Dry matter accumulation in citrus fruit is not limited by transport capacity of the pedicel

The vascularization of the pedicel in Marisol clementine (Citrus clementina Hort. ex Tanaka) has been characterized in relation to fruit growth. Phloem and xylem formation occurred during the first half of the period of fruit growth. Phloem cross-sectional area reached its maximum value by the end of fruitlet abscission, 78 d after anthesis (DAA), shortly after the rate of accumulation of dry matter in fruitlets reached its maximum value. Secondary xylem formation occurred until day 93, well after the end of fruitlet abscission. At fruit maturity, xylem accounted for 42-46 % of the cross-section of the pedicel. Vessels differentiated in this late-formed xylem. Formation of phloem and early xylem was directly related to fruitlet size (and growth rate). Differences in the rate of formation of conductive tissues in the pedicel of the developing fruitlets followed rather than preceded the differences in growth rate. Specific mass transfer (SMT) in the phloem was highest in the fastest growing fruitlets, and peaked during the late stages of fruitlet abscission (72-78 DAA) and during the main period of fruit growth (107-121 DAA). Application of a synthetic auxin to developing fruits, either at the end of flowering (2,4-D) or by day 64 after flowering (2,4-DP), increased the growth rate of the fruit and fruit size at maturity (8-13 % increase in fruit diameter at maturity). These auxin applications also enhanced the formation of conductive tissues in the pedicel, with a specific effect on phloem formation. Applying auxin at flowering resulted in a reduction in the phloem SMT by days 72-78, whereas auxin application on day 64 increased this parameter. Despite this difference in behaviour, which resulted from the different time-course of the growth response of the fruit to auxin applications, these applications increased fruit size to a similar extent. Severing 37 % of the phloem of the pedicel during the main period of fruit growth resulted in an increase in the specific mass transfer in the phloem but had no influence on fruit growth. These observations demonstrate that the transport capacity in the phloem of the pedicel does not limit fruit growth and, within the limits of our experiments, an increase in demand by the fruit appeared to be matched by an increase in SMT. The dependence of late xylem formation (after the period of fruitlet abscission) on fruitlet growth was demonstrated in Salustiana orange [Citrus sinensis (L.) Osbeck] by means of controlling fruit growth through the manipulation of leaf area. Fruit growth at this time was more closely related to leaf area than to carbohydrate levels, suggesting that it may be limited by current photosynthesis.     

Carbon Partitioning among Leaves, Fruits, and Seeds during Development of Phaseolus vulgaris L

Development of vegetative and floral buds was found to be a key factor in establishing the way carbon is distributed among growing leaves and fruits in Phaseolus vulgaris L. plants. Leaves emerged principally during a period 14 to 32 days after planting while flowers were produced during a 10- to 12-day period near the end of leaf emergence. Timing of anthesis established the sigmoidal time course for dry weight accumulated by the composite of all fruits on the plant. During the first 12 days following anthesis, fruit growth mainly consisted of elongation and dry weight accumulation by the pod wall. Thereafter, seed dry weight increased for about 1 week, decreased markedly for several days, and then increased again over the next 2 weeks. Accumulation of imported carbon in individual seeds, measured by steady-state labeling, confirmed the time course for dry weight accumulation observed during seed development. Seed respiration rate initially increased rapidly along with dry weight and then remained nearly steady until seed maturation. A number of developmental events described in the literature coincided with the different phases of diauxic growth. The results demonstrated the feasibility of relating current rates of carbon import in individual seeds measured with tracer ¹⁴C to the rates of conversion of imported sucrose and use of the products for specific developmental processes. The resulting data are useful for evaluating the roles of conversion and utilization of imported sucrose in regulating import by developing seeds.     

