Identification of calmodulin in the green alga Mougeotia and its possible function in chloroplast reorientational movement

Two-Track Control of Cellular Machinery for Photomovement in Spirogyra varians (Streptophyta, Zygnematales)

Plants and freshwater algae devoid of flagella evolved various photomovements to optimize their photosynthetic efficiency. The filaments of Spirogyra varians exhibit complex swaying and undulating movement and form a compact mat which enables them to adjust their light exposure. Photomovement of filament fragments (1-10 cells) was analyzed using various photoreceptor and cytoskeleton inhibitors under monochromatic light. Different patterns of movement were observed under red and blue light. The filaments showed positive phototropism under blue light. Under red light, the filaments bent to undulating shape, but rapidly became unbent by a short exposure to far-red light suggesting the involvement of phytochrome in this movement. The mechanical effector for the red-light response was microtubules; the movement was inhibited effectively by the microtubule inhibitor, oryzalin. The blue-light movement was partially inhibited by the single treatment of either cytochalasin D or oryzalin, but was completely blocked when both chemicals were applied together. Phototropin-signaling inhibitors, wortmannin and LY294002, reversibly inhibited the blue-light movement. Caffeine treatment reversibly stopped the blue-light movement, while the red-light movement was not affected by calcium inhibitors. Our results suggest that the complex photomovement of S. varians is the result of a two-track control of microtubules and microfilaments signaled by the combination of phytochrome and phototropin-like receptors.

A comparative transcriptome and proteomics analysis reveals the positive effect of supplementary Ca(2+) on soybean sprout yield and nutritional qualities

Effects of Ca(2+) on yield and nutritional qualities of soybean sprout were investigated. Ca-treated sprouts had higher yield than water-treated ones. Metabolism of selected storage materials and bioactive substances in soybean sprouts was strengthened by Ca(2+). The phytic acid and saponin content of Ca-treated soybean sprouts were lower than those of control. Supplemental Ca(2+) increased content of gamma-aminobutyric acid, isoflavones, phenolics, and vitamins, respectively. These findings indicate that supplemental Ca(2+) can increase soybean sprout yield and improve its nutritional qualities. The comparative transcriptome and proteomics between water-treated and Ca-treated soybean sprouts were studied. As consequence 1912 genes and 460 proteins were up- or down-regulated after 4days of Ca(2+) treatment. The functional classification of these differentially expressed genes and proteins indicated their connection with primary/secondary metabolic pathways, ion transport, signal transduction, and transcriptional regulation. The results obtained here will enable to understand how changes in yield and nutritional quality are regulated by extra Ca(2+) in soybean sprouts.

BIOLOGICAL SIGNIFICANCE

In this study, a total of 1912 genes and 460 proteins involved in the growth, storage material decomposition, and bioactive substance synthesis in soybean sprouts after treated with Ca(2+) were identified. This is the first report of a comprehensive transcriptomic and proteomic analysis of soybean sprout in response to supplemental Ca(2+).

Blue light-dependent changes in loosely bound calcium in Arabidopsis mesophyll cells: an X-ray microanalysis study

Calcium is involved in the signal transduction pathway from phototropins, the blue light photoreceptor kinases which mediate chloroplast movements. The chloroplast accumulation response in low light is controlled by both phot1 and phot2, while only phot2 is involved in avoidance movement induced by strong light. Phototropins elevate cytosolic Ca(2+) after activation by blue light. In higher plants, both types of chloroplast responses depend on Ca(2+), and internal calcium stores seem to be crucial for these processes. Yet, the calcium signatures generated after the perception of blue light by phototropins are not well understood. To characterize the localization of calcium in Arabidopsis mesophyll cells, loosely bound (exchangeable) Ca(2+) was precipitated with potassium pyroantimonate and analyzed by transmission electron microscopy followed by energy-dispersive X-ray microanalysis. In dark-adapted wild-type Arabidopsis leaves, calcium precipitates were observed at the cell wall, where they formed spherical structures. After strong blue light irradiation, calcium at the apoplast prevailed, and bigger, multilayer precipitates were found. Spherical calcium precipitates were also detected at the tonoplast. After red light treatment as a control, the precipitates at the cell wall were smaller and less numerous. In the phot2 and phot1phot2 mutants, calcium patterns were different from those of wild-type plants. In both mutants, no elevation of calcium after blue light treatment was observed at the cell periphery (including the cell wall and a fragment of cytoplasm). This result confirms the involvement of phototropin2 in the regulation of Ca(2+) homeostasis in mesophyll cells.

Calmodulin and wound healing in the coenocytic green alga Ernodesmis verticillata (Kützing) Børgesen : Immunofluorescence and effects of antagonists

The involvement of calmodulin (CaM) in wound-induced cytoplasmic contractions in E. verticillata was investigated. Indirect immunofluorescence of CaM in intact cells showed a faint, reticulate pattern of fluorescence in the cortical cytoplasm. Diffuse fluorescence was evident deeper within the cytoplasm. In contracted cells, CaM co-localizes with actin in the cortical cytoplasm in extensive, longitudinal bundles of microfilaments (MFs), and in an actin-containing reticulum. No association of CaM with tubulin was ever observed in the cortical cytoplasm at any stage of wound-healing. When contraction rates in wounded cells are measured, a lag period of 2 min is followed by a rapid, steady rate of movement over the subsequent 10 min. The delay in the initiation of longitudinal contraction corresponds to the time necessary for the assembly of the longitudinal MF bundles. Cytoplasmic motility was inhibited in a dose-dependent manner by CaM antagonists. In these inhibited cells, MF bundles did not assemble, or were poorly formed. In the latter case, CaM was always found associated with MFs. These results indicate a direct spatial and temporal correlation between CaM and actin, and a potential role for CaM in regulating the formation of functional MF bundles during wound-induced cytoplasmic contraction in Ernodesmis.

