Growth and gibberellin-A1 metabolism in normal and gibberellin-insensitive (Rht3) wheat (Triticum aestivum L.) seedlings

Growth parameters were determined for tall (rht3) and dwarf (Rht3) seedlings of wheat (Triticum aestivum L.). Plant statures and leaf length were reduced by 50% in dwarfs but root and shoot dry weights were less affected. Leaves of dwarf seedlings had shorter epidermal cells and the numbers of cells per rank in talls and dwarfs matched the observed relationships in overall length. Talls grew at twice the rate of dwarfs (2.3 compared with 1.2 mm h^-1). [³H]Gibberellin A₁ ([³H]GA₁) was fed to seedlings via the third leaf and metabolism was followed over 12 h. Immature leaves of tall seedlings transferred radioactivity rapidly to compounds co-chromatographing with [³H]gibberellin A₈ ([³H]GA₈) and a conjugate of [³H]GA₈, whereas leaves of dwarf seedlings metabolised [³H]GA₁ more slowly. Roots of both genotypes produced [³H]GA₈-like material at similar rates. Isotopic dilution studies indicated a reduced 2-hydroxylation capacity in dwarfs, but parallel estimates of the endogenous GA pool size, obtained by radioimmunoassay, indicated a 12–15 times higher level of GA in the dwarf immature leaves. Dwarfing by the Rht3 gene does not appear to operate through enhanced, or abnormal metabolism of active gibberellins and the act of GA metabolism does not bear an obligate relationship to the growth response.Abbreviations GA_n gibberellin A_n - HPLC high-performance liquid chromatography     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The flag leaf of wheat was examined for changes in quantity and activity of ribulose-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39), in the proteolytic degradation of RuBPCase and other native proteins, and in the ultrastructure of the leaf cells during grain development. Proteolytic degradation of RuBPCase at pH 4.8 increased until 8–10 d after anthesis, then declined, and increased again 16–18 d after anthesis. The second peak coincided with the onset of a preferential loss of immunologically recognizable RuBPCase. The specific activity and number of active sites per molecule of RuBPCase did not change during senescence. Examination of ultrastructure with the electron microscope showed little change in the appearance of the mitochondria as the flag leaf aged. Prominent cristae were still evident 35 d after anthesis. In contrast, the chloroplasts showed a progressive disruption of the thylakoid structure and an increasing number of osmiophilic glubules. The double membrane envelope surrounding the chloroplast appeared intact until at least 20 d after anthesis. The tonoplast also appeared intact up to 20 d. At later stages of senescence of the leaf the outer membrane of the chloroplast adjacent to the tonoplast appeared to break but the inner membrane of the envelope appeared intact until at least 35 d after anthesis.Abbreviation RuBPCase ribulose-1,5-bisphosphate carboxylase (EC. 4.1.1.39) I=Waters et al. 1980     

ent-Kaurene synthase is located in proplastids of meristematic shoot tissues

Previous studies have indicated that ent-kaurene synthase (KS) is located in the proplastid stroma of rapidly dividing plant tissues. Here we present further and more direct evidence for this hypothesis and follow the activity of KS throughout the entire vegetative growth period of wheat plants. During germination of wheat caryopses, KS activity was maximal for a short period culminating on the third day in the scutellum and on the forth day in the meristematic shoot base. Throughout further development of the wheat plant, KS was found in the nodes but not in internodes or leaves. The activity of KS in each node increased when the internode above it was elongating and decreased again when this internode had almost reached its final size. The correlation of KS activity with growth was particularly striking in the case of tiller development from the forth node: here KS activity had already declined, but was restored when the tiller began elongating. Electron micrographs of wheat seedling tissue with high KS activity (shoot base) showed the presence of proplastids, whereas electron micrographs of tissue without such activity (primary leaves) showed only developing or mature chloroplasts. On density-gradient centrifugation, the plastids that yielded stroma preparations with KS activity became distributed over a greater density range and also had a lower NADP⁺-glyceraldehyde 3-phosphate dehydrogenase:shikimate oxidoreductase ratio than plastids yielding KS-inactive stroma preparations. Pea shoot apices contain both proplastids and mature chloroplasts. Here also, KS activity was associated with the stroma of plastids with characteristics similar to those of the wheat proplastids, indicating that KS is associated with proplastids in pea shoot apices as well. We conclude that the stromal location of KS may be a general feature of proplastids in rapidly dividing tissue. Received: 31 July 1996 / Accepted: 9 November 1996     