The roles of abscisic acid and ethylene in the abscission and senescence of cocoa flowers

Cocoa flowers have a limited period of longevity; more than 90% of unpollinated flowers abscised within 32 h after anthesis. Abscisic acid (ABA) levels increased significantly prior to abscission. By 21 h after anthesis, ABA levels had increased almost 10-fold, and by 32 h flowers had 20-fold higher levels of ABA than at anthesis. Fluridone completely inhibited both the increase in ABA, the formation of an abscission zone, and the abscission and senescence of flowers. In contrast, ethylene production increased only slightly 21 h after anthesis and was only 2-fold higher after 32 h. Aminoethoxyvinylglycine (AVG) delayed but did not prevent abscission. In cocoa flowers, ABA is the primary regulator of abscission; ethylene accelerates abscission but only in the presence of ABA. Naphthalene acetic acid (NAA) treatment of flowers at anthesis prevented abscission zone formation and flower abscission, but did not induce fruit set. All parts of the NAA-treated flower except the pedicel senesced after 6 days. NAA+AVG treatment only delayed, whereas fluridone treatment completely prevented flower senescence.     

The effect of partial flower removal on the relation betwen root, shootand fruti growth in the indeterminate tomato

The root, vegetative shoot and fruit growth of November and January sown glasshouse tomato plants grown in flowing water culture was followed over 6–7 months. The relationship between vegetative and reproductive growth was examined after two-thirds of the flowers were removed from half the experimental plants. This resulted in larger plants which had fewer, larger fruits and eventually a fruit yield almost as large as the controls. In the control plants, fruit growth increased steadily until it reached 90% of the total incremental fresh weight of the plant 50–60 days after first anthesis. Leaf growth was markedly depressed at this stage and root growth ceased 4 wk after anthesis. Some root death was observed from anthesis onwards. When fruit growth subsequently diminished, vegetative growth recovered but to a lower rate than before fruiting commenced. Following partial flower removal, only 64% or less of the total increment of fresh weight went into the fruit. Although vegetative growth at this stage was thus greater than in the control plants, both shoot and root growth followed the same qualitative pattern with time. The ratio of vegetative shoot to root fresh weight remained essentially constant throughout the fruiting phase in plants of both sowings whether flowers were removed or not. This suggests that the fruit grew in competition with the vegetative organs as a whole, although, for a short period at early fruiting, root growth was more seriously affected. The pattern and amount of fruiting in this indeterminate plant was influenced by the size of the vegetative organs at fruiting, and by the effect of the existing developing fruit on further vegetative and reproductive growth.     

Cytokinins and fruit development in the kiwifruit (Actinidia deliciosa). I. Changes during fruit development

The cytokinin content in fruit tissue of the kiwifruit ( Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) was monitored during fruit development to identify which cytokinins were present and if they were linked with specific stages of fruit growth. Cytokinins were isolated and purified by column chromatography and high-performance liquid chromatography and quantified by radioimmunoassay. A novel HPLC step utilising an amine column was successfully introduced as a preparative step in the separation of the O - and 9-glucosides from the free bases and ribosides. The radioimmunoassay results were validated, and the different cytokinins identified, by gas chromatography-mass spectrometry. Cytokinins detected in fruit included the cytokinin free bases, zeatin and isopentenyladenine, their ribosides, nucleotides and both O - and 9-glucosides. Both qualitative and quantitative changes of the cytokinins occurred during fruit development. A decrease in cytokinin concentration occurred after anthesis (from 342 pmol g⁻¹ fresh weight at anthesis to 41 pmol g⁻¹ fresh weight 27 days after anthesis). A large increase in cytokinin concentration and content per fruit occurred as the fruit reached commercial maturity (to 1900 pmol g⁻¹ fresh weight). Individual cytokinins showed quite different patterns. Zeatin, in particular, showed a peak in concentration (13 pmol g⁻¹ fresh weight) 11 days after anthesis that correlated with the beginning of the cell division phase of fruit growth. The accumulation of cytokinin (mostly zeatin riboside or zeatin nucleotide) in mature fruit may be of significance for the postharvest storage of kiwifruit fruit.     

