Calcium-calmodulin is required for abscisic acid-induced antioxidant defense and functions both upstream and downstream of H2O2 production in leaves of maize (Zea mays) plants

* Using pharmacological and biochemical approaches, the role of calmodulin (CaM) and the relationship between CaM and hydrogen peroxide (H(2)O(2)) in abscisic acid (ABA)-induced antioxidant defense in leaves of maize (Zea mays) plants were investigated. * Treatment with ABA or H(2)O(2) led to significant increases in the concentration of cytosolic Ca(2+) in the protoplasts of mesophyll cells and in the expression of the calmodulin 1 (CaM1) gene and the content of CaM in leaves of maize plants, and enhanced the expression of the antioxidant genes superoxide dismutase 4 (SOD4), cytosolic ascorbate peroxidase (cAPX), and glutathione reductase 1 (GR1) and the activities of the chloroplastic and cytosolic antioxidant enzymes. The up-regulation of the antioxidant enzymes was almost completely blocked by pretreatments with two CaM antagonists. * Pretreatments with CaM antagonists almost completely inhibited ABA-induced H(2)O(2) production throughout ABA treatment, but pretreatment with an inhibitor or scavenger of reactive oxygen species (ROS) did not affect the initial increase in the contents of CaM induced by ABA. * Our results suggest that Ca(2+)-CaM is involved in ABA-induced antioxidant defense, and that cross-talk between Ca(2+)-CaM and H(2)O(2) plays a pivotal role in ABA signaling.     

Calmodulin is involved in heat shock signal transduction in wheat

The involvement of calcium and calcium-activated calmodulin (Ca(2+)-CaM) in heat shock (HS) signal transduction in wheat (Triticum aestivum) was investigated. Using Fluo-3/acetoxymethyl esters and laser scanning confocal microscopy, it was found that the increase of intracellular free calcium ion concentration started within 1 min after a 37 degrees C HS. The levels of CaM mRNA and protein increased during HS at 37 degrees C in the presence of Ca(2+). The expression of hsp26 and hsp70 genes was up-regulated by the addition of CaCl(2) and down-regulated by the calcium ion chelator EGTA, the calcium ion channel blockers LaCl(3) and verapamil, or the CaM antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide and chlorpromazine. Treatment with Ca(2+) also increased, and with EGTA, verapamil, chlorpromazine, or trifluoperazine decreased, synthesis of HS proteins. The temporal expression of the CaM1-2 gene and the hsp26 and hsp70 genes demonstrated that up-regulation of the CaM1-2 gene occurred at 10 min after HS at 37 degrees C, whereas that of hsp26 and hsp70 appeared at 20 min after HS. A 5-min HS induced expression of hsp26 after a period of recovery at 22 degrees C after HS at 37 degrees C. Taken together, these results indicate that Ca(2+)-CaM is directly involved in the HS signal transduction pathway. A working hypothesis about the relationship between upstream and downstream of HS signal transduction is presented.     

A calmodulin-binding/CGCG box DNA-binding protein family involved in multiple signaling pathways in plants

We reported earlier that the tobacco early ethylene-responsive gene NtER1 encodes a calmodulin-binding protein (Yang, T., and Poovaiah, B. W. (2000) J. Biol. Chem. 275, 38467-38473). Here we demonstrate that there is one NtER1 homolog as well as five related genes in Arabidopsis. These six genes are rapidly and differentially induced by environmental signals such as temperature extremes, UVB, salt, and wounding; hormones such as ethylene and abscisic acid; and signal molecules such as methyl jasmonate, H(2)O(2), and salicylic acid. Hence, they were designated as AtSR1-6 (Arabidopsis thaliana signal-responsive genes). Ca(2+)/calmodulin binds to all AtSRs, and their calmodulin-binding regions are located on a conserved basic amphiphilic alpha-helical motif in the C terminus. AtSR1 targets the nucleus and specifically recognizes a novel 6-bp CGCG box (A/C/G)CGCG(G/T/C). The multiple CGCG cis-elements are found in promoters of genes such as those involved in ethylene signaling, abscisic acid signaling, and light signal perception. The DNA-binding domain in AtSR1 is located on the N-terminal 146 bp where all AtSR1-related proteins share high similarity but have no similarity to other known DNA-binding proteins. The calmodulin-binding nuclear proteins isolated from wounded leaves exhibit specific CGCG box DNA binding activities. These results suggest that the AtSR gene family encodes a family of calmodulin-binding/DNA-binding proteins involved in multiple signal transduction pathways in plants.     

