Endosperm response to pollen irradiation in kiwifruit

 Cytological details of endosperm development after pollination with irradiated pollen were studied in Actinidia deliciosa (kiwifruit) cultivar Hayward. Pollinations were carried out involving five different sources of pollen (Matua, Tomuri, Burt, Berryman, and fruiting male) irradiated with gamma rays at doses of 700 and 900 Gy. Non-irradiated crosses were used as controls. Irradiated pollen induced development of approximately 25–30% of the ovules. Two types of ovules were observed: (1) with both embryo and endosperm and (2) with endosperm only. No mitotic abnormalities were found in control or irradiated endosperms. Mitotic divisions were regular and nuclei spherical and evenly spaced. However, the cells of irradiated endosperm usually contained low amounts of storage products. Ploidy level of the endosperms was evaluated by nuclear size (volume) with the use of image analyzis. Mean nuclear size in control and irradiated endosperms was 1598.3 and 750.9 μm³, respectively. It is concluded that endosperm produced after pollination with irradiated pollen is autonomous and represents the 2n level. Received: 14 October 1998 / Revision accepted: 10 March 1999     

Comparison of Four Methods Calculating the Seasonal Pattern of Plant Growth Efficiency of a Kiwifruit Berry

Four methods of determining the substrate requirements for synthesisof a kiwifruit [Actinidia deliciosa (A. Chev.) C. F. Liang etA. R. Ferguson var. deliciosa cv. Hayward] berry were comparedusing data derived from common kiwifruit berry samples collectedfrom anthesis to fruit maturity. The four methods were basedon fruit proximal analysis, elemental analysis, heats of combustion,or tissue carbon content. All methods gave similar patternsof seasonal costs and values of final cost to the plant (mean1.21 g glucose g^–1 season^–1) but there was lessagreement for growth respiration (mean 0.147 g glucose g^–1season^–1). This is the first time that a continuous recordof growth cost over the course of development has been presented,and the trends in seasonal cost reflect the uptake into andsynthesis of the different biochemical constituents in the fruit.The differences between the results of each method reflect theunderlying assumptions used in their development. It appearsfrom this work that the method of McDermitt and Loomis (1981),utilizing elemental analyses, is most preferred. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson var deliciosa cv Haywood, kiwifruit, true growth yield, plant growth efficiency, production value, glucose value, bioenergetic cost     

Changes in Cell Wall Composition and Water-soluble Polysaccharides During Kiwifruit Development

Changes in both cell wall and water-soluble polysaccharide compositionduring the growth of kiwifruits [Actinidia deliciosa (A. chev.) C. F. Liang and A. R. Ferguson var. deliciosa ‘Hayward’]were investigated. Cellulose was the major wall polysaccharide,with galactose and uronics the main non-cellulosic sugars. Muchsolubilization of cell wall pectic polysaccharides was detected.While wall-galactose solubilization started 3 months after anthesis,polyuronide degradation did not start until the fifth month,1 month prior to the harvest date. Parallel to these processes,a linear increase in water-soluble polysaccharides was detected.These mainly comprised galactose-rich polymers in the first3 months and little-branched polyuronides after the fifth month.Two different mechanisms for galactose and uronic acid solubilizationfrom kiwifruit cell walls during fruit development are proposed. Actinidia deliciosa ; cell wall; fruit growth; kiwifruit; water-soluble polysaccharides     

Shoot Axillary Bud Morphogenesis in Kiwifruit (Actinidia deliciosa)

