Poly(A) polymerase in Dormant Embryos of Triticum durum

Triticum durum‘Cappelli’ has a ‘relative’dormancy which can be broken by dry after-ripening at room temperature.The breakage of dormancy in the embryos of T. durum , is accompaniedby a decline in content and a different degree of synthesisof poly(A)⁺RNA. This work studies the activity of poly(A) polymerase(E.C. 2.7.7.19), the enzyme which permits polyadenylation. Anincrease in the activity of this enzyme in parallel with theenhanced rate of germination is revealed. Since poly(A) polymeraseactivity is the same in dormant and non-dormant dry embryos,it seems that the activity of the enzyme is not involved inthe breakage of dormancy. The use of cycloheximide and cordycepinshows the presence of enzymes with different origins: a storedenzyme and one bound to a long lived mRNA, present in dormantand non-dormant embryos, plus an enzyme bound to newly synthesizedmRNA which is mainly active in non-dormant embryos. Since dormancycould be the result of an interaction between hormones, thiswork analyses the effects of GA₃and ABA on poly(A) polymerase.GA₃enhanced poly(A) polymerase activity only in dormant embryoswhile ABA inhibited this activity only in non-dormant embryos.Cycloheximide applied to excised wheat embryos represses thestimulatory and inhibitory effects of GA₃and ABA, respectively.The hormone action on poly(A) polymerase activity is thus dependenton de novo protein synthesis. Results using cordycepin suggestthe presence of a stored mRNA for poly(A) polymerase, togetherwith hormonal regulation of enzyme activity at a translationallevel. Copyright 1999 Annals of Botany Company Triticum durum , wheat, dormancy breakage, poly(A) polymerase, GA₃, ABA, germination.     

Ageing and Osmotic Priming in Wheat Seeds: Effects Upon Certain Components of Seed Quality

Deteriorated wheat seed lots were osmotically primed and surface-dried,dried-back, then aged for two more weeks Osmotic priming didnot affect the final germination in any of the aged seed lots,but mean germination time was decreased The response of unagedseed lot to treatments was studied in the following the timecourses of germination, as well as L-[4, 5-²H]leucine and [6-³H]thymidineincorporation (as a measure of protein and DNA synthesis, respectively)into dissected embryos during the early hours of germinationIt was found that the variation in mean germination time andthe rate of synthetic reactions were related The greatest improvementin the components of seed lot quality was achieved after primingand surface drying The beneficial effects of priming were apparenteven after dehydration followed by two further weeks of ageingCumulative correlations between mean germination time and variousbiochemical tests in variously treated aged seed lots were highlysignificant The physiological processes involved in deteriorationand recovery and the potential application of biochemical testsin detecting vigour changes are discussed Triticum durum, seed, ageing, osmotic priming, mean germination time, protein DNA synthesis     

The Effect of Salinity Stress upon Protein Synthesis of Germinating Wheat Embryos

Two differently salt-sensitive wheat genotypes were imbibedin 0·4 M NaCl for 72 h or, alternatively, for 48 h andthen transferred to water. Seed germination, fresh weight andprotein synthesis in embryos were determined. The followingdifferences were found in the synthesis of in vivo [³⁵S]methionine-labelledproteins during salt imbibition: (a) a general decrease or disappearanceof polypeptides specific to the radicle emergence phase in thesalt-sensitive genotype; (b) a new synthesis of polypeptideswhich are not found during water imbibition and are common toboth genotypes; (c) a differential synthesis of polypeptidesthat are unique to each cultivar. Upon return to water, salt-inducedproteins ceased to be synthesized while proteins associatedwith an advanced germination phase were actively produced. Theseresults suggest that the expression of 'salt stress' proteinsis related to the adaptation process of seeds to salinity aswell as to the genetic constitution of a selected salt-tolerantgenotype.Copyright 1993, 1999 Academic Press Triticum durum, wheat, embryo, salt stress, protein synthesis     

The effect of potassium on germinating wheat embryos at different viability levels

The effect of potassium administration in early germination of wheat (Triticum durum L., cv. Appulo) was studied by incubating isolated embryos at different viability levels with 1 mM KC1. The stimulation of germination and growth in aged embryos by K⁺ was accompanied by a significant increase in (³H) leucine incorporation into protein and in phospholipid synthesis as evidenced by TLC analysis of embryo phospholipids extracted after 24 h of imbibition. The metabolic improvement mediated by the cation would in turn repair aging damage occurring at subcellular sites including membranes.     