Interrelationship between calmodulin (CaM) and H2O2 in abscisic acid-induced antioxidant defense in the seedlings of Panax ginseng

Calmodulin (CaM), the predominant Ca(2+) receptors, is one of the best-characterized Ca(2+) sensors in all eukaryotes. In this study the role of CaM and the possible interrelationship between CaM and hydrogen peroxide (H(2)O(2)) in abscisic acid (ABA) induced antioxidant defense were investigated in the seedling of Panax ginseng. Treatment of ABA (100 μM) and H(2)O(2) (10 mM) increased the expression of Panax ginseng calmodulin gene (PgCaM) and significantly enhanced the expression of the antioxidant marker genes such as superoxide dismutase, ascorbate peroxidase, glutathione reductase and the activities of chloroplastic and cytosolic antioxidant enzymes. Pretreatments with two CaM antagonists, trifluoperazine (TFP), N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide hydrochloride (W7) and inhibitor or scavenger, diphenyleneiodonium chloride, and dimethylthiourea of reactive oxygen species almost completely suppressed the up-regulation of antioxidant and PgCaM gene. Moreover, H(2)O(2) production and CaM content was almost completely inhibited by pretreatments with two CaM antagonists. In addition, the expressions of PgCaM gene under different biotic stress were analyzed at different time intervals. Thus it may suggests that CaM are involved in ABA-induced increased expression of PgCaM which triggers H(2)O(2) production through activating trans-plasma membrane NADPH oxidase, resulting in up-regulation of defense related antioxidant gene and also plays a pivotal role in defense response against pathogens.     

Cross-talk between calcium-calmodulin and nitric oxide in abscisic acid signaling in leaves of maize plants

Using pharmacological and biochemical approaches, the signaling pathways between hydrogen peroxide （H2O2）, calcium （Ca^2＋）-calmodulin （CAM）, and nitric oxide （NO） in abscisic acid （ABA）-induced antioxidant defense were investigated in leaves of maize （Zea mays L.） plants. Treatments with ABA, H2O2, and CaCl2 induced increases in the generation of NO in maize mesophyll cells and the activity of nitric oxide synthase （NOS） in the cytosolic and microsomal fractions of maize leaves. However, such increases were blocked by the pretreatments with Ca^2＋ inhibitors and CaM antagonists. Meanwhile, pretreatments with two NOS inhibitors also suppressed the Ca^2＋-induced increase in the production of NO. On the other hand, treatments with ABA and the NO donor sodium nitroprusside （SNP） also led to increases in the concentration of cytosolic Ca^2＋ in protoplasts of mesophyll cells and in the expression of calmodulin 1 （CaM1） gene and the contents of CaM in leaves of maize plants, and the increases induced by ABA were reduced by the pretreatments with a NO scavenger and a NOS inhibitor. Moreover, SNP-induced increases in the expression of the antioxidant genes superoxide dismutase 4 （SOD4）, cytosolic ascorbate peroxidase （cAPX）, and glutathione reductase 1 （GR1） and the activities of the chloroplastic and cytosolic antioxidant enzymes were arrested by the pretreatments with Ca^2＋ inhibitors and CaM antagonists. Our results suggest that Ca^2＋-CaM functions both upstream and downstream of NO production, which is mainly from NOS, in ABA- and H2O2-induced antioxidant defense in leaves of maize plants.     

Comparative analysis of plant and animal calcium signal transduction element using plant full-length cDNA data

We obtained 32K full-length cDNA sequence data from the rice full-length cDNA project and performed a homology search against NCBI GenBank data. We have also searched homologs of Arabidopsis and other plants' genes with the databases. Comparative analysis of calcium ion transport proteins revealed that the genes specific for muscle and nerve calcium signal transduction systems (VDCC, IP3 receptor, ryanodine receptor) are very different in animals and plants. In contrast, Ca elements with basic functions in cell responses (CNGC, iGlu receptor, Ca(2+)ATPase, Ca2+/Na(+)-K+ ion exchanger) are basically conserved between plants and animals. We also performed comparative analyses of calcium ion binding and/or controlling signal transduction proteins. Many genes specific for muscle and nerve tissue do not exist in plants. However, calcium ion signal transduction genes of basic functions of cell homeostasis and responses were well conserved; plants have developed a calcium ion interacting system that is more direct than in animals. Many species of plants have specifically modified calcium ion binding proteins (CPK, CRK), Ca2+/phospholipid-binding domains, and calcium storage proteins.     