The control of respiration in wheat (Triticum aestivum L.) leaves

The aim of this work was to discover whether the respiration of wheat (Triticum aestivum L. cv. Huntsman) leaves, transferred to darkness after 7 h photosynthesis, showed an initial period of wasteful respiration. For young and old leaves, CO₂ production and O₂ uptake after 7 h photosynthesis were up to 56% higher than at the end of an 8-h night. The maximum catalytic activities of citrate synthase (EC 4.1.3.7), aconitase (EC 4.2.1.3), fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) at the end of the day did not differ from those at the end of the night. Changes in the contents of glucose 6-phosphate, fructose-1,6-bisphosphate, dihydroxyacetone phosphate, and -ketoglutarate did not as a group parallel the changes in the rate of respiration. The detailed distribution of label from [U-¹⁴C] sucrose supplied to leaves in the dark was similar at the end of the day and the end of the night. No correlation was observed between the rates of leaf respiration and extension growth. It is argued that the higher rate of respiration at the beginning of the night cannot be attributed to wasteful respiration.Abbreviation RQ respiratory quotient We thank Dr H. Thomas and Professor C.J. Pollock, Institute for Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, UK for their generous help in measuring leaf extension. R.H.A. thanks the Science and Engineering Research Council for a studentship.     

The kinetics of type 1 phytochrome in green,light-grown wheat (Triticum aestivum L.)

The kinetics of type 1 phytochrome were investigated in green, light-grown wheat. Phytochrome was measured by a quantitative sandwich enzyme-linked immunosorbent assay using monoclonal antibodies. The assay was capable of detecting down to 150 pg of phytochrome. In red light, rapid first-order destruction of the far-red-light-absorbing form of phytochrome (Pfr) with a half-life of 15 min was observed. Following white light terminated by red, phytochrome synthesis was delayed in darkness by about 15 h compared to plants given a terminal far-red treatment. Synthesis of the red-light-absorbing form of phytochrome (Pr) was zero-order in these experiments. Phytochrome synthesis in far-red light was approximately equal to synthesis in darkness in wheat although net destruction occurred in light-grown Avena sativa tissues in continuous far-red light, as has been reported for other monocotyledons. In wheat, destruction of Pfr apparently did not occur below a certain threshold level of Pfr or Pfr/total phytochrome. These results are consistent with an involvement of type 1 phytochrome in the photoperiodic control of flowering in wheat and other long-day plants.Abbreviations ELISA enzyme-linked immunosorbent assay - FR far-red light - HIR high-irradiance response - Pfr farred-light-absorbing form of phytochrome - Pr red-light-absorbing form of phytochrome - Ptot total phytochrome (Pr + Pfr) - R red light The authors wish to thank Prof. Daphne Vince-Prue (University of Reading) for many helpful discussions regarding this work. Hugh Carr-Smith was supported by a Science and Engineering Research Council studentship and Chris Plumpton by an Agricultural and Food Research Council (AFRC) studentship. B. Thomas and G. Butcher were supported by the AFRC.     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The activity of a range of endo- and exopeptidase enzymes have been measured in the glumes, flag leaf and stem during the period of grain development in wheat. The enzymes show a sequential pattern of appearance with activity peaks occurring at a number of intervals from anthesis until just prior to the cessation of grain growth. Of the enzymes studied only the haemoglobin- and casein-degrading activity and alanylglycine-dipeptidase activity increased during the period of rapid protein loss, while aminopeptidase, carboxypeptidase and leucyltyrosine dipeptidase reached maximum activity prior to this period.     

