Synthesis of an Atrazine-Binding Protein of the PSII Reaction Center in Isolated Wheat Etiochloroplasts

Isolated wheat (Triticum aestivum L. cv Norin 61) etiochloroplastssynthesized membrane polypeptides of 34, 33 and 30 kDa whichwere resolved by lithium dodecyl sulfate polyacrylamide gelelectrophoresis at 4?C. One-dimensional peptide-mapping analysis,as well as differential labelling with (³H)-lysine or (³⁵S)-methionine,showed that the 34- and 30-kDa polypeptides are atrazine-bindingproteins of the PSII reaction center. ¹Present address: Research Center for Molecular Genetics, HokkaidoUniversity, Sapporo 060, Japan. (Received March 9, 1987; Accepted June 29, 1987)     

Reconstitution of Tonoplast H+-ATPase from Mung Bean (Vigna radiata L.) Hypocotyls in Liposomes

Reconstituted proteoliposomes of tonoplast ATPase are formedon solubilization of tonoplast membranes from mung bean (Vignaradiata L.) with deoxycholate (DOC) in the presence of a mixtureof soybean phospholipids (asolectin), after removal of DOC bypassage through a PD-10 column (Pharmacia). This method is idealbecause of its simplicity and rapidity. Selective insertionof sets of tonoplast H⁺-ATPase polypeptides (68 kDa, 60 kDa,16 kDa and several minor polypeptides) into liposomes usingthis method was confirmed by SDS-PAGE and immuno-blotting withantibodies raised against 68-kDa and 60-kDa polypeptides. Pumping of protons across the membranes of the proteoliposomeswas demonstrated by quinacrine-fluorescence quenching in thepresence of ATP-Mg²⁺. ATP-Mg²⁺ was shown to be the preferredsubstrate in both reconstituted and native tonoplast vesicles,and its optimum concentration was 0.75 to 3.0 mM. Quenchingwas completely abolished by a channel-forming ionophore, gramicidinD, and an inhibitor of tonoplast H⁺-ATPase, KNO₃. Antibodiesto 68-kDa and 60-kDa peptides partially inhibited the pumpingof protons. The rate of pumping of protons increased with thenumber of proteoliposomes, the maximal concentration of whichwas equivalent to 250 µg of protein per reaction mixture.The optimum pH for pumping was 6.5 when inside of proteoliposomeswere loaded pH at 7.2. The rate of pumping of protons was reducedwhen proteoliposomes were made using asolectin and cholesterolat 3 : 1 (w/w), as compared with those made with asolectin alone. The ATPase activity in reconstituted proteoliposomes was inhibitedby KNO₃, with half-maximal inhibition at approximately 7 mM.The enzyme actively hydrolyzed ATP in preference to GTP, CTP,UTP, and ADP, but it did not hydrolyze pNPP or AMP. Antibodiesagainst the 60-kDa polypeptide strongly inhibited ATPase activityas compared to antibodies against the 68-kDa polypeptide. Theresults obtained in this study demonstrate directly that functionaltonoplast H⁺-ATPase can be inserted selectively into liposomes. (Received August 31, 1990; Accepted April 18, 1991)     

Purification and Characterization of a Ca2+-Dependent Protein Kinase from the Halotolerant Green Alga Dunaliella tertiolecta

