Calmodulin-binding drugs affect responses to cytokinin, auxin, and gibberellic Acid

6-Benzyladenine increasing subsequent waterlogging-induced waterlogging tolerance of summer maize by increasing hormone signal transduction

Summer maize is frequently subjected to waterlogging damage because of increased and variable rainfall during the growing season. The application of 6-benzyladenine (6-BA) can effectively mitigate the waterlogging effects on plant growth and increase the grain yield of waterlogged summer maize. However, the mechanisms underlying this process and the involvement of 6-BA in relevant signal transduction pathways remain unclear. In this study, we explored the effects of 6-BA on waterlogged summer maize using a phosphoproteomic technique to better understand the mechanism by which summer maize growth improves following waterlogging. Application of 6-BA inhibited the waterlogging-induced increase in abscisic acid (ABA) content and increased the phosphorylation levels of proteins involved in ABA signaling; accordingly, stomatal responsiveness to exogenous ABA increased. In addition, the application of 6-BA had a long-term effect on signal transduction pathways and contributed to rapid responses to subsequent stresses. Plants primed with 6-BA accumulated more ethylene and jasmonic acid in response to subsequent waterlogging; accordingly, leaf SPAD, antioxidase activity, and root traits improved by 6-BA priming. These results suggest that the effects of 6-BA on hormone signal transduction pathways are anamnestic, which enables plants to show faster or stronger defense responses to stress.

Pharmacological Strategies for Manipulating Plant Ca2+ Signalling

Calcium is one of the most pleiotropic second messengers in all living organisms. However, signalling specificity is encoded via spatio-temporally regulated signatures that act with surgical precision to elicit highly specific cellular responses. How this is brought about remains a big challenge in the plant field, in part due to a lack of specific tools to manipulate/interrogate the plant Ca2+ toolkit. In many cases, researchers resort to tools that were optimized in animal cells. However, the obviously large evolutionary distance between plants and animals implies that there is a good chance observed effects may not be specific to the intended plant target. Here, we provide an overview of pharmacological strategies that are commonly used to activate or inhibit plant Ca2+ signalling. We focus on highlighting modes of action where possible, and warn for potential pitfalls. Together, this review aims at guiding plant researchers through the Ca2+ pharmacology swamp.

Calcium-promoted protein phosphorylation in plants

Phosphorylation of several polypeptides in corn coleoptiles was promoted by adding calcium. Chlorpromazine, a calmodulin inhibitor, reduced calcium-promoted phosphorylation, suggesting that the phosphorylation was modulated by calmodulin. This is evidence for the role of calcium in protein phosphorylation in plants and could serve as an experimental approach to understanding the molecular mechanism by which calcium modulates various physiological processes in plants.

Calcium Antagonists Inhibit Sustained Gibberellic Acid-Induced Growth of Avena (Oat) Stem Segments

The elongation response of Avena sativa (oat) stem segments to gibberellic acid (GA3) is of large magnitude, with high hormonal sensitivity and specificity, but without cell division activity. This system is therefore an excellent model for mechanistic studies on higher plant cell elongation and the action of gibberellin. At millimolar concentrations, the calcium antagonists verapamil, D-600, nicardipine, diltiazem, bepridil, 8-(N,N,-diethylamino)-octyl-3,4,5-trimethoxybenzoate HCl, and lanthanum substantially inhibited the growth of GA3-treated segments but had no effect on the elongation of nonhormone-treated segments. Although verapamil reduced the maximum growth rate and caused premature cessation of growth, even preincubation of the segments with the drug prior to treatment with GA3 failed to inhibit the earliest measured stimulation of growth by the hormone. Inhibition by verapamil was not reversed by increased concentrations of GA3 or calcium. Neither the calcium ionophore A23187 nor agonist BAY K 8644 had any effect on growth. Light microscopic examination of epidermal peels from antagonist-treated internodal tissue revealed no obvious differences from the control except that the cells were not as elongated. Although these results may support a role for calcium ion movement in maintaining the GA3-induced growth of Avena stem segments, they do not support the involvement of calcium ion movement in the hormone-mediated initiation of growth.

Inhibition of phytoalexin biosynthesis in elicitor-treated tobacco cell-suspension cultures by calcium/calmodulin antagonists

