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.     

Competition and fruit set in the Washington navel orange

In the Washington navel orange [ Citrus sinensis (L.) Osbeck] an increase in the number of flowers results in a reduction of flower weight at anthesis and the initial fruit growth rate, and the number of developing fruitlets increases. Most of these fruitlets are shed during post-anthesis, and the final set of fruit is unrelated to the number of flowers and to the total amount of metabolites and mineral elements used up in fructification but appears to be controlled by the capacity of the tree to supply metabolites to the developing fruitlets during post-anthesis. When the number of flowers is too large, there is a reduction both in the number of initially developing fruitlets and in their growth rate. The final set of fruit is reduced through a different mechanism acting at anthesis and involving differences in mineral composition, which impairs the capacity of the fruit to act as a sink.     

Changes in the accumulation of flavonoid and isoflavonoid conjugates associated with plant age and nodulation in alfalfa (Medicago sativa)

Carbohydrate and mineral nutrition was studied in relation to abscission in fruitlets from leafy inflorescences of the Washington navel orange ( Citrus sinensis [L.] Osbeck). Differences in the growth rate of the fruitlets permitted to predict abscission several weeks in advance. This allowed characterization of early differences in composition and behaviour of persisting and abscising fruitlets.
Inflorescences with persisting fruitlets accumulated more mineral elements than inflorescences with abscising fruitlets, and for the phloem-mobile elements the excess accumulation was allocated to the fruitlets. Starch accumulated in the inflorescence leaves during early fruitlet growth, and this accumulation was enhanced by the persisting fruitlets despite their higher growth rate and mobilizing ability. The relations between the fruitlets and the inflorescence leaves cannot be explained totally in terms of source sink relationships; a hormonal regulation of the leaves by the fruitlets is postulated.
Acid invertase activities and hexose concentration in the pericarp were higher in the abscising fruitlets. The lower early growth rate of these fruitlets is thus not caused by a limitation in carbohydrate supply. It seems more related to carbohydrate utilization, probably hormonally mediated, as demonstrated by the higher dependence on hormone supply for the growth in vitro of the endocarp explants.     

Fruit Set, Abscission and Dry Matter Accumulation on Girdled Branches of Macadamia

The patterns of fruit growth, abscission and dry matter accumulationwere determined for ungirdled macadamia branches and comparedwith the patterns on girdled branches. The relationships betweenfruit set, fruit drop, and the number of available leaves werealso assessed. Approximately 50 leaves were required to supportdevelopment of each fruit on girdled branches, so that finalfruit numbers on girdled branches were higher or lower thanon ungirdled controls, depending on leaf number. High leaf numbersdid not cause any increase in fruit size on girdled branches,but low leaf numbers resulted in fruit volumes up to 23% lowerthan the controls. The number of fruits set on ungirdled brancheswas independent of the number of leaves on the branch. Defoliationof ungirdled branches had no effect on the number of fruitsset, with fruit set on these branches apparently being supportedalmost entirely from carbohydrates obtained elsewhere in thetree. Three phases of fruit drop were observed, with maximaat 2, 6-7, and 10 weeks post-anthesis, separated by phases ofrelatively low fruit drop at 4 and 8 weeks post-anthesis. Themaximum dry weight increase of the crop occurred between 10and 20 weeks post-anthesis, when there was very little fruitdrop. Therefore, although limited availability of assimilatesmay influence fruit retention in macadamia, there is no simplerelationship between structural carbon demand and fruit drop.Copyright1994, 1999 Academic Press Macadamia integrifolia Maiden and Betche, Macadamia tetraphylla L. A. S. Johnson, Proteaceae, macadamia, fruit set, fruit drop, girdling     

Flower abscission and inflorescence carbohydrates in sensitive and non-sensitive cultivars of grapevine

The Gewurztraminer (GW) and the Pinot noir (PN) cultivars of grapevine differ in their sensitivity to environmental factors that can cause flower abscission, cv. GW being the most sensitive. In order to further define the mechanisms leading to abscission, and owing to the importance of sugars in the achievement of sexual organ ontogenesis, we attempted to correlate the chronology of flower ontogenesis with the variations of carbohydrates in the inflorescence. In the vineyard, under optimal climatic conditions, fruit set of cv. GW and cv. PN was 82% and 65%, respectively. The sugar distribution was different in their inflorescences during the entire duration of flower development. Between stages 15 and 17, flowers of GW and PN reached the crucial meiosis stage. At that time, the inflorescences of cv. GW exhibited higher concentrations of starch and sucrose, whereas those of PN presented higher levels of glucose and fructose. Despite higher starch concentrations in GW inflorescences, starch reserves were present in the ovules and anthers of PN but not in those of GW. These results suggest that the higher content of reserve and transport carbohydrates in the inflorescences of GW favour flower development and fruit set under optimal environmental conditions. Furthermore, since meiosis represents a key step of female development, the different sugar concentrations in the inflorescences of the two cultivars at stages 15 and 17 could be related to the sensitivity to flower abscission under climatic stress. In particular, the presence of starch granules in PN ovules and anthers might explain the higher resistance of this cultivar to flower abscission.     

