Sink Demands Research Articles

Impact of Within-Tree Organ Distances on Floral Induction and Fruit Growth in Apple Tree: Implication of Carbohydrate and Gibberellin Organ Contents.

In plants, organs are inter-dependent for growth and development. Here, we aimed to investigate the distance at which interaction between organs operates and the relative contribution of within-tree variation in carbohydrate and hormonal contents on floral induction and fruit growth, in a fruit tree case study. Manipulations of leaf and fruit numbers were performed in two years on “Golden delicious” apple trees, at the shoot or branch scale or one side of Y-shape trees. For each treatment, floral induction proportion and mean fruit weight were recorded. Gibberellins content in shoot apical meristems, photosynthesis, and non-structural carbohydrate concentrations in organs were measured. Floral induction was promoted by leaf presence and fruit absence but was not associated with non-structural content in meristems. This suggests a combined action of promoting and inhibiting signals originating from leaves and fruit, and involving gibberellins. Nevertheless, these signals act at short distance only since leaf or fruit presence at long distances had no effect on floral induction. Conversely, fruit growth was affected by leaf presence even at long distances when sink demands were imbalanced within the tree, suggesting long distance transport of carbohydrates. We thus clarified the inter-dependence and distance effect among organs, therefore their degree of autonomy that appeared dependent on the process considered, floral induction or fruit growth.

In vivo action of RNA G-quadruplex in phloem development

Phloem network integrates cellular energy status into post-embryonic growth, and development by tight regulation of carbon allocation. Phloem development involves complicated coordination of cell fate determination, cell division, and terminal differentiation into sieve elements (SEs), functional conduit. All of these processes must be tightly coordinated, for optimization of systemic connection between source supplies and sink demands throughout plant life cycle, that has substantial impact on crop productivity. Despite its pivotal role, surprisingly, regulatory mechanisms underlying phloem development have just begun to be explored, and we recently identified a novel translational regulatory network involving RNA G-quadruplex and a zinc-finger protein, JULGI, for phloem development. From this perspective, we further discuss the role of RNA G-quadruplex on post-transcriptional control of phloem regulators, as a potential interface integrating spatial information for asymmetric cell division, and phloem development.

MA Assisted and Restrained Sink Mobility based Economical Data Processing in WSNs: MARS

Wireless Sensor Network (WSN) is composed of large number of tiny sensor node which have sensing and computation ability. In past WSNs, lots of Data Aggregation scheme has been proposed for prolong network lifetime and eliminate data redundancy. In general sink collects data from all deployed nodes in single processing cycle but region critical WSNs and long communication distance between nodes and sink demands a scheme which process data region wise. The presented scheme adopts sink mobility for region critical data gathering and avails Mobile Agent (MA) for prolonging network lifetime. This paper proposes MA assisted and Restrained Sink mobility based economical data processing in WSNs i.e. MARS. The proposed scheme works for sink trajectory as well as for Data Aggregation. Our simulation result shows that MARS utilizes networks’ energy efficiently and prolongs Sensor Network lifetime.

Performance analysis of a thermoelectric cooler with a corrugated architecture

A thermoelectric (TE) cooler architecture is presented that employs thin film thermoelectric elements on a plastic substrate in a corrugated structure sandwiched between planar thermal interface plates. This design represents a hybrid of a conventional bulk TE device and an in-plane thin film TE design. This design is attractive as it may benefit from low cost thin-film processing in a roll-to-roll fashion onto low-cost plastics substrates while maintaining a cross-plane heat flux for large area applications and a geometry that assists in maintaining a significant temperature difference across the thermoelectric elements. First, the performance of a single thermocouple is analyzed and the effect of the parasitic heat loss through the plastic substrate is examined. The performance of an array of thermocouples is then considered and the effects of various geometric parameters are analyzed with particular focus on the packing density of thermoelectric legs. The results show that while the coefficient of performance (COP) is comparable to a conventional bulk element TE cooler, the cooling power density drops off dramatically with a decrease in stacking angle of the legs. A comparison is then made between the heat sink demands of the hybrid TE design and a conventional bulk TE device where it is found that the lower cooling power density of the hybrid TE results in a reduction of heat sink demands as compared to bulk TE modules. The modeled performance suggest that the hybrid TE device may be advantageous in low cooling power density applications over relatively large areas where the low-cost nature of the device is maximized and less elaborate heat sink designs work effectively, cumulatively improving cost competitiveness.