The annual cycle of kiwifruit [Actinidia deliciosa(A. Chev.)C. F. Liang et A. R. Ferguson var.deliciosacv. Hayward] shootaxillary bud (first-order axillary bud, FOAB) morphogenesisis described. FOABs developed quickly with the majority of budscales and leaf primordia present approx. 125 d after budbreak(dab). Mature FOABs had, on average, 23.2 bud scales and leafprimordia. Most second-order axillary structures were also presentapprox. 125 dab. During the growing season, the second-orderstructures developed into second-order axillary buds (SOABs)or remained as simple, dome-shaped meristems (SDSMs). At maturity,nearly all FOABs had four SOABs and, on average, 12.4 SDSMs.Most SDSMs were fused to the subtending leaf primordia, butsome SDSMs developed so that they were ‘free’ fromthe subtending leaf primordia. Third-order axillary meristems(third-order SDSMs) were observed in the axils of most SOABs,and, on average, there were 20.6 per FOAB. Our observationson the development of second-order axillary structures are consistentwith evocation in kiwifruit occurring earlier than the generally-acceptedtime of late summer. Actinidia deliciosa; bud morphogenesis; development; flowering; evocation     

The Importance of Light Intensity for Pollen Tube Growth and Embryo Survival in Wheat x Maize Crosses

The success of Triticum aestivumxZea mays crosses, used to producewheat doubled haploids, is influenced by light intensity. Toexamine the basis for this response, pollen tube growth, embryosurvival and indicators of photosynthetic rate were measuredin two wheat cultivars (‘Karamu’ and ‘Kotuku’)crossed with maize at two irradiance levels (250 or 750 µmolm^-2s^-1, PAR). Pollen tube growth was significantly affectedby light intensity in ‘Karamu’ plants but not in‘Kotuku’ plants, despite both cultivars being pollinatedby the same maize source. The percentage of pollen tubes reachingthe cavity between the ovarian wall and integuments, or in themicropyle of ‘Karamu’ plants at high light intensity(65%) was nearly three-times greater than that at low lightintensity (22%). Thus, either low light intensity can affectthe maternal wheat plant in a way that inhibits pollen tubegrowth and/or high light intensity may promote pollen tube growthin ‘Karamu’ plants. Significant differences in ratesof electron transport in plants grown at the two light intensitiesindicated that the rate of photosynthesis may also have an effecton pollen tube growth. These results have importance for improvingthe efficiency of wheat x maize crosses and other wide cerealcrosses. Copyright 2001 Annals of Botany Company Intergeneric hybridization, light intensity, pollen tube growth, embryo survival, Triticum aestivum, wheat,Zea mays , maize     

Estimating the Bioenergetic Cost of a Developing Kiwifruit Berry and its Growth and Maintenance Respiration Components

A response surface was developed by regression analysis to quantifythe seasonal respiratory losses by a kiwifruit [Actinidia deliciosa(A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa cv.Hayward] berry growing in Fresno, CA. The equation of the surfacewas LNRESP = 1·622 + 0·0697 x TEMP –0·0472x DAY + 0·000165 x DAYSQ, where LNRESP is the naturallogarithm of the respiration rate (nmol CO₂ g d. wt^–1s^–1), TEMP is fruit temperature (°C), DAY is the numberof days after flowering, and DAYSQ is the square of the numberof days after flowering. Respiratory losses for a fruit witha final dry mass of 18·5 g were calculated to be 5·57and 5·92 g glucose per fruit per season in 1985 and 1986,respectively. Maintenance respiration was estimated to be 2·84and 3·19 g glucose per fruit per season for 1985 and1986, respectively. The total calculated bioenergetic cost ofkiwifruit berry growth and respiration was 25·25 and25·60 g glucose per fruit per season for 1985 and 1986,respectively. Respiratory losses, expressed as a proportionof the total carbohydrate required for fruit growth, were significant(mean 22·6%). The cost of fruit growth was estimatedto be very similar for two cooler sites (Davis and Watsonville)but estimates of maintenance respiration based on Fresno fruitrespiration data were unrealistically low for the Watsonvillesite. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward, kiwifruit, growth respiration, maintenance respiration, bioenergetic costs, model     

Anoxia tolerance in rice seedlings: exogenous glucose improves growth of an anoxia-'intolerant', but not of a 'tolerant' genotype