Kinetic parameters of Zn uptake by wheat are affected by the herbicide chlorsulfuron

Kinetic parameters of Zn uptake were determined for wheat plants(Triticum aestivum cvs Excalibur and Gatcher, and Triticum turgidumconv. durum cv. Durati) pre-grown at deficient or sufficientZn supply and with 0 or 4 mg m^-3 sulphonylurea herbicide chlorsulfuron(2-chloro-N-(((4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino)carbonyl)-benzenesulphonamide].Net Zn uptake generally showed a saturable response to increasingsolution Zn concentrations; this response fitted a modifiedMichaelis-Menten equation incorporating the C_min term (solutionconcentration when net uptake is     

Seed germination and growth in Triticum I. Biological activity of extracts from T. durum endosperms

The nature of germination inhibitors in seeds of Triticum durumwas investigated. From a methanol extract of isolated endospermsof "Cappelli" wheat, two fractionations were carried out andfractions were tested for their influence on mitotic processesand growth of Triticum "Cappelli" plantlets. One of the sub-fractionsdepressed root growth, caused accumulation of metaphases, andinduced chromosome aberrations. The biological activity of thissub-fraction closely resembles that of the germinations inhibitorsof wheat seeds. ¹ This work was supported by a grant from the Consiglio Nazionaledelle Ricerche. (Received October 19, 1971; )     

Water Uptake and Protein Synthesis in Germinating Wheat Embryos under the Osmotic Stress of Polyethylene Glycol

The effect of osmotic stress on wheat-seed germination was testedby imbibition in aqueous polyethylene glycol solutions at differentconcentrations. The experiments were designed to allow blockingand the subsequent recovery of germination by 12 h or 24 h pre-imbibitionof seeds in osmoticum, followed by transfer to water. Seedswere alternatively presoaked in water for 12 or 24 h, then transferredto polyethylene-glycol solutions to study the induced blockingof germination. Water content and [³H]leucine incorporationinto embryo tissues (as a measure of in vivo protein synthesis)were determined over a 48-h imbibition period. A close relationshipwas established overall between hydration status and proteinsynthesis rate. Osmotic stress seems to have a strong influenceupon the quantitative synthesis of proteins, suggesting thatthis biochemical activity is associated with the regulationof the germination process. Triticum durum, embryo, osmotic stress, water uptake, protein synthesis     

Polyamine metabolism during early germination of Triticum durum Desf. cv. Cappelli

Abstract

Changes in polyamine metabolism have been studied during early germination of Triticum durum Desf. cv. Cappelli. In the embryos of dry seeds, the adequate polyamine content decreases with a minimum at 36 h of water imbibition. A great need for polyamines during germination is expressed by reactivation of their biosynthetic enzymes. Putrescine biosynthesis mostly occurs via the ornithine–decar–boxylase pathway until 42 hours of hydration. Arginine–decarboxylase activity, almost absent in the first stages of imbibition, reaches its maximal level around 36–42 hours, when ornithine–decarboxylase falls. These changes suggest that the polyamine metabolism could be differently activated depending on the growth process related to the germination phases.     

The Effect of Ageing Conditions on Loss of Viability in Wheat (T. durum)

The effect of fusicoccin (FC), potassium and sodium was testedon artificially aged wheat seeds. The treatments were unableto stimulate significantly the germination, contrary to theresults found in naturally aged wheat. When the embryos isolatedfrom the artificially aged seeds were germinated, they grewvery poorly and showed a marked decrease in proton extrusionwith respect to both the unaged and the naturally aged ones.Moreover, FC and K⁺ did not stimulate their germinability unlikethe naturally aged embryos. The changes are interpreted in termsof the effects of different ageing conditions on seed performanceand particularly on cell membrane state. Key words: Triticum durum, Seed viability, Ageing     

Physiological and Ultrastructural Changes in Isolated Wheat Embryos During Salt and Osmotic Shock

Physiological and ultrastructural changes were followed duringearly germination in isolated wheat embryos exposed to isotonicsolutions of NaCl and sorbitol. Both NaCl and sorbitol enteredthe embryos, and imbibition during the first 4 h was similar.Thereafter, the increase in embryo fresh weight, respiration,and the uptake and incorporation of precursors into proteinsand nucleic acids were strongly inhibited by NaCl while sorbitolonly slightly reduced these aspects of metabolic reactivation.Electron microscopic observations also showed that the effectsinduced by NaCl were more severe than those produced by sorbitol.The results are discussed in relation to the previously observedlack of sodium toxicity in wheat embryos germinating withinthe intact seeds. Germination, osmotic stress, salinity, sorbitol, Triticum durum L, wheat embryo     

