Observations on the Germ Aleurone of Barley. Morphology and Histochemistry

The germ aleurone over the embryonic axis of barley was examinedin strips of tissue peeled off harvest-ripe grains. The germaleurone is only one cell thick but resembles 'normal' aleuronein being composed of living cells with dense, lipid-rich cytoplasmand thick walls containing phenolic material. In contrast tothe cells of the 'normal' aleurone, germ aleurone cells containvery few phytin or protein deposits. When the germ aleuroneis ruptured during germination, the walls at the torn edge becomethickened with shiny golden-brown material, and 'sealed' tothe testa. Two days after germination, lignin can be detectedin the walls of a single row of germ aleurone cells adjoiningthe scutellum. The role of the germ aleurone in defence againstmicroorganisms is discussed. It is suggested that the metabolicactivities in the germ aleurone in imbibed grains compete withthe embryo for oxygen, and thus may be one of the factors whichdetermine whether a grain germinates or remains dormant.Copyright1994, 1999 Academic Press Barley, Hordeum vulgare L., germ aleurone, histochemistry, defence mechanism, lignin, dormancy, microorganisms, pre-mature germination     

Localization of ATPase Activity on the Plasmalemma of Scutellar Epithelial Cells of Germinating Barley (Hordeum vulgare L.)

Chaffey, N. J. and Harris, N. 1985. Localization of ATPase activityon the plasmalemma of scutellar epithelial cells of germinatingbarley (Hordeum vulgare L.).—J. exp. Bot 36: 1612–1619. ATPase activity has been localized at an ultrastructural levelin the absorptive region of the scutella of germinating barley(Hordeum vulgare L.). The enzyme is localized on the plasmalemmaof the epithelial cells. Using the Gomori reaction the depositionof reaction product on the plasmalemma, which is dependent uponthe presence of supplied ATP, was precluded or reduced by theinhibitors orthovanadate, mercuric chloride and DCCD, whilstß-glycerophosphate would not act as an alternativesubstrate. The mitochondria demonstrated phosphatase activitywith both ATP and ß-glycerophosphate as substrate.The results are discussed in relation to the active uptake ofmetabolites by the scutellum during germination and the structuralmodification of the plasmalemma of the epithelial cells to formplasmatubules. Key words: ATPase, Hordeum vulgare L., localization (ultrastructural)     

Effects of Kinetin and Salinity on Germination of Tomato, Barley and Cotton Seeds

The effects of kinetin and the interaction between kinetin andsalinity on seed germination of three plant species namely Lycopersiconesculentum, Hordeum vulgare and Gossypium hirsutum were studiedKinetin was applied exogenously to the seeds in order to determinewhether this growth-promoting hormone would promote germinationand to see if osmotically-induced dormancy caused by NaCl couldbe alleviated The results indicate that kinetin is capable ofbreaking dormancy in these species and there is a significantinteraction with salinity in tomato and cotton Kinetin, germination, salinity, water stress, salt stress, Lycopersicon esculentum Mill, tomato, Hordeum vulgare L, barley, Gossypium hirsutum L, cotton     

Rates of Cell Division in Developing Barley Endosperms

Counts of nuclei in enzyme digested endosperms of barley cultivarBomi show that the final number of cells, 170000, is reachedbetween 18 and 21d after anthesis. Based on the number of cellprofiles in transverse mid-grain sections, starchy endospermcells divide up to day 14. Thereafter, cell proliferation isrestricted to the aleurone layer. Hordeum vulgare, starchy endosperm, aleurone, mitotic activity, light microscopy     

Fine Structural Changes in Barley Aleurone Cells During Gibberellic Acid-induced Enzyme Secretion

The fine structure of barley aleurone cells was studied in theenzyme secretion phase. An ultrastructural feature of this phaseis the formation of stacked rough endoplasmic reticulum (rER),for such a structure was never found in cells during the enzymesynthesis phase. Other structural features frequently observedin the secretion phase were amoeboid-shaped nuclei, the stackedrER wound round the nucleus and mitochondria, and a stream ofthe stacked rER directed to the plasmamembrane. Hordeum vulgare L, barley, aleurone cells, enzyme secretion, gibberellic acid     

Localization of carboxypeptidase I in germinating barley grain

Activity measurements and Northern blot hybridizations were used to study the temporal and spatial expression of carboxypeptidase I in germinating grains of barley (Hordeum vulgare L. cv Himalaya). In the resting grain no carboxypeptidase I activity was found in the aleurone layer, scutellum, or starchy endosperm. During germination high levels of enzyme activity appeared in the scutellum and in the starchy endosperm but only low activity was found in the aleurone layer. No mRNA for carboxypeptidase I was observed in the resting grain. By day 1 of germination the mRNA appeared in the scutellum where its level remained high for several days. In contrast, little mRNA was observed in the aleurone layer. These results indicate that the scutellum plays an important role in the production of carboxypeptidase I in germinating barley grain.     

Monitoring intra- and extracellular redox capacity of intact barley aleurone layers responding to phytohormones

Redox regulation is important for numerous processes in plant cells including abiotic stress, pathogen defence, tissue development, seed germination and programmed cell death. However, there are few methods allowing redox homeostasis to be addressed in whole plant cells, providing insight into the intact in vivo environment. An electrochemical redox assay that applies the menadione-ferricyanide double mediator is used to assess changes in the intracellular and extracellular redox environment in living aleurone layers of barley (Hordeum vulgare cv. Himalaya) grains, which respond to the phytohormones gibberellic acid and abscisic acid. Gibberellic acid is shown to elicit a mobilisation of electrons as detected by an increase in the reducing capacity of the aleurone layers. By taking advantage of the membrane-permeable menadione/menadiol redox pair to probe the membrane-impermeable ferricyanide/ferrocyanide redox pair, the mobilisation of electrons was dissected into an intracellular and an extracellular, plasma membrane-associated component. The intracellular and extracellular increases in reducing capacity were both suppressed when the aleurone layers were incubated with abscisic acid. By probing redox levels in intact plant tissue, the method provides a complementary approach to assays of reactive oxygen species and redox-related enzyme activities in tissue extracts.     

Intact tissue assay for nitrite reductase in barley aleurone layers

A method has been devised for the detection and measurement of nitrite reductase activity in intact barley (Hordeum vulgare L. cv. Himalaya) aleurone layers. The technique involves feeding aleurone layers nitrite and measuring nitrite disappearance after a given time period. The method also allows simultaneous determination of nitrite uptake by the tissue. Quantitative recovery of nitrite is obtained by rapid heating of tissue in the presence of dimethyl sulfoxide.     

Transient gene expression in aleurone protoplasts isolated from developing caryopses of barley and wheat

Methods have been developed for the isolation of aleurone protoplasts from developing caryopses of Hordeum vulgare and Triticum aestivum in order to study transient expression of introduced genes. Chimaeric gene constructs were introduced into aleurone protoplasts by polyethylene glycol (PEG). Transient expression directed by the 35S promoter from cauliflower mosaic virus (CaMV) of the reporter gene encoding chloramphenicol acetyl transferase (CAT) was detected in aleurone protoplasts from developing barley and wheat grains. Using a similar construct, CAT activity increased when the alcohol dehydrogenase intron 1 fragment from maize was ligated between the 35S promoter and the CAT coding region. The demonstration of transient expression in protoplasts from developing aleurone layers indicates that they may be useful for investigating tissue and developmental control of genes coding for cereal seed proteins.     

Effects of Ageing on Amylase Activity and Scutellar Cell Structure during Imbibition in Wheat Seed

In wheat seed the scutellum plays an important role in the hydrolysisof stored substrate during germination. This layer is activatedfirst, whilst the aleurone becomes activated later. A good correlationexists between the initiation of visible germination and theappearance of enzyme activity in the scutellum. Enzyme activityin the aleurone becomes apparent only when the germinating seedlingreaches the rapid growth phase. Electron microscopic observationsshow that during the later stages of germination the scutellarcells develop finger like projections. These may serve to absorbendospermic reserves hydrolysed by aleurone amylase. The scutellumof aged non-germinating seeds showed no amylase activity andno finger like projections were produced even after prolongedimbibition.Copyright 1993, 1999 Academic Press Wheat (Triticum aestivum L.), deteriorated, germination, scutellum, scanning electron microscopy, aleurone     

A Model for Germination Rate during Dormancy Loss in Hordeum vulgare

A quantitative model for change in germination rate of barley(Hordeum vulgare L.) during and after loss of primary dormancyis presented. Change in mean germination time on a logarithmicscale is normally distributed within the period of after-ripeningand the standard deviation of this distribution is shown tobe a quantitative function of after-ripening temperature. Therate of change of mean germination time is in inverse proportionto the product of the standard deviation and a parameter whichis characteristic of the seed population. The latter parameteris the rate constant for change in probit cumulative germinationas a negative linear function of the logarithm of mean germinationtime. A model based solely on dormancy loss is combined withan existing model of change in probit viability as a functionof mean germination time to produce a model which predicts thetime to and optimum value of mean germination rate of a populationas it after-ripens. The model provides a quantitative link betweenthe effect of pre-germination and germination environments ontotal and rate of germination of an initially dormant population.Experimental data from dormant barley (cv. Triumph) stored at27, 38, 45, 50 and 60 °C, and germinated at 18 °C wereused to validate the model. The data show that germination ratecontinues to increase after primary dormancy is lost until itreaches an upper limit determined by the intrinsic germinativevigour of the seed lot. Rate of loss of primary dormancy andincrease in germination rate thus appear to be quantitativelylinked as a function of after-ripening temperature and factorswhich may be specific to the mode of induction of dormancy withina seed lot prior to harvest.Copyright 1995, 1999 Academic Press Hordeum vulgare L. barley, germination rate model, dormancy, vigour, after-ripening temperature     

Modes of ethylene action in the release of amylase from barley aleurone layers

The development of xylanase activity by isolated barley (Hordeum vulgare cv. Himalaya) aleurone layers exposed to gibberellic acid was enhanced by ethylene, whereas the rate of glucanase synthesis was unaffected by ethylene. The elevated xylanase activity expressed in ethylene-treated tissue may be responsible for enhanced release of amylase in response to ethylene.     

The Effect of Calmodulin Antagonists on Gibberellic Acid-induced Enzyme Secretion in Barley Aleurone Layers

Calmodulin activity was detected and assayed in barley aleuronecells. The effect of calmodulin antagonists on GA₃-induced enzymesynthesis and secretion in barley aleurone layers was also investigated.These calmodulin antagonists (chlorpromazine, haloperidol) inhibitedonly GA₂-induced -amylase secretion. This inhibitory effectwas intensified after 6 h of GA₃-incubation. This leads us tosuggest that some calmodulin-controlled mechanism is involvedin GA₂-induced -amylase secretion. Hordeum vulgare L., barley aleurone cells, gibberellic acid, -amylase secretion, calmodulin, calmodulin antagonist     

Agmatine Metabolism and Hordatine Formation in Barley Seedlings

In the shoots of dark-grown barley seedlings coumaroylagmatineconcentration reaches a peak 3 d after germination; however,none could be detected 5 d after germination. Concentrationsof hordatines A, B and M show maxima 6 d after germination andthe concentrations decline to less than 50 per cent of the maximumby the 11th d. Putrescine, agmatine and spermidine peak respectively3,4 and 8 d after germination. Putrescine concentration declinesrapidly between the 8th and 9th d after germination. Agmatinecoumaroyl transferase (ACT) activity is greatest 3–4 dafter germination and activity is undetectable 5 d from germination.In the shoots of barley seedlings grown under diurnal illumination,hordatine M reached a peak 7 d after germination but no distinctpeaks could be found for hordatines A and B or coumaroylagmatine. Hordeum vulgare L., barley, coumaroylagmatine, hordatines, agmatine coumaroyltransferase, putrescine, spermidine     

Response of Cultured Embryos of Phaseolus vulgaris and Hordeum vulgare to Farnesol

Excised embryos of Phaseolus vulgaris incubated in a mediumcontaining 10 mg dm^–3 farnesol showed enhanced root growthwhereas the leaves remained rudimentary At lower concentrationsof exogenous farnesol normal leaf development occurred and rootgrowth was comparable to untreated cultures. Enhanced root growthalso occurred when excised embryos of Hordeum vulgare were treatedwith farnesol but only at 10 mg dm^–3 and this treatmentdid not prevent leaf growth X-ray micro-probe analysis of leavesrevealed an increased phosphorus content in P vulgaris and adecreased sulphur content in H vulgare in comparison to untreatedplants. Hordeum vulgare L., barley, Phaseolus vulgaris, bean, embryo culture, farnesol, X-ray microprobe analysis, root growth     

Wild Oat/Barley Interactions: Varietal Differences in Competitiveness in Relation to K+ Supply

