Carbon integration in Plantago aristata (Plantaginaceae): the reproductive effects of defoliation

Patterns of carbon integration in aclonal species are poorly understood in spite of their potential to influence individual fitness. To provide more information about these patterns, we performed a defoliation experiment with P. aristata. We examined, at the metameric level, the reproductive responses to the removal of the major carbon sources within metamers. Bracts on marked reproductive spikes and leaves subtending these spikes were removed at three stages of reproductive maturity: spike elongation, flowering, and fruiting. Spike dry weight and length, capsule number, seeds per capsule, and seed weight were measured. We tested the hypothesis that seed weight would respond least to defoliation. We also performed a complementary ¹⁴C translocation experiment to measure the amount of radioactive carbon moving into the marked spikes from outside the metamer. Defoliation depressed all components of reproduction within marked spikes, and little ¹⁴C was translocated from outside the metamer into the reproductive spikes, even those that were defoliated. Both results support the view that reproductive metamers in this species are largely autonomous with respect to their carbon budget. Defoliation during spike elongation most depressed reproduction, and bract removal depressed reproduction more than did leaf removal. The data suggest that bracts compensate for leaf removal by increasing their photosynthetic rate; however, the ability to compensate differs among plant populations. Of all the reproductive components, seed weight was least affected by defoliation. The data show, however, that the time of defoliation relative to reproductive development influences which reproductive components are affected.     

The Effect of Nitrogen Supply to Urtica dioica L. Plants on the Distribution of Assimilate Between Shoot and Roots

In this study the influence of nitrogen nutrition on the patterns of carbon distribution was investigated with Urtica dioica. The nettles were grown in sand culture at 3 levels of NO^?₃, namely 3 (low), 15 (medium) and 22 (high) mM. These levels encompassed a range within which nitrogen did not affect total biomass production. The ratio of root: shoot biomass of the low nitrogen plants was, however, significantly higher than that of the nettles grown at medium and high N supply. Carbon allocation from one leaf of each pair of leaves was examined after a ¹⁴CO₂-pulse and a subsequent ¹⁴C distribution period of one night. Only the youngest two leaf pairs did not export assimilates. Carbon (¹⁴C) export to the shoot apex and to the roots, as measured at the individual nodes responded to the nitrogen status: At medium and high nitrogen supply the 3rd, 4th and 5th leaf pairs exported to the shoot apex, while lower leaves exported to the root. At low nitrogen supply only the 3rd leaf exported towards the shoot apex. The results illustrate the plastic response of carbon distribution patterns to the nitrogen supply, even when net photosynthesis, carbon export from the source leaves and biomass production were not affected by the nitrogen supply to the plant.     

Distribution patterns of assimilated 14C in vegetative and reproductive shoots of Lolium perenne and L. temulentum

The movement of ¹⁴C-labelled assimilate to the terminal meristem, stem, mature leaves, tillers and roots was measured in Loliurn perenn and Lolium temulentum after exposure to ¹⁴C0₂ of the youngest fully-expanded leaf and, on fewer occasions, the oldest healthy leaf on the main shoot. During early vegetative growth, the terminal meristem, tillers and roots received most of the ¹⁴C exported from the youngest leaf. As the shoot aged, more ¹⁴C was exported to the terminal meristem and tillers and less to roots. When the stem became a sizeable sink for ¹⁴C at the six-leaf (L. temulentum) or eleven-leaf (L. perenne) stage, less ¹⁴C moved to tillers and much less to roots. The terminal meristem continued to receive ¹⁴ at a steady rate throughout late vegetative growth. The transition from vegetative to reproductive growth in both species was marked by an abrupt increase in the export of ¹⁴C to stem from the upper leaf, but there was little change in the proportion of ¹⁴C which moved to the developing leaves and incipient inflorescence at the terminal meristem. At the same time, less ¹⁴C moved to tillers and much less to roots. Immediately before ear emergence, the export of ¹⁴C from the upper leaf (flag leaf) to the stem declined and the proportion moving to the ear increased, reaching a maximum of 55–75% as the ear emerged. The relative patterns of export of upper and lower leaves showed that while some ¹⁴ moved from each leaf to all meristems, the proximity of actively growing meristems appeared to be the main factor which determined the destination of most exported ¹⁴C. The distribution of ¹⁴C from upper and lower leaves was most alike in young vegetative plants of L. perenne. At later stages of development of both species, the terminal meristem and stem received most 14¹⁴C from the upper leaf, while roots and tillers received mos 14¹⁴C from the oldest leaf at the base of the shoot.     