This study demonstrated that, in rice seedlings, genotypic differencein tolerance to anoxia only occurred when anoxia was imposedat imbibition, but not at 3 d after imbibition. When seeds wereimbibed and grown in anoxia, IR22 (anoxia-‘intolerant’)grew much slower and had lower soluble sugar concentrationsin coleoptiles and seeds than Amaroo (anoxia-‘tolerant’),while Calrose was intermediate. After 3 d in anoxia, the sugarconcentrations in embryos and endosperms of anoxic seedlingswere nearly 4-fold lower in IR22 than in Amaroo. Sugar deficitin the embryo of IR22 is presumably due to the limitation ofsugar mobilization rather than the capacity of transport asshown by similar sugar accumulation ratios of 1.8 between embryoand endosperm in IR22 and Amaroo at 3 d in anoxia. With 20 molm^–3 exogenous glucose, coleoptile extension and freshweight increments in anoxic seedlings of IR22 were much closerto those in the two other genotypes, nevertheless protein concentrationremained lowest on a fresh weight basis in the coleoptiles ofIR22; indicating that protein synthesis has a lower priorityfor energy apportionment during anoxia than processes crucialto coleoptile extension. In contrast to these responses to anoxiaimposed at imbibition, IR22 had nearly the same high toleranceto anoxia as Calrose and Amaroo, when anoxia was imposed onseedlings subsequent to 48 h aeration followed by 16 h hypoxicpretreatment. In fact, coleoptiles of anoxic IR22 had highersugar concentrations and grew faster than Calrose, and exogenousglucose had no effect on the coleoptile extension of IR22. Excisedcoleoptile tips of IR22 and Amaroo with exogenous glucose hadsimilar rates of ethanol production and were equally tolerantto anoxia. In conclusion, much of the anoxia ‘intolerance’of IR22 when germinated in anoxia could be attributed to limitedsubstrate availability to the embryo and coleoptile, presumablydue to slow starch hydrolysis in the endosperm. Key words: Anoxia, coleoptile, embryo, endosperm, ethanol production, germination, growth, Oryza sativa L., solute net uptake or loss, sugar availability.     

Nature of 'Pollinator' Effect in Potato (Solanum tuberosum L.) Haploid Production

Haploids (2n =24) of the common tetraploid (2n=48) potato (SolanumtuberosumL.) provide promising material for attacking many problemsconcerned with the genetics, cytogenetics and breeding of thisspecies. Interspecific 4xx2xcrosses betweenSolanum tuberosumgp.Andigenaorgp.Tuberosumcultivars as pistillate parents andSolanum tuberosumgp.Phurejaassource of pollen (hereafter ‘pollinator’) have beenused to produce maternally derived haploids through parthenogenesis.This paper discusses the nature of the ‘pollinator’effect in haploid extraction. The ‘pollinator’ hada significant effect on haploid frequencies following 4xx2xcrosses.The ‘pollinator’ effect seems to operate via theendosperm, in which haploid (n=2x) embryos are associated withhexaploid endosperm. A superior ‘pollinator’ appearsto have its effect by contributing two haploid (n) gametes tothe central cell. 2n pollen; double fertilization; endosperm; ploidy manipulations; Solanum tuberosum     

Estimation of the Annual Cost of Kiwifruit Vine Growth and Maintenance

Elemental analysis (for carbon, hydrogen, nitrogen and sulphur)and ash data for kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A. R. Ferguson var. deliciosa cv. Hayward] stems,leaves and fine roots were used to calculate the specific costs(kg carbohydrate kg^-1 dry matter) of organ synthesis with ammoniacalnitrogen supply. Those costs ranged between 1·19 and1·35 for stems and 1·19 and 1·27 for leaves.The mean annual specific cost for fine roots was 1·17.Seasonal vine growth costs were calculated by multiplying thespecific costs by biomass data for a typical vine. Total costof synthesis was 57·2 kg carbohydrate per vine year^-1,taking fine root turnover as three times per season. Nitratenitrogen supply increased that cost by 6·6% to 61·0kg carbohydrate per vine year^-1. Fruit growth accounted forthe largest proportion of synthetic costs. Vine growth respiration(expressed in terms of carbohydrate equivalents) accounted forapproximately 11·5% of the total cost of synthesis. Maintenancerespiration was estimated to be 5·28, 8·44, 1·90,8·62 and 13·3 kg carbohydrate per organ year^-1for stems, leaves, fruit, above-ground perennial componentsand roots, respectively. Total annual cost of growth and maintenancefor a mature vine was 94·7 and 98·5 kg carbohydrateper vine year^-1 with ammoniacal and nitrate nitrogen supply,respectively. Both values are similar to an estimate of vinephotosynthesis. Maintenance respiration accounted for approximately40% of the total annual cost of vine growth, regardless of theform of nitrogen supplied. Peak carbohydrate demand was duringthe period from 60 to 160 d after budbreak.Copyright 1995, 1999Academic Press Actinidia deliciosa, kiwifruit, carbon economy, growth respiration, maintenance respiration     