A Ca²⁺-dependent protein kinase (CDPK) that has been partiallypurified and characterized previously [Yuasa and Muto (1992)Arch. Biochem. Biophys. 296: 175] was further purified to about20,000-fold from the soluble fraction of Dunaliella tertiolecta.The enzyme preparation contained 60- and 52-kDa polypeptidesboth of which phosphorylated casein as a substrate. Both polypeptidesshowed a Ca²⁺-dependent increase in mobility during SDS-PAGEand ⁴⁵Ca²⁺-binding activity after SDS-PAGE and electroblottingonto a nitrocellulose membrane, suggesting that both the 60-and 52-kDa CDPKs directly bind Ca²⁺. The protein kinase inhibitors,K-252a and staurosporine, inhibited the CDPK competitively withrespect to ATP. An antibody raised against the 60-kDa CDPK crossreactedwith both the 60- and 52-kDa polypeptides. Both molecular specieswere autophosphorylated in the presence of Ca²⁺, and a highlyphosphorylated 80-kDa band appeared in addition to these phosphorylatedbands at 60 and 52 kDa in SDS-PAGE. However, the specific activityof CDPK was not changed by prior autophosphorylation when theautophosphorylated enzyme was assayed as a mixture of thesephosphorylated molecular species. Only the 60-kDa polypeptidewas immunodetected in subcellular fractions of Dunaliella cells.The 52-kDa polypeptide increased during storage of the enzyme.These results suggest that the 52-kDa polypeptide is a proteolyticartifact produced during purification. Immunoreactive bandsof 60-kDa were detected in extracts of several green algae butnot in extracts of higher plants or a brown alga. ¹This research was partly supported by Grants-in-Aid from theMinistry of Education, Science and Culture, Japan (No. 06454013and 06304023) and Research Fellowship of the Japan Society forthe Promotion of Science for Young Sciencists. ²Research Fellow (PD) of the Japan Society for the Promotionof Science.     

Partial Purification and Characterization of An ATPase in Mung Bean Hypocotyl Plasma Membrane: Suggestion for A New Type of Higher Plant Plasma Membrane ATPase

A vanadate-sensitive and nitrate-resistant ATPase was solubilizedwith Zwittergent 3–14 from a highly purified plasma membranefraction of mung bean hypocotyls and partially purified by glyceroldensity gradient centrifugation and phenyl-Sepharose columnchromatography. Either phosphatidylcholine or phosphatidylserinein addition to Mg^{2 +} was required for the enzyme activity, whereasK⁺, phosphatidylethanolamine and lysophosphatidylcholine hadno effect on the activity. The purified enzyme preparation containedtwo major polypeptides with molecular masses of 67 and 55 kDaas analyzed by SDS-polyacrylamide gel electrophoresis. Whenthe plasma membrane fraction was incubated with [-³²P]ATP, a45-70-kDa polypeptide(s) was labeled, and the label could berapidly chased with cold ATP. When the fraction was incubatedwith [¹⁴C]N,N'-dicyclohexylcarbodiimide, an inhibitor for theATPase, a 15-20-kDa polypeptide was labeled. We propose thatthe enzyme is a new type of higher plant plasma membrane ATP-aseand is composed of 67- and 55-kDa subunits and probably alsoa 15-20-kDa subunit. ¹Present address: Takarazuka Institute, Sumitomo Chemical IndustriesLtd., Takatsukasa, Takarazuka, Hyogo 665, Japan (Received September 2, 1987; Accepted May 20, 1988)     

Targeted inactivation of the gene psaK encoding a subunit of photosystem I from the cyanobacterium Synechocystis sp. PCC 6803

Mutant strains of the unicellular cyanobacterium Synechocystissp. PCC 6803, in which the psaK gene was insertionally inactivatedby targeted mutagenesis, were constructed. The gene is one ofthe two potential PsaK-coding genes which have been found asa result of the genome project with this cyanobacterium. Oneof the mutants was characterized in detail. A monocistronic,480-nucleotide mRNA of psaK was absent in total RNA from themutant cells. Inactivation of psaK had little effect on theaccumulation of polypeptides in the isolated PSI complexes exceptfor a polypeptide with an apparent molecular mass of 4.6 kDawhich was absent in the mutant. The amino-terminal amino acidsequence of the 4.6-kDa polypeptide confirmed that it was thetranslation product of psaK and further revealed a presequenceof PsaK. Characteristics of photoautotrophic growth at differenttemperatures, the amount of chlorophyll per cell, photosyntheticelectron transport rates with various electron acceptors, thekinetics of charge recombination between P700⁺ and reduced F_A/F_B,and the molar ratio of chlorophyll to P700, of the mutant werenot significantly different from those of the wild type. Furthermore,the trimer to monomer ratio of the PSI complexes isolated fromthe mutant was similar to that isolated from the wild type. (Received July 27, 1998; Accepted October 13, 1998)     