Effect of shading individual soybean reproductive structures on their abscisic Acid content, metabolism, and partitioning

Pod set in soybean is related to carbon partitioning and may be, at least partially, regulated by abscisic acid (ABA) concentrations. The studies reported here examine the relationship between carbon and ABA partitioning, reproductive abscission and ABA metabolism. The partitioning of radiolabeled ABA and photoassimilates from leaves to flowers and endogenous ABA concentrations were determined in shaded and unshaded reproductive structures. Aluminum foil was gently placed over individual soybean reproductive structures for 48 hours at 0, 4, 12, 17, and 22 days after anthesis (DAA). Shading of flowers at 12, 17, and 22 DAA resulted in significantly reduced concentration of ABA. However, shading had no effect on the catabolism of exogenously supplied [³H] ABA. The shading treatment on the first four of the five dates reduced partitioning of photoassimilates and ABA from the subtending leaf to the flower. Shading of reproductive structures also caused a significant reduction in the amount of assimilate exported from the subtending leaf, at 17 DAA. We conclude that shade-induced premature reproductive abscission in soybean is not stimulated by high levels of ABA within reproductive structures, but that ABA may inhibit abscission of reproductive structures by playing a role in preferential assimilate partitioning.     

Inter-Specific Differences in Cotton for Nutrient Partitioning from Subtending Leaves to Reproductive Parts at Various Developmental Stages: Consequences for Fruit Growth and Yield

A field study was carried out to unravel the inter-specific differences in cotton for the partitioning of N, P, K, S, Ca, Mg, Na and Cl from the subtending leaves to the reproductive parts of Gossypium hirsutum, G. barbadense and G. arboreum at various developmental stages. Results revealed significant differences among the species for the various parameters studied. Overall there was a greater fresh and dry matter yield of various reproductive parts and subtending leaves of G. hirsutum and G. barbadense than G. arboreum, although the leaf photosynthetic rate was similar. Age-dependent increase in leaf area/leaf mass ratio indicated a greater partitioning of earlier acquired assimilates to the growth of reproductive parts. Results indicated greater partitioning of N, P, S and Ca during later reproductive growth (from boll production to its opening) in G. hirsutum and G. barbadense but during earlier reproductive growth in G. arboreum (from bud up to flower formation) as was evident by decreased subtending leaf/reproductive parts ratio. It is concluded that better N, P, S and Ca partitioning ability of G. hirsutum and G. barbadense at the onset of boll development played a major role in the better yield and good quality fiber characteristics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Physiological integration in the clonal perennial herb Trifolium repens L.

Summary Translocation of ¹⁴C-labelled carbohydrates between the parent stolon and branches, and among branches, of Trifolium repens plants was investigated in two glasshouse experiments to determine patterns of physiological organisation in this clonal species. Differential defoliation treatments were applied to the parent stolon and/or branches to test the sensitivity of translocation to the short-term carbon needs of defoliated sinks. Strong reciprocal exchange of carbohydrate between the parent stolon and branches was observed, with 18 41% of the ¹⁴C exported from leaves on the parent stolon moving to branches, while branches simulta-neously exported 25% (for old source branches) to 54% (for young source branches) of the ¹⁴C they assimilated to the parent plant, including translocation to other branches. Branch-to-branch translocation occurred both acropetally and basipetally. Parent-to-branch, branch-to-parent and branch-to-branch carbon fluxes all increased in response to defoliation of the sink, at the expense of carbon supply to stolon tissue or roots of the source module. Reduced export to stolon tissue of the parent axis played a major role in facilitating C reallocation from leaves on the parent stolon to defoliated branches. The observed patterns of C allocation and translocation could be adequately explained by accepted source-sink theory, and are consistent with a high degree of intra-plant physiological integration in resource supply and utilisation. This information provides mechanistic explanations for aspects of the growth dynamics and ecological interactions of T. repens in the patchy environment of a grazed pasture.     

Manihot allemii sp. nov. (Euphorbiaceae s.s.) with entire and unlobed leaves from northern Brazil,with notes about foliar anatomy

Manihot allemii M. J. Silva is described and illustrated as a new species, and its morphological affinities and conservation status is discussed. It is most similar to M. salicifolia Pohl in having a subshrubby and erect habit and in the general aspect of its unlobed leaves, but differs from it in having leaves that are conspicuously petiolate, an inflorescence that is a congested spike‐like thyrse, entire and diminute bracts and bracteoles subtending flowers of both sexes, pistillate calyx that is deeply lobed with oblong lobes, and staminate flowers with 8 or 10 stamens. Both species belong to a group of 14 species recognized by their possession of entire and unlobed leaves, which are the subject of taxonomic studies by the second author. Some notes on the leaf anatomy of species of Manihot that have entire and unlobed leaves are also presented.     