Studies on Mature Seeds of Cuscuta pedicellata and C. campestris by Electron Microscopy

The seeds of Cuscuta pedicellata have been investigated by transmissionand scanning electron microscopy. Additional observations havebeen made on seeds of C. campestris by SEM only. The seed coatconsists of an outer single epidermis, two different palisadelayers, and an inner multiparenchyma layer. The outer epidermalwall in C. pedicellata has a thick cuticle and zones rich inpectic substances. The thicker ‘U-shaped’ cell wallsin the outer palisade layer are strengthened by a wall layerof hemicellulose. The inner palisade layer has thick walledcells with a ‘light line’. The inner cell wall ofthe compressed multiparenchyma layer has a thin cuticle. A fairlythick cuticle is positioned directly on the endosperm surface.The aleurone cell walls are different from the remaining endospermwalls. The latter are thick and believed to be of galactomannans.There is a ‘clear’ zone between the plasmalemmaand the cell wall in the aleurone cells. The embryo cells arepacked with lipids and proteins. In Cuscuta campestris mostendosperm has been absorbed during the seed development. Theembryo apex has two minute leaf primordia. The features of theCuscuta seeds are discussed in relation to functional and environmentalconditions. Cuscuta pedicellata, Cuscuta campestris, seed, seed coat, cuticle, cell walls, endosperm, aleurone cells, galactomannan, embryo, TEM, SEM     

Vibratory Collection of Actinidia deliciosa (Kiwifruit) Pollen

Dry, powdery pollen grains were expected from 'buzz pollinated'flower species. However, vibration of Actinidia deliciosa (kiwifruit)anthers (a buzz pollinated species) by a mechanical shaker,at similar vibrations to Bombus terrestris caused clumps ofpollen joined by small droplets of tapetal fluid to be ejected.Pollen that was largely covered with tapetal fluid could notbe removed by vibration, whereas dehydrated pollen was easilyremoved, even without vibration. The late desiccation of A.deliciosa anthers after anthesis meant that pollen removed byvibration depended on the anther maturity. The presence of thedroplets gives insects which vibrate while foraging advantagesover insects which do not. A vibration attachment on a commercialpollen harvester increased the weight of pollen collected by57% over the whole day; 91% in the afternoon.Copyright 1994,1999 Academic Press Actinidia deliciosa, Bombus spp., bumblebees, buzz pollinate, kiwifruit, pollen collection, tapetal fluid, vibration     

Pollen Tube Distribution in the Kiwifruit (Actinidia deliciosaA. Chev. C. F. Liang) Pistil in Relation to its Reproductive Process