Calcium/Calmodulin Activation of Soybean Glutamate Decarboxylase

Recently, we provided preliminary evidence for calcium (Ca2+)/calmodulin (CaM) stimulation of plant glutamate decarboxylase (GAD; EC 4.1.1.15). In the present study, a detailed characterization of the phenomenon is described. GAD was partially purified from various soybean (Glycine max L. Merr.) tissues (developing seed coat and cotyledons, leaf, and root) in the presence of EDTA by a combination of ammonium sulfate precipitation and anion-exchange fast protein liquid chromatography. GAD activity showed a sharp optimum at pH 5.8, with about 12% of maximal activity at pH 7. It was stimulated 2- to 8-fold (depending on the tissue source) in the presence of Ca2+/CaM at pH 7 but not at pH 5.8. Furthermore, when the protease inhibitor phenylmethylsulfonyl fluoride was omitted from the purification procedure, GAD activity was insensitive to Ca2+/CaM but was similar in magnitude to CaM-stimulated activity. The stimulation by Ca2+/CaM was fully inhibited by the CaM antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulfon-amide and trifluoperazine. With saturating CaM or Ca2+, the concentrations of Ca2+ and CaM required for half-maximal stimulation were about 7 to 11 [mu]M and 25 nM, respectively. The effect of Ca2+ and CaM appeared to be through a 2.4-fold stimulation of Vmax and a 55% reduction in Km. The results suggested that GAD is activated via Ca2+ signal transduction.     

Extracellular calmodulin: A polypeptide signal in plants?

Traditionally, calmodulin (CaM) was thought to be a multi-functional receptor for intra-cellular Ca2+ signals. But in the last ten years, it was found that CaM also exists and acts extracel-lularly in animal and plant cells to regulate many important physiological functions. Laboratory studies by the authors showed that extracellular CaM in plant cells can stimulate the proliferation of suspension cultured cell and protoplast; regulate pollen germination and pollen tube elongation, and stimulate the light-independent gene expression of Rubisco small subunit (rbcS). Furthermore, we defined the trans-membrane and intracellular signal transduction pathways for extracellular CaM by using a pollen system. The components in this pathway include heterotrimeric G-protein, phospholipase C, IP3, calcium signal and protein phosphorylation etc. Based on our findings, we suggest that extracellular CaM is a polypeptide signal in plants. This idea strongly argues against the traditional concept that there is no interce     

Physical Localization of Genes for CaM and Ca2+- ATPase in Rice by in situ Hybridization

CaM and Ca2 + -ATPase genes are important components of signal transduction chains which affect the regulation of' gene expression and development in plants. These two genes are tunctionally closely related. The rice ( Oryza sativa L. )cDNA probes C419 and SSU304 for these two genes, which are small single-copy ones and 0.8 and 0.3 kb in size respectively, were first physically mapped on rice chromosomes by biotin-labeled in situ hybridization. Both probes were detected on chromosome 5. The detection rate was 6.18 %, and the average chromosome ann ratios and standard deviations of detected chromosomes for probes C419 and SSU304 were 1.79 ± 0.06 and 1.91 ± 0.08 respectively. Probe C419 for CaM gene was located at the end of the long ann, and probe SSU304 for Ca2 + -ATPase gene -- on the short arm near the centromere. As it was reported before, they were closely linked in the high density genetic map. This demonstrated that there was a large discrepancy between the results of genetic and physical mapping of genes, and it indicated that the region between the functionally related genes could be the cold spot. What relationship there is between the region and gene expression is to be shudied further. The nonradioactive in situ hybridization technique about the physical mapping of low/single copy, short DNA fragments is also discussed.     