Carbohydrate Availability in Relation to Fruitlet Abscission in Citrus

Abscission of flowers and fruitlets in the Washington navelorange (Citrus sinensis [L.] Osbeck) has been characterizedin relation to carbohydrate availability. A main wave of flowerabscission occurs shortly after anthesis while the carbohydratereserves in the tree are high. Fruitlet abscission starts approx.30 d after the commencement of flowering, while carbohydrates(mainly starch) are being accumulated in the leaves. Flowerand early fruitlet abscission are not caused by carbohydrateshortage. During late fruitlet abscission sucrose concentrationin the leaves falls to a low value demonstrating a limitationin supply and competition among the developing fruitlets forcarbohydrates. Concentrations of sucrose and reducing sugarsin the peel of the fruitlets also fall to low values, and arelationship could be demonstrated between these free sugarlevels and abscission. Ringing increases carbohydrate supplyto fruit and reduces late fruitlet abscission, but only hasa marginal effect on the growth of the fruitlets, which seemsless sensitive than abscission to carbohydrate shortage. Thelimitation of carbohydrate supply to the fruitlets occurs whilestarch levels in the leaves remain high. Slow mobilization ofstarch reserves may be one factor limiting set in Citrus. Copyright2001 Annals of Botany Company Carbohydrate supply, citrus, fruit growth and abscission, ringing, navel orange, starch, sugar metabolism     

Mechanical wounding and abscission in citrus

Fruit detachment force (FDF), ethylene evolution, fruit and leaf drop were determined in Citrus sinensis for periods up to 96 h after mechanical wounding. Injury by removing a thin section of mature fruit flavedo reduced FDF, increased ethylene evolution and promoted abscission. Injuring flavedo 1 cm below the calyx was more effective at reducing FDF than injuring flavedo at the equator or the blossom‐end of mature fruit. Injuring the calyx or peduncle of mature fruit, or injuring three leaves closest to the mature fruit did not reduce FDF. Immature fruitlets either did not abscise or underwent low rates of abscission in response to mechanical wounding, depending on age. Inhibiting ethylene binding in wounded mature fruit with 1‐methylcyclopropene (1‐MCP) increased ethylene evolution compared with wounded fruit alone, but the reduction in FDF was similar. When an ethylene biosynthesis inhibitor (aminoethoxyvinylglycine, AVG) was used, reduction in FDF of wounded mature fruit exposed to AVG was similar to that of wounded fruit alone but ethylene production was markedly reduced. Wounding mature leaf blades in the presence or absence of 1‐MCP resulted in elevated but equal ethylene evolution up to 48 h after wounding, however, no leaf drop occurred. Thereafter, ethylene evolution was higher in 1‐MCP‐treated wounded leaves. Removing up to 77% of the total mature leaf area did not cause leaf drop, nor did wounding tissue across the laminar or petiolar abscission zones. Leaflets of 5 mm length reached nearly 100% abscission after mechanical wounding, whereas wounding leaves 20 mm length resulted in 15% abscission. The data suggest that mechanical wounding of flavedo results in mature fruit abscission, and ethylene binding may not be mandatory to initiate abscission in citrus fruit. The differential response of fruit and leaves at different ages to wounding may be related to potential contribution to carbohydrate accumulation, and production and sensitivity of tissues to an abscission signal(s).     

Carbohydrate and ethylene levels related to fruitlet drop through abscission zone A in citrus

Citrus fruits have two abscission zones (AZ), named A (in the pedicel) and C (in the calyx). Early fruitlet abscission takes place exclusively through AZ A, while at June drop it is progressively inactivated and AZ C begins to operate. In previous work, it has been demonstrated that carbohydrate and ethylene regulate fruit drop through abscission zone C. In this paper, we have analysed the effect of these two factors in developing fruitlets of Satsuma mandarins (Citrus unshiu [Mak.] Marc.) cv. Okitsu to elucidate their involvement on abscission through AZ A. The data indicated that ACC content and ethylene production of fruitlets paralleled abscission rates. Sucrose supplementation increased fruit set, although did not counteract the abscising effect induced by ACC. Branch girdling of terminal fruitlets carrying several leaves significatively reduced ethylene production and abscission rates, and increased sugar content. Pedicel girdling showed the opposite. Taken together, the results revealed that the carbohydrate content may be a biochemical signal involved in the mechanisms controlling abscission through AZ A. The evidence also showed parallelisms between ethylene and its activation. As the induction of higher ethylene levels after the period of AZ A activity, however, was not able to promote fruit drop, it is also concluded that solely ethylene is not sufficient to activate abscission.     

