Alleviation of Seed Dormancy in the Desert ForbZygophyllum simplexL. from Pakistan

Zygophyllum simplexL. is a succulent annual that grows on thecoastal and inland saline flats around Karachi, Pakistan. Theseeds are moderately salt tolerant during germination. GerminationofZygophyllum simplexseeds under various salinity, proline,betaine, GA and kinetin treatments was determined. Proline (0.1and 1 mM) and betaine (0.1 and 1 mM) alleviated the innate dormancyof seeds, and germination reached 60–70% compared to 12%in the control set. At low salinity compatible osmotica alleviatedsome effects of salinity, but at higher NaCl concentrationsboth proline and betaine were ineffective. Gibberellic acid(0.3 and 3 mM) and kinetin (0.05 and 0.5 mM) substantially alleviatedboth innate as well as salinity-induced seed dormancy. At highersalinity (125 mM), low concentrations of kinetin (0.05 mM) andhigh concentrations of GA (3 mM) were more effective. GA completelyalleviated the effect of salinity at all concentrations used. Betaine; desert; dormancy; forb; GA; germination; halophyte; kinetin; proline; seeds; Zygophyllum simplex     

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     

Effect of Dormancy Relieving Compounds on the Seed Germination of Non-dormantAllenrolfea occidentalisunder Salinity Stress

Allenrolfea occidentalis(Chenopodiaceae) is a highly salt tolerantplant species that is widely distributed in inland salt marshesand salt playas of the western United States. We investigatedthe influence of dormancy-relieving compounds (fusicoccin, ethephon,nitrate and thiourea) in alleviating salinity stress on theseed germination ofA. occidentalis. Seed germination decreasedwith an increase in salinity and no seed germinated at 800 mMNaCl.Fusicoccin (5 µM), ethephon (10 mM) and nitrogenous compounds(20 mMnitrate and 10 mMthiourea) were able to counteract theinhibition produced by salinity treatments. All dormancy relievingcompounds significantly (P<0.0001) promoted germination atall salinity concentations. Fusicoccin completely reversed theinhibitory effects of salinity on seed germination ofA. occidentalis.Ethephon application significantly promoted germination at allsalinities. Nitrate and thiourea were relatively less effectivein alleviating the effects of high salinity on germination.Copyright1998 Annals of Botany Company Allenrolfea occidentalis, ethephon, fusicoccin, halophyte, dormancy, nitrate, salinity, seed germination, thiourea.     

A Comparison of Leaf Anatomy in Field-grown Gossypium hirsutum and G. barbadense

Gossypium hirsutum L. (upland cotton) and G. barbadense L. (Pimacotton) are two of the most important fibre producing cottonspecies in cultivation. When grown side-by-side in the field,G.hirsutum has higher photosynthetic and transpiration rates (Luet al., 1997. Australian Journal of Plant Physiology24: 693–700).The present study was undertaken to determine if the differencesin physiology can be explained by leaf and canopy morphologyand anatomy. Scanning electron microscopy was used to comparethe leaf anatomy of field-grown upland (‘Delta’and ‘Pine Land 50’) and Pima (‘S6’)cotton. Compared to G. hirsutum, mature leaves of G. barbadenseare larger and thinner, with a thinner palisade layer. G. barbadenseleaves show significant cupping or curling which allows fora more even absorption of insolation over the course of theday and much more light penetration into the canopy. AlthoughG. barbadense leaves have a 70–78% higher stomatal densityon both the abaxial and the adaxial surfaces, its stomates areonly one third the size of those of G. hirsutum. This resultsin G. barbadense having only about 60% of the stomatal surfacearea per leaf surface area compared to G. hirsutum. These resultsare indicative of the anatomical and physiological differencesthat may limit the yield potential of G. barbadense in certaingrowing environments. Copyright 2000 Annals of Botany Company Cotton, leaf anatomy, leaf development, photosynthesis, Gossypium hirsutum, Gossypium barbadense, stomatal density     

Movement of Kinetin and Gibberellic Acid in Leaf Petioles during Water Stress-induced Abscission in Cotton

Movement of [¹⁴C]kinetin and [¹⁴C]gibberellic acid was examined in cotton (Gossypium hirsutum L.) cotyledonary petiole sections independent of label uptake or exit from the tissue. Sections 20 millimeters in length were taken from well watered, stressed, and poststressed plants. Transport capacity was determined using a pulse-chase technique. Movement of both kinetin and gibberellic acid was found to be nonpolar with a velocity of 1 millimeter per hour or less, suggesting passive diffusion. Neither water stress nor anaerobic conditions during transport of labeled material affected the transport capacity of the petioles.     

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)     

Leaf Growth in Cotton (Gossypium hirsutum L.) 2. The Influence of Temperature, Light, Water Stress and Root Restriction on the Growth and Initiation of Leaves

The rate parameters R₁, R₂, I/LI and I/t_0.5, which characterizethe growth in area of successive main-stem leaves, probablyall have the same temperature response. Temperature thereforeonly operates on the time scale. Water stress reduces both therelative growth rate and the advance of developmental age, thelatter however to a lesser extent than the former. The effectof root restriction is explained as resulting from mineral shortage. Gossypium hirsutum L., cotton, leaf growth, leaf initiation, relative growth rate, temperature, light, water stress, root restriction     

Inhibition of cottonseed germination with abscisic Acid and its reversal

Germination of cottonseed (Gossypium hirsutum L.) was inhibited by abscisic acid. Inhibition was greater when seeds were soaked in abscisic acid for 5 hours and dried prior to germination than when abscisic acid was applied in the germination medium. (2-Chloroethyl)phosphonic acid, gibberellic acid, and kinetin partially overcame the inhibitory action of abscisic acid. Combinations of (2-chloroethyl)phosphonic acid with gibberellic acid or kinetin were more effective than the individual substances. Germination also was partially restored by removal of seed coats. Fusicoccin completely restored germination of abscisic acidtreated seeds.     

Observations on the Germ Aleurone of Barley. Phenol Oxidase and Peroxidase Activity

Strips of tissue containing the germ aleurone layer were removedfrom dry, harvest-ripe grains of barley (Hordeum vulgare L.)and incubated in buffered solutions of phenolic compounds, withand without the addition of hydrogen peroxide. Peroxidase ando-diphenol oxidase activity were found in the material releasedinto the incubation medium, and in the cytoplasm of the germaleurone cells. Peroxidase activity was located in the cellwalls and appeared to be high in the region where the germ aleuronecovering the embryonic axis merges into that which adheres tothe scutellum i.e. the region in which a row of germ aleuronecells becomes lignified following germination. Monophenol oxidaseactivity was not detected in the released enzymes or in theintact tissue. Although hydroquinone was oxidized in the cytoplasmof the germ aleurone tissue, unequivocal evidence of the presenceof laccase was not obtained. The oxidation of endogenous phenolicsubstances by phenol oxidases and peroxidases is discussed inrelation to anti-microbial defence mechanisms which appear tooperate in the germ aleurone during germination.Copyright 1994,1999 Academic Press Barley, Hordeum vulgare L., germ aleurone, catechol oxidase, laccase, peroxidase, defence mechanisms, germination     

Spatial and Temporal Aspects of Growth in the Primary Root of Cotton Seedlings: Effects of NaCl and CaCl2