A new multigene family encoding calcium-dependent calmodulin-binding membrane proteins of Paramecium tetraurelia

Ca2+/calmodulin (CaM) regulates various physiological processes in a wide variety of organisms, metazoa and protists alike. To better understand Ca2+/CaM-dependent processes, particularly those with membrane-associated components, we studied Ca2+/CaM-binding membrane proteins in Paramecium tetraurelia, a unicellular model system. A CaM-binding protein, PCM1 (Paramecium CaM-binding membrane-bound protein), from a detergent-solubilized ciliary membrane fraction was identified and purified through Ca2+-dependent CaM-affinity chromatography. PCM1 has an apparent molecular mass of approx. 65kDa. It binds radiolabeled CaM in blot overlay assays and binds to CaM-affinity columns, both only in the presence of 10 microM or higher Ca2+. Three peptide sequences from PCM1 were obtained, and polymerase chain reaction (PCR) and Southern hybridization experiments were designed accordingly, leading to a partial cDNA clone for PCM1 and the discovery of three homologs: PCM2, PCM3 and PCM4. Amino acid sequences predicted by the full-length coding sequence for PCM3 and partial genes for PCM1, PCM2 and PCM4 are very similar (approx. 85% amino-acid identities). Their sequences indicate that they are hitherto novel proteins with beta/gamma-crystallin domains, cysteine-rich regions and potential CaM-binding domains. These protein motifs are suggested to mediate protein-protein interaction important for Ca2+/CaM signal transduction event(s) through the PCM family of proteins.     

Wound- and systemin-inducible calmodulin gene expression in tomato leaves

Using a calmodulin (CaM) cDNA as a probe in northern analyses, transgenic tomato plants that overexpress the prosystemin gene were found to express increased levels of CaM mRNA and protein in leaves compared to wild-type plants. These transgenic plants have been reported previously to express several wound-inducible defense-related genes in the absence of wounding. Calmodulin mRNA and protein levels were found to increase in leaves of young wild-type tomato plants after wounding, or treatment with systemin, methyl jasmonate, or linolenic acid. CaM mRNA appeared within 0.5 h after wounding or supplying young tomato plants with systemin, and peaked at 1 h. The timing of CaM gene expression is similar to the expression of the wound- or systemin-induced lipoxygenase and prosystemin genes, signal pathway genes whose expression have been reported to begin at 0.5–1 h after wounding and 1–2 h earlier than the genes coding for defensive proteinase inhibitor genes. The similarities in timing between the synthesis of CaM mRNA and the mRNAs for signal pathway components suggests that CaM gene expression may be associated with the signaling cascade that activates defensive genes in response to wounding.     

Impact of external calcium and calcium sensors on ginsenoside Rb1 biosynthesis by Panax notoginseng cells

The effects of external calcium concentrations on biosynthesis of ginsenoside Rb1 and several calcium signal sensors were quantitatively investigated in suspension cultures of Panax notoginseng cells. It was observed that the synthesis of intracellular ginsenoside Rb1 in 3-day incubation was dependent on the medium Ca2+ concentration (0-13 mM). At an optimal Ca2+ concentration of 8 mM, a maximal ginsenoside Rb1 content of 1.88 +/- 0.03 mg g(-1) dry weight was reached, which was about 60% and 25% higher than that at Ca2+ concentrations of 0 and 3 mM, respectively. Ca2+ feeding experiments confirmed the Ca2+ concentration-dependent Rb1 biosynthesis. In order to understand the mechanism of the signal transduction from external Ca2+ to ginsenoside biosynthesis, the intracellular content of calcium and calmodulin (CaM), activities of calcium/calmodulin-dependent NAD kinase (CCDNK) and calcium-dependent protein kinase (CDPK), and activity of a new biosynthetic enzyme of ginsenoside Rb1, i.e., UDPG:ginsenoside Rd glucosyltransferase (UGRdGT), in the cultured cells were all analyzed. The intracellular calcium content and CCDNK activity were increased with an increase of external Ca2+ concentration within 0-13 mM. In contrast, the CaM content and activities of CDPK and UGRdGT reached their highest levels at 8 mM of initial Ca2+ concentration, which was also optimal to the ginsenoside Rb1 synthesis. A similar Ca2+ concentration-dependency of the intracellular contents of calcium and CaM and activities of CCDNK, CDPK, and UGRdGT was confirmed in Ca2+ feeding experiments. Finally, a possible model on the effect of external calcium on ginsenoside Rb1 biosynthesis via the signal transduction pathway of CaM, CDPK, and UGRdGT is proposed. Regulation of external Ca2+ concentration is considered a useful strategy for manipulating ginsenoside Rb1 biosynthesis by P. notoginseng cells.     