TRANSPORT OF CARBON AMONG CONNECTED RAMETS OF EICHHORNIA CRASSIPES (PONTEDERIACEAE) AT NORMAL AND HIGH LEVELS OF CO2

The floating, stoloniferous plant, Eichhornia crassipes, has high rates of productivity and rapidly invades new sites. Because the transport of carbon among connected ramets is known to increase the growth of clonal plants, we asked whether there is intraclonal carbon transport in E. crassipes. Because net photosynthesis of E. crassipes is significantly higher at high levels of atmospheric CO₂, we also asked if high CO₂ can change patterns of carbon transport in ways that might modify clonal growth. We exposed individual ramets within groups of connected ramets to ¹⁴CO₂ for 15–45 min and measured the distribution of ¹⁴C in the group after 4 days of growth at 350, 700, 1,400, or 2,800 μ1 1^−-1 CO₂. At 350 μ1 1^−-1 CO₂, a parent ramet exported approximately 10% of the ¹⁴C that it assimilated to its first rooted offspring ramet. The offspring exported a similar percentage of the ^l4C it assimilated toward the parent; two-thirds of this ¹⁴C was retained by the parent, and one-third moved into new offspring of the parent. In all ramets, imported carbon moved into leaves as well as roots. At the higher levels of CO₂, the percentage of assimilated carbon exported from a parent ramet to the leaf blades of its first offspring was lower by half. High CO₂ had little other effect on carbon transport. E. crassipes maintains bidirectional transport of carbon between ramets even under uniform and favorable environmental conditions and when external CO₂ levels are very high.     

THE FERTILE SPIKE OF OPHIOGLOSSUM PETIOLATUM. I. MECHANISM OF ELONGATION

The frond of Ophioglossum consists of a sterile segment and a fertile segment or spike. An investigation of fertile spike elongation reveals that growth of the spike proceeds by activity of an intercalary meristem located in the most distal region of the peduncle subtending the sporangial area. Anatomical comparisons of all regions of developing spikes, counts of mitotic figures along the length of spikes of various ages, determination of cell lengths of peduncle ground parenchyma cells, and historadioautography of spikes treated with H³-thymidine confirms the presence in the apical portion of the peduncle of a region of frequently dividing cells intercalated between two regions of more mature tissues. Marking experiments indicate that the petiole of the sterile segment of the frond elongates in a similar fashion. Although this type of intercalary meristem is rather common in angiosperm flower scapes and peduncles, this is the first detailed analysis of this type of growth in a pteridophyte genus.     

Sectoriality and physiological organisation in herbaceous plants: an overview

The physiological organisation of plants is considered in relation to the carbon economy of plant parts. Although assimilate is partitioned according to the relative strength of sinks, in many species there is also a very close relationship between partitioning and shoot phyllotaxy, giving rise to sectorial patterns of allocation whereby only certain sinks are supported by any source leaf. Essentially these sinks are in the same orthostichy as the source leaf. This constraint of the vascular architecture on assimilate distribution to developing sinks such as leaves, flowers and fruits is not always absolute, as following the loss of their principal source leaves these sinks can in many cases be supplied with assimilate by other leaves via new inter-orthostichy pathways. The supply of assimilate to major sinks such as developing fruits becomes more and more localised with time so that a fruit in an axillary position becomes largely supported by its subtending leaf; the reproductive node—a metamer-can thus be regarded as a relatively autonomous unit of the plant (an IPU). Similary, once established after a developmental phase of assimilate import, tiller ramets and branches in unitary plants tend to become physiologically autonomous modules. However, the functional autonomy of tillers is reversed following defoliation or shading as they are then sustained by the import of assimilate, subject to its availability, from unaffected tillers. Consequently the plant becomes physiologically integrated by the flow of assimilate from one part to another. The mainly autonomous ramets of many stoloniferous and rhizomatous species display a similar pattern of physiological integration in response to source manipulation, but in some species the ramets appear to maintain their independent functioning as a normal feature of the carbon allocation within the clone. In other clonal species, as the clone develops and becomes more structurally complex, vascular constraints start to restrict the movement of resources, and the clone becomes composed of a number of semi-autonomous IPUs. In unitary plants branches appear to remain very physiologically isolated in terms of their carbon economy once they become established, irrespective of a range of source-sink manipulations.These different patterns of physiological integration and organisation are discussed in relation to different strategies of assimilate utilisation and conservation.     