A role for calcium/calcium-binding proteins in a mechanism of signaling elicitor-inducible phytoalexin biosynthesis was investigated. Two classes of calcium/calmodulin antagonists, phenothiazines and naphthalenesulfonamides, inhibited sesquiterpene phytoalexin accumulation in tobacco (Nicotiana tabacum) cell-suspension cultures when added 1 h before elicitor. The antagonists also inhibited the induction of sesquiterpene cyclase enzyme activity, a key regulatory enzyme for sesquiterpene biosynthesis. The antagonists suppressed the induction of sesquiterpene cyclase only if added before or simultaneously with elicitor. Additionally, the antagonists inhibited (a) accumulation of the cyclase protein as measured in immunoblots; (b) the in vivo synthesis rate of the cyclase protein, measured as the incorporation of [(35)S]methionine into immunoprecipitable cyclase protein; and (c) the cyclase mRNA translational activity, measured as the incorporation of [(35)S]methionine into immunoprecipitable cyclase protein synthesized by in vitro translation of RNA isolated from antagonist-treated, elicitor-induced cells. In contrast, elicitor-inducible phenylalanine ammonia lyase enzyme activity, the level of the enzyme protein, the in vivo synthesis rate, and the mRNA translational activity were not affected by any of the antagonist treatments. Uptake and incorporation of [(35)S]methionine into total cellular proteins and total in vitro translation products were also not indiscriminately altered by the antagonist treatments. The current results suggest that calcium and/or calmodulin-like proteins may be elements of a signal transduction pathway mediating elicitor-induced accumulation of phytoalexins in tobacco.

Similarity between Cytokinin and Blue Light Inhibition of Cucumber Hypocotyl Elongation

The cytokinin benzyladenine inhibited endogenous hypocotyl elongation in intact etiolated seedlings of cucumber (Cucumis sativus L.). In hypocotyl segments, the inhibitory effect of benzyladenine on growth was clearly detectable in the presence of indoleacetic acid. Fusicoccin-induced elongation was unaffected by the presence of cytokinin. The effect of cytokinin on elongation of the segments was determined by measuring changes in fresh weight, a linear function of extension growth. The effect of benzyladenine on hypocotyl growth was at least as large in segments prepared from red-light-grown seedlings as in those from seedlings grown in total darkness. A comparison was made between the inhibitory effects of cytokinin and blue light. The use of the calcium chelator ethyleneglycol-bis(beta-aminoethyl ether)-N, N'-tetraacetic acid indicated that calcium ions are required for manifestation of benzyladenine-induced inhibition.

Changes in the Levels of Calmodulin and of a Calmodulin Inhibitor in the Early Phases of Radish (Raphanus sativus L.) Seed Germination: Effects of Aba and Fusicoccin

An inhibitor of Ca(2+)-calmodulin (Cam)-dependent brain phosphodiesterase was present in the soluble fraction of embryo axes from ungerminated radish (Raphanus sativus L.) seeds. This inhibitor is a Ca(2+)-dependent, Cam-binding protein; in fact: (a) its effect was strongly reduced by treatment with proteases; (b) the inhibition was counteracted by Cam but not by Ca(2+); (c) on gel filtration in the presence of Ca(2+), Cam co-chromatographed with the inhibitor. The inhibitor is heat stable and positively charged at pH 7.5. During early phases of germination, the fresh weight and the levels of DNA and RNA of embryo axes increased, the level of the inhibitor decreased, and the level of Cam increased. Abscisic acid (ABA) inhibited germination, the decrease of inhibitor, and the increase of Cam. Fusicoccin (FC) stimulated the increase in fresh weight but not the increase in the RNA and DNA levels; in this condition, the inhibitor level decreased and the increase in Cam level was higher than in the control. In the presence of both ABA and FC, there was an increase in fresh weight not accompanied by an increase in DNA and RNA levels; Cam increased and, on a fresh weight basis, reached the value of the control. These results indicate that the Ca(2+)-Cam system was activated in early germination of radish seeds by an increase in Cam and a decrease in the inhibitor levels, that FC, probably through the activation of membrane functions, increased Cam level, and that the ABA inhibition on germination was not mediated by the Ca(2+)-Cam system.

Adenylate cyclase activity in a higher plant, alfalfa (Medicago sativa)

An adenylate cyclase activity in Medicago sativa L. (alfalfa) roots was partially characterized. The enzyme activity remains in the supernatant fluid after centrifugation at 105,000 g and shows in crude extracts an apparent Mr of about 84,000. The enzyme is active with Mg2+ and Ca2+ as bivalent cations, and is inhibited by EGTA and by chlorpromazine. Calmodulin from bovine brain or spinach leaves activates this adenylate cyclase.

Properties of Single K and Cl Channels in Asclepias tuberosa Protoplasts

Potassium and chloride channels were characterized in Asclepias tuberosa suspension cell derived protoplasts by patch voltage-clamp. Whole-cell currents and single channels in excised patches had linear instantaneous current-voltage relations, reversing at the Nernst potentials for K(+) and Cl(-), respectively. Whole cell K(+) currents activated exponentially during step depolarizations, while voltage-dependent Cl(-) channels were activated by hyperpolarizations. Single K(+) channel conductance was 40 +/- 5 pS with a mean open time of 4.5 milliseconds at 100 millivolts. Potassium channels were blocked by Cs(+) and tetraethylammonium, but were insensitive to 4-aminopyridine. Chloride channels had a single-channel conductance of 100 +/- 17 picosiemens, mean open time of 8.8 milliseconds, and were blocked by Zn(2+) and ethacrynic acid. Whole-cell Cl(-) currents were inhibited by abscisic acid, and were unaffected by indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid. Since internal and external composition can be controlled, patch-clamped protoplasts are ideal systems for studying the role of ion channels in plant physiology and development.