High resolution light and fluorescence microscopy were usedto investigate the structural and cytochemical features of thekiwifruit(Actinidia deliciosa)pistil and to follow the pollentube pathway after pollination. The multicarpellary ovary issyncarpous only at the ovary level thus leaving 30–40free styles on top. The fusion of the longitudinally-foldedcarpels to form the syncarpous ovary forms a central parenchymatousaxis, the columella, from which the ovules radiate outwardsinto the ovary cavity. A prominent cup shaped depression onthe columella at the top end of the ovary, termed the pollentube distributor cup (PTDC) was detected. Pollen tubes fromthe stigma travel through the transmitting tract and enter thePTDC from where they are distributed towards the ovary. Evenwhen pollination is restricted to two stigmas, the PTDC seemsto ensure that the pollen tubes are evenly distributed aroundthe ovary resulting in an even distribution of seeds. This suggestedrole of the PTDC which could compensate for over and under pollinationof individual stigmatic arms is another adaptive feature whichplays a crucial role in the reproductive process of kiwifruit.The significance of this structure for pollination by insectsis discussed.Copyright 1998 Annals of Botany Company Actinidia deliciosa, kiwifruit, pollination, floral anatomy, reproductive success, pollen tube distribution.     

Polyamine Content in Relation to Embryo Growth and Dedifferentiation in Barley (Hordeum vulgare L.)

Putrescine, spermidine, and spermine content were analysed inzygotic embryos of barley (Hordeum vulgare L.). Changes in polyaminecontent were observed during zygotic embryo growth. In two cultivars,‘Bomi’ and ‘Golden Promise’, the totalpolyamine content in the embryos was 2.6–2.9 nmol mg^–1fresh weight 10 d after anthesis, the highest content observed.It dropped to 1.3 nmol mg^–1 fresh weight 14 d after anthesis.This drop was caused by decreases in all three polyamine concentrations.From 14 to 35 d after anthesis the putrescine content continuedto decrease while the spermidine and spermine content increased,thus the total polyamine content remained constant until 35d after anthesis. The mutant ‘Ris? 1508’ showeda constant polyamine content around 1.3 nmol mg^–1 freshweight from 14 to 35 d after anthesis. The polyamine patternwas conserved in all three lines throughout the period of investigationshowing a spermidine content higher than putrescine contentwhich was, in turn, higher or equal to the spermine content.The polyamine content measured as nmol µg^–1 proteindecreased from 14 to 21 d post anthesis in all three lines,because the protein content (µg mg^–1 fresh weight)increased during the period. In dedifferentiating zygotic embryoscultured in vitro the putrescine content (nmol mg^–1 freshweight) rose by a factor of nine and the spermidine contentdoubled within the first week of cultivation, whereas sperminecontent did not change. For embryoderived calli a repeated patternof change in polyamine content was observed throughout the subculturingperiod. Key words: Polyamines, Hordeum vulgare L., embryo development     

The Acquisition and Utilization of Carbon in Early Spring by Kiwifruit Shoots

Measurements of net photosynthetic rate (at 1450µ molm^-2s^-1photosynthetically active radiation) of leaves, of leafand stem respiration, and of shoot growth of potentially-fruitinglaterals on kiwifruit (Actinidia deliciosa ) were used to estimateweekly shoot carbon balances over the first 10 weeks of shootgrowth (budburst to anthesis). Consistent differences in therate of shoot elongation, of internode expansion and of increasein basal diameter were found among shoots. Faster-growing (long)shoots acquired carbon by photosynthesis at a faster rate evenin the first few weeks after budburst, but the amount of carbonrequired to sustain this growth resulted in shoot carbon deficitswhich were approx. seven times greater than those of the slower-growing(short) shoots. It was estimated that the transition from shootcarbon deficit to carbon surplus occurred 3–4 weeks afterbudburst, irrespective of shoot growth rate. As a result ofsubsequent rapid increases in shoot photosynthetic rate, longshoots had a shoot carbon surplus of 4.4 g C week^-1in the weekbefore anthesis, approx. three times that of the short shoots.Defoliation (66%) of shoots 1 week after budburst, and subsequentremoval of later-emerging leaves to maintain the level of defoliation,had the effect of slowing shoot growth in the carbon deficitperiod, particularly for the long shoots. However, the durationof shoot expansion in the defoliated shoots was longer, resultingultimately in shoots which were longer than the control shoots.Linkages among early carbon balance dynamics of shoots, shootlength at anthesis, and fruit growth are discussed. Actinidia deliciosa ; kiwifruit; shoot growth; carbon acquisition; respiration; photosynthesis     

