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PubMedDate not supplied

[Hormonal balance of wheat infected with Helminthosporium sativum].

Using immunoenzyme assay, we studied the levels of phytohormones in resistant and susceptible varieties of wheat infected with Helminthosporium sativum. The infection of wheat with this pathogen leads to an increase in cytokinins in plants of the resistant variety in the presence of stable IAA/ABA ratio. The level of ABA increases in the infected plants of the susceptible variety. The role of hormones in the mechanisms of plant resistance to fungal infections is discussed.

Abscisic Acid↗
PubMed1983

Inhibiting action of fusicoccin on the ethylene production of Pisum sativum.

The ability of several auxins to induce C2H4 production was examined. There is an ability scale among the various products in which IAA is the more efficient compound while 2,4-D seems to be the less efficient one. As well as other general phenomena, e.g. enlargement or weight increase, even in this case a biphasic action seems to exist, with an activation at the lower concentrations and an inhibition at the higher ones. The dose corresponding to the critical point, in which one can observe the inversion of the response, seems to be common to all the substances and to be 1 X 10(-4)M. Subsequently we verified the FC influence on the C2H4 production in the presence of the optimal dose of different auxins. The inhibiting action exerted by the toxine is a function of the concentration and does not depend on the inducing substance. The FC determines a drastic reduction in C2H4 production, nearly 60%, for the entire range of the concentrations studied. The described data give evidence of a strong FC interference on ethilene production of etiolated pea internodes.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1993

Selective antagonism of native and cloned kainate and NMDA receptors by polyamine-containing toxins.

Antagonism of rat excitatory amino acid receptors by a synthetic analog [philanthotoxin-343 (PhTX-343)] of a polyamine amide, wasp toxin (philanthotoxin-433) and a structurally related spider toxin, argiotoxin-636 (ArgTX-636), was examined in Xenopus oocytes injected with rat brain RNA or RNA transcribed from the excitatory amino acid receptor clones GluR1, GluR2 and NMDAR1. Antagonism of both kainate- and N-methyl-D-aspartate (NMDA)-elicited responses by PhTX-343 and ArgTX-636 was reversible, noncompetitive and partly voltage-dependent. Dose-inhibition curves were constructed using EC50 concentrations of kainate (100 microM) and N-methyl-D-aspartate (33 microM) in the presence of variable concentrations of ArgTX-636 and PhTX-343. In oocytes injected with rat brain RNA, IC50s for antagonism of kainate-induced currents were similar, i.e., 0.07 microM and 0.12 microM for ArgTX-636 and PhTX-343, respectively, whereas IC50s for antagonism of NMDA-induced currents were dissimilar, i.e., 0.04 microM for ArgTX-636 and 2.5 microM for PhTX-343. In oocytes expressing NMDAR1, IC50s were similar to those for the antagonism of NMDA-induced currents of oocytes injected with rat brain RNA. PhTX-343 and ArgTX-636 were more or less equally potent (IC50s were 2.8 microM and 3.4 microM, respectively) antagonists of the response of GluR1 to 100 microM kainate. However, GluR1 was approximately 50 times less sensitive to the toxins than non-N-methyl-D-aspartate receptors expressed in oocytes injected with rat brain RNA. Receptors co-expressed from GluR1 + GluR2 were virtually insensitive to PhTX-343 (IC50 = 270 microM) and to ArgTX-343 (IC50 approximately 300 microM).

Animals↗
PubMed1997

Differential dependence on GluR2 expression of three characteristic features of AMPA receptors.

The GluR2 subunit controls three key features of ion flux through the AMPA subtype of glutamate receptors-calcium permeability, inward rectification, and channel block by external polyamines, but whether each of these features is equally sensitive to GluR2 abundance is unknown. The relations among these properties were compared in native AMPA receptors expressed by acutely isolated hippocampal interneurons and in recombinant receptors expressed by Xenopus oocytes. The shape of current-voltage (I-V) relations between -100 and +50 mV for either recombinant or native AMPA receptors was well described by a Woodhull block model in which the affinity for internal polyamine varied over a 1000-fold range in different cells. In oocytes injected with mixtures of GluR2:non-GluR2 mRNA, the relative abundance of GluR2 required to reduce the log of internal blocker affinity by 50% was two- to fourfold higher than that needed to half-maximally reduce divalent permeability or channel block by external polyamines. Likewise, in interneurons the affinity of externally applied argiotoxin for its blocking site was a steep function of internal blocker affinity. These results indicate that the number of GluR2 subunits in AMPA receptors is variable in both oocytes and interneurons. More GluR2 subunits in an AMPA receptor are required to maximally reduce internal blocker affinity than to abolish calcium permeability or external polyamine channel block. Accordingly, single-cell RT-PCR showed that approximately one-half of the physiologically characterized interneurons exhibiting inwardly rectifying AMPA receptors expressed detectable levels of edited GluR2. The physiological effects of a moderate change in GluR2 relative abundance, such as occurs after ischemia or seizures or after chronic exposure to morphine, thus will be dependent on the ambient GluR2 level in a cell-specific manner.

Animals↗