Effects of abscisic acid on K+ channels in Vicia faba guard cell protoplasts

Potassium channels were resolved in Vicia faba guard cell protoplasts by patch voltage-clamp. Whole-cell currents and single K+ channels had linear instantaneous current-voltage relations, reversing at the calculated Nernst potential for K+. Whole cell K+ currents activated exponentially during step depolarizations, with half-activation times of 400-450 msec at +80 mV and 90-110 msec at +150 mV. Single K+ channel conductance was 65 +/- 5 pS with a mean open time of 1.25 +/- 0.30 msec at 150 mV. Potassium channels were blocked by internal Cs+ and by external TEA+, but they were insensitive to external 4-aminopyridine. Application of 10 microM abscisic acid increased mean open time and caused long-lasting bursts of channel openings. Since internal and external composition can be controlled, patch-clamped protoplasts are ideal systems for studying the role of ion channels in plant physiology.

Membrane-directed effects of the plant hormones abscisic acid, indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid

This study examines two ways plant hormones might influence membrane processes, effects on overall permeability and modifications of specific ion channels. Abscisic acid (ABA) and indole-3-acetic acid (IAA) greatly enhanced erythritol permeability in mixed egg lecithin bilayers. In single component dioleoylphosphatidylcholine bilayers ABA was less effective than IAA, while 2,4-dichlorophenoxyacetate (2,4-D) did not affect either system or alter their ABA response. In Myxicola axons ABA and IAA had no effect, while 2,4-D (10 uM) caused a depolarizing shift of voltage-dependent Na+ and K+ activation by 25 +/- 4 mV and 15 +/- 3 mV, consistent with internal negative surface charge changes of -0.002 e-/A2 and -0.0007 e-/A2. We conclude that both generalized and ion channel-directed effects may link plant hormones and intracellular regulation.

In vitro and in vivo protein phosphorylation in Avena sativa L. coleoptiles: effects of Ca2+, calmodulin antagonists, and auxin

In vitro and in vivo protein phosphorylations in oat (Avena sativa L.) coleoptile segments were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and by two-dimensional gel electrophoresis. In vitro phosphorylation of several polypeptides was distinctly promoted at 1 to 15 micromolar free Ca2+ concentrations. Ca2(+)-stimulated phosphorylation was markedly reduced by trifluoperazine, chlorpromazine, and naphthalene sulfonamide (W7). Two polypeptides were phosphorylated both under in vitro and in vivo conditions, but the patterns of phosphorylation of several other polypeptides were different under the two conditions indicating that the in vivo phosphorylation pattern of proteins is not truly reflected by in vitro phosphorylation studies. Trifluoperazine, W7, or ethylene glycol-bis-(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) + calcium ionophore A23187 treatments resulted in reduced levels of in vivo protein phosphorylation of both control and auxin-treated coleoptile segments. Analysis by two-dimensional electrophoresis following in vivo phosphorylation revealed auxin-dependent changes of certain polypeptides. A general inhibition of phosphorylation by calmodulin antagonists suggested that both control and auxin-treated coleoptiles exhibited Ca2+, and calmodulin-dependent protein phosphorylation in vivo.

Interaction of wheat germ ca-dependent protein kinases with calmodulin antagonists and polyamines

The two soluble Ca(2+)-dependent protein kinases resolved from wheat (Triticum aestivum) embryo (protein kinases I and II) are inhibited by the phenothiazine-derived calmodulin antagonists trifluoperazine fluphenazine, and chlorpromazine. Protein kinases I and II are also inhibited by a variety of other calmodulin antagonists (including calmidazolium, amitriptyline, and iprindole), phosphodiesterase inhibitors (including flufenamic acid and papavarine) and by lanthanides. A number of compounds that inhibit mammalian Ca(2+) - and phospholipid-activated protein kinase (protein kinase C) including quercetin, polymixin B sulfate, and polyamines (as well as phenothiazine derivatives) also inhibit protein kinases I and II. Poly-l-lysine and poly-l-ornithine activate both plant Ca(2+)-dependent protein kinases.