Seedlings of cotton (Gossypium hirsutum L. cv. Acala SJ-2) weregrown in modified Hoagland nutrient solution with various combinationsof NaCl and CaCl₂. Marking experiments and numerical analysiswere conducted to characterize the spatial and temporal patternsof cotton root growth at varied Na/Ca ratios. At 1 mol m^–3Ca, 150 mol m^–3 NaCl reduced overall root elongation rateto 60% of the control, while increasing Ca to 10 mol m^–3at the same NaCl concentration restored the elongation rateto 80% of the control. Analysis of the spatial distributionof elongation revealed that the presence of 150 mol m^–3NaCl in the medium shortened the growth zone by about 2 mm fromthe approximate 10 mm in the control and also reduced the relativeelemental elongation rate (i.e. the longitudinal strain rate,defined as the derivatives of displacement velocity of a cellularparticle with respect to position on root axis). Supply of 10mol m^–3 Ca at the high salt condition restored partiallythe relative elemental elongation rate, but not the length ofthe growth zone. Compared to the control, the growth trajectoriesshowed that at 1 mol m^–3 CaCl2 it took more time for acellular particle to move through the growth zone at 150 molm^–3 NaCl, while at 10 mol m^–3 CaCl it took lesstime and there was no difference between the NaCl treatments Key words: Gossypium hirsutum, salinity stress, root growth kinematics     

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     

Characterization of the Light Environment in Canopies Using 3D Digitising and Image Processing

A method to measure light interception by vegetation canopiesis presented which uses a 3D digitiser and image processingsoftware. The 3D digitiser allows for simultaneous acquisitionof the spatial co-ordinates of leaf locations and orientations.Software for image synthesis is used to make virtual photographsof the real canopy. Information on light interception is derivedfrom the virtual images by using simple features of image analysissoftware. The method is applied to cotton, grapevine and youngmango plants. Calculations are made of light interception atthe canopy level, light partitioning between plant organs, verticalprofiles of light interception, fisheye photographs and leafirradiance distribution.Copyright 1998 Annals of Botany Company 3D digitising, image analysis, light interception,Gossypium hirsutumL.Vitis viniferaL.,Mangifera indicaL., cotton, grapevine, mango, canopy.     

Hormonal Control of Germination under Saline Conditions of Three Halophytic Taxa in the Genus Suaeda

The interaction between hormones and salinity on seed germination of three halophytic taxa in the genus Suaeda: S. maritima (L.) Dum. var. flexilis Focke and var. macrocarpa Moq., and S. depressa (Pursh) Wats, was studied. Exogenous applications of kinetin and gibberellic acid (GA3) were applied in order to determine if either of these growth-promoting hormones would promote germination in the two dormant taxa, Suaeda depressa and S. maritima var. flexilis and to see if osmotically induced dormancy by NaCl could be alleviated. Our results indicate that gibberellic acid is capable of breaking dormancy in these species with dormant seeds, but kinetin proved to be ineffective. A seed dormancy that was induced by osmotic stress could also be alleviated by treatments with gibberellic acid. Endogenous concentrations of both cytokinins and gibberellins were measured in seeds exposed to osmotic stress (0.85 M NaCl), and we found a reduction in cytokinin activity in these three taxa. Gibberellin-like activity was reduced in S. depressa when seeds were soaked in 0.85 M NaCl.     

Primary and Lateral Root Development of Dark- and Light-Grown Cotton Seedlings under Salinity Stress*

Primary root growth dynamics and lateral root development of dark- and light grown cotton seedlings (Gossypium hirsutum L., cv. Acala SJ-2) were studied under control and salinity stress conditions. The seedlings were grown by two methods: A) in paper-lined, vermiculite-filled beakers with the plants growing between the paper and the glass wall (Gladish and Rost, 1993), and B) in hydroponics after germination and initial growth in germination paper rolls saturated with the treatment solutions (Kent and Läuchli, 1985). After germination, daily primary root elongation rate gradually incrased to a maximum, then gradually declined to close to zero for dark-grown seedlings, or to sustained rates of about 10 mm per day for light-grown control plants. Salinity stress delayed primary root growth and reduced peak elongation rates, without changing the general primary root growth pattern. These results suggest that salinity changed the time-scale, but did not modify the normal developmental sequence. Lateral root growth was more inhibited by salinity than primary root growth. In addition, elongation of lateral roots was more inhibited by salinity than their initiation and emergence. Light exposure of the shoot favored both sustained primary root growth from 7 days after planting, and lateral root emergence and growth. Salinity effects were more severe on seedlings germinated and grown in hydroponics (method B) than on vermiculite-grown plants (method A). These results emphasize the importance of growing conditions for the NaCl-induced effects on cotton root development. In addition, the differential effects of salinity on primary and lateral roots became evident, pointing to diverse control mechanisms for the development of these root types.     

