Acid↗