Effect of calmodulin antagonists on auxin-induced elongation

Coleoptile segments of oat (Avena sativa var Cayuse) and corn (Zea mays L. var Patriot) were incubated in different concentrations of calmodulin antagonists in the presence and absence of alpha-naphthaleneacetic acid. The calmodulin antgonists (chlorpromazine (CP), trifluoperazine, and fluphenazine) inhibited the auxin-induced elongation at 5 to 50 micromolar concentrations. Chlorpromazine sulfoxide, an analog of chlorpromazine, did not have significant effect on the elongation of oat and corn coleoptiles. A specific inhibitor of calmodulin N-(6-aminohexyl)5-chloro-1-naphthalenesulfonamide hydrochloride (W-7, a naphthalenesulfonamide derivative) inhibited coleoptile elongation, while its inactive analog N-(6-aminohexyl)-1-naphthalenesulfonamide hydrochloride (W-5) was ineffective at similar concentrations. During a 4-hour incubation period, coleoptile segments accumulated significant quantities of (3)H-CP. About 85 to 90% of auxin-induced growth was recovered after 4 hours of preincubation with CP or 12 hours with W-7 and transferring coleoptiles to buffer containing NAA. Leakage of amino acids from coleoptiles increased with increasing concentration of CP, showing a rapid and significant increase above 20 micromolar CP. The amount of amino acids released in the presence of W-7 and W-5 was significantly lower than the amount released in the presence of CP. Both W-5 and W-7 increased amino acid release but only W-7 inhibited auxin-induced growth. Calmodulin activity measured by phosphodiesterase activation did not differ significantly between auxin-treated and control coleoptile segments. These results suggest the possible involvement of calmodulin in auxin-induced coleoptile elongation.

Evidence for Ca++-calmodulin control of transplasmalemma electron transport in carrot cells

Cultured carrot cells exhibit transmembrane ferricyanide reduction through a plasma membrane redox system, which may be associated with an iron reduction and uptake system in plant roots. Here we provide evidence for the inhibition of transplasma membrane ferricyanide reduction by four different Ca2+-calmodulin type antagonists, calmidazolium, trifluoperazine, pimozide and fluphenazine. These compounds inhibit in low concentrations (approximately 5-10 microM) in a time-dependent manner. Higher concentrations (50-100 microM) are required to inhibit transmembrane ferricyanide reduction in 10 min rather than in 30 min. The permeable calcium chelator, TMB-8, also inhibits transmembrane ferricyanide reduction in carrot cells. Since the redox system is controlled by hormones, the effects of anticalmodulin agents on hormone response may be mediated through the redox system.

Ecophysiological aspects of biomass production in higher plants

Photosynthesis as a cosmic process of local entropy decrease is the basic phenomenon for life on Earth. Biomass production is energetically understood as a long-term storage of hydrogen. Endogeneously, the hierarchy of energy storage begins with the electric and proton gradient across the thylakoid membrane. At all higher levels of energy-converting system, efficiency is determined by the interactions between the autotrophic and heterotrophic part of the studied biosystem. Specially, the regulatory function of anabolic and catabolic reduction charge is discussed. From the frame of exogeneous factors, the action of calcium in connection with calmodulin is described as a second messenger.Summarizing, the findings are integrated into the energy-overflow concept in which the loss terms act as system stabilizers especially under injuring conditions.

Calcium- and calmodulin-regulated phosphorylation of soluble and membrane proteins from corn coleoptiles

In vitro phosphorylation of several membrane polypeptides and soluble polypeptides from corn (Zea mays var. Patriot) coleoptiles was promoted by adding Ca(2+). Ca(2+)-promoted phosphorylation of the membrane polypeptides was further increased in the presence of calmodulin. Both Ca(2+)-stimulated and Ca(2+)- and calmodulin-stimulated phosphorylations of membrane polypeptides were inhibited by chlorpromazine, a calmodulin antagonist. Ca(2+)-stimulated phosphorylation of soluble polypeptides increased with increasing Ca(2+) concentration. The calmodulin antagonists chlorpromazine and trifluoperazine inhibited the Ca(2+)-promoted phosphorylation of soluble polypeptides. Added calmodulin promoted the Ca(2+)-dependent phosphorylation of a 98 kilodaltons polypeptide. Both Ca(2+)-dependent and Ca(2+)-independent phosphorylations required Mg(2+) at an optimal concentration of 5 to 10 millimolar. Cyclic AMP was found to have no stimulatory effect on protein phosphorylation. Sodium molybdate, an inhibitor of protein phosphatase, increased the net phosphorylation of several polypeptides. Rapid loss of radioactivity from the phosphorylated polypeptides following incubation in unlabeled ATP indicated the presence of phosphoprotein phosphatase activity.

Ca(II)-calmodulin regulation of fungal dimorphism in Ceratocystis ulmi

We have shown that Ca(II) ions, ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetic acid, LaCl3, and six known calmodulin inhibitors shift the yeast-mycelium dimorphic potential of Ceratocystis ulmi. Our data are consistent with the conclusions that Ca(II)-calmodulin interaction is necessary for mycelial growth in C. ulmi and that the absence of this interaction leads to the yeast phase.