The role of calcium ions in phytochrome-controlled swelling of etiolated wheat (Triticum aestivum L.) protoplasts

Protoplasts from dark-grown wheat (Triticum aestivum L.) maintained at a constant osmotic potential at 22°C, were found to swell upon red irradiation (R) and the effect was negated by subsequent far-red light (FR), indicating phytochrome involvement. Swelling only occurred when Ca²⁺ ions were present in the surrounding medium, or were added within 10 min after R. Furthermore, Mg²⁺, Ba²⁺ or K⁺ could not replace this requirement for Ca²⁺. The presence of K⁺ did not enhance the Ca²⁺-dependent swelling response. When the Ca²⁺-ionophore A 23187 was added to the medium, protoplasts swelled in the dark to the same extent as after R. Both the Ca²⁺-channelblocker Verapamil and La³⁺ inhibited R-induced swelling. It is proposed that R causes the opening of Ca²⁺-channels in the plasma membrane. Boyle-van't Hoff analyses of protoplast volume after R and FR are consistent with the conclusion that R irradiation causes changes in membrane properties.Abbreviations EDTA ethylenediaminetetraacetic acid - FR far-red light - nov non-osmotic-volume - Pfr FR-absorbing form of phytochrome - Pr R-absorbing form of phytochrome - R red light     

Gibberellin biosynthesis from gibberellin A12-aldehyde in a cell-free system from germinating barley (Hordeum vulgare L., cv. Himalaya) embryos

Gibberellin (GA) metabolism from GA₁₂-aldehyde was studied in cell-free systems from 2-d-old germinating embryos of barley. [¹⁴C]- or [17-²H₂]Gibberellins were used as substrates and all products were identified by combined gas chromatography-mass spectrometry. Stepwise analysis demonstrated the conversion of GA₁₂-aldehyde via the 13-deoxy pathway to GA₅₁ and via the 13-hydroxylation pathway to GA₂₉, GA₁ and GA₈. In addition, GA₃ was formed from GA₂₀ via GA₅. We conclude that the embryo is capable of producing gibberellins that can induce -amylase production in the aleurone layer. There was no evidence for 12- or 18-hydroxylation and GA₄ was neither synthesised nor metabolised by the system. All metabolically obtained GAs, with the exception of GA₃, were also found as endogenous components of the cell-free system in spite of ammonium-sulfate precipitation and desalting steps.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography We thank Mrs. G. Bodtke and Mrs. B. Schattenberg for preparing the barley embryos and the Deutsche Forschungsgemeinschaft for supporting this work.     

Influence of acetylcholine agonists and antagonists on the swelling of etiolated wheat (Triticum aestivum L.) mesophyll protoplasts

Etiolated wheat (Triticum aestivum L.) mesophyll protoplasts swell within 30 min in darkness after a red light (R) pulse or addition of acetylcholine (ACh), if 0.5 mM CaCl₂ is present in the medium. In addition, ACh is also able to induce swelling in the presence of both 0.1 mM KCl or NaCl. Besides ACh, only carbamylcholine out of the choline derivatives tested was active in induction of swelling in the presence of K⁺ or Na⁺. The K⁺/Na⁺-dependent ACh-induced protoplast swelling was nullified by a ‘calmodulin inhibitor’, but not by Ca²⁺-channel blockers, Li⁺ or VO ₄ ^3- . The antagonists atropine (of muscarine-sensitive ACh receptors, mAChRs) andd-tubocurarine (of nicotine-sensitive ACh receptors, nAChRs) nullified the Ca²⁺ — and the K⁺/Na⁺-dependent protoplast swelling responses, respectively, while having no effect on the Ca²⁺-dependent R-induced swelling response. Moreover, muscarine and nicotine mimicked ACh in the Ca²⁺- and K⁺/Na⁺-dependent swelling responses respectively. Just as is the case in animal cells, the proposed mAChRs appear to be associated with a phosphatidylinositol-dependent pathway, whereas the proposed nAChRs are phosphatidylinositol independent. Similarity between the action of ACh via the proposed mChRs and R via phytochrome in protoplast swelling indicates they share in common signal-transduction pathway. We dedicate this paper to Hans Mohr on the occasion of his 60th birthday We thank the Department of Molecular Biology of the Agricultural University, Wageningen for the use of the photomicroscope and Dr. G. Fassina, Department of Pharmacology, University of Padua, Italy for the gift of nifedipine. These studies were supported by The Foundation for Fundamental Biological Research (BION) which is subsidized by The Netherlands Organization for the Advancement of Research (NWO). A.T. was also supported by: a Research Fellowship from the Agricultural University, Wageningen; a Visitors Fellowship from NWO, the Netherlands; RP II 12.15 from Ministry of Education, Poland.     