SECONDARY-FRUIT ONTOGENY IN NAVEL ORANGE

Ontogeny of the secondary fruit of navel orange (Citrus sinensis [L.] Osbeck) was studied using flower buds and fruit from groves in north central Florida. The secondary fruit, or navel, develops as a whorl of secondary-carpel primordia within the primary-carpel whorl when the flower bud is 1.5 to 2.0 mm in length. A complete secondary gynoecium with fused ovary but separate styles and stigmas develops within the primary gynoecium before anthesis. The stigma and style of secondary carpels are not as distinct as those of primary carpels. Three types of tissue protrusions from the secondary fruit into primary-fruit locules were abnormal placentae, free secondary carpels, and secondary-carpel outgrowths, the last being the most common. An abscission layer is present in the central axis of the primary fruit near the base of the secondary ovary. This layer is indistinguishable from adjacent tissues prior to commencement of secondary fruit abscission. Parenchyma cells in the abscission layer, however, contain large numbers of starch grains during abscission. Secondary and primary fruit have similar sigmoid growth patterns; however, onset of the cell-enlargement stage is approximately 2 wk later in secondary fruit.     

Delay of early fruitlet abscission by branch girdling in citrus coincides with previous increases in carbohydrate and gibberellin concentrations

Current evidence in citrus indicates that gibberellins (GAs) are main determinants of early fruit set while subsequent growth of developing fruits is mostly dependent upon carbohydrate availability. In this work, branch girdling performed at anthesis in Satsuma mandarin (Citrus unshiu (Mak.) Marc.) cv. Okitsu transitorily reduced early abscission rates (12–32 days after anthesis, DAA) delaying initially the process of natural fruitlet drop. The effects of girdling on growth, gibberellin (GA) and carbohydrate concentrations in developing ovaries and fruitlets were assessed during this initial growth stage (0–69 DAA). In girdled branches, abscission rate reduction was preceded by elevated concentrations of carbohydrate and GA in developing ovaries and fruitlets. Girdling at anthesis stimulated higher hexose (21 DAA) and starch (6–20 DAA) concentrations and also higher GA₁ (6 DAA), GA₁₉ (13–20 DAA) and GA₂₀ (6–20 DAA). The results established a relationship between the reduction of early abscission rates and higher concentrations of carbohydrates and GAs induced by girdling in developing fruitlets. These findings revealed that girdling certainly increased GA concentration and strongly suggested that its effect on early fruitlet abscission delay is likely mediated by both GA and carbohydrates.     

CsPLDalpha1 and CsPLDgamma1 are differentially induced during leaf and fruit abscission and diurnally regulated in Citrus sinensis

Understanding leaf and fruit abscission is essential in order to develop strategies for controlling the process in fruit crops. Mechanisms involved in signalling leaf and fruit abscission upon induction by abscission agents were investigated in Citrus sinensis cv. 'Valencia'. Previous studies have suggested a role for phospholipid signalling; hence, two phospholipase D cDNA sequences, CsPLDalpha1 and CsPLDgamma1, were isolated and their role was examined. CsPLDalpha1 expression was reduced in leaves but unaltered in fruit peel tissue treated with an ethylene-releasing compound (ethephon), or a fruit-specific abscission agent, 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP). By contrast, CsPLDgamma1 expression was up-regulated within 6 h (leaves) and 24 h (fruit peel) after treatment with ethephon or CMNP, respectively. CsPLDalpha1 expression was diurnally regulated in leaf blade but not fruit peel. CsPLDgamma1 exhibited strong diurnal oscillation in expression in leaves and fruit peel with peak expression around midday. While diurnal fluctuation in CsPLDalpha1 expression appeared to be light-entrained in leaves, CsPLDgamma1 expression was regulated by light and the circadian clock. The diurnal expression of both genes was modulated by ethylene-signalling. The ethephon-induced leaf abscission and the ethephon- and CMNP-induced decrease in fruit detachment force were enhanced by application during rising diurnal expression of CsPLDgamma1. The results indicate differential regulation of CsPLDalpha1 and CsPLDgamma1 in leaves and fruit, and suggest possible roles for PLD-dependent signalling in regulating abscission responses in citrus.     