Pollination and Resource Constraints on Fruit Set and Fruit Size ofPersoonia rigida(Proteaceae)

Flower and immature fruit abscission can be caused by proximatefactors preventing the development of all flowers into maturefruits. Two potential limiting factors, pollen supply and carbohydrateavailability, were assessed as relative constraints on accumulationof fruit dry matter inPersoonia rigida(Proteaceae). Naturalpollen transfer was highly efficient, and no evidence of self-incompatibilitywas found. Levels of fruit set (67.4% following open-pollinationand 50.4–58.8% following hand-pollinations) may be thehighest recorded for a species of Proteaceae with hermaphroditicflowers. Fruit abscission occurred principally in a single phasefrom 4–10 weeks post-anthesis, with a peak during theeighth week post-anthesis, and this early abscission was theresult of fertilization failure in some flowers. Manipulationof carbohydrate availability by girdling and/or defoliationof branches provided evidence that carbohydrate supply affectedfruit set only when supply was very low. Fruit abscission dueto very low carbohydrate availability on defoliated brancheswas evident during the early abscission phase but was more pronouncedduring the second half of the fruit development period (>17weeks post-anthesis), coinciding with the period of greatestdry matter demand by the fruits. Minimal fruit abscission occurredduring this later period on leaf-bearing branches. Increasesin carbohydrate supply had no effect on fruit set, but fruitsize was highly sensitive to carbohydrate availability. Subtendingand adjacent leaves were identified as major contributors tothe carbohydrate supply of fruits, although some carbohydratecould be obtained from beyond the fruiting branch. Despite thehigh levels of natural fruit set, both pollen supply and resourceavailability were indicated as potential constraints on accumulationof fruit dry matter inP. rigida.Copyright 1999 Annals of BotanyCompany. Persoonia rigidaR.Br., Proteaceae, pollination, carbohydrates, fruit set, fruit size, abscission, girdling.     

Xyloglucan endotransglycosylase activity during fruit development and ripening of apple and kiwifruit

Xyloglucan endotransglycosylase (XET) activity was measured in apple (Malus domestica Borkh. cv. Braeburn) pericarp and kiwifruit (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) outer pericarp and core tissues in order to establish whether a correlation exists between the activity of the enzyme and different stages of fruit development Whereas the growth rate of kiwifruit paralleled changes in XET activity throughout fruit growth, that of apple did not. Both fruits showed the highest XET activity, on a fresh weight basis, in the first two weeks after anthesis when cell division was at its highest. XET activity then decreased sharply, but as the fruit increased in size (4–8 weeks after anthesis) there was a concomitant increase in XET activity in both fruits. In the latter stage of fruit development (16–26 weeks after anthesis) XET activity increased to peak at harvest in apple fruit. During this time there was relatively little increase in fruit size and presumably therefore minimal cell expansion. XET activity then declined as fruit softened after harvest. In core tissue from kiwifruit, XET activity increased throughout the later stages of fruit growth to harvest maturity in a similar manner to apple, but continued to increase after harvest until fruit were ripe. In contrast, XET activity in the outer pericarp of kiwifruit did not increase until ripening after harvest. In apple tissue up to 30% of the XET activity was cell wall bound and could not be solubilised, even in buffer containing 2 M NaCl. The results implicate XET in cell wall assembly during cell division and expansion early in apple and kiwifruit growth. However, the disparity between apple and kiwifruit with respect to XET activity late in fruit development and ripening and the different affinities of the enzyme for the cell wall in each fruit, suggest that XET has several roles in plant development, not all of which are related to cell wall loosening during periods of accelerated growth.     

Fruit age and changes in abscisic Acid content, ethylene production, and abscission rate of cotton fruits

The relationships of fruit age, abscisic acid (ABA) concentration, ethylene evolution, and abscission rates were studied in an effort to determine why cotton (Gossypium hirsutum L., cv. Deltapine 16) fruits rarely abscise more than 15 days after anthesis. Because abscission of cotton fruits is increased by conditions that limit photosynthesis, greenhouse-grown plants with fruits of various ages were placed in dim light for 3 days to induce high rates of fruit abscission. Abscission rates, ABA concentrations, and ethylene evolution rates were determined for fruits of various ages. Almost all of the young fruits abscised, but abscission rate declined with age until almost no abscission was observed in fruits that were 15 or more days past anthesis.     