The NADPH-protochlorophyllide oxidoreductase is the major protein constituent of prolamellar bodies in wheat (Triticum aestivum L.)

A fraction of highly purified prolamellar bodies was isolated from etioplasts of wheat (Triticum aestivum L. cv. Starke II, Weibull), as previously described by Ryberg and Sundqvist (1982, Physiol. Plant., 56, 125–132). Studies on the protein composition revealed that only one major polypeptide of an apparent molecular weight of 36000 is present in the fraction of prolamellar bodies. This polypeptide was identified as the NADPH-protochlorophyllide oxidoreductase. The highest specific activity of the enzyme in etiolated leaf tissue was confirmed to be in the fraction of prolamellar bodies.Abbreviations PChlide protochlorophyllide - PLB prolamellar body - PT prothylakoid     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The technique of EDTA-enhanced phloem exudation (King and Zeevaart, 1974: Plant Physiol. 53, 96–103) was evaluated with respect to the collection and identification of amino acids exported from senescing wheat leaves. Whilst the characteristics of the exudate collected conform with many of the accepted properties of phloem exudate, unexpectedly high molar proportions of phenylalanine and tyrosine were observed. By comparing exudation into a range chelator solutions with exudation into water, the increased exudation of phenylalanine and tyrosine relative to the other amino acids occurring when ethylene-diaminetetracetic acid was used, was considered to an artefact.In plants thought to be relying heavily on mobilisation of protein reserves to satisfy the nitrogen requirements of the grain, the major amino acids present in flag-leaf phloem exudate were glutamate, aspartate, serine, alanine and glycine. Only small proportions of amides were present until late in senescence when glutamine became the major amino acid in phloem exudate (25 molar-%). Glutamine was always the major amino acid in xylem sap (50 molar-%).The activities of glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 1.4.7.1), glutamate dehydrogenase (EC 1.4.1.3) and asparagine synthetase (EC 5.3.5.4) were measured in the flag leaf throughout the grain-filling period. Glutamine synthetase and glutamate-synthase activities declined during this period. Glutamate-dehydrogenase activity was markedly unchanged despite variation in the number of multiple forms visualised after gel electrophoresis. The activity of the enzyme reached a peak only very late in the course of senescence of the flag leaf. No asparagine-synthetase activity could be detected in the flag leaf during the grain-filling period.II. Peoples et al. (1980)     

Metabolism of gibberellins in a cell-free system from immature seeds of Phaseolus vulgaris L.