Cold-Induced Alterations in Plasma Membrane Proteins That are Specifically Related to the Development of Freezing Tolerance in Cold-Hardy Winter Wheat

The objective of this study was to identify plasma membraneproteins that are specifically induced by cold acclimation inwheat (Triticum aestivum L.). Two cultivars with a marked differencein the genetic ability to cold-acclimate, namely, spring wheat(cv. Chinese Spring) and winter wheat (cv. Norstar), were usedas the experimental material. After four weeks of growth ina cold chamber, the freezing tolerance in the shoots of winterwheat increased to –18°C, whereas it increased onlyto –8°C in the shoots of spring wheat. In the caseof roots from both cultivars, freezing tolerance increased onlyslightly after the growth in the cold environment. Cold acclimationinduced remarkable changes in the electrophoretic patterns ofplasma membrane proteins which depended on both the cultivarand the tissue examined. Levels of polypeptides with molecularmasses from 22 to 31 kDa decreased in both the root and shootplasma membranes from both cultivars. Among these polypeptides,levels of those of 28 and 26 kDa decreased abruptly after oneweek of cold acclimation. By contrast, levels of polypeptidesof 89, 83, 52, 23, 18 and 17 kDa increased specifically in theshoots of winter wheat. The increases in the levels of the 23-,18- and 17-kDa polypeptides were proportional to the developmentof freezing tolerance. Freeze-fracture electron microscopy ofplasma membranes from shoot cells revealed that the number ofintramembrane particles on the fracture faces decreased markedlyin winter wheat after cold acclimation, but to a lesser extentin spring wheat. These results suggest that the plasma membranesmight undergo molecular reorganization during cold acclimation. ¹Contribution no. 3709 from the Institute of Low TemperatureScience, Hokkaido University.     

Characterization of Proteins of Nuclear Envelopes Prepared from Mung Bean Hypocotyls

The polypeptide composition of nuclear envelopes prepared fromhypocotyls of mung bean (Vigna radiata) was investigated. Thetissue was homogenized in the presence of Triton X-100 and nucleiwere isolated by differential and discontinuous Percoll gradientcentrifugation. The nuclei were subjected to sonication in 2M KC1 or 50 mM lithium diiodosalicylate and then the nuclearenvelopes were collected by centrifugation. Proteins in theenvelope fraction were analyzed by sodium dodecylsulfate-polyacrylamidegel electrophoresis and blotting techniques. When the envelopefraction was incubated with [-³²P]ATP, 10 to 15 polypeptideswere labeled and the intensity of labeling of some of thesepolypeptides was enhanced by the addition of calcium ions. Theresults suggest the presence of a protein-phosphorylation systemin nuclear envelopes. Three polypeptides of 100, 42, and 40kDa stained blue with the cationic carbocyanine dye "Stains-all",and they were labeled with ⁴⁵Ca²⁺ on a transfer membrane. Thelectin concanavalin A recognized glycoproteins that migratedas polypeptides of 50, 49, 47, 43, 35 and 32 kDa, respectively.Of these polypeptides the two larger ones were prominent andwere solubilized by treatment of the envelope fraction withKCl at 2 M but not at less than 100 mM. These results suggestthat the mung bean nuclear envelope contains some calcium-bindingproteins and glycoproteins. These newly identified proteinsmay become useful as characteristic markers of the nuclear envelope. (Received July 16, 1993; Accepted December 15, 1993)     