AXILLARY AND DICHOTOMOUS BRANCHING IN THE PALM CHAMAEDOREA

In both Chamaedorea seifrizii Burret and C. cataractarum Martius each adult foliage leaf subtends one axillary bud. The proximal buds in C. seifrizii are always vegetative, producing branches (= new shoots or suckers); and the distal buds on a shoot are always reproductive, producing inflorescences. The prophyll and first few scale leaves of a vegetative branch lack buds. Transitional leaves subtend vegetative buds and adult leaves subtend reproductive buds. Both types of buds are first initiated in the axil of the second or third leaf primordia from the apex, P2 or P3. Later development of both types of bud tends to be more on the adaxial surface of the subtending leaf base than on the shoot axis. Axillary buds of C. cataractarum are similarly initiated in the axil of P2 or P3 and also have an insertion that is more foliar than cauline. However, all buds develop as inflorescences. Vegetative branches arise irregularly by a division of the apex within an enclosing leaf (= P1). A typical inflorescence bud is initiated in the axil of the enclosing leaf when it is in the position of P2 and when each new branch has initiated its own P1. No scale leaves are produced by either branch and the morphological relationship among branches and the enclosing leaf varies. Often the branches are unequal and the enclosing leaf is fasciated. The vegetative branching in C. cataractarum is considered to be developmentally a true dichotomy and is compared with other examples of dichotomous (= terminal) branching in the Angiospermae.     

Reproductive characteristics of wild female Phayre's leaf monkeys

Understanding female reproductive characteristics is important for assessing fertility, interpreting female behavior, and designing appropriate conservation and captive management plans. In primate species lacking morphological signs of receptivity, such as most colobines, determination of reproductive parameters depends on the analysis of reproductive hormones. Here, we use fecal hormone analysis to characterize cycle patterns (N=6 females) and gestation length (N=7 females) in a group of wild Phayre's leaf monkeys (Trachypithecus phayrei crepusculus) in Phu Khieo Wildlife Sanctuary, Thailand. We found that both fecal estrogen (fE) and progestin (fP) levels showed clear biological patterns indicative of ovulation and conception. However, because fP patterns were inadequate in determining the end of the luteal phase, we used fE rather than fP patterns to delineate menstrual cycle parameters. We found a mean cycle length of 28.4 days (N=10), with follicular and luteal phases of 15.4 (N=10) and 12.5 days (N=14), respectively. On average, females underwent 3.57 (N=7) cycles until conception. Average gestation length was 205.3 days (N=7), with fE levels increasing over the course of pregnancy. Overall, the reproductive characteristics found for Phayre's leaf monkeys were consistent with results for other colobine species, suggesting that fecal hormone monitoring, particularly for fE metabolites, can provide useful reproductive information for this species. Am. J. Primatol. 72:1073–1081, 2010. © 2010 Wiley‐Liss, Inc.     

Photosynthetic Capacity and Carbon Contribution of Leaves and Bracts to Developing Floral Buds in Cotton

During ontogeny of Gossypium hirsutum L. floral buds (squares), increases in area and dry mass (DM) of floral bracts and the subtending sympodial leaf followed a sigmoid growth curve with increasing square age. The maximum growth rates of the bract area and bract DM occurred between 15 and 20 d after square first appearance (3 mm in diameter). Net photosynthetic rate (P_N) of the sympodial leaf at first fruiting branch position of main-stem node 10 reached a maximum when the subtended square developed into a white flower. Floral bracts had much lower P_N and higher dark respiration than the subtending leaf. The amount of ¹⁴CO₂ fixation by the bracts of a 20-d-old square was only 22 % of the subtending leaf, but 56 % of ¹⁴C-assimilate in the floral bud was accumulated from the bracts, 27 % from the subtending leaf, and only 17 % from the main-stem leaf at 6 h after ¹⁴C feeding these source s. Hence floral bracts play an important role in the carbon supply of developing cotton squares. This revised version was published online in September 2006 with corrections to the Cover Date.     