The biosynthetic steps from gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) to C₁₉-GAs were studied by means of a cell-free system from the embryos of immature Phaseolus vulgaris seeds. Stable-isotope-labeled GAs were used as substrates and the products were identified by gas chromatography-mass spectrometry. Gibberellin A₁₂-aldehyde was converted to GA₄ via non-hydroxylated intermediates and to GA₁ via 13-hydroxylated intermediates. 13-Hydroxylation took place at the beginning of the pathway by the conversion of GA₁₂-aldehyde to GA₅₃-aldehyde. The conversion of GA₂₀ to GA₅ and GA₆ was also shown but no 2-hydroxylating activity was found. Endogenous GAs from embryos and testas of 17-dold seeds were re-examined by gas chromatography-selected ion monitoring using stable-isotopelabeled GAs as internal standards. Gibberellins A₉, A₁₂, A₁₅, A₁₉, A₂₃, A₂₄, and A₅₃ were identified for the first time in P. vulgaris, in addition to GA₁, GA₄, GA₅, GA₆, GA₈, GA₁₇, GA₂₀, GA₂₉, GA₃₇, GA₃₈ and GA₄₄, which were previously known to occur in this species. The levels of all GAs, except the 2-hydroxylated ones, were greater in the embryos than in the testas. Conversely, the contents of GA₈ and GA₂₉, both 2-hydroxylated, were much higher in the testas than in the embryos.Abbreviations GA_n gibberellin A_n - GC-MS gas chromatography-mass spectrometry - GC-SIM gas chromatography-selected ion monitoring - HPLC high-performance liquid chromatography - TLC thin-layer chromatography - m/z ion of mass     

Heat modification of ribulose-1,5-bisphosphate carboxylase/oxygenase by temperature pretreatment of wheat (Triticum aestivum L.) seedlings

The effect of low-, ambient- and high-temperature pretreatments (48 h at 4° C, 20° C or 36° C) of wheat seedlings (spring wheat Triticum aestivum L., cv. Kolibri) on the solubility properties of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCase; EC 4.1.1.39) was studied. The extractable protein moiety of heat-pretreated plants exhibited increased solubility in dilute buffer (50 mM k-phosphate, pH 6.8), compared with protein extracted from 4° C- or 20° C-plants. The salting-out characteristics for ammonium-sulfate precipitation confirmed this finding since a delayed precipitation of extractable protein from 36°C-plants was observed. Using polyacrylamide gel electrophoresis, the in-vivo temperature-induced differences in protein solubility could be traced back to a change in the solubility of RuBPCase. The RuBPCase was purified from wheat seedlings, and the purified enzyme also exhibited differential solubility. In order to evaluate this further, purified RuBPCase was subjected to probing for conformational properties. A decrease of fluorescence of the RuBPCase 1-anilino-8-naphtalene sulfonate complex revealed that the RuBPCase from 36° C-plants had a more hydrophilic protein surface. Titration of the sulfhydryl groups of native RuBP-Case with 5,5-dithiobis (2-nitrobenzoic acid) pointed to a reduced accessibility of the R-SH groups in the case of the 36° C-type of RuBPCase. The large subunit of RuBPCase from 4° C/20° C-plants tended to give rise to an artificial lower-molecular-weight polypeptide which could not be found in crude or purified RuBPCase from heat-pretreated wheat seedlings.Abbreviations ANS 1-anilino-8-naphtalene sulfonate - DTNB 5,5-dithiobis(2-nitrobenzoic acid) - PAGE polyacrylamide gel electrophoresis - RuBPCase ribulose-1,5-bis-phosphate carboxylase/oxygenase - RuBP ribulose-1,5-bis-phosphate     

Specific binding of a hypersensitive lignification elicitor from Puccinia graminis f. sp. tritici to the plasma membrane from wheat (Triticum aestivum L.)