Amylase Activity and Loss of Viability in Wheat

Changes in total and -amylase synthesis were compared in twowheat samples aged up to 70% viability level. The results showedthat differences in amylase levels can be detectable betweenunaged and aged wheats and also between the two aged samples.Thus seed viability loss is characterized by decreases in amylaseproduction. However, these changes appear to affect the germinationrate, but not the final germinability. Trticum durum L. cv. Appulo, wheat, seed ageing, amylase, -amylase     

Uptake of zinc from chelate-buffered nutrient solutions by wheat genotypes differing in zinc efficiency

Zinc-efficient Triticum aestivum (cv. Warigal) and Zn-inefficientTriticum turgidum conv. durum (cv. Durati) were grown in chelate-buffered,complete nutrient solutions providing either deficient or sufficientZn supply. When transferred to fresh chelatebuffered nutrientsolutions containing a wide range of Zn supplies (0–1.28µmol m^–3 Zn²⁺ activity) for 24–48 h, bothgenotypes increased net Zn uptake linearly with an increasein solution Zn²⁺ activities. Zincefficient Warigal accumulatedZn at a greater rate than Zn-inefficient Durati. The greaterrate of net Zn uptake was observed by plants of both genotypeswhen pretreated at deficient Zn supply. Net loss of Zn to thesolution was higher in plants pretreated with sufficient Znand was inversely related to Zn²⁺ activity in the external solution.When continuously supplied with 40 nmol m^–3 Zn²⁺, netZn uptake by Zn-efficient Warigal was significantly greaterthan that of Zn-inefficient Durati, but the difference diminishedwith plant age. Shoot concentrations of Fe, Mn and Cu were higherwhen plants were grown at deficient than at sufficient Zn supply.The Zn-efficient genotype transported less Zn and Fe to shootsand had higher Fe concentrations in roots than the Zn-inefficientgenotype, supporting the hypothesis that Zn efficiency may beconnected with inefficient transport of Fe from roots to shootsand thus initiation of the Fe-deficiency response resultingin increased release of Zn- and Fe-binding phytosiderophores.It is concluded that differential Zn efficiency of wheat genotypesis at least partly due to a greater ability of efficient genotypesto accumulate Zn. Key words: Chelate-buffering, genotypes, micronutrients, Triticum spp., uptake, zinc efficiency     

Normalizing Development of Cultured Triticum aestivum L. Embryos: I. LOW OXYGEN TENSIONS AND EXOGENOUS ABA

Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O₂ tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m^–3 ±ABA and 2.·1, 2·5 or 7·4mol m^–3 (6, 7 and 21%, respectively) gaseous O₂. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O₂ levels (2·1to 2·5 mol m^–3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m^–3).The combination of physiological levels of both ABA and O₂ largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O₂ and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat     

Salt Tolerance in the Triticeae: K/Na Discrimination in Barley

Concentrations of ions were measured in the youngest fully-expandedleaves of Triticum aestivum, T. durum, Hordeum vulgare, H. spontaneum,Secale cereale, and Aegilops squarrosa accessions grown in hydroponicculture in the presence of salt (NaCl+CaCl₂). Triticum aestivum,Secale cereale, and Ae. squarrosa had the low leaf Na and highleaf K concentrations typical of plants which contain the enhancedK/Na discrimination character originally found in Ae. squarrosa.T. durum and the Hordeum species did not have this character.The better growth of H. vulgare than of T. durum with similarsalt concentrations in the youngest fully-expanded leaves maybe a result of better compartmentation of Na, Cl, and K betweendifferent tisssues or between different compartments withincells. The enhanced K/Na discrimination character was expressedin disomic addition lines of H. vulgare chromosomes in Triticumaestivum. The H. vulgare variety Herta and its slender mutantboth had similar leaf cation concentrations, although they differedin growth rate when grown at 60 mol m^–3 NaCl. H. vulgareand T. durum seedlings grown in the absence of monovalent cationsaccumulated more ²²Na in their shoots than seedlings of otherspecies when incubated in 1.0 mol m^–3 NaCl labelled with²²Na. Key words: Salt, ion transport, I genome, barley, wheat     

Protein Dysfunction and Inhibition of Amino Acid Incorporation in Root Segments from Wheat and Mung Bean Seedlings caused by some Amino Acid Analogues