A Matroidal Framework for Network-Error Correcting Codes

Matroidal networks were introduced by Dougherty et al. and have been well studied in the recent past. It was shown that a network has a scalar linear network coding solution if and only if it is matroidal associated with a representable matroid. A particularly interesting feature of this development is the ability to construct (scalar and vector) linearly solvable networks using certain classes of matroids. Furthermore, it was shown through the connection between network coding and matroid theory that linear network coding is not always sufficient for general network coding scenarios. The current work attempts to establish a connection between matroid theory and network-error correcting and detecting codes. In a similar vein to the theory connecting matroids and network coding, we abstract the essential aspects of linear network-error detecting codes to arrive at the definition of a matroidal error detecting network (and similarly, a matroidal error correcting network abstracting from network-error correcting codes). An acyclic network (with arbitrary sink demands) is then shown to possess a scalar linear error detecting (correcting) network code if and only if it is a matroidal error detecting (correcting) network associated with a representable matroid. Therefore, constructing such network-error correcting and detecting codes implies the construction of certain representable matroids that satisfy some special conditions, and vice versa. We then present algorithms that enable the construction of matroidal error detecting and correcting networks with a specified capability of network-error correction. Using these construction algorithms, a large class of hitherto unknown scalar linearly solvable networks with multisource, multicast, and multiple-unicast network-error correcting codes is made available for theoretical use and practical implementation, with parameters, such as number of information symbols, number of sinks, number of coding nodes, error correcting capability, and so on, being arbitrary but for computing power (for the execution of the algorithms). The complexity of the construction of these networks is shown to be comparable with the complexity of existing algorithms that design multicast scalar linear network-error correcting codes. Finally, we also show that linear network coding is not sufficient for the general network-error correction (detection) problem with arbitrary demands. In particular, for the same number of network errors, we show a network for which there is a nonlinear network-error detecting code satisfying the demands at the sinks, whereas there are no linear network-error detecting codes that do the same.

Precoding-Based Network Alignment Using Transform Approach for Acyclic Networks With Delay

The algebraic formulation for linear network coding in acyclic networks with the links having integer delay is well known. Based on this formulation, for a given set of connections over an arbitrary acyclic network with integer delay assumed for the links, the output symbols at the sink nodes, at any given time instant, is a F(p)m-linear combination of the input symbols across different generations, where F(p)m denotes the field over which the network operates (p is prime and m is a positive integer). We use finite-field discrete Fourier transform to convert the output symbols at the sink nodes, at any given time instant, into a F(p)m-linear combination of the input symbols generated during the same generation without making use of memory at the intermediate nodes. We call this as transforming the acyclic network with delay into n-instantaneous networks (n is sufficiently large). We show that under certain conditions, there exists a network code satisfying sink demands in the usual (nontransform) approach if and only if there exists a network code satisfying sink demands in the transform approach. When the zero-interference conditions are not satisfied, we propose three precoding-based network alignment (PBNA) schemes for three-source three-destination multiple unicast network with delays (3-S 3-D MUN-D) termed as PBNA using transform approach and time-invariant local encoding coefficients (LECs), PBNA using time-varying LECs, and PBNA using transform approach and block time-varying LECs. We derive sets of necessary and sufficient conditions under which throughputs close to n' + 1/2n' + 1, n'/2n' + 1, and n'/2n' + 1 are achieved for the three source-destination pairs in a 3-S 3-D MUN-D employing PBNA using transform approach and time-invariant LECs, and PBNA using transform approach and block time-varying LECs, where n' is a positive integer. For PBNA using time-varying LECs, we obtain a sufficient condition under which a throughput demand of n(1)/n, n(2)/n, and n(3)/n can be met for the three source-destination pairs in a 3-S 3-D MUN-D, where n(1), n(2), and n(3) are positive integers less than or equal to the positive integer n. This condition is also necessary when n(1) + n(3) = n(1) + n(2) = n where n(1) >= n(2) >= n(3).