Reversal of the Direction of Photosynthate Allocation in Urtica dioica L. Plants by Increasing Cytokinin Import into the Shoot

The natural cytokinin import from the root into the shoot of Urtica dioica plants was enhanced by supplying zeatin riboside (ZR) solutions of various concentrations to a portion less than 10 % of the root system after removal of their tips. After 6 h ZR pretreatment of the plants, ¹⁴CO₂ was supplied for 3 h to a mature (source) leaf or to an expanding leaf and the ¹⁴C-distribution in the whole plant was determined after a subsequent dark period of 14 h. ZR substantially increased ¹⁴C fixation by the expanding leaves and also enhanced export of carbon and transport to the shoot apex. The effect of the hormone treatment was, however, more pronounced when the ¹⁴CO₂ was supplied to a mature leaf. In the control plants these leaves exported carbon only to the roots: When the amount of the natural daily ZR input from the roots to the shoot was enhanced by 20%, the bulk of the ¹⁴C exported from a mature leaf moved to the shoot apex and only a minor portion of ¹⁴C was still detected in the root fraction. A several-fold increase of the natural daily ZR input into the shoot resulted in a flow of ¹⁴C only to the growing parts of the shoot. The results suggest control of the sink strength of the shoot apex by ZR in Urtica diocia.     

Trade-offs between the persistence of foliage and productivity in two<Emphasis Type="Italic"> Pinus</Emphasis> species

We investigated interspecific variation in leaf lifespan (persistence) and consequent differences in leaf biochemistry, anatomy, morphology, patterns of whole-tree carbon allocation and stand productivity. We tested the hypothesis that a species with short-lived foliage, Pinus radiata D. Don (mean leaf lifespan 2.5 years), grows faster than P. pinaster Ait., a species with more persistent foliage (leaf lifespan 5.6 years), and that the faster growth rate of P. radiata is associated with a greater allocation of nitrogen and carbon to photosynthetic tissues across a range of scales. In fully sunlit foliage, the proportion of leaf N in the major photosynthetic enzyme Rubisco (ribulose-1, 5-bisphosphate carboxylase) was greater in P. radiata than in P. pinaster, and, in mid-canopy foliage, the proportion of leaf N in thylakoid proteins was greater in P. radiata. A lesser proportion of needle cross-sectional area was occupied by structural tissue in P. radiata compared to P. pinaster. Foliage mass in stands of P. radiata was 9.7 t ha^–1 compared with 18.2 t ha^–1 in P. pinaster while leaf area index of both species was similar at 4.6 m² m^–2, owing to the compensating effect of differences in specific leaf area. Hence trade-offs between persistence and productivity were apparent as interspecific differences in patterns of whole-tree carbon allocation, needle morphology, anatomy and biochemistry. However, these interspecific differences did not translate into differences at the stand scale since rates of biomass accumulation were similar in both species (P. radiata 6.9±0.9 kg year^–1 tree^–1; P. pinaster 7.4±0.9 kg year^–1 tree^–1). The similarities in performance at larger scales suggest that leaf area index (and radiation interception) determines growth and productivity. Received: 13 July 1999 / Accepted: 31 January 2000     

A Method for Calculating Sucrose Synthesis Rates throughout a Light Period in Sugar Beet Leaves

Sucrose synthesis rate in an exporting sugar beet (Beta vulgaris L.) leaf was calculated from simultaneous measurements of export and changes in leaf sucrose level. The amount of recently fixed carbon exported was determined from net carbon assimilated minus the tracer carbon accumulated in the leaf. The relative amount of ¹⁴C accumulated in the leaf supplied with ¹⁴CO₂ throughout an entire light period was recorded continuously with a Geiger-Mueller detector. To produce a continuous time course for tracer carbon accumulated in the leaf during the light period, the latter curve was superimposed on values for tracer carbon accumulated in leaves sampled at hourly intervals. Validity of the method requires that nearly all of the carbon that is exported be sucrose and that nearly all of the sucrose that is synthesized be either exported or accumulated as sucrose in the exporting leaves. These conditions appeared to be fulfilled in the situations where the method was applied. The method was used to study the effect of increasing atmospheric CO₂ concentration on the rate of sucrose synthesis. Further, the method can be used in conjunction with the gathering of other data such as gas exchange, metabolite levels, and enzyme activities in a set of leaves of a similar age on the same plant. This assemblage of data was found to be useful for understanding how rates of photosynthesis, sucrose synthesis, and translocation are regulated in relation to each other in an intact plant.     

