Evidence for the acid-growth theory of fusicoccin action

Three predictions of the acid-growth theory of fusicoccin (FC) action in inducing cell elongation were reinvestigated using abraded segments of maize (Zea mays L.) coleoptiles. i) Quantitative comparison of segment elongation and medium-acidification kinetics measured in the same sample of tissue shows that these FC-induced processes are strictly correlated in time and respond coordinately to cations present in the medium. ii) Fusicoccin (1 mol l^-1) induces a rapid acidification of the cell-wall solution, reaching a final level of pH 3.8–4.0. Exogenous protons are able to substitute quantitatively for FC in causing segment elongation at pH 3.8–4.0. At pH 4, FC has no additional effect on cell elongation. iii) Neutral buffers (pH 7) completely abolish the FC-mediated growth response. iv) Cycloheximide (10 mg l^-1) inhibits both FC-induced and acid-buffer(pH 4)-induced elongation after a lag of 40–45 min, and FC-induced H⁺ excretion after a lag of 2 h. Under the same conditions, indole-3-acetic acid-induced elongation and H⁺ excretion are inhibited without detectable lag. It is concluded that these results are fully compatible with the acid-growth theory of FC action.Abbreviations IAA indole-3-acetic acid - CHI cycloheximide - FC fusicoccin     

The growth-promoting action of Iron upon Acanthamoeba

Summary The growth-promoting effect of iron salts upon Acanthamoeba sp. Neff. was analyzed and it was found that this action persists after ultrafiltration and thus does not depend upon phagocytosis of particulate material, as has been suggested. Neither is the ultrafiltrable growth-promoting factor in proteose peptone of particulate nature but should have a gel structure. The mitogenetic action of iron was different for amoebae cultivated in neopeptone and proteose peptone, respectively. In neopeptone mainly the duration of growth is prolonged, while in proteose peptone only the rate of growth is increased. The growth-promoting actions of iron and phytohemoagglutinin are compared and found to he different. The iron may interfere with the ultrastructure of the nuclear membrane.Valuable technical assistance was given by Miss Brita Nilsson.     

Mechanisms of fusicoccin action: A dominant role for secondary transport in a higher-plant cell

Fusicoccin (FC) is commonly thought to promote electrogenic H⁺ extrusion through its action on the H⁺-ATPase of the plant plasma membrane. Nonetheless, essential support from rigorous electrophysiological analysis has remained largely absent. The present investigation surveys the effects of FC on the charge transport properties at the membrane of a higher-plant cell — stomatal guard cells of Vicia faba L. — for which the electrical geometry is defined, and from which the voltage-dependent kinetic characteristic for the pump has been identified. Current-voltage (I-V) relations of the guard cells were determined before and during treatments with FC, and during brief exposures to NaCN plus salicylhydroxamic acid. Responses of the pump and of the ensemble of secondary transport processes were identified in the whole-membrane conductance-voltage relations and in the difference-current-voltage (dI-V) characteristic for the pump. In 0.1 mM K⁺, exposure to 10 M FC shifted guard-cell potentials negative by 29–61 mV. Current-and conductance-voltage profiles indicated limited changes in the pump I-V characteristic, an observation which was confirmed through explicit kinetic analysis of pump dI-V relations. However, the voltage response was accompanied by a 1.5-to 2.6-fold fall in membrane conductance. These results challenge conventional views of fusicoccin action by ascribing the electrical responses to reduced current passage through secondary transport pathways as well as to enhanced electrogenic ion pumping.Abbreviations and symbols Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - SHAM salicylhydroxamic acid - FC fusicoccin - V _m free-running membrane potential - G _m membrane slope conductance at V _m - (d)I-V (difference) current-voltage (relation) - G-V slope conductance-voltage (relation)     

Induction of elongation in maize coleoptiles by hexachloroiridate and its interrelation with auxin and fusicoccin action

The demonstration of an auxin-stimulated NADH-oxidase in the plasma membrane (Brightman et al. 1988. Plant Physiol. 86: 1264–1269) has led to the suggestion that the plasma membrane redox system is involved in the mechanism of auxin action. To evaluate the relevance of this concept in vivo, the influence of micromolar concentrations of hexachloroiridate (IV), an impermeable electron acceptor for the plant plasma membrane redox system, on elongation growth of excised, abraded maize coleoptile ( Zea mays L. cv. Golden Bantam) segments was studied. It was found that the substance induced a rapid growth response if the experiment was carried out in an unbuffered solution. This effect was entirely prevented by a 2 m M phosphate buffer. Nevertheless, the acid-growth-theory does not seem sufficient to explain this effect, since proton extrusion is induced without a lag, whereas increased growth rates commence after a lag phase of 40 min.
If growth is stimulated by a pretreatment with fusicoccin or auxin, hexachloroiridate IV transiently inhibits growth. The kinetics of the response are then determined by the concentrations of hexachloroiridate and auxin or fusicoccin. These results are compatible with the view that the plasma membrane redox system is somehow involved in the control of elongation growth.     