Cotton somatic embryo morphology affects its conversion to plant

Somatic embryos differentiated from hypocotyl explant in cotton (Gossypium hirsutum L.) exhibited very divergent morphologies. Six different types of somatic embryos based on cotyledon development were observed. The growth hormones (2,4-dichlorophenoxyacetic acid and kinetin) used in induction and maintenance media did not affect embryo rooting and germination. The 95 % conversion of normal embryos (with two cotyledons) was achieved, while an overall conversion was only 38 %. Horn shaped embryos failed to exhibit shoot growth. Poorly developed apical meristems were responsible for lower conversion percentages in some of embryo classes. However, regenerated plants phenotypically resembled to seed grown control plants regardless of somatic embryo morphology.     

Analysis of Low-temperature Tolerance of a Tomato (Lycopersicon esculentum) Cybrid with Chloroplasts from a more Chilling-tolerant L. hirsutum Accession

Growth and photosynthesis of an alloplasmic tomato (cybrid),i.e. line AH47, containing the nuclear genome of the chilling-sensitivecytoplasmic albino mutant of L. esculentum Mill. ‘LargeRed Cherry’ (LRC) and the plastome of a more chilling-toleranthigh-altitude accession of the related wild species L. hirsutumHumb. & Bonpl. LA 1777, were investigated at an optimal(25/20°C) and suboptimal (16/14°C) day/night temperatureregime and their performance compared with that of both euplasmicparents. The cybrid shoot had a similar biomass and developmentrate to the nuclear tomato (L. esculentum) parent at both temperatureregimes. Compared with the biomass production of shoots grownat optimal temperature, the reduction in shoot biomass at suboptimaltemperature was smaller for L. hirsutum than for L. esculentumand the cybrid. This difference was related to a stronger inhibitionof leaf area expansion in L. esculentum and the cybrid in thesuboptimal temperature regime than in L. hirsutum. Irrespectiveof the temperature regime under which the plants were grown,photosynthetic performance and leaf pigment, carbohydrate andsoluble-protein contents of the cybrid resembled those of thenuclear parent. No advantages of the alien L. hirsutum chloroplastwith respect to growth and photosynthesis-related characteristicswere observed in the cybrid in the suboptimal temperature regime,indicating that the temperature sensitivity of the photosyntheticapparatus is regulated by nuclear genes. An adverse consequenceof interspecific chloroplast transfer was the increased susceptibilityto chill-induced photoinhibition of the cybrid. It is concludedthat cybridization is not a useful tool for improving low-temperaturetolerance of tomato. Copyright 2000 Annals of Botany Company Alloplasmic tomato, chloroplast, cybrid(ization), growth, low-temperature tolerance, Lycopersicon esculentum, L. hirsutum, photosynthesis, plastome, tomato     

Changes in Root Resistance as a Function of Applied Suction, Time of Day, and Root Temperature

Water uptake rate of decapitated root systems of cotton (Gossypium hirsutum L.), tomato (Lycopersicon esculentum L. cv. Rutgers), and kidney bean (Phaseolus vulgaris L.) plants shows an exponential increase with applied suction up to about —1 bar. The water uptake rate was higher on the descending path of applied suction than on the ascending path, indicating a hysteresis effect in the roots. The root resistance in a cotton plant increased between 3-to 5-fold during the photoperiod of 12 hours. The water uptake rate increased with increasing temperature of the root medium up to 30°C in cotton and 25°C in tomato and bean plants.     