Distribution of 14C-sucrose applied to leaves at different nodes of okra (Abelmoschus esculentum) during flowering and early pod growth

The distribution pattern of ¹⁴C-sucrose from ¹⁴C-sucrose applied to vegetative okra plants and leaves 1–9 on separate plants during the green pod development stage were investigated in relation to duration and leaf position. Results indicated bi-directional transport of assimilates to both apical and basal portions of the stem. Within 48 h ¹⁴C moved to all plant parts; stem and leaves appeared to be strong sinks. In plants fed at the vegetative stage, 48 h after feeding, 66% of the fed activity was exported from the fed leaf. At the pod development stage, about 35% of the activity exported from the fed leaf was present in green pods and 65% in vegetative parts. In plants where leaf 1–9 was fed, irrespective of the position of the fed leaf, the subtending fruit was the strongest sink among the reproductive parts. Leaves and stems were the principal sinks.     

Manipulation of food resources by a gall-forming aphid: the physiology of sink-source interactions

Summary We examined the capacity of the galling aphid, Pemphigus betae, to manipulate the sink-source translocation patterns of its host, narrowleaf cottonwood (Populus angustifolia). A series of ¹⁴C-labeling experiments and a biomass allocation experiment showed that P. betae galls functioned as physiologic sinks, drawing in resources from surrounding plant sources. Early gall development was dependent on aphid sinks increasing allocation from storage reserves of the stem, and later development of the progeny within the gall was dependent on resources from the galled leaf blade and from neighboring leaves. Regardless of gall position within a leaf, aphids intercepted ¹⁴C exported from the galled leaf (a non-mobilized source). However, only aphid galls at the most basal site of the leaf were strong sinks for ¹⁴C fixed in neighboring leaves (a mobilized source). Drawing resources from neighboring leaves represents active herbivore manipulation of normal host transport patterns. Neighboring leaves supplied 29% of the ¹⁴C accumulating in aphids in basal galls, while only supplying 7% to aphids in distal galls. This additional resource available to aphids in basal galls can account for the 65% increase in progeny produced in basal galls compared to galls located more distally on the leaf and limited to the galled leaf as a food resource. Developing furits also act as skins and compete with aphid-induced sinks for food supply. Aphid success in producing galls was increased 31% when surrounding female catkins were removed.     

PHOTOSYNTHESIS AND CARBON ALLOCATION IN TIPULARIA DISCOLOR (ORCHIDACEAE), A WINTERGREEN UNDERSTORY HERB

Seasonal patterns of photosynthesis and carbon allocation were determined for Tipularia discolor, a summer-deciduous wintergreen orchid of the southeastern United States, to assess the effects of environmental conditions and leaf age on carbon acquisition and allocation patterns. There was no shift in the optimum temperature for photosynthesis (T_opt) on a seasonal basis and T_opt (≈26 C) was at least 10 C higher than daily maximum air temperature during most of the growing season. Lack of photosynthetic adjustment in Tipularia to seasonal fluctuations in temperature and light suggested that the photosynthetic characteristics of this wintergreen were more similar to those of spring ephemerals than to those of evergreens and summer-active herbs. The decline in photosynthetic capacity during the winter growing season for Tipularia, largely due to leaf age effects, gradually reduced net photosynthetic rates in the field despite more favorable light and temperature conditions. Photosynthesis in the field was primarily limited by environmental conditions in early- and mid-season and by photosynthetic capacity in late-season. A ¹⁴CO₂ labelling experiment demonstrated that patterns of carbon allocation to vegetative structures were affected by the season of photosynthetic carbon fixation, whereas reproductive structures received 21% of the recovered labelled carbon regardless of the period of labelling. Carbon acquired and stored during all periods of the growing season was used to produce new vegetative and reproductive structures.     

The Translocation of 14C-photosynthate in Pisum sativum L.

Short-term studies were undertaken of source and sink relationshipsin Pisum sativum, cultivar Orfac, plants grown in a controlledenvironment. ¹⁴C-distribution assays were conducted after 24or 48 h ¹⁴Cphotoassimilate translocation from a single leafsubtending either a vegetative or a reproductive node. The primaryallocation of ¹⁴C-assimilate was achieved within 24 h: therewas no significant secondary movement of ¹⁴C within the subsequent24 h. The pod was strongly but not exclusively dependent onthe subtending leaf. Out of the total ¹⁴C fixed by a leaf theproportion that was exported within 24 h was related to the¹⁴C-sink capacity of the pods. A rapid non-combustive ¹⁴C-assay method is described whereby¹⁴C-tissue fragments are rendered translucent prior to directscintillation counting of the sample. In terms of cpm per mgobtained the latter method was comparable to a wet combustionmethod adapted for insoluble ¹⁴C-tissue.