Heat Shock Induced Change in Protein Ubiquitination in Chlamydomonas

Ubiquitin was purified from pea (Pisum sativum L.) and its antibodywas produced. Western blot analysis showed that the antibodycross-reacted with ubiquitins from a green alga Chlamydomonasreinhardtii, a brown alga Laminaria angustata and a red algaPorphyridium cruentum but not with ubiquitin from a blue-greenalga Synechococcus sp. In Chlamydomonas, the antibody also reactedwith some ubiquitinated proteins including 28- and 31-kDa polypeptides.The isoelectric points of Chlamydomonas ubiquitin and the 28-and 31-kDa ubiquitinated proteins were 8.0, 8.9 and 10.3, respectively.The ubiquitinated proteins, including the 28- and 31-kDa polypeptideswere detected after in vitro ATP-dependent ubiquitination ofChlamydomonas cell extract with ^l25I-labeled bovine ubiquitin.Heat treatment of Chlamydomonas cells (>40°C) causeddrastic increase of ubiquitinated proteins with high mol wt(>60kDa), and coordinated redistribution or decrease of otherubiquitinated proteins and free ubiquitin. Quantitative analysisrevealed that the 28- and 31-kDa ubiquitinated proteins showeddifferent responses against heat stress, i.e. the former beingmore sensitive than the latter. (Received July 10, 1988; Accepted October 4, 1988)     

Cell-Free Synthesis of Rice Prolamin

Polyadenylated RNA was isolated from the protein-body rich fractionof developing rice (Oryza sativa. L) seeds. In a wheat germcell-free system, the isolated polyadenylated RNA produced polypeptideswith the same solubility as prolamin subunits. The electrophoreticmobility of the polypeptides suggested the presence of a signalpeptide. ⁴To whom correspondences should be addressed (Received May 13, 1986; Accepted July 25, 1986)     

Increased Resistance to Acriflavine by Amplification of the acrA Gene of Escherichia coli K-12

The wild-type acrA⁺ gene of Escherichia coli K-12, cloned intoplasmid pAF1, was expressed as resistance to acriflavine (AF)in AF-sensitive acrA mutant cells (N43). When acrA⁺ genes wereamplified by treatment of cultures with chloramphenicol (50µg/ml), cells expressed much higher resistance to AF thanthat of the wild-type strain (N90). (Received November 22, 1989; Accepted July 7, 1990)     

Light Inhibits Flagellation in a Chlamydomonas Mutant

We have isolated a new flagellar mutant in Chlamydomonas reinhardtii.When the mutant was cultured under the white fluorescent lamp({small tilde}4,800 lux), most cells had no flagella. However,when the cultures were put in the dark, flagellation occurred.Greater than 70% of the cells had flagella within 12–16h after the transfer. The flagellar morphology varied from "rod-shape"(same as the wild-type flagella) to "disk-shape". The disk-shapedflagella had the axonemes which were curved into a loop withinthe swollen membrane. Hence, this mutant is called loop-1. Light-inhibitionof flagellation was restored in the presence of 10^–5 MDCMU. The spectral dependency of the photo-inhibition of flagellation,determined using the Okazaki Large Spectrograph, showed maximaleffectiveness at 400–420 nm and 600–680 nm. Theseresults suggest that photosynthesis inhibits flagellation ofloop-1 cells. (Received July 27, 1989; Accepted January 29, 1990)     

Mutations that affect flightin expression in Drosophila alter the viscoelastic properties of flight muscle fibers