Effects of sink demand and nutrient status on leaf photosynthesis of spring-cycle shoot in ‘Newhall’ navel orange under natural field conditions

Many studies have been performed to evaluate the effects of sink demand on photosynthesis using artificial defruiting experiments. However, information is scarce regarding photosynthesis changes in field citrus trees with naturally varying sink demands. In this study, we compared photosynthesis in three types of shoots of ‘Newhall’ navel oranges (Citrus sinensis Osbeck), including no fruit bearing shoots, one-fruit bearing shoots and two-fruit bearing shoots, in field conditions. The results showed that the highest sink demand of shoots corresponded to the lowest net photosynthetic rate (Pn). The determination of stomatal conductance (Gs), substomatal CO2 concentration (Ci) and transpiration rate (E) suggested that the Gs and E were not significantly different between these three types of shoots, while the Ci increased as the sink demand increased. Further analysis of leaf morphology features and nutrient status showed that the higher fruit load shoots had smaller leaf area, length, width, thickness and dry weight, and also lower concentrations of nitrogen, phosphorous and potassium. The quality comparison of fruits on one-fruit bearing shoots and two-fruit bearing shoots suggested that there was no difference in internal quality such as total soluble solids (TSS), titratable acidity (TA) and the TSS/TA ratio except for some external features. Overall, our data indicated that the reduction of Pn with sink demand increasing was mainly caused by limited development and a lower nutritional supply in source leaves. This limitation may be derived from competition between fruit and adjacent leaves under a high fruit load. This finding provides new insights into sink demand effects on photosynthesis in field conditions and useful guidance for citrus orchard management practices.

Glucose, sucrose, and steviol glycoside accumulation in Stevia rebaudiana grown under different photoperiods

The amount of free glucose and sucrose within the leaves of Stevia rebaudiana has been evaluated under different photoperiods and related to steviol glycoside (SVgly) accumulation. The diurnal dynamics of glucose and sucrose in leaves, internodes, apices, and roots revealed considerable fluctuations. Within leaves, glucose and sucrose content decreased up to three-fold during the night whereas SVgly amounts did not show any significant diurnal fluctuations. Ontogenetic variations in glucose content was markedly different under long-day (LD) and short-day (SD) regimes. Under LD, glucose content increased two-fold after the onset of flower bud formation, whereas under SD, a stagnation or small decrease was observed. This increase under LD was already noticed in the upper sink leaves at the end of the vegetative stage, possibly acting as a metabolic trigger for the phase transition to reproductive development. Under SD, glucose content appeared more controlled resulting in a better linear relationship with dry matter and SVgly content. The increased sink demands of the transitional apex led to a rapid decline in leaf sucrose which showed little or no correlation with SVgly amounts. From our results, it becomes clear that the correlation between glucose or sucrose as substrates and SVglys as products is very dynamic and is significantly influenced by day-length and ontogeny.

A CAM- and starch-deficient mutant of the facultative CAM species Mesembryanthemum crystallinum reconciles sink demands by repartitioning carbon during acclimation to salinity.

In the halophytic species Mesembryanthemum crystallinum, the induction of crassulacean acid metabolism (CAM) by salinity requires a substantial investment of resources in storage carbohydrates to provide substrate for nocturnal CO2 uptake. Acclimation to salinity also requires the synthesis and accumulation of cyclitols as compatible solutes, maintenance of root respiration, and nitrate assimilation. This study assessed the hierarchy and coordination of sinks for carbohydrate in leaves and roots during acclimation to salinity in M. crystallinum. By comparing wild type and a CAM-/starch-deficient mutant of this species, it was sought to determine if other metabolic sinks could compensate for a curtailment in CAM and enable acclimation to salinity. Under salinity, CAM deficiency reduced 24 h photosynthetic carbon gain by >50%. Cyclitols were accumulated to comparable levels in leaves and roots of both the wild type and mutant, but represented only 5% of 24 h carbon balance. Dark respiration of leaves and roots was a stronger sink for carbohydrate in the mutant compared with the wild type and implied higher maintenance costs for the metabolic processes underpinning acclimation to salinity when CAM was curtailed. CAM required the nocturnal mobilization of >70% of primary carbohydrate in the wild type and >85% of carbohydrate in the mutant. The substantial allocation of carbohydrate to CAM limited the export of sugars to roots, and the root:shoot ratio declined under salinity. The data suggest a key role for the vacuole in regulating the supply and demand for carbohydrate over the day/night cycle in the starch-/CAM-deficient mutant.