Abscisic acid increases in non-growing and paclobutrazol-treated fruits of seedless mandarins

Clementine ( Citrus reticulata [Hort.] Ex. Tanaka cv. Oroval) is a self-incompatible mandarin with a slow rate of fruit growth and high percentage of fruit abscission. Seedless Satsuma ( Citrus unshiu [Mak] Marc. cv. Clausellina) shows natural parthenocarpy and higher fruit set. Application of 25 μg fruit⁻¹ of paclobutrazol (PP333), an inhibitor of gibberellin biosynthesis, reduced the rate of growth and accelerated fruit abscission in both varieties. In contrast, gibberellin A₃ (GA₃) stimulated fruit growth only in the self-incompatible mandarin. Clementine fruits, in the absence of pollination, showed an approximately 2-fold transient increase in the free abscisic acid (ABA) content shortly after petal fall. In Satsuma, a very small accumulation of ABA was detected. Paclobutrazol treatment induced a 3-fold increase in ABA in Satsuma fruits but did not substantially affect the pattern of ABA accumulation in Clementine. In this variety, GA₃ suppressed the ABA increase observed in untreated fruits. These effects were observed 24 h after treatment. However, in Satsuma fruits, the effect of GA₃ on the ABA content was negligible. In addition, a comparative analysis of growing and non-growing fruits of Clementine showed that ABA, on a per unit weight basis, was always higher in the non-growing fruits. Treatment with 85 μM fluridone, an inhibitor of carotenoid biosynthesis and thus indirectly of ABA, delayed fruit abscission in Clementine, but also decreased fruit growth. Collectively, these observations indicate a relationship between high ABA content and a reduced rate of fruit growth and an acceleration of fruit abscission.     

The Effect of the Fruit and Exogenous Hormones on Leaf Expansion and Composition in Citrus

Sanz, A., Martinez Cortina, C. and Guardiola, J. L. 1987. Theeffect of the fruit and exogenous hormones on leaf expansionand composition in Citrus.—J. exp. Bot. 38: 2033-2042. The effect of the developing flowers and fruitlets on leaf expansionand composition has been determined in leafy inflorescencesof Citrus sinensis L. Osbeck. During leaf expansion the developingflowers do not compete with the leaves, and their early removaldoes not affect leaf size and composition. Competition for mineralelements is established after flower opening, once leaf expansionis complete. No effect of the fruit on metabolizable carbohydratesin the leaves was found up to day 22 after flower opening. The response to exogenously applied growth regulators suggeststhat the differences in weight and composition between inflorescenceleaves and leaves from vegetative sprouts may be due to hormonally-mediateddifferences in sink strength. Gibberellic acid enhances laminaexpansion and increases the sink strength of the leaves. Kinetinenhances lamina expansion without affecting sink strength. Leafgrowth is directly related to both soluble and wall-bound acidinvertase activities; however, the GA₃ effects on leaf growthand sink strength are unrelated to invertase activity and tothe rate of starch accumulation. Key words: Acid invertase, amylase, carbohydrates, Citrus, leaf growth     

The Role of Abscisic Acid in Flower Abscission of Lupinus luteus

The role of abscisic acid in the control of flower abscission in Lupinus luteus L. was examined. Using a modified extraction and purification technique, endogenous abscisic acid levels in the upper flowers of an inflorescence were found to increase markedly some days before abscission could be detected. When abscisic acid was injected into flower-bearing nodes or fed via the roots, no increase in the abscission rate was obtained at any position in the flowerhead. Application of abscisic acid to only the leaves resulted in a marked increase in flower abscission. The role of abscisic acid per se as a primary controlling factor of flower abscission in yellow lupin is questioned.     

生长调节剂调控龙眼冲梢的研究

为高效、安全地调控龙眼冲梢,在龙眼花芽形态分化开始期(露红点期)和花穗主轴长6～9 cm的花穗展叶期,施用生长调节剂,比较了不同方法调控龙眼冲梢的效果。结果发现龙眼花芽形态分化开始期树冠喷施200 mg/kg乙烯利+150 mg/kg多效唑混合液和土施多效唑每株4 g处理控冲梢效果都显著高于对照,冲梢率分别是10.5%和7.6%,在花穗小叶处于展叶期虹吸输300 mg/kg乙烯利防控龙眼冲梢有效且安全。     

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     

Post-pruning shoot growth increases fruit abscission and reduces stem carbohydrates and yield in macadamia

Background and Aims

There is good evidence for deciduous trees that competition for carbohydrates from shoot growth accentuates early fruit abscission and reduces yield but the effect for evergreen trees is not well defined. Here, whole-tree tip-pruning at anthesis is used to examine the effect of post-pruning shoot development on fruit abscission in the evergreen subtropical tree macadamia (Macadamia integrifolia, M. integrifolia × tetraphylla). Partial-tree tip-pruning is also used to test the localization of the effect.