Calmodulin and Ca2+/calmodulin-binding proteins are involved in Tetrahymena thermophila phagocytosis

The ciliated protist, Tetrahymena thermophila, possesses one oral apparatus for phagocytosis, one of the most important cell functions, in the anterior cell cortex. The apparatus comprises four membrane structures which consist of ciliated and unciliated basal bodies, a cytostome where food is collected by oral ciliary motility, and a cytopharynx where food vacuoles are formed. The food vacuole is thought to be transported into the cytoplasm by a deep fiber which connects with the oral apparatus. Although a large number of studies have been done on the structure of the oral apparatus, the molecular mechanisms of phagocytosis in Tetrahymena thermophila are not well understood. In this study, using indirect immunofluorescence, we demonstrated that the deep fiber consisted of actin, CaM, and Ca2+/CaM-binding proteins, p85 and EF-1alpha, which are closely involved in cytokinesis. Moreover, we showed that CaM, p85, and EF-1alpha are colocalized in the cytostome and the cytopharynx of the oral apparatus. Next, we examined whether Ca2+/CaM signal regulates Tetrahymena thermophila phagocytosis, using Ca2+/CaM inhibitors chlorpromazine, trifluoperazine, N-(6-aminohexyl)-1-naphthalenesulfonamide, and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide HCI. In Tetrahymena, it is known that Ca2+/CaM signal is closely involved in ciliary motility and cytokinesis. The results showed that one of the inhibitors, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide HCl, inhibited the food vacuole formation rather than the ciliary motility, while the other three inhibitors effectively prevented the ciliary motility. Considering the colocalization of CaM, p85, and EF-1alpha to the cytopharynx, these results suggest that the Ca2+/CaM signal plays a pivotal role in Tetrahymena thermophila food vacuole formation.     

Short Communication Involvement of Calcium-calmodulin in the Expression of hsp26 Gene in Wheat

The treatment of wheat ( Triticum aestivum L.) seedlings with CaCl2 increased mRNA levels of hsp26 gene at 37 ℃ for 1 h, while that with Ca2+ chelator EGTA decreased the expression of the hsp26 gene. The expression of the wheat calmodulin gene CaM1-2 is rapidly up-regulated in wheat seedlings by heat shock at 37 ℃. The heat-induced up-regulation of CaM1-2 occurred earlier than that of the hsp26 gene did. Calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamid (W7) inhibited the expression of the hsp26 gene in wheat seedlings at 37 ℃ for 1 h. These results implied that the calcium-calmodulin is probably involved in the signal transduction of the hsp26 gene expression induced by heat shock.     

钙在植物乙烯生成及信号传递中的生理作用

Ｃａ＾２＋对植物乙烯生成的调节与作用位点有关,胞外Ｃａ＾２＋在维持质膜功能的同时,抑制乙烯生成,延缓衰老;过量Ｃａ＾２＋进入胞质,胞内Ｃａ＾２＋促进乙烯生成和衰老。内源ＣａＭ与乙烯生成关系密切,介入了乙烯代谢和外源激素对乙烯的调控。此外,Ｃａ＾２＋是乙烯信号传递所必需的。     

Characterisation of a novel gene family of putative cyclic nucleotide- and calmodulin-regulated ion channels in Arabidopsis thaliana

In plants, cyclic GMP is involved in signal transduction in response to light and gibberellic acid. For cyclic AMP, a potential role during the plant cell cycle was recently reported. However, cellular targets for cyclic nucleotides in plants are largely unknown. Here we report on the identification and characterisation of a new gene family in Arabidopsis, which share features with cyclic nucleotide-gated channels from animals and inward-rectifying K⁺ channels from plants. The identified gene family comprises six members (Arabidopsis thaliana cyclic nucleotide-gated channels, AtCNGC1–6) with significant homology among the deduced proteins. Hydrophobicity analysis predicted six membrane-spanning domains flanked by hydrophilic amino and carboxy termini. A putative cyclic nucleotide binding domain (CNBD) which contains several residues that are invariant in other CNBDs was located in the carboxy terminus. This domain overlaps with a predicted calmodulin (CaM) binding site, suggesting interaction between cyclic nucleotide and CaM regulation. We demonstrated interaction of the carboxy termini of AtCNGC1 and AtCNGC2 with CaM in yeast, indicating that the CaM binding sites are functional. Furthermore, it was shown that both AtCNGC1 and AtCNGC2 can partly complement the K⁺-uptake-deficient yeast mutant CY162. Therefore, we propose that the identified genes constitute a family of plant cyclic nucleotide- and CaM-regulated ion channels.     