Multiple-Access Network Information-Flow and Correction Codes

This work considers the multiple-access multicast error-correction scenario over a packetized network with $z$ malicious edge adversaries. The network has min-cut $m$ and packets of length $\ell$, and each sink demands all information from the set of sources $\sources$. The capacity region is characterized for both a "side-channel" model (where sources and sinks share some random bits that are secret from the adversary) and an "omniscient" adversarial model (where no limitations on the adversary's knowledge are assumed). In the "side-channel" adversarial model, the use of a secret channel allows higher rates to be achieved compared to the "omniscient" adversarial model, and a polynomial-complexity capacity-achieving code is provided. For the "omniscient" adversarial model, two capacity-achieving constructions are given: the first is based on random subspace code design and has complexity exponential in $\ell m$, while the second uses a novel multiple-field-extension technique and has $O(\ell m^{|\sources|})$ complexity, which is polynomial in the network size. Our code constructions are "end-to-end" in that all nodes except the sources and sinks are oblivious to the adversaries and may simply implement predesigned linear network codes (random or otherwise). Also, the sources act independently without knowledge of the data from other sources.

Growth yield of Vicia faba L in response to microbial symbiotic associations

A multifactor experiment was undertaken to investigate the influence of Rhizobium and arbuscular mycorrhizal fungi (AMF) on biomass production, leaf area generation, whole plant photosynthetic and respiration rates, growth yield and maintenance respiration in Vicia faba L under low phosphorus (P) supply. Treatments consisted of low (LN) or high nitrogen (HN) supply with or without microbial symbiont(s). Plants were harvested at 54 (T 1) and 63 (T 2) days after planting. In all instances, plants colonized with both microbial symbionts had significantly higher total biomasses, leaf areas, whole plant photosynthesis and respiration rates than plants with only one or no microbial symbionts. Similarly, plants with both microbial symbionts also had significantly higher (≥ 0.7) growth yield ( Y g) values than all the other treatments. There were no significant differences in Y g values between harvest intervals within individual treatments. Maintenance respiration rates were also highest in plants with two microbial symbionts (> 30 CO 2 (g DM) − 1 d − 1 ). In LN plants colonized by both microbial symbionts there was evidence of compensatory increases in the photosynthetic rates in response to the carbon sink demands of the microbial symbionts. Finally, the results of this investigation are consistent with the hypothesis that the plant potential photosynthetic capacity exceeds the carbon demand of the Rhizobium–AMF symbiotic complex.

Impact of eastern dwarf mistletoe (Arceuthobium pusillum) infection on the needles of red spruce (Picea rubens) and white spruce (Picea glauca): oxygen exchange, morphology and composition

Eastern dwarf mistletoe (Arceuthobium pusillum Peck) is a hemiparasitic angiosperm that infects white spruce (Picea glauca (Moench) Voss) and red spruce (P. rubens Sarg.) in northeastern North America. The effects of mistletoe infection differ substantially between white and red spruce, with white spruce suffering greater infection-induced mortality. In the present study, we sought to determine the role that species-specific differences in needle-scale responses to parasitism may play in the observed differences in the effect of infection on host tree health. Based on the measurements made, the most apparent effect of parasitism was a reduction in needle size distal to infections. The magnitude of this reduction was greater in white spruce than in red spruce. Eastern dwarf mistletoe was a sink for host photosynthate in red spruce and white spruce; however, there were no adjustments in needle photosynthetic capacities in either host to accommodate the added sink demands of the parasite. Needle total nonstructural carbohydrate concentrations (TNC) were also unaltered by infection. Red spruce needles had higher TNC concentrations despite having lower overall photosynthetic capacities, suggesting that red spruce may be more sink limited and therefore better able to satisfy the added sink demands of parasitic infection. However, if carbon availability limits the growth of the mistletoe, one may expect that the extent of the parasitic infection would be greater in red spruce. Yet in the field, the extent of infection is generally greater in white spruce. Taken together, these results suggest that dwarf mistletoe may not substantially perturb the carbon balance of either host spruce species and that species-specific differences in needle-scale responses to the parasite cannot explain the contrasting effects of infection on white spruce and red spruce.