The effects of para-fluorophenylalanine (p-FPA) and azetidine-2-carboxylicacid (AZ) on acid phosphatase and peroxidase activity, and onL-leucine incorporation, in root segments of Triticum aestivumL. cv. Fenman and Vigna radial a (L.) Wilczek, were studied.Incubation with 50 mmol^–3 AZ significantly reduced phosphataseand peroxidase activities in wheat roots, but with 20 mol m^–3p-FPA, only the peroxidase activity was reduced. In mung beanroots, phosphatase activity was inhibited by both AZ and p-FPA.Effects of the ortho- and meta- isomers of FPA on wheat rootphosphatase and peroxidase, and on mung bean phosphatase, werealso examined. Leucine uptake and incorporation were not inhibitedby 5 h pre-incubation with either p-FPA or AZ, but were inhibitedafter 24 h of pre-incubation. The results support the view that,in the shorter term, the analogues inhibit enzyme activity bybecoming incorporated to produce non-functional protein and,in the longer term, metabolism is further affected by inhibitionof protein synthesis. Key words: Fluorophenylalanin, Azetidine-2-carboxylic acid, Triticum aestivum, Vigna radiata     

The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

Onset of deoxyribonucleic Acid synthesis in germinating wheat embryos

Germinating wheat embryos (Triticum vulgare var. Florence) synthesize proteins before the onset of DNA synthesis. The onset of DNA replication occurs at about 15 hours of germination and was shown to depend on proteins synthesized before 9 hours of germination with the use of blasticidin S, a specific inhibitor of protein synthesis. A 10-fold increase in the activity of DNA-dependent DNA polymerase was found in extracts derived from germinated embryos, as compared to the activity found in extracts from ungerminated embryos.     

Nucleic acid and protein synthesis and loss of vigour in germinating wheat embryos

A study has been made of the RNA and protein synthesising systems of wheat embryos isolated from seed lots having high viability but differing in vigour. The rate of RNA and protein synthesis in wheat embryos during the early hours of germination is related to the vigour of the seed lot. The imposition of a stress factor, in the nature of a sub-optimal germination temperature, during germination of isolated wheat embryos magnifies the differences in rates of protein and RNA synthesis between high and low vigour seed. Using cell-free protein synthesising systems it has been demonstrated that an important difference between high and low vigour embryos lies in the relative levels of messenger RNA in the embryo. High vigour embryos contain relatively higher levels of poly A⁺-RNA (i.e. potential mRNA species) than lower vigour embryos and furthermore the level of poly A⁺-RNA in high vigour embryos increases during early germination whilst in lower vigour embryos the level decreases. The difference in poly A⁺-RNA levels accounts, at least partially, for the differences in rates of protein synthesis observed between embryos from high and low vigour wheat seed during early germination at both optimal and sub-optimal germination temperatures.Abbreviations HEPES N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid - poly A⁺-RNA polyadenylated RNA - GM germination medium - PMS post-mitochondrial supernatant fraction     

Molecular Cytogenetics of an Amphiploid Trigeneric Hybrid between Triticum durum, Thinopyrum distichum and Lophopyrum elongatum

In situ hybridization of total genomic DNA was used to analyselines derived from an amphiploid between tetraploid wheat,Triticumdurum Desf. (2n =4x =28), and the wheatgrassesThinopyrum distichum(Thunb.) A. Löve (2n =4x =28) andLophopyrum elongatum (Host)A. Löve (2n =2x =14). A range of chromosome numbers wasdetected, arising from loss or gain of chromosomes. Total genomicDNA probes fromThinopyrum species,L. elongatum andTriticum monococcumL. were able to discriminate chromosomes from the A and B genomesof tetraploid wheat and those of wheatgrass-origin. The methoddid not discriminate the two wheatgrass genomes, J and E, indicatingtheir close similarity. Chromosomal aberrations—includingtelocentric and ring chromosomes—were frequent. Distalinter-genomic translocations of parts of A and B genome chromosomearms, unusual in wheat itself, were more frequent than translocationsbetweenT. durum and wheatgrass.In situ hybridization of an rDNAprobe most frequently revealed four sites associated with secondaryconstrictions onT. durum chromosomes and four onTh. distichumorL. elongatum chromosomes, although there was variation inthe number of loci between and within plants. Within interphaseand prophase nuclei, the three genomes were not intermixed andoften lay in distinct sectors. Wheat; hybrids; Triticum ; Triticeae; evolution; introgression; nuclear architecture; rDNA; in situ hybridization