Striated muscles across phyla share a highly conserved sarcomere design yet exhibit broad diversity in contractile velocity, force, power output, and efficiency. Insect asynchronous flight muscles are characterized by high-frequency contraction, endurance, and high-power output. These muscles have evolved an enhanced delayed force response to stretch that is largely responsible for their enhanced oscillatory work and power production. In this study we investigated the contribution of flightin to oscillatory work using sinusoidal analysis of fibers from three flightless mutants affecting flightin expression: 1) fln⁰, a flightin null mutant, 2) Mhc¹³, a myosin rod point mutant with reduced levels of flightin, and 3) Mhc⁶, a second myosin rod point mutant with reduced levels of phosphorylated flightin. Fibers from the three mutants show deficits in their passive and dynamic viscoelastic properties that are commensurate with their effect on flightin expression and result in a significant loss of oscillatory work and power. Passive tension and passive stiffness were significantly reduced in fln⁰ and Mhc¹³ but not in Mhc⁶. The dynamic viscous modulus was significantly reduced in the three mutants, whereas the dynamic elastic modulus was reduced in fln⁰ and Mhc¹³ but not in Mhc⁶. Tension generation under isometric conditions was not impaired in fln⁰. However, when subjected to sinusoidal length perturbations, work-absorbing processes dominated over work-producing processes, resulting in no net positive work output. We propose that flightin is a major contributor to myofilament stiffness and a key determinant of the enhanced delayed force response to stretch in Drosophila flight muscles. flight muscles; muscle mutants; myosin     

Functional upregulation of H+-ATPase by lethal acid stress in cultured inner medullary collecting duct cells

The response ofH⁺-ATPase to lethal acid stress isunknown. A mutant strain (called NHE2d) was derived from cultured inner medullary collecting duct cells (mIMCD-3 cells) following three cyclesof lethal acid stress. Cells were grown to confluence on coverslips,loaded with2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, andmonitored for intracellular pH(pH_i) recovery from an acid load. The rate of Na⁺-independentpH_i recovery from an acid load inmutant cells was approximately fourfold higher than in parent cells(P < 0.001). TheNa⁺-independentH⁺ extrusion was ATP dependent and K⁺ independent and wascompletely inhibited in the presence of diethylstilbestrol, N, N'-dicyclohexylcarbodiimide,or N-ethylmaleimide. Theseresults indicate that theNa⁺-independentH⁺ extrusion in cultured medullarycells is mediated via H⁺-ATPaseand is upregulated in lethal acidosis. Northern hybridization experiments demonstrated that mRNA levels for the 16- and 31-kDa subunits of H⁺-ATPase remainedunchanged in mutant cells compared with parent cells. We propose thatlethal acid stress results in increased H⁺-ATPase activity in innermedullary collecting duct cells. Upregulation ofH⁺-ATPase could play a protectiverole against cell death in severe intracellular acidosis.

     

The Large Subunit of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase is Fragmented into 37-kDa and 16-kDa Polypeptides by Active Oxygen in the Lysates of Chloroplasts from Primary Leaves of Wheat

Lysates of chloroplasts isolated from wheat (Triticum aestivumL. cv. Aoba) leaves were incubated on ice (pH 5.7) for 0 to60 min in light (15 µmol quanta m^–2 s^–1),and degradation of the large subunit (LSU) of ribulose-l,5-bis-phosphatecarboxylase/oxygenase (Rubisco: EC 4.1.1.39 [EC] ) was analyzed byapplying immunoblotting with site-specific antibodies againstthe N-terminal, internal, and C-terminal amino acid sequencesof the LSU of wheat Rubisco. The most dominant product of thebreakdown of the LSU and that which was first to appear wasan apparent molecular mass of 37-kDa fragment containing theN-terminal region of the LSU. A 16-kDa fragment containing theC-terminal region of the LSU was concomitantly seen. This fragmentationof the LSU was inhibited in the presence of EDTA or 1,10-phenanthroline.The addition of active oxygen scavengers, catalase (for H₂O₂)and n-propyl gallate (for hydroxyl radical) to the lysates alsoinhibited the fragmentation. When the purified Rubisco fromwheat leaves was exposed to a hydroxyl radical-generating systemcomprising H₂O₂, FeSO₄ and ascorbic acid, the LSU was degradedin the same manner as observed in the chloroplast lysates. Theresults suggest that the large subunit of Rubisco was directlydegraded to the 37-kDa fragment containing the N-terminal regionand the 16-kDa fragment containing the C-terminal region ofthe LSU by active oxygen, probably the hydroxyl radical, generatedin the lysates of chloroplasts. (Received October 28, 1996; Accepted February 7, 1997)     

Mutant dn Influences Dry Matter Distribution, Assimilate Partitioning and Flowering in Lathyrus odoratus L.