Effect of respiratory homeostasis on plant growth in cultivars of wheat and rice

ABSTRACTSome plants have the ability to maintain similar respiratory rates (measured at the growth temperature), even when grown at different temperatures, a phenomenon referred to as respiratory homeostasis. The underlying mechanisms and ecological importance of this respiratory homeostasis are not understood. In order to understand this, root respiration and plant growth were investigated in two wheat cultivars (Triticum aestivum L. cv. Stiletto and cv. Patterson) with a high degree of homeostasis, and in one wheat cultivar (T. aestivum L. cv. Brookton) and one rice cultivar (Oryza sativa L. cv. Amaroo) with a low degree of homeostasis. The degree of homeostasis (H) is defined as a quantitative value, which occurs between 0 (no acclimation) and 1 (full acclimation). These plants were grown hydroponically at constant 15 or 25 °C. A good correlation was observed between the rate of root respiration and the relative growth rates (RGR) of whole plant, shoot or root. The plants with high H showed a tendency to maintain their RGR, irrespective of growth temperature, whereas the plants with low H grown at 15 °C showed lower RGR than those grown at 25 °C. Among several parameters of growth analysis, variation in net assimilation rate per shoot mass (NARm) appeared to be responsible for the variation in RGR and rates of root respiration in the four cultivars. The plants with high H maintained their NARm at low growth temperature, but the plants with low H grown at 15 °C showed lower NARm than those grown at 25 °C. It is concluded that respiratory homeostasis in roots would help to maintain growth rate at low temperature due to a smaller decrease in net carbon gain at low temperature. Alternatively, growth rate per se may control the demand of respiratory ATP, root respiration rates and sink demands of photosynthesis. The contribution of nitrogen uptake to total respiratory costs was also estimated, and the effects of a nitrogen leak out of the roots and the efficiency of respiration on those costs are discussed.

Seasonal patterns of vegetative growth and competition with reproductive sinks in peach (Prunus persica)

SummaryGrowth of leaves, wood, and stems were studied over an entire growing season on four year old peach (Prunus persica (L.) Batsch.) trees having no crop, commercial crop loads, or heavy crop loads. Leaf, wood, and stem growth were reduced on cropping trees relative to defruited trees. The presence of fruit reduced leaf biomass growth during Stage I and II of fruit growth but not thereafter. Wood biomass growth was reduced by the presence of fruit during all stages of fruit growth. Stem biomass growth was most strongly affected by fruit during Stage III of fruit growth. Carbon partitioning to stems appeared to be influenced by both fruit sink demands and set developmental capacity for secondary radial growth. Total above-ground biomass production was similar in all three treatments, despite significantly greater leaf area in defruited trees. The total carbohydrate cost of the above ground biomass (the sum of biomass costs, calculated growth and maintenance respiration costs) was estimated to be similar for all three treatments. Cropping reduced root starch content and flowering density but did not influence percent fruit set during the subsequent growing season relative to non-cropped trees.

Carbohydrate partitioning in crassulacean acid metabolism plants: reconciling potential conflicts of interest.

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001. The construction of diel leaf carbon budgets, together with analyses of the δ13C composition of biochemical fractions, was used to examine how crassulacean acid metabolism (CAM) plants adjust carbohydrate partitioning in response to shifting sink demands. For Mesembryanthemum crystallinum L., net carbon budgets indicated clear shifts in assimilate partitioning and in the relative proportions of day : night export as CAM was induced. Different patterns of carbohydrate partitioning in primary and axillary leaves of this species may reflect the different sink priorities of determinate and indeterminate growth. In primary leaves, the high level of diel starch turnover may be a strategy for ensuring production of a critical mass of juvenile tissue that poises the plant for CAM induction. In axillary leaves, the high day-night flux through soluble sugars may ensure ready availability of assimilates for export to reproductive sinks. Carbon isotope ratios were measured for various organic fractions isolated from leaves and fruits of two species of Clusia that differ in CAM expression. Similar and C3-like isotopic signatures were obtained for the structural material isolated from fruits of Clusia minor L. and Clusia rosea Jacq. The data suggest that the partitioning of C4- and C3-derived assimilates into discrete storage and transport pools of soluble sugars will ensure reproductive output, regardless of the level of CAM that is induced in these species.