ERRATA

Effects of coupled solute and water flow in plant roots withspecial reference to Brouwer's experiment. Edwin L. Fiscus. p. 71 Abstract: Line 3 delete ‘interval’ insert‘internal’. p. 73 Materials and Methods: line 6: delete ‘diversion’ insert ‘division’ line 9 equation should read J_v=L_p P–RT(C⁰–C¹). 74 Last line of figure legend: 10^–1 should read 10^–11. 75 Line 11: delete ‘seems’ insert ‘seem’. le 1 column heading—10⁶ should read 10¹¹. 77 delete ‘...membrane in series of...’ insert ‘membranein series or...’ Delete final paragraph.     

Seed and Pod Wall Development in Pisum sativum, L. in Relation to Extracted and Applied Hormones

Developing fruits of Pisum sativum, L., cv. ‘Alaska’,contain relatively large amounts of hormones, mainly concentratedin the embryos and liquid endosperm. A close relationship canbe demonstrated between changes in extractable amounts of gibberellins(mainly GA₂₀), auxins (methyl 4-chloroindol-3yl acetate andprobably 4-chloroindol-3yl acetic acid), and abscisic acid,and changes in growth rates of both the pod wall and seeds.Growth of the pod wall appears to depend largely on hormonessupplied by the seeds. Marked changes in the germination capacity of the maturing seedsare closely associated with changes in extractable amounts ofmethyl-4-chloroindol-3yl acetate and abscisic acid. It is believedthat high concentrations of these substances in the embryo,rather than any restriction imposed by the testa, may preventprecocious germination of the seeds     

Dormancy in Dioscorea: Rapid Germination of Detached Embryos from Dormant Seeds of D. tokoro

The intact dormant seeds of Dioscorea tokoro germinate slowlyif at all between 11-23°C; for full and rapid germinationthey require prior chilling treatment [Okagami and Kawai (1982)Bot. Mag. Tokyo 95: 155]. The germination abilities of zygoticembryos detached from dormant seeds of this species were studiedunder various nutritional and temperature regimes. For germinationof embryos, the minimum nutritional components in Murashigeand Skoog's (1962) medium that were required were sucrose andNO^–₃ or SO^2–₄. As the source of carbohydrate forgermination of detached embryos, sucrose, mannose and maltosewere effective; glucose and fructose were less effective; andrhamnose was entirely unable to support germination. Embryos detached from dormant seeds, incubated with the sucroseplus KNO₃, germinated more rapidly with increasing temperatureup to 35°C. However, application of sucrose and KNO₃ didnot induce germination of intact seeds above 26°C. Therefore,it is very possible that the endosperm exerts an inhibitoryfunction on germination at such high temperatures. When seeds were incubated after a cut was made over a smallpart of the edge of the endosperm in which the radicle of theembryo is encased, germination occurred rapidly but the increasein germination percentage was slight. This result suggests thatthe endosperm suppots part of the germination inhibition bymeans of a mechanical barrier or its impermeability to wateror gases. Physiological features of the endosperm alone or interactionsbetween the embryo and endosperm may contribute significantlyto the characteristics of dormancy of intact seeds of this species. (Received May 30, 1988; Accepted January 11, 1989)     

Use of Interactive Computer Graphics for Simulation of Radiation Interception and Photosynthesis for Canopies of Kiwifruit Vines with Heterogeneous surface Shape and Leaf Area Distribution

