摘要:

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 a

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01426.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The chemical state of calcium in the soil and the effects, both direct and indirect, which this can have on the growth and distribution of plants are considered. Recent advances in knowledge refer mainy to interactions (between nitrogen source, aluminium and pH, for example) for which there is now experimental evidence and which themselves are influenced by calcium. The impact of physical variables is less marked than first thought although seasonal effects of waterlogging and drought can be critical. It is emphasized that the terms ‘calcicole’ and ‘calcifuge’ are generally acceptable in classifying plants according to the degree of calcareousness of the soils in which they occur but only if the wider implications are appr

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01427.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Calcium is the soluble cation that occurs in largest amount in most soils. It does not take part directly in the proton transfer reactions involved in pH‐buffering, but it provides the cation charge balance for these reactions. It is also the complementary cation in formulations of chemical potential for many other ions in soils. The presence of free calcium carbonate in calcareous soils. The presence of free calcium carbonate in calcareous soils ensures a very high soil buffer capacity;dAB/dpH ≃ 1000 Eq. m−3.In acid mineral soils, dissolution and precipitation of aluminium ions contribute to the buffering processes, but most of the buffering in non‐calcareous soils is caused by specific ion adsorption at variable‐charge sites, in particular those associated with the dissociation of humus acids. Typical buffer capacity values of non‐calcareous soils vary from 10 Eq. m−3for sandy soils to 100 Eq. m−3for peats. The pH changes associated with buffering are produced by leaching of calcium from soil, or by adding calcium to soil in l

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01428.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Calcium occurs as a relatively large, divalent ion which readily enters the apoplast and is bound in exchangeable form in cell walls and on the exterior surface of the plasmalemma. It occurs in only very low concentrations in the cytoplasm and chloroplasts and appears to have a limited role as an enzymatic cofactor. The soil solution usually provides an adequate supply of Ca to plants. The well known physiological disorders resulting from localized Ca deficiencies within the plant are thus attributable to poor Ca distribution rather than restriction in uptake. Calcium is moved largely in the xylem and only to a very limited extent in the phloem. The phloem/xylem ratio of the solute input can be particularly critical in organs which are naturally low in Ca, such as fruits and young leaves. Factors which influence the distribution of Ca such as humidity, root pressure, phytohormone activity, can also affect the occurrence of these disorders.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01429.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.An account is given of the characterization of calcium fluxes across plasmalemma and tonoplast membranes of root cortical cells, using compartmental analysis. Some of the assumptions associated with the method are discussed. Recent evidence regarding the concentration of free Ca2+in plant cells, and the mechanisms driving active calcium transport across cell membranes, is reviewed. It is proposed that the evidence from whole cell studies and work at the molecular level is mutually supportive, and some speculation is ventured about the general pattern of calcium transport in higher plant cells.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01430.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.Under normal conditions the action potential in Characeae is dependent on the presence of both Cl−and Ca2+. Cl−seems to play a straightforward part as a transient depolarizing flow. The role of Ca2+, however, is emerging as an increasingly complex one: there are Ca2+concentration changes in the cytoplasm, as well as transient Ca2+currents across the plasmalemma and possibly the tonoplast. In most Characeae Ca2+is necessary for the Cl−channel to function, and it is also involved in the cessation of the cytoplasmic streaming observed at the time of excitation.The function of Ca2+at the time of the action potential is being revealed by experimental techniques of increasing sophistication. The development of these methods and possible associated artefacts are consi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01431.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The role of intracellular organelles in the regulation of cytosolic Ca2+levels and whether changes in these levels affect organelle metabolism is considered. We have assessed the biochemical properties of the Ca2+transporting systems in mitochondrial, chloroplast and microsomal fractions. It is proposed that although all of these organelles can transport Ca2+to varying extents it would appear that in some tissues at least mitochondria do not play a significant role in the maintenance of cytosolic Ca2+. The most important Ca2+transporting systems are probably the ATP dependent Ca2+extrusion across the plasma membrane and Ca2+uptake by endoplasmic reticulum, as well as light driven Ca2+uptake by chloroplasts. Changes in cytoplasmic [Ca2+] do appear to regulate the activity of NAD kinase in chloroplasts, the mitochondrial external NADH dehydrogenase and intra‐mitochondrial glutamate dehydrogenase, all of which play a key role in plant cell metabolism. Since some of these enzymes are affected by primary stimuli such as light or hormones, it is concluded that Ca2+may act as a second messenger mediating some of the primary response

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01432.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The regulation of the plant cytoskeleton by the concentration of free ionized Ca2+in the cytosol is discussed. The effect is illustrated by considering the role of Ca2+in regulating cytoplasmic streaming inPhysarumand characean algae, and flagellar beating inChlamydomonas. Examples are given of cytoskeletal processes in other plant cells that may be Ca2+‐regulated, together with an appraisal of some technical difficulties that currently limit their stud

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01433.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.From this brief review it appears that the interactions between calcium ions and cell walls play a key role in plant physiology. Calcium ions are involved in many mechnisms: for example, stabilization of cell wall structures, acidic growth, ion exchange properties, control of the activities of wall enzymes. All these properties originate from the tight binding of calcium ions to the pectins present in the cell walls. The factor most important for controlling wall behaviour is the density of non‐diffusible charges and, due to its high affinity, calcium can significantly affect this factor. We also discuss the theoretical ion exchange models in relation to the specific role of calcium ion

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01434.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Abstract.The low cytosol concentration of free Ca2+makes the symplast of roots an ineffective pathway for the supply of the calcium needed for healthy growth in the aerial parts of plants. Ca2+moves rapidly across the cortical apoplast by diffusion and mass flow but is probably diverted across the plasmamembranes of endodermal cells by Casparian bands. A proposal is made to account for the movement of calcium across the endodermis and it is estimated that Ca‐fluxes are likely to be appreciably greater than in the regulation of cell Ca level by cortical cells.Ca transport in the xylem occurs by mass flow of free Ca2+, and some organically complexed Ca, and by chromatographic movement along Ca‐exchange sites in the xylem walls. Delivery of Ca to transpiring leaves and to weakly transpiring meristematic zones is discussed in relation to the two modes of Ca movement in the xylem. Competition between sinks is intensified when [Ca2+] in xylem is low and transpiration is great.Tropic growth responses involve pumping of vacuolar calcium into the apoplast followed by its migration along gradients of electrical potential which develop in the apoplast after geo‐stimulation. An attempt is made to estimate plasmalemma efflux during this process.Redistribution from mature tissues to meristems in the pholem is likely to be small, if it occurs at all, since sieve tubes cannot have more than micro‐molar concentrations of free‐Ca

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1984.tb01435.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY