Respiration, Carbon Balance and Translocation of Dry Matter in the Corolla of Rose Flowers

The effects of import of dry matter from the leaves on respiration,metabolism of carbohydrates and development of the corolla werestudied in intact flowering rose shoots and compared with cutflowering shoots bearing either seven leaves on 45 cm stemsor two leaves on 30 cm stems. Over 4 days, corollas of two-leaf shoots imported and respiredless carbon than either the intact or the seven-leaf shootsand they developed more slowly. Starch levels in the corollaat the end of this time depended on the stage at which it wascut; more advanced flowers (stage 3–4) tended to losestarch whereas less advanced ones (stage 1–2) tended toaccumulate it. Total carbohydrate in the corolla was dependenton leaf number. Loss of d. wt of leaves indicated that they provided dry matterto the corollas even in cut shoots, and this observation wassupported by the recovery of ¹⁴C-leaf assimilate from corollas.The depletion of dry matter from leaves and the slight delayin corolla development of the two-leaf cut shoots suggest thata dynamic source-sink (leaves—corolla) relationship existsin the senescing cut rose as in the intact rose. Rosa sp, corolla, respiration, carbon balance, translocation     

The Relationship between Sucrose Supply, Sucrose-cleaving Enzymes and Flower Abortion in Pepper

Abortion of pepper flowers depends on the light intensity perceivedby the plant and on the amounts of sucrose taken up by the flower(Aloni B, Karni L, Zaidman Z, Schaffer AA. 1996.Annals of Botany78: 163–168). We hypothesize that changes in the activityof sucrose-cleaving enzymes within the flower ovary might beresponsible for the changes in flower abortion under differentlight conditions. In the present study we report that the activityof sucrose synthase, but not of cytosolic acid invertase, increasesin flowers of pepper plants which were exposed, for 2 d, toincreasing photosynthetically active radiation (PAR) in therange of 85–400 µmol m^-2s^-1at midday. Sucrose synthaseactivity increased in parallel with the increasing concentrationsof starch in the flower ovary. Feeding flower explants, preparedfrom 3-d-predarkened plants, with 100 mM sucrose for 24 h, causeda 23% increase in reducing sugars and a 2.5-fold increase instarch concentration, compared with explants fed with buffer.Likewise, feeding explants of pepper flowers with sucrose, glucose,fructose and also mannitol increased the sucrose synthase activityin the ovaries. Concomitantly, sucrose, glucose and fructose,but not mannitol, reduced the abortion of flower explants. Itis suggested that sucrose entry into the flower increases theflower sink activity by inhibiting abscission and inducing metabolicchanges, thus enhancing flower set. Pepper; Capsicum annuum L.; abscission; light; pepper flowers; sucrose; glucose; fructose; starch; acid invertase; sucrose synthase     

The Coordination of Organ Growth in Developing Citrus Flowers: A Possibility for Sink Type Regulation

The interrelationships between simultaneously developing organsof citrus flowers were investigated. Examination of flower organgrowth kinetics shows that petals grow mainly through enhancedwater absorption whereas ovaries accumulate a high percentageof dry matter. Using excised flowers implanted in an agar—sucrose mediumand supplied with [¹⁴C]-sucrose, [³H]-acetate, and [¹⁴C]-acetate,a characteristic distribution of label among organs could beestablished for each isotope. Wounding or application of -naphthaleneacetic acid (NAA) toa single petal completely changed the normal distribution patterns,shifting the bulk of [¹⁴C]-sucrose towards the treated organs. The findings are interpreted in the light of the ‘sink’hypothesis. It is proposed that each flower organ meristem createsa sink of its own which acts in a typical manner according toits specific endogenous hormonal balance. The sink activityof all meristems in concert results in a sensitive regulatorymechanism which is responsible for the coordination observedin flower development.     

Effects of Ethylene and Sucrose on Translocation of Dry Matter and 14C-Sucrose in the Cut Flower of the Glasshouse Carnation (Dianthus caryophyllus) During Senescence

The translocation and distribution of dry matter were studiedin the floral and vegetative parts of the cut carnation duringsenescence. The change in dry weights of the tissues and theamount of radioactivity recovered from them after feeding with¹⁴C-sucrose were measured. Treatments with ethylene and sucrosewere used to alter the rate of senescence of the flowers. Sucrosemoved through the stem relatively unchanged but was rapidlyinverted and metabolized in the petals. During natural ageing,¹⁴C moved from the stem to the flower and the movement was enhancedby exogenous sucrose, which also reduced the loss of dry matterin the petals and promoted their growth. Treatment with ethylenecaused petals to wilt and lose dry weight, and ovaries to enlargeand increase in dry weight. The distribution of radioactivityin flowers fed with 14C-sucrose before and after ethylene treatmentsupported the observation that dry matter was translocated betweenthe flower parts. The results indicate that a change in thesource-ink relationships of the flower parts contributes tothe factors that determine the rate of flower senescence.     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18 °C). With a temperatureregime of 35 °C day, 25 °C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35 °C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves     

Partitioning of [14C]sucrose and Acid Invertase Activity in Reproductive Organs of Pepper Plants in Relation to Their Abscission Under Heat Stress

The effect of heat stress on processes related to carbohydratepartitioning was investigated in young bell pepper (Capsicumannum L. cv. Maor) plants in relation to abscission of theirreproductive organs at different stages of development. None of the reproductive organs abscised after 5 d in a normalday/night temperature regime (25/18°C). With a temperatureregime of 35°C day, 25°C night, abscission occurredin only a small portion of the flower buds and none of the flowersand fruitlets. However, when temperatures in the day and nightwere reversed (25/35°C, day/night) all the buds and someof the flowers abscised during that time period. The young fruitat the first node did not abscise under any temperature regime.The abscission rate of the flower buds was reduced under heatstress if the developing fruit at the first node had been removed. High temperature during either the light or dark periods reducedthe export of [¹⁴C]sucrose from the source leaf (fed for 48h with [¹⁴C]sucrose). Both heat stress and fruit presence reduced the relative amountof [¹⁴C]sucrose which was exported to the flower buds, flowersand roots. Likewise, these treatments reduced the concentrationof reducing sugars in the reproductive organs. Concomitantly,the heat stress and fruit presence on the first node reducedthe activity of soluble acid invertase in the flower buds andthe roots, but not in young leaves. Overall, the results show that heat stress causes alternationin sucrose distribution in the plant, but may also have specificeffects on metabolic activities related to sucrose import andutilization in flower buds and flowers which in turn may enhancetheir abscission. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acidinvertase, heat stress, reproductive organs, sink leaves. Bell pepper, (Capsicum annuum L. cv. Maor), abscission, acid invertase, heat stress, reproductive organs, sink leaves.     

The Role of Phloem Transport in the Translocation of Sucrose Along the Stem of Carnation Cut Flowers

The pathway and distribution of ¹⁴C-sugars in flower parts havebeen examined to find out in which tissue sugars are translocatedin the stem of the cut carnation; ¹⁴C-sucrose or ¹⁴C-glucosewas supplied at the base of the cut stem from a feeding solutionand the localization and chemical nature of the carbon-14 recoveredfrom flower parts were investigated. By reducing the rate oftranspiration it was found that the uptake of feeding solutionwas also reduced, but the distribution of absorbed ¹⁴C-sucrosein the flower parts was different from that which would be expectedif sucrose moved exclusively in the transpiration stream. Autoradiographsdemonstrated that ¹⁴C absorbed from the feeding solution as¹⁴C-sucrose appeared in both xylem and phloem but predominantlyin the latter; girdling failed to stop the translocation ofthe absorbed ¹⁴C-sucrose. Results of experiments with ¹⁴C-sucroseand ¹⁴C-glucose showed that sucrose was the mobile sugar andthat glucose was converted to sucrose before it was translocated.It was concluded that the translocation of sucrose absorbedfrom the feeding solution takes place both in xylem and phloemand is regulated by a mechanism involving the loading and translocationof sucrose in the phloem.     

Effect of Heat Stress on Assimilate Partitioning in Tomato

Differences in assimilate partitioning in response to heat stresswere observed between the heat-sensitive tomato cultivar, RomaVF and the heat-tolerant cultivar, Saladette. Transport of carbonto the trusses and apex was inhibited in both cultivars, particularlyin Roma VF. Basipetal transport to the roots was inhibited inRoma VF only. Assimilate partitioning within the young trusswas also affected by heat stress in both cultivars, but wasmore pronounced in Roma VF: at higher temperatures more ¹⁴Cwas found in the peduncle and in the older flower buds thanin the younger flower buds. The youngest flower buds were moresensitive than other parts of the truss to heat stress. Theuptake of [¹⁴C]sucrose by detached flower buds from agar mediumwas lower at higher temperatures. Alteration of assimilate partitioningwas also observed following the application of GA₃+Kinetin tothe first truss. The possible relationship between flower-setin tomato and carbohydrate stress is discussed. Lyeopersicon esculentum Mill., carbon translocation, starch     

The Effect of Cooling on Photosynthesis, Amounts of Carbohydrate and Assimilate Export in Sunflower

Sunflower plants (Helianthus annuus L.) grown at 30°C werecooled to 13°C in the light in atmospheric CO² or low CO²,or in darkness. Photosynthetic rate at 30°C after coolingwhole plants in atmospheric CO² for 12 h during a photoperiodwas significantly lower than at the start of the photoperiodcompared to plants cooled at low CO², those cooled in the darkand those maintained at 30°C. Amounts of sucrose, hexosesand starch in leaves at 13°C increased throughout a 14 hphotoperiod to levels higher than in leaves at 30°C, whereamounts of sucrose and hexoses were stable or falling after4 h. Carbohydrate accumulation at 13°C during this photoperiodwas more than twice that at 30°C. After three photoperiodsand two dark periods at 13°C carbohydrate levels in leaveswere still as high as at the end of the first photoperiod, butless carbohydrate accumulated during the photoperiods than duringthe first photoperiod, and more was partitioned as starch. Amountsof soluble carbohydrate in roots were greater after 14 h at13°C than in roots of plants at 30°C. Loss of ¹⁴C fromleaves at 30°C as a proportion of ¹⁴CO2 fixed by them at30°C, decreased after exposure of plants to 13°C inthe light for 30 min prior to ¹⁴CO²feeding. Results indicatean effect of cold on the transport process that was light-dependent.It is inferred that the reduction in the proportion of ¹⁴C lostfrom leaves after 10 h cooling was due to reduced sink demand,whereas the rise in the proportion of ¹⁴C lost from leaves after24 h reflects reduced photosynthetic rate. The coincidence ofreduced photosynthetic rate with raised carbohydrate levelsin leaves maintained at 30°C throughout, whilst the restof the plant was cooled to 13°C in the light implies feedbackinhibition of photosynthesis. This may reduce the imbalancebetween source and sink in sunflower during the first days oflong-term cooling. Key words: Temperature, carbon export, carbohydrates, photosynthesis, sunflower     

The Relationship between Sucrose and Starch during 'Dark' Export from Leaves of Uniculm Barley

Uniculm barley plants were grown in 8 h photoperiods at a quantumflux density of 655 µE m^–2 s^–1. Groups ofplants were transferred to four different light environmentsfor one 8 h photoperiod (106, 270, 665, and 975 µE m^–2s^–1) and harvested at intervals throughout the succeedingdark period for subsequent carbohydrate analysis of the youngestmature leaf. Sucrose was the predominant carbohydrate in the leaves (attaininga level of c. 100 mg dm^–2 after 8 h at 975 µE m^–2s^–1) but starch was also of significance (20 mg dm^–2after 8 h at 975 µE m^–2 s^–1). During the dark period, following a photoperiod at the threehighest light levels (270, 665, and 975 µE m^–2 s^–1),sucrose was exported first while the starch level remained fairlyconstant. When the-sucrose level fell to 15–20 mg dm^–2starch degradation began. This critical sucrose level was reachedearlier in those plants subjected to lower quantum flux densitiesduring the preceding photoperiod. The delay in the remobilizationof starch suggests an important regulatory mechanism which maybe dependent upon the sucrose level. At 106 µE m^–2s^–1 the sucrose level rose to only 10 mg dm^–2. Herethere was no discernible delay in the depletion of sucrose orstarch.     

Effect of Temperature on Starch Degradation in Chlorella vulgaris 11h Cells

Analysis of products formed in Chlorella vulgaris 11 h cellsduring photosynthesis in air containing 3,000 ppm ¹⁴CO₂ at varioustemperatures revealed that the level of ¹⁴C-starch was maximumaround 20–24?C and decreased with further rise in temperatureuntil 40?C, while ¹⁴C-sucrose greatly increased at temperaturesabove about 28?C. Elevating the temperature from 20 to 38?Cduring photosynthetic ¹⁴CO₂ fixation resulted in a remarkabledecrease in ¹⁴C in starch and a concomitant increase in ¹⁴Cin sucrose. This conversion of starch to sucrose when shiftingthe temperature from 20 to 38?C proceeded even in the dark.Hydrolysis of sucrose by rß-fructosidase showed that,irrespective of the experimental conditions, the radioactivitiesin sucrose were equally distributed between glucose and fructose.The enhancement of starch degradation with temperature risewas more remarkable than that of the activity of ribulose bisphosphatecarboxylase from the same cells. When Chlorella cells whichhad been preloaded with ¹⁴C-starch after photosynthesis for30 min at 20?C were incubated in the dark for an additional30 min at 20?C, ¹⁴C-starch was degraded by only about 4%. However,the values after 30-min dark incubation at 28, 32, 36 and 40?Cwere increased by about 10, 19, 36 and 50%, respectively. Duringthe temperature-dependent conversion of starch to sucrose, nosignificant amount of radioactivity accumulated in free glucoseand maltose. (Received October 27, 1981; Accepted January 9, 1982)     

The Uptake of Surcrose and its Conversion to Starch in Detached Ears of Wheat

Detached ears of wheat were cultured on solutions of ¹⁴C-sucroseand the distribution of carbon-14 in the ear was followed. Within 8 h radioactive sucrose was found in all the tissuesof the cultured ear, and considerable amounts of carbon-14 hadaccumulated in other ethanol-soluble compounds. Carbon-14 accumulatedrapidly in the starch deposited in the endosperm, but littlewas found in the starch of the pericarp, or in other materialinsoluble in ethanol in the vegetative organs. During 48 h the specific radioactivity of the sucrose in theendosperm increased in a hyperbolic pattern and was equal tothat of the starch produced. Carbon-14 in the glucose and fructoseaccumulated more slowly and in a Linear fashion. Experiments with sucrose containing carbon-14 in both moietiesequally, or in the fructosyl moiety exclusively, confirmed thatboth moieties are converted into starch and at about the samerate. As sucrose in endosperm provided with asymmetric sucroseretained a considerable degree of asymmetry, it seems as thoughinversion is not a necessary step in the transport of sucroseinto the grain. In ears provided with ¹⁴C-sucrose at 30 mg ml^–1 the rateof accumulation of ¹⁴C-sucrose in the culm, rachis, and floralorgans was about 0.6 times the value at 50 mg ml^–1. However,in the sucrose of the endosperm, and in the starch depositedthere, the rates of accumulation of carbon-14 from both levelswere identical. This finding supports the concept that the transportof sucrose is limited during the final stages of its passageinto the grain.     

Changes of Carbohydrates in Pepper (Capsicum annuum L.) Flowers in Relation to Their Abscission Under Different Shading Regimes

Abscission of pepper flowers is enhanced under conditions oflow light and high temperature. Our study shows that pepperflowers accumulate assimilates, particularly in the ovary, duringthe day time, and accumulate starch, which is then metabolizedin the subsequent dark period. With the exception of the petals,the ovary contains the highest total amounts of sugars and starch,compared with other flower parts and contains the highest totalactivity, as well as activity calculated on fresh mass basis,of sucrose synthase, in accordance with the role of this enzymein starch biosynthesis. Low light intensity or leaf removaldecreased sugar accumulation in the flower and subsequentlycaused flower abscission. The threshold of light intensity fordaily sugar accumulation in the sink leaves was much lower thanin flowers, resulting in higher daytime accumulation of sugarsin the sink leaves than in the adjacent flower buds under anylight intensity, suggesting a competition for assimilates betweenthese organs. Flowers of bell pepper cv. ‘Maor’and ‘899’ (sensitive to abscission) accumulatedless soluble sugars and starch under shade than the flowersof bell pepper cv. ‘Mazurka’ and of paprika cv.‘Lehava’ (less sensitive). The results suggest thatthe flower capacity to accumulate sugars and starch during theday is an important factor in determining flower retention andfruit set. Pepper; Capsicum annuum L.; abscission; shading; pepper flowers; ovary; leaves; sugars; starch; acid invertase; sucrose synthase     

Effects of Sucrose on Petiolar Carbohydrate Accumulation and Photosynthesis in Excised Sinapis Cotyledons

Petioles of Sinapis cotyledons cultured in 6x10^–2 M sucrosein the light increased 28-fold in total carbohydrate contentover a 7-d period compared with an 8-fold increase in petiolesof cotyledons cultured on water. The starch and reducing sugarfractions were the major components of this accumulation. Labelledsucrose applied to the petiole base moved quickly up the petioleand into the main veins of the lamina. Some basipetal redistributionoccurred subsequently and after 24 h radioactivity accumulatedstrongly at the petiole base. Culture in sucrose reduced basalaccumulation and increased acropetal movement of the label. Fixation of ¹⁴CO₂ by petioles remained constant when cotyledonswere cultured in water, whereas in sucrose, fixation fell by50 per cent during the first 2 d. The pattern of inhibitionof fixation matched the pattern of sucrose distribution in thepetiole. Petiolar chlorophyll content remained constant in controlsbut fell rapidly after 4 d culture in sucrose. The results are discussed in relation to the role of petiolarcarbohydrate accumulation in the regulation of CO₂ fixation,primordium development, and senescence in this system.     

Effects of Ca2+ and Cd2+ on the Carbohydrate Metabolism in Sugar Beet (Beta vulgaris)

Sugar beet (Beta vulgaris L. cv. Monohill) were cultivated ina nutrient solution with different combinations of Ca²⁺ (36,180, 720 or 3560µM) and Cd²⁺ (0, 1, 5 or 20µM).The dry and fresh weights, the content of Ca²⁺ and Cd²⁺ , sucrose,fructose, glucose and starch in 5-week-old plants was analysedas well as the rate of [¹⁴C]-sucrose uptake in discs from 3-month-oldstorage roots. The carbohydrate metabolism was indirectly affectedby the presence of calcium or cadmium. Cadmium caused a diminisheddry weight and carbohydrate concentration. The dry weight wasunaffected by the Ca²⁺ level but the carbohydrate distributionbetween storage and growth processes was affected; at low Ca²⁺in the tissue, the growth was retarded and the level of storagecarbohydrate increased, while at high Ca²⁺ the opposite wasfound. The [¹⁴C]-sucrose uptake decreased in tap roots cultivatedat low Ca²⁺ . Long term exposure to Cd²⁺ also decreased thesucrose uptake in tap roots. Direct Cd²⁺ addition to the assaymedium, however, increased the sucrose uptake, probably at thetonoplast, while Ca²⁺ had no transient effect on the uptake.Cadmium increased the Ca²⁺ concentration in the plant, but Ca²⁺did not affect the net-uptake of Cd²⁺. Key words: Sugar beet, cadmium uptake, calcium uptake, carbohydrate formation, growth     

Effects of postharvest pretreatments and preservative solutions on vase life longevity and flower quality of sweet pea (Lathyrus odoratus L.)

The effects of postharvest pretreatments on vase life, keeping quality and carbohydrate concentrations in cut sweet pea (Lathyrus odoratus L.) flowers were investigated. Compared to the control, all treatments promoted floret quality and extended longevity. The cut flowers held in the solution containing sucrose + 8-hydroxyquinoline (Suc+HQS) was more effective in promoting absorption rate, achieved greater maximum fresh mass, had better water balance for a longer period, extended the vase life (up to 17 d), and delayed degradation of chlorophylls. The same treatment also enhanced the concentration of soluble carbohydrates in the petals and stems and leaf chlorophyll (Chl) content, whereas it was lowest in silver thiosulphate (STS) treatment. However, concentrations of anthocyanin in the petals were higher for treatment with sucrose or STS plus sucrose than in control or STS alone treatments. Our results suggest that pulse treatment with HQS plus sucrose for 12 h is the most effective for improving pigmentation and use as a commercial cut flower preservative solution to delay flower senescence, enhance quality, and prolong the vase life of sweet pea. The results also showed that soluble carbohydrate concentration in petals and stems is an important factor in determining the vase life of sweet pea flowers.     

Development and Control of the Number of Flowers per Node in Pisum sativum L.

Non-dormant flower initials are laid down in the axils of successiveleaf initials as they are formed by the apical meristem of Pisumsativum L. In cultivars with a maximum capability of two flowersper raceme, the undeveloped flower meristem divides into twoportions. One forms the first flower and the other either developsinto a small protrusion on one side of the first flower or becomesthe second flower, depending on the prevailing environment.Flower development in conditions favouring single-flowered racemeswas advanced by one plastochron. Variation in the number offlowers per raceme occurs between cultivars and between environments.The number of double flowers formed was favoured by higher lightintensity (120 Js^–1 m^–2) and carbon dioxide concentration(330 µ11^–) and lower temperature (15°C). Incultivars producing more than two flowers per raceme, lowerlight intensity (60 Js^–1 m^–2) plus higher temperature(20°C) increased the mean number of flowers per raceme.Soluble sugar levels in all varieties were higher (36.05 mgeq glucose g^–1 fresh weight) in the low temperature/highlight environment than the high temperature/low light environment(14.80 mg eq glucose g^–1 fresh weight). The flowering potential and stability of 13 cultivars have beenassessed in controlled environment and in sowing date trialsin the field. A stable variety, which consistently producedtwo flowers per raceme, was identified in controlled environmentand its stability was maintained in field trials. A linear regressionof stability of flower number in the field on stability in controlledenvironment accounted for 89.6 per cent of the variance (P<5per cent), but the flowering potential in a sowing date experimentwas not related to temperature or radiation intensity.     

The Effect of Fruit Load, Defoliation and Night Temperature on the Morphology of Pepper Flowers and on Fruit Shape

The shape and regularity of bell pepper (Capsicum annuumL.)fruit are known to be determined at a very early stage of flowerdevelopment. Small, flattened fruit which are commonly parthenocarpicdevelop under low-temperatures (below 16 °C) from flowerswith enlarged ovaries. In such flowers self-pollination is notefficient because of the large distance between the stigma andstamens. Flower deformation of this kind is common during thewinter season. In the present study it was found that deformationsof flowers, similar to those found under low temperatures, wereinduced in 15 d by complete removal of fruit from plants growingunder night-time temperatures of 18 °C. Only flowers whichwere at the pre-anthesis stage at the time of fruit removalwere deformed by this treatment. Removal of leaves from thelower part of the plant (source leaves) partially reduced theeffect of fruit removal on the shape of the flowers and on subsequentfruit morphology. Fruit removal induced significant increasesin the concentrations of starch and reducing sugars, but notsucrose, in the flower buds. Likewise, flower buds of plantswhich grew under a night-time temperature of 12 °C containedmore carbohydrate than those which grew at 18 °C. Theseresults suggest that flower morphology in pepper is at leastpartly controlled by source-sink relationships. Assimilateswhich are normally transferred to developing fruit may be transported,upon fruit removal, to the flower buds which subsequently swell.A similar increase in assimilate translocation to flower budsmay occur under low temperatures, subsequently causing deformationof fruit.Copyright 1999 Annals of Botany Company Pepper, (Capsicum annuumL), flower shape, low temperatures, source-sink relationship, fruit shape, seeds, reducing sugars, sucrose, starch.     

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)     

Effect of Temperature on Carbohydrate Metabolism in Potato Plants

The effect of temperature on partitioning of newly fixed ¹⁴Cbetween the various carbohydrate fractions was studied in differentplant organs of three potato varieties. Incorporation of ¹⁴Cinto starch in the tubers was reduced at high temperatures,but the amount of labelled sucrose increased. In all varietiesthe incorporation of ¹⁴C into the cell wall components in theapex of the plant and in the stem, as well as its incorporationinto starch in the stem, was increased at high temperatures.The variety Norchip, which was found to be less sensitive tohigh temperature as indicated by carbon translocation to thetubers, was found to be less affected also in terms of ¹⁴C incorporationinto starch in the tubers. We suggest that high temperatureaffects carbon metabolism in the various plant organs and theresulting changes are associated with the change in the partitioningof assimilates between these organs.