We have recently reported the isolation and characterization of a glycoprotein (M_r 67 000) from germ-tube walls of Puccinia graminis f. sp. tritici which elicits the cellular hypersensitive lignification response in wheat (G. Kogel et al., 1988, Physiol. Mol. Plant Pathol. 33, 173–185). The present study uses this glycoprotein, referred to as Pgt elicitor, to identify putative elicitor targets in wheat cell membranes. In enzyme-linked immunosorbent assays using anti-Pgt elicitor antibodies, specific binding sites for Pgt elicitor were detected in highly purified plasma-membrane vesicles of wheat (Triticum aestivum L.) primary leaf cells. Binding proved to be independent of the presence or absence in wheat of the Sr5 gene for rust resistance, and also occurred on barley (Hordeum vulgare L.) plasma membrane. The binding sites have an Mr of 30 000 and 33 000, respectively, and binding activity was not lost in the presence of sodium dodecyl sulfate. [¹⁴C]imido-Pgt elicitor was used to determine the apparent K _d value for specific binding, found to be 2.0 M, and the maximum content of binding sites, found to be 250 pmol per mg of plasma-membrane protein. The relevance of the elicitor binding for the outcome of the interaction of P. graminis and wheat is discussed.Abbreviations BSA bovine serum albumin - ELISA enzyme linked immunosorbent assay - IDPase inosine 5-diphosphatase - MPLC medium-pressure liquid chromatography - MF microsomal fraction - Pgt elicitor elicitor of Puccinia graminis f. sp. tritici - SDS sodium dodecyl sulfate - Pre U₃, Pre U₁ pure plasma membrane from wheat cultivar Prelude and plasma membrane contaminated by intracellular membrane, respectively This work was supported by the Deutsche Forschungsgemeinschaft. We wish to thank C. Larsson, Lund, Sweden for his kind support in the preparation of plasma membrane.     

Pathways of starch and sucrose biosynthesis in developing tubers of potato (Solanum tuberosum L.) and seeds of faba bean (Vicia faba L.)

Tissue slices from developing potato tubers (Solanum tuberosum L.) and developing cotyledons of faba bean (Vicia faba L.) were incubated with specifically labelled [¹³C]glucose and [¹³C]ribose. Enriched[¹³C]glucose released from starch granules was analysed by nuclear magnetic resonance (NMR). Spectral analyses were also performed on sucrose purified by high-performance liquid chromatography. In both tissues a low degree of randomisation (< 11 % in potato and < 14% in Vicia) was observed between carbon positions 1 and 6 in glucose released from starch when material was incubated with [¹³C]glucose labelled in positions 6 and 1, respectively. Similarly, with [2-¹³C]glucose a low degree of randomisation was observed in position 5. These findings indicate that extensive transport of three-carbon compounds across the amyloplast membrane does not occur in storage organs of either species. This is in agreement with previously published data which indicates that sixcarbon compounds are transported into the plastids during active starch synthesis. When [1-¹³C]ribose was used as a substrate, ¹³C-NMR spectra of starch indicated the operation of a classical pentose-phosphate pathway. However, with [2-¹³C]glucose there was no preferential enrichment in either carbon positions 1 or 3 relative to 4 or 6 of sucrose and starch (glucose). This provides evidence that entry of glucose in this pathway may be restricted in vivo. In both faba bean and potato the distribution of isotope between glucosyl and fructosyl moieties of sucrose approximated 50%. The degree of randomisation within glucosyl and fructosyl moieties ranged between 11 and 19.5%, indicating extensive recycling of triose phosphates.Abbreviation NMR nuclear magnetic resonance We are grateful to Dr. George Ratcliffe for his critical reading of the text and Dr. Bernard Goodman for helpful suggestions on the NMR measurements. The research was funded by a European Economic Community research grant, which the authors duly acknowledge.     

The Golgi apparatus in developing endosperm of wheat (Triticum aestivum L.)

The ultrastructure and distribution of the Golgi apparatus in developing wheat endosperm was investigated using a zinc iodide-osmium tetroxide staining complex in conjunction with low and high voltage electron microscopy. Dictyosomes were numerous in starchy endosperm and aleurone at 15 days after anthesis, and during the period of rapid storage protein deposition 25 d after anthesis. Fewer dictyosomes were seen in maturing endosperm. Two types of vesicles were associated with the dictyosomes; small, heavily-stained vesicles were sited at the ends of fine tubules which extend from the cisternae, and larger less-stained vesicles were associated with the periphery of the cisternae. Stereo-pairs of micrographs up to 1 m thick were taken to demonstrate the interconnections between cisternal and tubular endoplasmic reticulum. Elements of tubular ER were closely associated with dictyosomes, but connections were not observed. These results are discussed in relation to the transport of endosperm storage proteins from their site of synthesis on the cisternal ER to their site of storage, the protein bodies.     