Changes of Respiration Rate, Ethylene Evolution, and Abscisic Acid Content in Developing Inflorescence and Young Fruit of Olive (Olea europaea L. cv. Konservolia)

Simultaneous measurements of respiration, ethylene production, and abscisic acid (ABA) concentrations, as well as the growth parameters length, fresh weight (FW), and dry weight (DW) of olive (Olea europaea L. cv. Konservolia) inflorescence were carried out at short intervals (3–7 days) during the period from bud burst until the 3rd week after full bloom (AFB), when young fruit reached 8 mm in length. The axis of inflorescence elongated remarkably during the 3rd week after bud burst (ABB), massive bract shedding occurred during the 4th week ABB, full bloom (FB) was observed 7 weeks ABB, and massive floral organ abscission 1 week AFB. The results showed a continuous increase in inflorescence FW and DW from bud burst until 4 days before FB. Respiration rate, ethylene production, and levels of ABA were relatively high during the first 3 weeks ABB. After this period, respiration and ethylene followed a similar pattern of changes, inversely to that of ABA concentration. An accumulation of inflorescence ABA 6 and 4 days before FB was associated with the minimum values of respiration and ethylene production on the same dates. The sharp decrease in the ABA concentration during FB and 3 days later was followed by a high rise in ethylene and an increase in respiration rate, which both rose further 1 week AFB. The results suggest a possible correlation of ABA with the early stage of floral abscission, whereas ethylene production seems to be correlated with the terminal separatory activity in olive inflorescence abscission processes. Received May 28, 1998; accepted November 17, 1998     

Endogenous polyamines in apple and their relationship to fruit set and fruit growth

The distribution of free and bound polyamines was investigated from blooming until harvest on flower, fruitlets and fruits of Malus domestica Borkh cv. Golden Delicious, Relationships between polyamines and fruit set and growth were also investigated. The level of free polyamines was high only during the first weeks after full bloom and then decreased gradually. The amount of bound trichloroacetic acid-insoluble polyamines was much higher than free polyamines. Bound spermine in particular showed a high value for almost 40 days after full bloom, while spermidine and putrescine were no longer detectable even a few days after full bloom.
In relation to fruit set, it was possible to observe that abscission peaks took place when free polyamine levels were low or decreasing. Insofar as fruit growth is concerned, the most substantial variations in polyamine levels occurred very early in the season when fruit dry weight and protein amount were also changing rapidly and fruit diameter was almost impossible to measure.     

绞股蓝果实的发育解剖学研究

应用石蜡切片和扫描电镜的方法,观察了绞股蓝果实与种子的发育过程,结果表明:花后12 d左右,绞股蓝合子开始进行第一次分裂,极核分裂在花后6～7 d,核型胚乳在胚的发育中被吸收,胚的发育为茄型,外珠被呈网格状花纹。假果,表面有蜡质,果壁可明显分为3层,内侧细胞后期解体,种子倒三角形,表面瘤状突起。脱落花果的结构表现为珠被萎缩和胚发育受阻。     

Development of the Almond Nut (Prunus dulcis (Mill.) D. A. Webb). Anatomy and Chemical Composition of Fruit Parts from Anthesis to Maturity