Mutations in the Ca2+/H+ transporter CAX1 increase CBF/DREB1 expression and the cold-acclimation response in Arabidopsis

Transient increases in cytosolic free calcium concentration ([Ca2+]cyt) are essential for plant responses to a variety of environmental stimuli, including low temperature. Subsequent reestablishment of [Ca2+]cyt to resting levels by Ca2+ pumps and antiporters is required for the correct transduction of the signal [corrected]. C-repeat binding factor/dehydration responsive element binding factor 1 (Ca2+/H+) antiporters is required for the correct transduction of the signal. We have isolated a cDNA from Arabidopsis that corresponds to a new cold-inducible gene, rare cold inducible4 (RCI4), which was identical to calcium exchanger 1 (CAX1), a gene that encodes a vacuolar Ca2+/H+ antiporter involved in the regulation of intracellular Ca2+ levels. The expression of CAX1 was induced in response to low temperature through an abscisic acid-independent pathway. To determine the function of CAX1 in Arabidopsis stress tolerance, we identified two T-DNA insertion mutants, cax1-3 and cax1-4, that display reduced tonoplast Ca2+/H+ antiport activity. The mutants showed no significant differences with respect to the wild type when analyzed for dehydration, high-salt, chilling, or constitutive freezing tolerance. However, they exhibited increased freezing tolerance after cold acclimation, demonstrating that CAX1 plays an important role in this adaptive response. This phenotype correlates with the enhanced expression of CBF/DREB1 genes and their corresponding targets in response to low temperature. Our results indicate that CAX1 ensures the accurate development of the cold-acclimation response in Arabidopsis by controlling the induction of CBF/DREB1 and downstream genes.     

Regulation of the dual specificity protein phosphatase, DsPTP1, through interactions with calmodulin

Reversible phosphorylation is a key mechanism for the control of intercellular events in eukaryotic cells. In animal cells, Ca2+/CaM-dependent protein phosphorylation and dephosphorylation are implicated in the regulation of a number of cellular processes. However, little is known on the functions of Ca2+/CaM-dependent protein kinases and phosphatases in Ca2+ signaling in plants. From an Arabidopsis expression library, we isolated cDNA encoding a dual specificity protein phosphatase 1, which is capable of hydrolyzing both phosphoserine/threonine and phosphotyrosine residues of the substrates. Using a gel overlay assay, we identified two Ca2+-dependent CaM binding domains (CaMBDI in the N terminus and CaMBDII in the C terminus). Specific binding of CaM to two CaMBD was confirmed by site-directed mutagenesis, a gel mobility shift assay, and a competition assay using a Ca2+/CaM-dependent enzyme. At increasing concentrations of CaM, the biochemical activity of dual specificity protein phosphatase 1 on the p-nitrophenyl phosphate (pNPP) substrate was increased, whereas activity on the phosphotyrosine of myelin basic protein (MBP) was inhibited. Our results collectively indicate that calmodulin differentially regulates the activity of protein phosphatase, dependent on the substrate. Based on these findings, we propose that the Ca2+ signaling pathway is mediated by CaM cross-talks with a protein phosphorylation signal pathway in plants via protein dephosphorylation.     

钙在植物乙烯生成及信号传递中的生理作用

Ca2+对植物乙烯生成的调节与作用位点有关,胞外Ca2+在维持质膜功能的同时,抑制乙烯生成,延缓衰老;过量Ca2+进入胞质,胞内Ca2+促进乙烯生成和衰老。内源CaM与乙烯生成关系密切,介入了乙烯代谢和外源激素对乙烯的调控。此外,Ca2+是乙烯信号传递所必需的。