Identification of three Wx proteins in wheat (Triticum aestivum L.)

Nullisomic analysis of waxy (Wx) protein of hexaploid wheat (Triticum aestivum L.) cv. “Chinese Spring” using two-dimensional polyacrylamide gel electrophoresis revealed that threeWx loci,Wx-A1, Wx-B1, andWx-D1, located on chromosome arms 7AS, 4AL, and 7DS, produce three distinct Wx subunit groups, subunit group-A (SGA), SGB, and SGD, respectively. SGA has a higher molecular weight and a more basic isoelectric point (pI) than the other two. SGB and SGD have the same molecular weight but a slightly different pI range. Owing to the detection of these three subunit groups, we were able to identify the expression of three waxy genes in wheat endosperm and to find two types of mutants among Japanese wheat cultivars, one lacking SGA and the others SGB. These results suggest the possibility of breeding a waxy wheat.     

Action spectrum for the effect of day-extensions on flowering and apex elongation in green,light-grown wheat (Triticum aestivum L.)

Fluence-rate response curves for wavelengths from 640 nm to 730 nm were constructed for the day-extension promotion of flowering in green, light-grown, wheat (Triticum aestivum L., cv. Alexandria), a long-day plant. The resultant action spectrum had action maxima at 660 nm and 716 nm and resembles spectra for the high-irradiance reaction (HIR) seen in etiolated plants. Because, the HIR is thought to be controlled by type I pytochrome (that which is most abundant in etiolated tissue) our results indicate the involvement of type I phytochrome in the photomorphogenesis of a light-grown, green plant.Abbreviations Pr red-light-absorbing form of phytochrome - Pfr far-red-light-absorbing form of phytochrome - Ptot total phytochrome level (Pr+Pfr) - HIR high-irradiance reaction - SDP short-day plant(s) - LDP long-day plant(s)     

Phytochrome modulation of calcium fluxes in wheat (Triticum aestivum L.) protoplasts

Employing the metallochromic dye murexide and by monitoring the uptake of radiolabelled calcium, photoreversible calcium fluxes were measured in wheat leaf protoplast suspensions. Results obtained by both methods were identical — red light promoted and subsequent far-red irradiation reversed an influx of Ca⁺⁺ ions into the protoplasts. These findings imply phytochrome regulation of Ca⁺⁺ fluxes across the plasma membrane. The influx of Ca⁺⁺ stimulated by 2 min red irradiation could be maintained in total darkness for the initial 16–18 min after illumination, after which a 6–8 min efflux process was triggered and the basal Ca⁺⁺ level restored. Verapamil, a calcium channel blocker, inhibited the red-promoted influx, whereas the far-red mediated efflux could be checked by the use of the ATPase inhibitor vanadate, and also by the calmodulin antagonist chlorpromazine, thus suggesting a role of ion channels and pumps in phytochrome-controlled Ca⁺⁺ fluxes. The possible involvement of phosphoinositides in phytochrome-modulated calcium fluxes was also investigated.Abbreviations A difference in absorbance - CPZ chlorpromazine - FR far-red (light) - MX murexide - PI phosphatidylinositol - PIP₂ phosphatidylinositol 4, 5-bisphosphate - PIPES piperazine-N,N-bis[2-ethanesulfonic acid] - POPOP 1, 4-bis [2-(5-phenyl-1, 3-oxazolyl)]-benzene - PPO 2, 5-diphenyl-1, 3-oxazole - R red (light) - SOV sodium orthovanadate