The growth of the fruit of two varieties of almond (Prunus dulcis(Mill.) D. A. Webb) was studid from anthesis (week 0) to maturity(week 32). The dimensions, fresh weight, moisture content, anatomyand chemical composition of the pericarp, testa, embryo, endospermand nucellus are recorded diagrarnmatically, graphically andby micrographs for one variety. Of the two ovules present atflowering only one normally developed further. By 12 weeks afterflowering the whole fruit had reached full size. The space encloscdby the pericarp was filled by nuallus until weck 10, with subsequentenlargement of both endosperm and embryo. From week 16 to week20 the embryo increased to full size with a concumnt decreasein the size of the endosperm. Sixteen weeks after flowering,the embryo began to accumulate protein and lipid, little ofwhich originated from either the nucellus or endosperm. Theembryo contained no starch or reducing sugar but up to 3% sucrosein the early stags which dtcreascd as lipid and protein increased.Starch and sucrose levels were high in the testa at week 16but subsbquently dropped, starch more rapidly than sucrose.The role of the testa in transport of metabolites to the embryois discussed. Prunus dulcis, almond, fruit development, anatomy, embryo, endosperm     

Hormonal control of floral abscission in zucchini squash (<Emphasis Type="Italic">Cucurbita pepo</Emphasis>)

In the zucchini squash, Cucurbita pepo, a well coordinated abscission of the female flower during fruit set is essential to obtain a fruit of commercial value. In Spain zucchini is mainly produced in greenhouses in Almería, where high temperatures during the spring-summer period provoke a cultivar-dependent defect in fruits known as the “sticky flower” syndrome. This disorder is characterised by an arrest in growth and maturation of floral organs, and a lack of female floral abscission, thus diminishing fruit shelf-life, commercial quality and value. The aim of the present work was to improve knowledge of the abscission process in C. pepo to better understand the fundamental causes of this disorder. The anatomical analysis of abscission shows a well defined male floral abscission zone (AZ), few hours after anthesis, which differs from the female zone which is not differentiated from the adjacent tissue until the abscission process has begun, and which occurs as a consequence of AZ cell enlargement and the dissolution of their cell walls. To evaluate the role of ethylene and auxins in the regulation of floral abscission in zucchini we performed several treatments, with: ethylene, added as 0.25% ethrel solution; AVG, the inhibitor of ethylene synthesis, at 100 μM; indol-3-acetic acid, 100 μM; and TIBA, the inhibitor of auxin polar transport, at 10 mM. These treatments show that ethylene is an accelerator of zucchini floral abscission, and also promotes abscission in isolated AZs of sticky flowers. On the other hand, IAA delays abscission of the female flowers, whilst the inhibitor of auxin polar transport promotes it. The activity of the cell wall hydrolytic enzymes, polygalacturonase and cellulase, sharply increased just before the shedding of zucchini floral organs (72 h after anthesis). Moreover, both enzyme activities were induced by ethylene, which partly explains the ethylene promoting effect.     

Light and Shade Effects on Abscission and C-Photoassimilate Partitioning among Reproductive Structures in Soybean

Field experiments were conducted in 1981 and 1982 to study the effects of low-irradiance supplemental light on soybean (Glycine max [L.] Merr. cv Evans) flower and pod abscission. Cool-white and red fluorescent lights illuminated the lower part of the soybean canopy during daylight hours for 3 weeks late in flowering. At the same time, flowers and young pods on half the plants were shaded with aluminum foil. Flowers were tagged at anthesis and monitored through abscission or pod maturity.

Responses to red and white lights were similar. Supplemental light tended to reduce abscission and increase seed weight per node compared to natural light. Shading flowers and pods increased abscission and reduced seed weight per node. Number of flowers produced per node, individual seed weight, and seeds per pod were not affected by light or shade treatments.

Further studies examined the effects of shading reproductive structures on their capacity to accumulate ¹⁴C-photoassimilates. Individual leaves were pulse labeled with ¹⁴CO₂ 1, 2, and 4 weeks post anthesis. Flowers and pods in the axil of the labeled leaf were covered with aluminum foil 0, 24, 72, and 120 hours before pulsing.

Shading flowers and pods resulted in a 30% reduction in the relative amount of radiolabel accumulated from the source leaf. The reduction in ¹⁴C accumulation due to shading was evident regardless of the length of the shading period and was most pronounced when the shades were applied early in reproductive development. We conclude that light perceived by soybean flowers and young pods has a role in regulating both their abscission and their capacity to accumulate photoassimilates.