Characterization of the isolated calcium-binding vesicles from the green alga Mougeotia scalaris, and their relevance to chloroplast movement

The calcium-binding vesicles from the green alga Mougeotia scalaris were isolated and characterized after staining in vivo by neutral red or rhodamine B. They were found to possess, a protonated group with a pKa-9.9, typifying phenolic hydroxyl groups; upon titration, both, phenolic compound(s) and vital dye were concomitantly released from the vesicular matrix. A shift in peak absorbance from 450 nm to 540 nm of the vitally stained vesicles indicated that the neutral form of neutral red was bound to the vesicular, matrix as an intermediate form, stabilized via intermolecular hydrogen bonds to the phenolic compound(s). Up to 8.5.10(9) dye molecules were calculated to be adsorbed to a mean-size vesicle. Analysis of Langmuir adsorption isotherms, indicated that there were two binding sites each for both neutral red and rhodamine B. The isolated vesicles were devoid of calcium, probably because vesicular calcium, bound to the vesicle matrix, was displaced upon dye binding. Dye adsorption to the vesicles in vivo results in substantial inhibition of the reorientational movement of the Mougeotia chloroplast and is explained by dye-mediated disorder of the cellular calcium homoeostasis.

Vital staining permits isolation of calcium vesicles from the green alga Mougeotia

The calcium vesicles of the green alga Mougeotia (G. Wagner and R. Rossbacher, 1980, Planta 149, 298-305) were isolated for characterization in vitro by fractionation of algal homogenate on sucrose density gradients. A new technique, based on vital staining by neutral red or rhodamine B, permitted isolation. Minimum dye binding to the calcium vesicles prevented desintegration, and for isolation a single, thoroughly defined centrifugation step sufficed, facilitated by the exceptionally high vesicular density of ≥1.3 g· cm(-3). Neutral red in particular seems to be accumulated by the vesicles via hydrogen bonds to abundant phenolic hydroxyl groups which, reversibly bound to an as yet undefined vesicle core, may well provide coordination sites for the observed calcium binding.

Electron spectroscopic imaging (ESI) applied to the detection of potential Ca(2+)-binding sites in plant cells

The applicability of the electron spectroscopic imaging technique for detection of the intracellular distribution of calcium in plant cells was tested with calyptra cells ofZea mays and with pollen tubes ofLilium longiflorum. After fixation in enhanced Ca(2+) levels and embedding in resin, ultrathin sections were analyzed for the elemental distribution. Calcium and phosphorus were enriched in cell wall, plasma membrane, endoplasmic reticulum, mitochondria, and Golgi vesicles, mainly in granular or globular deposits appearing electron dense in transmission electron microscopy. The results demonstrated that the ESI-technique allows exact localization of calcium enrichment relative to specific cell organelles.

Calmodulin-like protein from the fern Anemia phyllitidis L. Sw

Spores and prothallia of the fern Anemia phyllitidis L. Sw. contain a protein which in its physicochemical properties corresponds largely to calmodulin. It shows immunoreactivity with a calmodulin antiserum and activates bovine brain phosphodiesterase. Its content increases during the early processes of light-induced spore germination, indicating that the Ca(2+)-dependence of these processes may be mediated by this protein.

Distribution of calmodulin in pea seedlings: Immunocytochemical localization in plumules and root apices

Immunofluorescence techniques have been used to study the distribution of calmodulin in several tissues in young etiolated pea (Pisum sativum L.) seedlings. A fairly uniform staining was seen in the nucleoplasm and background cytoplasm of most cell types. Cell walls and nucleoli were not stained. In addition, patterned staining reactions were seen in many cells. In cells of the plumule, punctate staining of the cytoplasm was common, and in part this stain appeared to be associated with the plastids. A very distinctive staining of amyloplasts was seen in the columella of the root cap. Staining associated with cytoskeletal elements could be shown in division stages. By metaphase, staining of the spindle region was quite evident. In epidermal cells of the stem and along the underside of the leaf there was an intense staining of the vacuolar contents. Guard cells lacked this vacuolar stain. Vacuolar staining was sometimes seen in cells of the stele, but the most distinctive pattern in the stele was associated with young conducting cells of the xylem. These staining patterns are consistent with the idea that the interactions of plastids and the cytoskeletal system may be one of the Ca(2+)-mediated steps in the response of plants to environmental stimuli. Nuclear functions may also be controlled, at least in part, by Ca(2+).

3,4,5-Triiodobenzoic acid affects [3H]verapamil binding to plant and animal membrane fractions and smooth muscle contraction

3,4,5-Triiodobenzoic acid, known as auxin transport inhibitor, stimulates specific [3H]verapamil binding to zucchini microsomes by 100% (EC50 = 1 microM). This stimulatory effect is due to a decrease of the apparent equilibrium dissociation constant KD for verapamil from 60 nM to 33 nM without significantly changing the maximum number of binding sites. 3,4,5-Triiodobenzoic acid also increases specific [3H]verapamil binding to rabbit skeletal muscle membranes (EC50 greater than or equal to 20 microM) without affecting [3H]nitrendipine and [3H]-d-cis-diltiazem binding. If 3,4,5-triiodobenzoic acid is added to isolated rings of rabbit A. saphena contracted by potassium depolarization, a dose-dependent relaxation is observed with an IC50 value of about 8 microM. Contractions initiated by the addition of 3 microM norepinephrine can also be abolished by 3,4,5-triiodobenzoic acid with half maximal inhibition at 40 microM.