植物根际促生菌促生特性研究进展

根际微生物组是决定农作物健康状况的关键因素之一,也是调节农作物与生物和非生物环境相互作用的重要因素。植物根际促生菌(plant growth-promoting rhizobacteria, PGPR)为农作物宿主提供了多种有益作用,通过化学交流以复杂的方式与农作物、土壤相互作用,进而促进农作物生长。本文综述了PGPR对农作物的促生机制、PGPR与农作物的互作及其在农业实践中的应用,并展望了PGPR在农业实践中应用的发展趋势,以期为今后PGPR的应用和研究提供新的思路和理论支撑。     

Change in the activity of lectins in cell structure of winter wheat crown under the action of low-temperature hardening and fusicoccin

Haemagglutinating activity was determined in cell walls and total cell organelles of crown cells of Winter wheat (Triticum aestivum L. ) plants. The effect of fusicoccin (FC) was investigated using fractions obtained from plants hardened for 7 days at 2 degrees C and from untreated plants. FC concentration (5x10(-7) m) increased the frost resistance of the plants. The temporal pattern of lectin activity during hardening could be described by a single-peak curve. In the cell wall fraction, the highest activity manifested itself after one-day hardening, and in the fraction of organelles it peaked after five-days hardening. The carbohydrate specificity of lectins also changed during hardening; cell wall lectins completely lost their capacity for interaction with uridine diphosphoglucose, glucose 6-phosphate, D-galactosamine, and N-acetylglucosamine and the lectins of organelles retained some affinity only for amino sugars. After hardening the test plants, the activity of the lectins increased substantially in the cell walls and plastids, decreased in the nuclei, and was practically flat in mitochondria and microsomes. Consequently, low temperature and FC with their antistress effect improved frost resistance and stimulated the activity of the lectins of some cell structures of the tillering node of winter wheat. A similar action of low temperature and FC in increasing the activity of lectins of plastids was found. Further information was obtained on the subcellular localization of lectins providing additional information on their possible participation in the development of frost resistance of winter wheat.     

Correlation of cotylenol with the aglycone of fusicoccin

The stereostructure of cotylenol, the aglycone of the cotylenins, has been confirmed by chemical correlation with the aglycone of fusicoccin A.     

Mechanism of melatonin action

Melatonin transduces the effect of photoperiod on the neuroendocrine system. Synthesis of melatonin in the pineal gland is well described, but the location of its target(s) and the mechanism of its action are little known. In attempt to localize melatonin target(s), the presence of high affinity binding sites in rat brain was determined. Such sites were detected in discrete brain areas, including the hypothalamus and anterior pituitary. Subcellular analysis indicated these binding sites were on plasma membranes, which suggests that melatonin modulates cell functions through intracellular second messengers. The effects of melatonin on second messengers were studied using the neonatal anterior pituitary, in which melatonin is known to inhibit the LHRH-induced release of LH. Studies on the effects of melatonin on second messenger indicated [corrected] that melatonin inhibits accumulation of cAMP and cGMP as well as synthesis of diacylglycerol and release of arachidonic acid. Time-course analysis indicates that inhibition by melatonin of the LHRH-induced release of LH increases following long preincubation. Since the effect of melatonin on LHRH-induced release of LH is prevented by dibutyryl cAMP, we conclude that melatonin might act by inhibiting production of cAMP.     

Mechanism of prolactin action

Most experimental information regarding the mechanism of action of prolactin in its diverse array of target tissues has been discovered using mammary tissues. Evidence has recently been presented that suggests that prolactin may be "internalized" into its target cells and have intracellular actions. Accordingly, it has been reported that prolactin stimulates RNA synthesis in isolated nuclei from mammary tissues; and by immunoflorescent studies, prolactin has been located within its target cells. It has been further suggested from additional experimental studies that the primary action of prolactin may involve its initial interaction with fixed plasma membrane receptor sites. Subsequent actions of prolactin may involve the following: a) an increased intracellular concentration of potassium and a reduced level of sodium, b) an increased level of cGMP and a reduced level of cAMP, c) an enhanced rate of prostaglandin biosyntheesis mediated by a stimulation of phospholipase A2 activity, and d) a stimulation of polyamine synthesis. It has also been shown that the actions of prolactin require calcium ions in the extracellular environment. Laboratory studies have thus indicated that the actions of prolactin may be carried out by a number of processes; but a single, primary action of this hormone that accounts for all of its actions has not yet been proven.     

Studies of the mechanism of action of fusicoccin,the fungal toxin that induces wilting,and its interaction with abscisic acid

Summary Effects of fusicoccin alone and together with abscisic acid were observed on the stomatal complex of Commelina communis. The experimental material consisted of isolated epidermal strips incubated in a medium containing the ions required for stomatal opening. Fusicoccin stimulated opening and this was accompanied by potassium entry into the guard cells, and hydrolysis of the starch in their chloroplasts. Abscisic acid alone inhibited potassium entry and starch hydrolysis, but these effects could be almost entirely overcome by fusicoccin.Attempts were made to measure the solute potential of the guard cells under the various treatments. Abscisic acid clearly increased their solute potential, but no absolute measurements could be made in the presence of fusicoccin owing to a failure of plasmolysis even with mannitol solutions of solute potential as low as —35 bars. Experiments using isotopically labelled mannitol indicated a massive uptake into the epidermis in the presence of fusicoccin.The mechanism of stimulation of stomatal opening by fusicoccin probably depends in part on a stimulation of the normal processes associated with opening in the guard cells, but may also involve release of pressure due to destruction of the surrounding cells. The effectiveness of this toxin under natural conditions may depend on its ability to counteract effects of abscisic acid, the stress hormone that induces stomatal closure.