     

Changes in Abscisic Acid and Indoleacetic Acid before and after Anthesis Relative to Changes in Abscission Rates of Cotton Fruiting Forms

Cotton (Gossypium hirsutum L.) fruiting forms exhibit pronounced changes, with age, in their probability of abscission. Large floral buds rarely abscise, but after anthesis the young fruits (bolls) have a high probability of abscising. Abscission rate reaches a peak about 5 to 6 days after anthesis and then gradually decreases. An experiment was conducted to try to determine the reason for the rapid and pronounced increase in probability of abscission just after anthesis. Cotton was grown in the field and fruiting forms of various ages from 9 days before to 9 days after anthesis were all harvested the same day and subsequently analyzed for ABA and IAA. The concentration of ABA decreased slightly at anthesis and increased gradually thereafter. In contrast, the concentration of IAA was high before anthesis and then decreased at anthesis to about one-fifth the previous concentration. IAA remained low for at least 4 days after anthesis and then increased rapidly between 7 and 9 days after anthesis. The high concentration of IAA in floral buds before anthesis is probably a major factor in their resistance to abscission. Likewise, the low concentration of IAA at anthesis and for about 4 days thereafter may promote fruit abscission during the young boll stage.     

Do Genetic Make-up and Growth Manipulation Affect Tomato Fruit Size by Cell Number,or Cell Size and DNA Endoreduplication?

This work investigated the link between genetic and developmental controls of fruit size and composition. On two isogenic lines (CF12-C and CF14-L), differing by fruit weight and sugar content quantitative trait loci (QTLs) identified previously, basal and tip fruits were characterized at anthesis and at maturity through their growth, dry matter and sugar content, number and size of cells and nuclei DNA content. The influence of competition was assessed by removing either basal or tip ovaries at anthesis. On an intact inflorescence, CF12-C fruits grew less than CF14-L fruits, with 1.67 fewer cell layers and similar cell size, suggesting that genes controlling cell division may be responsible for this fruit size variation. Truss thinning masked the QTL effect on fruit size, mainly by reducing the difference in cell number between the two lines and by promoting cell expansion in tip fruits, so that fruit growth was similar at both positions and for both lines. Thus, in these lines, cell number exerts a control on final fruit size only when there is competition among fruits. Different responses of basal and tip fruits after flower removal suggested that this treatment induced changes in hormonal relationships within the truss. No fixed relationship between DNA endoreduplication and cell size was found, as while cell size and dry matter and sugar contents differed with tomato lines, fruit position and truss size, endoreduplication patterns were the same. CF12-C fruits had a higher dry matter (+0.3% of fresh weight) and carbohydrates (+8% of dry matter) content than CF14-L fruits. The percentage dry matter was independent of truss size but decreased slightly from basal to tip fruits.     

Ethylene, a regulator of young fruit abscission

In an earlier study we reported that detached cotton flowers produced sufficient ethylene before the period of natural abscission to suggest that ethylene might be a natural regulator of young fruit abscission. The present report explores this probability further. Intact cotton (Gossypium hirsutum L.) fruits produced ethylene at rates as high as 36 μl ethylene/kg fresh wt·hr during the 2 days before they abscised. Direct measurements of ethylene in gas samples withdrawn from fruits indicated that production of 1 μl ethylene/kg fresh wt·hr is equivalent to an internal concentration of approximately 0.1 μl/l. Fumigation of fruiting cotton plants with only 0.5 μl/l caused 100% abscission of young fruits and floral buds within 2 days. This correlated with the estimated endogenous levels of ethylene. Reduced pressure, which reduced the internal levels of ethylene, delayed abscission of young fruits and leaves, a result which supports our conclusion from this study— that ethylene is one of the regulators of young fruit abscission in cotton.     