Methods

In the first experiment (2005/2006), all branches on trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R treatment) and shoots were removed from others (NR treatment). Fruit set and stem total non-structural carbohydrates (TNSC) over time, and yield were measured. In the second experiment (2006/2007), upper branches of trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R) and shoots were removed from others (NR). Fruit set and yield were measured separately for upper (pruned) and lower (unpruned) branches.

Key Results

In the first experiment, R trees set far fewer fruit and had lower yield than NR trees. TNSC fell and rose in all treatments but the decline in R trees occurred earlier than in NR trees and coincided with early shoot growth and the increase in fruit abscission relative to the other treatments. In the second experiment, fruit abscission on upper branches of R trees increased relative to the other treatments but there was little difference in fruit abscission between treatments on lower branches.

Conclusions

This study is the first to demonstrate an increase in fruit abscission in an evergreen tree in response to pruning. The effect appeared to be related to competition for carbohydrates between post-pruning shoot growth and fruit development and was local, with shoot growth on pruned branches having no effect on fruit abscission on unpruned branches.     

INFLORESCENCE TYPES AND FRUITING PATTERNS IN HAMLIN AND VALENCIA ORANGES AND MARSH GRAPEFRUIT

The structural, flowering, and fruit-setting patterns of inflorescences of mature Hamlin and Valencia orange and Marsh grapefruit trees were studied for three years. Several development patterns were found, some of which were relatively consistent for the different varieties or years of study. The sequence of anthesis on an inflorescence was: apical flower first, then basal flower, then the subapical flower. Terminals on which the earlier flowers appeared tended to have more inflorescences than those on which flowers appeared later. Inflorescences on which earlier flowers appeared also produced more flowers than those which began flowering later. Inflorescences that began flowering later were more likely to have leaves or have a greater number of leaves than earlier inflorescences. More than half of the inflorescences carried no leaves, and most of these had one flower. No evidence of a relationship between number of flowers and length of the inflorescence was found. Fruit set occurred primarily during the latter part of the flowering period. Many fruit were set on inflorescences without leaves, but on the basis of percent of flowers setting fruit, inflorescences with leaves were more productive. The greatest fruit set occurred in the subapical position on the inflorescence. With growth changes these fruit often appeared to be developing in the apical position. These patterns generally differed little from year to year. Variations may have been due to the differences in the number of flowers produced by the trees. Results were also similar between Hamlin and Valencia oranges. Patterns on Marsh grapefruit resembled those for the oranges but were frequently less consistent.     

Carbohydrate storage and use in an alpine population of the perennial herb, Oxytropis sericea

I tested hypotheses for ecological roles of storage carbohydrates in perennating organs (roots and branches) of alpine Oxytropis sericea, a leguminous herb. In naturally growing plants, total nonstructural carbohydrates achieved their maximal concentration in the fall, declined during winter, and reached minimal levels immediately after growth initiation in the spring. Experimental manipulation of carbon sink-source relations through shading of leaves of reproductive plants revealed that the normally unused portion of these carbohydrates is largely available for withdrawal. In another experiment, plants subjected to carbohydrate depletion through shading suffered decreased leaf growth after winter dormancy and had a lower probability of flowering and decreased inflorescence biomass. The dependence of reproductive growth on stored carbohydrates, however, was limited to its initial stages, because accumulation of storage carbohydrates occurred simultaneously with inflorescence expansion, flowering, and fruiting. Moreover, the whole-plant photosynthetic rate, estimated from gas exchange measurements also peaked at the time of inflorescence growth. To address whether stored reserves allow compensatory regrowth following defoliation, plants were subjected to experimental removal of leaves and inflorescences. Defoliated O. sericea partly regrew the lost leaves but withdrawal of stored carbohydrates was limited. Similarly, in a second defoliation experiment where infructescences were left intact, the plants used little stored carbohydrate and only partly compensated for fruit growth. However, carbohydrate accumulation was negatively affected by defoliation. While the ecological importance of stored nonstructural carbohydrates cannot be attributed to any function in isolation, winter respiration, leaf regrowth after winter, and early reproductive growth in O. sericea all depend to a significant extent on stored reserves. Maintaining a large storage pool may protect these functions in years when carbon status is less favorable than during this study. Received: 13 May 1998 / Accepted: 24 November 1998