The flowering mutant dn in sweet pea was used as a tool to study¹⁴C-assimilate and dry matter partitioning with respect to nutrientdiversion theories on the control of flower initiation. Wildtype plants (Dn^h) are photoperiodic and exhibit late floweringand profuse basal branching in short days while mutant plants(dn) are day neutral, early flowering and devoid of basal laterals.In short days, dn plants exported a significantly greater proportionof assimilate acropetally than (Dn^h) plants and the upper portionof dn plants had a greater dry weight. These differences werereduced dramatically when basal laterals were excised regularlyfrom the (Dn^h) plants although the difference in flowering remained.However, the effect of dn on resource allocation within theapical region may be more important in regard to flowering thanthe effect on acropetal versus basipetal movement. In shortdays, the dn plants partitioned significantly more resourcesinto their internodes and petioles, and less into their leaflets,than Dn^h plants as shown by dry weight and ¹⁴C-assimilate measurements.These differences were apparent from as early as node 7 up tothe node of flower initiation in dn plants (node 30) and theywere not eliminated by removal of basal laterals from Dn^h plants.Differences between dn and Dn^h plants in partitioning and floweringwere largely eliminated under long days. The fact that in thisspecies a single gene influences both resource allocation andflower initiation lends further support to nutrient diversionhypotheses on the control of flowering. Key words: Assimilate partitioning, branching, flowering, mutant, sweet pea     

Functional characterization of two S-nitroso-L-cysteine transporters, which mediate movement of NO equivalents into vascular cells

In myogenic C₂C₁₂ cells, 5 mM creatine increased the incorporation of labeled [³⁵S]methionine into sarcoplasmic (+20%, P < 0.05) and myofibrillar proteins (+50%, P < 0.01). Creatine also promoted the fusion of myoblasts assessed by an increased number of nuclei incorporated within myotubes (+40%, P < 0.001). Expression of myosin heavy chain type II (+1,300%, P < 0.001), troponin T (+65%, P < 0.01), and titin (+40%, P < 0.05) was enhanced by creatine. Mannitol, taurine, and -alanine did not mimic the effect of creatine, ruling out an osmolarity-dependent mechanism. The addition of rapamycin, the inhibitor of mammalian target of rapamycin/70-kDa ribosomal S6 protein kinase (mTOR/p70^s6k) pathway, and SB 202190, the inhibitor of p38, completely blocked differentiation in control cells, and creatine did not reverse this inhibition, suggesting that the mTOR/p70^s6k and p38 pathways could be potentially involved in the effect induced by creatine on differentiation. Creatine upregulated phosphorylation of protein kinase B (Akt/PKB; +60%, P < 0.001), glycogen synthase kinase-3 (+70%, P < 0.001), and p70^s6k (+50%, P < 0.001). Creatine also affected the phosphorylation state of p38 (–50% at 24 h and +70% at 96 h, P < 0.05) as well as the nuclear content of its downstream targets myocyte enhancer factor-2 (–55% at 48 h and +170% at 96 h, P < 0.05) and MyoD (+60%, P < 0.01). In conclusion, this study points out the involvement of the p38 and the Akt/PKB-p70^s6k pathways in the enhanced differentiation induced by creatine in C₂C₁₂ cells. protein synthesis; insulin-like growth factor; mitogen-activated protein kinase; extracellular signal-regulated kinase 1/2; 70-kDa ribosomal S6 protein kinase     

Extensin Secreted into the Culture Medium of Tobacco Cells II. Extensin Subfamilies of Similar Composition