Early Application of Ethrel Extends Tomato Fruit Cell Division and Increases Fruit Size and Yield with Ripening Delay

Flowers of tomato (Lycopersicon esculentum Mill.) plants cv. Castle Rock were sprayed with 100 ppm of ethrel, 0.5 mm aminooxyacetic acid (AOA), or water (control) 2 days after anthesis. The fruit period of cell division was extended up to 16–18 days after anthesis with the application of ethrel but reduced from 10–12 days (control) down to only 6–8 days with the application of AOA. In a trend opposite to AOA application, fruits that received ethrel treatment were of higher ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) levels than control. This was noticed not only during the first 2 weeks after anthesis but also during the fruit climacteric phase. Mesocarp cells of ethrel-treated fruits were greater in number/mm² but smaller in size than control; an opposite trend was obtained with the application of AOA. This was observed for a period of 18 days after anthesis, but by that time or at earlier ages, fruits of AOA treatment were larger in size and heavier in weight than control, and both were larger and heavier than ethrel-treated ones. At 5 weeks after anthesis and thereafter, the fruit response to all treatments was totally reversed because early ethrel-treated fruits became significantly larger in size and heavier in weight with a ripening delay of about 10 and 15 days compared with those of control and AOA-treated ones, respectively. When the same treatments were applied to the whole plant, similar results were obtained because the early application of ethrel increased the fruit yield by about 15% over control with a pronounced ripening delay; an opposite trend was obtained with the application of AOA. No significant differences were found among all treatments in terms of flower or fruit abscission or fruit number/plant. The data suggest that ethylene regulates tomato fruit transmission from cell division to cell enlargement. In addition, fruit cell division is terminated only when endogenous ethylene decreases to its basal level, allowing cell enlargement to dominate and proceed as in the case of the early application of AOA. The ripening delay of ethrel-treated fruits may be caused by the longer time required for the increased cell number to reach maturation. A low level of ethrel application at the tomato early fruiting stage may be used for increasing fruit yield by increasing fruit size and consequently its quality. Received June 1, 1998; accepted December 7, 1998     

Flowering and Fruiting Phenology of Magnolia hypoleuca

Abstract The floral biology of Magnolia hypoleuca , a tall tree species widely distributed in Japan, was studied in a deciduous broad-leaved forest in Hokkaido near the northern limit of distribution of the species. The flower is large, protogynous and nectarless. Its petals close after the female stage and again after the male stage. The mean duration of flowering of an individual flower is 3–4 days, while the flowering period of an individual tree lasts up to 40 days. The main pollinators of the flowers were beetles. Success of pollination is assumed to be affected by weather conditions at anthesis. Average fruit sets (ratios of fruits to flowers) were 13–25%. Hand-pollination of 44 flowers produced a significantly higher fruit set (28 fruits) than control flowers (33/133). These results suggest that the fruit set is limited by pollination. The frequency of infertile ovules was higher in controls than in hand-pollinated fruits, indicating that the seed set was also limited by pollination. We propose a mimicry hypothesis in which the non-rewarding female-stage flower mimics the rewarding male-stage flower to explain the short life-span of an individual flower, the long flowering period of an individual tree, and the coexistence of flowers of various stages on a single tree.     

Pattern of the Cyanide-Potential in Developing Fruits : Implications for Plants Accumulating Cyanogenic Monoglucosides (Phaseolus lunatus) or Cyanogenic Diglucosides in Their Seeds (Linum usitatissimum, Prunus amygdalus)

The absolute cyanide content of developing fruits was determined in Costa Rican wild lima beans (Phaseolus lunatus), oil flax (Linum usitatissimum), and bitter almonds (Prunus amygdalus). The cyanide potential (HCN-p) of the lima bean and the almond fruit began to increase shortly after anthesis and then stopped before fruit maturity. In contrast, the flax inflorescence had a higher HCN-p in absolute terms than the mature flax fruit. At all times of its development the bean fruit contained the monoglucosides linamarin and lotaustralin. The almond and the flax fruits contained, at anthesis, the monoglucosides prunasin, and linamarin and lotaustralin, respectively, while, at maturity, only the corresponding diglucosides amygdalin, and linustatin and neolinustatin, respectively, were present.