Eight cvs of barley (Hordeum vulgare L.) were separately plantedwith Wild Oats (Avena fatua L., genetically pure line CS40)in a sand culture with two external K⁺ concentrations. Substantialdifferences were observed among barley cvs in their abilityto compete with wild oat. The variety Fergus was highly competitiveat both high and low [K⁺]_e, whereas Steptoe was competitiveonly at high [K⁺]_e, and Compana was only weakly competitivewith wild oat. The differences between barley cvs were relatedto their previously reported efficiencies of K⁺ uptake and utilization. Hordeum vulgare L., Avena fatua L., barley, wild oat, competition, K⁺ nutrition, utilization efficiency     

A Comparative Study of Early Seed Development in Genotypes of Barley and Rye

Early seed development was studied in 17 genotypes of barley,Hordeum vulgare L., and 11 genotypes of rye, Secale cerealeL. The numbers of cells and nuclei in the embryos and endospermsof developing seeds were scored daily for 5 days after selfpollination. For embryos, the mean cell doubling times variedfrom 9.2–12.9 h for barley and 15.7–22.7 h for rye.Endosperm mitotic cycle times of both species were shortestover the first 24 h after pollination but then became longer.A non-linear correlation was found between the number of embryocells and the number of endosperm nuclei in barely and rye andis similar to that for other members of the Triticeae. Hordeum vulgare L., Secale cereale L., barley, rye, embryo, endosperm, mean cell doubling time     

Differentiation of a Functional Aleurone Layer Within the Seed Coat of Sinapis alba L.

The hitherto unresolved ontogenetic origin of the aleurone layerin mustard (Sinapis alba L.) seeds was investigated with lightand electron microscopy. Contrary to previous views, this layerof storage cells is neither derived from the endosperm nor fromthe nucellus, but from a particular cell layer within the innerintegument of the seed coat. These cells differentiate and becomefilled with storage protein and fat concurrently with the maturationof the embryo. They survive seed desiccation and become depletedof storage materials during seed germination. Temporally correlatedwith the germinating embryo, the aleurone cells produce microbodyenzymes, which are controlled by light in a similar fashionin both tissues. Sinapis alba L., mustard, aleurone layer, seed coat, seed formation, germination     

Localization of ATPase in the endoplasmic reticulum and golgi apparatus of barley aleurone

Summary The cytochemical localization of adenosine triphosphatase (ATPase) was studied in the aleurone layer of barley (Hordeum vulgare L. cv. Himalaya). Isolated barley aleurone layers secrete numerous enzymes having acid phosphatase activity, including ATPase. The secretion of these enzymes was stimulated by incubation of the aleurone layer in gibberellic acid (GA₃). ATPase was localized using the metal-salt method in tissue incubated in CaCl₂ with and without GA₃. In sections of tissue incubated without GA₃, cytochemical staining was confined to a narrow band of cytoplasm adjacent to the starchy endosperm and to the cell wall of the innermost tier of aleurone cells. Cytochemical staining was absent from the organelles of tissues not treated with GA₃. In tissue incubated in the presence of GA₃, cytochemical staining was evident throughout the cytoplasm and cell walls of the tissue. In the cell wall, electron-dense deposits were found only in digested channels. The cell-wall matrix of GA₃-treated aleurone did not stain, indicating that it does not permit diffusion of enzyme. In the cytoplasm of GA₃-treated aleurone, all organelles except microbodies, plastids, and spherosomes stained for ATPase activity; endoplasmic reticulum (ER), Golgi apparatus, and mitochondria showed intense deposits of stain. The ER of the aleurone is a complex system made up of flattened sheets of membrane, which may be associated with both the Golgi apparatus and the plasma membrane. The dictyosome did not stain uniformly for ATPase activity; rather there was a gradation in staining of the cisternae from thecis (lightly stained) to thetrans (heavily stained) face. Vesicles associated with dictyosome cisternae also stained intensely as did the protein bodies of GA₃-treated aleurone cells.     

Localizing a-Amylase Gene Expression in Germinated Rice Grains

In situ hybridization was used to localize the sites of expressionfor two a-amylase genes (RAmy1A and RAmy3D) in rice (Oryza sativaL.) over five days of germination. Messenger RNAs from bothgenes were initially detected in the scutellar epithelium andappeared at later stages of germination in the aleurone layer.RAmy3D mRNA reached its peak of accumulation 2 days(d) earlierin the scutellar epithelium than RAmy1A mRNA. Both mRNAs continuedto accumulate in the aleurone layer up to 5 d of germination,although RAmy1A mRNA reached significantly higher levels thanRAmy3D mRNA. Overall, the aleurone layer was responsible forproducing the majority of the total grain a-amylase mRNA. (Received July 27, 1991; Accepted November 6, 1991)