Quantifying the sensitivity of barley seed germination to oxygen, abscisic acid, and gibberellin using a population-based threshold model

Barley (Hordeum vulgare L.) seeds (grains) exhibit dormancyat maturity that is largely due to the presence of the glumellae(hulls) that reduce the availability of oxygen (O₂) to the embryo.In addition, abscisic acid (ABA) and gibberellins (GAS) interactwith O₂ to regulate barley seed dormancy. A population-basedthreshold model was applied to quantify the sensitivities ofseeds and excised embryos to O₂, ABA, and GA, and to their interactiveeffects. The median O₂ requirement for germination of dormantintact barley seeds was 400-fold greater than for excised embryos,indicating that the tissues enclosing the embryo markedly limitO₂ penetration. However, embryo O₂ thresholds decreased by anotherorder of magnitude following after-ripening. Thus, increasesin both permeability of the hull to O₂ and embryo sensitivityto O₂ contribute to the improvement in germination capacityduring after-ripening. Both ABA and GA had relatively smalleffects on the sensitivity of germination to O₂, but ABA andGA thresholds varied over several orders of magnitude in responseto O₂ availability, with sensitivity to ABA increasing and sensitivityto GA decreasing with hypoxia. Simple additive models of O₂–ABAand O₂–GA interactions required consideration of theseO₂ effects on hormone sensitivity to account for actual germinationpatterns. These quantitative and interactive relationships amongO₂, ABA, and GA sensitivities provide insight into how dormancyand germination are regulated by a combination of physical (O₂diffusion through the hull) and physiological (ABA and GA sensitivities)factors. Key words: Abscisic acid, barley, germination, gibberellin, Hordeum vulgare L., model, oxygen, sensitivity Received 2 August 2007; Revised 14 November 2007 Accepted 19 November 2007     

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     

The Effects of Kinetin and Gibberellin on the Germination of Dehusked Seeds of Indica and Japonica Rice (Oryza sativaL.) under Anaerobic and Aerobic Conditions

The effects of kinetin and gibberellin were examined under anaerobicconditions (0% oxygen) and aerobic conditions (20% oxygen) onthe germination of dehusked seeds of indica and japonica ricecultivars that had been harvested at different times duringthe formation of seeds. Surjamkhi was used as a representativeof deep dormant indica cultivars and Assam IV as a less dormantindica cultivar. Sasanishiki was used as the japonica rice cultivar.Both phytohormones were applied at a concentration of 10^-3Mwhichproved to have the greatest stimulatory effect in preliminarywork at concentrations of 10^-3–10^-5M. Under aerobic conditions,inhibition of germination by dehusking of Sasanishiki seedsthat had been harvested either 30 or 60 d after anthesis wasovercome by kinetin and all seeds germinated. Complete germinationinduced by kinetin under aerobic conditions was also achievedwith the dehusked seeds of the indica rice cultivar Assam IVthat had been harvested on two occasions and of Surjamkhi thathad been harvested 28 d after anthesis. In contrast, germinationof dehusked japonica seeds stimulated by anaerobiosis was inhibitedby kinetin. The stimulatory effects of gibberellin on the germinationof indica and japonica rice seeds were observed under aerobicand anaerobic conditions. Under anaerobic conditions, the responsesof dehusked indica and japonica rice seeds to kinetin and gibberellindiffered, being negative with kinetin and positive with gibberellin.Under aerobic conditions, the stimulatory effects of kinetinon germination of dehusked seeds were greater than those ofgibberellin. Thus, treatment with kinetin appears to be usefulfor breaking the considerable dormancy commonly observed inthe dehusked seeds of indica rice. Mechanisms are proposed toexplain the stimulatory effects of these phytohormones on thegermination of dehusked seeds of indica and japonica rice underaerobic and anaerobic conditions. Rice; Oryza sativaL.; seed germination; dehusking treatment; gibberellin; indica; japonica; kinetin; oxygen; dormancy; germination inhibition; seed formation