Second Messenger In Plants Research Articles

Evidence against specific binding of salicylic acid to plant catalase

It was demonstrated that salicylic acid (SA) not only binds to catalase from differentiated higher plants and plant cell suspension cultures but also to those of fungi and animals. SA bound specifically to iron-containing enzymes, such as catalase, aconitase, lipoxidase and peroxidase, while not to iron-free plant enzymes. On the grounds of these experiments, the claim is further challenged that SA is a signalling compound and second messenger in plants that activates plant defense-related genes through elevated H 2O 2 levels by specifically inhibiting catalase activity. SA may just function as a phytoalexin.

Ca 2+ ions and lysophospholipids activate phosphorylation of different proteins in plasma membranes and tonoplast

Summary Protein phosphorylation and regulation by phosphorylation of transport ATPases was studied in highly purified plasma membrane and tonoplast vesicles isolated from etiolated zucchini ( Cucurbita pepo L.) hypocotyls. Plant lysophosphatidylcholine and the chemically similar animal lipid platelet-activating factor activated H + transport activity of plasma membrane ATPase in vitro . In plasma membrane vesicles, purified by two-phase partitioning and subsequent free-flow electrophoresis, both lipids activated a membrane-associated protein kinase that phosphorylated a 97 kD polypeptide. A 97 kD polypeptide also gave a western blot signal generated by an antibody prepared against plasma membrane H + -ATPase. The phosphoprotein and the western blot signal were absent in tonoplast fractions purified by free-flow electrophoresis. In contrast, the B subunit of the tonoplast H + -ATPase was identified by western blot in those fractions but could not be found in plasma membrane fractions, corroborating membrane identity. When Ca 2+ -dependent and lysophospholipid-dependent protein phosphorylation in plasma membranes and in tonoplast were compared it was found for both membranes that the phosphorylation of several polypeptides was Ca 2+ -dependent but lysophospholipid-independent. These phosphoproteins were different in plasma membranes and tonoplast. Ca 2+ is an established second messenger in plants, and lysophospholipids are proposed as potential signal mediators activating membrane-associated protein kinase(s), Our data indicate that they could be distinguished by their substrates. A function of both plasma membrane and tonoplast in plant signal transduction pathways is indicated.

Reversible inactivation of K+ channels of Vcia stomatal guard cells following the photolysis of caged inositol 1,4,5-trisphosphate

RECENT investigations suggest that cytoplasmic D-myo-inositol 1,4,5-trisphosphate (InsP3) functions as a second messenger in plants, as in animals, coupling environmental and other stimuli to intracellular Ca2+ release. Cytoplasmic levels of InsP3 and the turnover of several probable precursors in plants are affected by physiological stimuli--including light, osmotic stress and the phytohormone indoleacetic acid--and InsP3 activates Ca2+ channels and Ca2+ flux across plant vacuolar and microsomal membranes. Complementary data also link changes in cytoplasmic free Ca2+ to several physiological responses, notably in guard cells which regulate gas exchange through the stomatal pores of higher plant leaves. Recent evidence indicates that guard cell K+ channels and, hence, K+ flux for stomatal movements may be controlled by cytoplasmic Ca2+. So far, however, direct evidence of a role for InsP3 in signalling in plants has remained elusive. Here we report that InsP3 released from an inactive, photolabile precursor, the P5-1-(2-nitrophenyl)ethyl ester of InsP3 (caged InsP3) reversibly inactivates K+ channels thought to mediate K+ uptake by guard cells from Vicia faba L. while simultaneously activating an apparently time-independent, inward current to depolarize the membrane potential and promote K+ efflux through a second class of K+ channels. The data are consistent with a transient rise in cytoplasmic free Ca2+ and demonstrate that intact guard cells are competent to use InsP3 in signal cascades controlling ion flux through K+ channels.

Calcium-Binding Proteins in Fungi and Higher Plants

Calcium has long been known to be required for many vital processes in fungi and plants. High levels of calcium are found in cell walls, vacuoles, and most organelles. In contrast, very low levels of calcium are present in the cytosol of fungal and plant cells. The most recent evidence indicates that calcium is a true second messenger in fungi and plants. Because cyclic AMP does not appear to be a second messenger in plants, calcium is the only known second messenger. Calcium-binding proteins are involved in the events that accompany the action of calcium as a second messenger; three types have been identified in fungi and plants. The first group includes several proteins that bind 45 Ca2+ and are not known to have any enzymatic activity. A second type includes the many enzymes from fungi and plants stimulated by millimolar levels of calcium. The third type of calcium-binding protein, calmodulin, responds to micromolar levels of Ca2+ by binding to certain enzymes and stimulating them. Calmodulin has been detected in every eukaryote thus far examined. The amino acid composition of several fungal and plant calmodulins have been elucidated and found to be very similar to calmodulin from animals. Eight enzymes from fungi and plants have been reported to be regulated either directly or indirectly by calmodulin. Calmodulin antagonists have been used to study the possible involvement of calmodulin in many cellular processes in fungi and plants. Recently, several endogenous calmodulin antagonists have been identified in fungi and plants. The physiological significance of these compounds is currently being evaluated.

Inositol 1,4,5-trisphosphate induced calcium release from corn coleoptile microsomes.

The effect of inositol 1,4,5-trisphosphate (IP3) on Ca2+ release from microsomes of corn coleoptiles was investigated. Addition of micromolar concentrations of IP3 to Ca2+ loaded microsomes resulted in rapid release of 20-30% of sequestered Ca2+. Maximal and half maximal Ca2+ release occurred at 20 and 8 microM of IP3 respectively. Part of the Ca2+ released by IP3 was reaccumulated into microsomes within 4 min. The amount of Ca2+ released by IP3 was found to be dependent on free Ca2+ concentration in the incubation medium at the time of release. Maximum Ca2+ release was observed around 0.1 microM free Ca2+ concentration in the assay medium. These data suggest that IP3 might act as a second messenger in plants in a manner similar to animal systems by altering cytosolic levels of calcium.

Calmodulin and calmodulin‐mediated processes in plants

Abstract. The Ca2+ ‐binding protein calmodulin is found in all plants investigated so far. The comparison of the biochemical and functional properties reveals that it is structurally conserved and functionally preserved throughout the plant and animal kingdom. Among the plant enzymes so far known to be dependent on the Ca2+ ‐calmodulin complex are NAD kinase(s), Ca2+ ‐transport ATPase, quinate: NAD+ oxidoreductase, soluble and membrane bound protein kinases, and H+ ‐transport ATPase. Calmodulin may play also an important role in the regulation of other cellular reactions, such as hormone‐mediated processes, secretion of enzymes, and contractile mechanisms. On the basis of the NAD kinase and its regulation by light and Ca2+ ‐calmodulin, it is suggested that changes in the cellular, free Ca2+ concentration following stimulation may alter the metabolism of a plant cell. According to this suggestion free Ca2+ may act as a second messenger in plants much as it does in animal cells.