Combining acetic acid extraction and high-performance gel chromatographyin guanidine HCl, extensin secreted into the medium by tobacco(Nicotiana tabacum L. var Xanthi) culture cells was separatedinto three component molecules, namely a major 74-kDa, and twominor 45-and 28-kDa components, in addition to larger oligomers.The sizes of these native extensin molecules were first reasonablyassessed using this gel-chromatography system. After deglycosylationwith hydrogen fluoride, the separation was improved and theestimated molecular sizes were reduced to 52 kDa, 34 kDa and18 kDa, respectively. The amino acid compositions of these componentswere similar, and N-terminal sequences of the 52- and 34-kDacomponents coincided. The relative abundance of the componentswas as follows: oligomers, 46%; 52-kDa, 44%; 34-kDa, 7.7%; 18-kDa,2.2%; respectively, on a protein basis (w/w). Fluorography ofthe acid extract of microsomes from cells labelled with ¹⁴C-prolinerevealed only one precursor band of 110-kDa or 42-kDa underthe glycosylating or non-glycosylating conditions, respectively.The smaller components in the medium may be derived, by proteolyticcleavage, from the major extensin molecule after secretion. (Received October 15, 1990; Accepted May 15, 1991)     

Purification and Characterization of Three Distinct Protein Kinases from Marchantia polymorpha

Three protein kinases (HK-I, HK-II and HK-III) have been partiallypurified from the 1.0 M KC1 extract of Marchantia polymorphaand biochemically characterized. It was found that (i) the molecularweights of HK-I, HK-II and HK-III were approximately 23 kDa,47 kDa and 28 kDa, respectively; (ii) these three kinases requireddivalent cations, such as Mn²⁺ and Mg²⁺, but not Ca²⁺, for activity;and (iii) histone H1 was an effective phosphate acceptor forboth HK-I and HK-II, whereas the other kinase (HK-III) effectivelyphosphorylated whole histone (Type II-A from calf thymus) ratherthan histone H1. Heparin (20µg/ml), an inhibitor of caseinkinase II, significantly stimulated the phosphorylation of cellularpolypeptides by HK-II, which was thermo sensitive even at 30?C,rather than that by the other kinases (HK-I and HK-III). Moreover,experiments in vitro and in vivo to determine the native phosphateacceptors for HK-II indicated that a 60-kDa cellular polypeptidemay be one of the native phosphate acceptors for the proteinkinase. In addition, the similarity in properties of cdc2-kinase,which plays an important role in the cell cycle (in the transitionfrom the G₂ phase to mitosis) of yeast and many eukaryotic cells,to HK-II is discussed. (Received May 2, 1990; Accepted December 6, 1990)     

Salt Tolerance in the Triticeae: The Contribution of the D Genome to Cation Selectivity in Hexaploid Wheat

Inorganic cation concentrations were measured in shoots of hexaploidbread wheat (Triticum aestivum L.) and its presumed ancestorsgrown at 100 mol m^–3 external NaCl. Aegilops squarrosaand T. aestivum had high K/Na ratios while T. dicoccoides andAe. speltoides had low K/Na ratios. T. monococcum although havinga high K/Na ratio, had the highest total salt load of the fivespecies tested. The effect of the D genome (from Ae. squarrosa)was further investigated in seedlings of synthetic hexaploidwheats, and was again found to improve cation selectivity. Differentresponses were obtained from root and shoot tissue in this experiment.One synthetic hexaploid and its constituent parents were grownto maturity at 100 mol m^-3 NaCl and the yields recorded. Despitecomplications due to increased tillering in the stressed hexaploid,it was possible to show that the addition of the D genome enhancedyield characteristics in the hexaploid wheat. An experimentwith synthetic hexaploids derived from the tetraploid wheatvariety "Langdon" and several Ae. squarrosa accessions revealeddifferences in vegetative growth rates between the differentsynthetic hexaploids in the presence or absence of 150 or 200mol m^–3 external NaCl. The possibility of transferringsalt tolerance genes from Ae. squarrosa to hexaploid wheat usingsynthetic hexaploids as bridging species is discussed. Key words: Salt stress, wheat, D genome, Aegiops squarrosa, synthetic hexaploids