A method incorporating interactive computer graphics to simulatespatially variable interception and canopy photosynthesis isdescribed. The method presents a graphical interface to a conventionalmodel of radiation interception and canopy photosynthesis. Includedis the capacity to consider a large number of positions withinthe canopy, thus providing a rapid and convenient representationof the dynamics of photosynthesis while also overcoming limitationsof one-dimensional models applied to complex plant canopies.The method was applied to examine spatial variability of photosynthesiswithin canopies of kiwifruit (Actinidia deliciosa) vines growingon two trellis types. The diurnal integral of simulated canopyphotosynthesis, assuming sunny conditions, for a vine trainedon a horizontal 'Pergola' trellis was 14% higher than that fora vine with similar leaf area distribution trained on a 'T-bar'trellis with inclined surfaces. Simulations of photosynthesisfor vines on a T-bar trellis, assuming spatially variable leafarea distributions as measured under filed conditions, indicateddisproportionate contributions from different regions of thecanopy. Canopy regions inclined to the east or the west wereusually the major sites for photosynthesis immediately aftersunrise and before sunset respectively, while regions near thecordon were the most important overall. For any day, the maximumsimulated photosynthetic rate generally declined with distancefrom the cordon and, at any distance from the cordon, increasedwith leaf index. For a vine with an average leaf area indexof 2·7, diurnal integrals of photosynthesis on a sunnyday in late summer ranged from 1·0 mol CO₂ m^-2 near thecordon to 0·5 mol CO₂ m^-2 at 1·5 m from the cordon.Within-canopy shading was more important on sunny days thanon cloudy days, while the spatial distribution of leaf areawas especially important on cloudy days. Comparison of simulationswith direct measurements of canopy photosynthesis indicatedthat a numerical integral of simulated photosynthesis, basedon a large number of canopy positions, provided a reasonableestimate of total canopy photosynthesis.Copyright 1993, 1999Academic Press Actinidia deliciosa, kiwifruit, interactive computer graphics, mathematical modelling, photosynthesis, radiation interception, spatial heterogeneity     

Uptake of 15N by Kiwifruit Vines from Applications of Nitrogen Fertilizer Prior to Budbreak

Mature field-grown kiwifruit vines (Actinidia deliciosa var.deliciosa cv. Hayward) were fertilized with ¹⁵N-labelled fertilizer(ammonium sulphate, 10 atom % ¹⁵N, 50 kgN ha^-1) to investigatethe timing of uptake of fertilizer nitrogen (N) and its availabilityfor new season's growth. Treatments were applied on four occasions,representing 2, 6, 10 and 14 weeks prior to budbreak. Samplesof root, stem, cordon, fruiting cane, vacuum-extracted xylemsap, and new season's growth were collected at fortnightly intervalfrom early winter until 2 months after budbreak. Two weeks after application of each treatment, ¹⁵N equivalentto an average of 7% of the applied label was recovered in rootmaterial. Although label was taken up by roots, there was nomovement of ¹⁵N within the plant until about 1 month prior tobudbreak when it was measured in the stem and cordon. Fertilizernitrogen was not detected at the distal end of fruiting canes,and in new season's growth until 3-4 weeks after budbreak. Beforebudbreak, all nitrogen in the xylem sap was in amino forms.Nitrate appeared 4 weeks after budbreak, and although more enrichedwith ¹⁵N than the amino nitrogen, accounted for only 19% ofthe label. Eight weeks after budbreak, nitrate nitrogen accountedfor 57% of the label. There were no major treatment effects of ¹⁵N on vines in eitherspring or at harvest, although enrichments in fruit and leavesfrom the earliest treatment tended to be less at the end ofthe season than those from the later applications.Copyright1993, 1999 Academic Press Actinidia deliciosa, kiwifruit, nitrogen, ¹⁵N, nutrient uptake     

Effect of the Osmotic Environment on K+ and Mg2+ Release from the Seed Coat and Cotyledons of Developing Seeds of Vicia faba and Pisum sativum. Evidence for a Stimulation of Efflux from the Vacuole at High Cell Turgor

After removal of the embryo from developing seeds of Vicia fabaL. and Pisum sativum L., the ‘empty’ ovules werefilled with a substitute medium (pH 5.5) and the effect of theosmolality of the medium on K⁺ and Mg²⁺ release from the seedcoat was examined. In long-term experiments (12 h or longer),with both attached and detached seed coats, the rate of K⁺ andMg²⁺ release from seed coats filled with a solution withoutosmoticum was enhanced, in comparison with release from seedcoats filled with a solution containing 400 mol m