Photoassimilate Production and Distribution in Cherry

The two commercially important fruiting cherries in North America are Prunus cerasus L. (sour) and P. avium L. (sweet). Carbon partitioning between individual organs, reproductive and vegetative, is dependent upon photoassimilate supply from photosynthesis and storage carbohydrate, as well as the ability of the translocation system to deliver these resources to sinks (Layne and Flore, 1995). Sink strength of individual organs varies with time of year, and age of the plant, as the sink demands and seasonal development pattern of the plant changes with time. Herein we will review assimilate supply and storage, seasonal partitioning patterns, and the impact that biotic and abiotic stress has on supply, partitioning, and control.

Carbohydrate metabolism in one‐ and two‐year‐old spruce needles, and stem carbohydrates from three months before until three months after bud break

Starch and sucrose metabolism of one‐ and two‐year‐old needles of Norway spruce (Picea abies [L.] Karst., about 30 years old) was investigated from three months before until three months after bud break at a natural site. We distinguish different metabolic states according to the extractable activities of enzymes (α‐amylase [EC 3.2.1.1], ADP‐glucose pyrophosphorylase [AGP, EC 2.7.7.27], D‐enzyme [EC 2.4.1.25], starch phosphorylase [STP. EC 2.4.1.1]), sucrose phosphate synthase [SPS, EC 2.4.1.14], sucrose syntbase [SS, EC 2.4.1.13]. acid invertase [AI, EC 3.2.1.261) and pool sizes of related metabolites (starch, glucose, fructose, sucrose, raffinose, stachyose, fructose 6‐phosphate [F6P], glucose 6‐phosphate [G6P], fructose 2,6‐bisphosphate [F26BP], and inorganic phosphate [P1]). The period ending with bud break was characterized by high rates of net photosynthesis, a pronounced decrease in the amount of soluble sugars, and a steep rise in starch (from the detection limit to approximately 600 nmol glycosyl units [mg dry weight]‐1). In parallel, the extractable activity of AGP increased, while D‐enzyme was on a relative high level when compared with the period after bud break. With respect to sucrose metabolism, F26BP, an inhibitor of sucrose synthesis, decreased from 1 to 0.4 pmol (mg dry weight)‐1. This was complemented by SPS activity, which was due to both increased protein levels shown by immunoblotting and activation under metabolite control (high levels of G6P and a low Pi/G6P ratio). This indicates a high capacity of synthesis of starch and sucrose in the period before bud break. These observations are in accordance with estimates of photosynthetic carbon gain, which indicate that in early spring large amounts of carbon from current photosynthesis are exported out of the needles. In addition, the content of nonstructural carbohydrates (expressed as hexoses) increased in the bark of the stem. This could also be a consequence of an enhanced carbon export from the needles.After the onset of bud break, starch concentration decreased in all tissues under investigation. In contrast, the level of total nonstructural carbohydrates in the outermost sapwood nearly doubled from bud break until the end of sampling. In the needles, net photosynthesis was reduced by about 75% and a decrease in SPS activity and protein level were found together with lower G6P concentration, and an increased Pi/G6P ratio. These results suggest that during that period sucrose synthesis was reduced in the older needles. In addition, under conditions of reduced photosynthesis, carbon demand of current year needles was in part ensured by the mobilization of starch in the older needles.Taken together our data show that before bud break carbon metabolism of mature leaves is related with the sink demands of storage organs. After bud break the accumulated assimilate pools in needles and stem, mainly the bark, are mobilized and support carbon supply to new tissues.

Sugar and starch metabolism during ex vitro rooting and acclimatization of micropropagated Spathiphyllum ‘Petite’ plantlets

Sugar and starch metabolism during ex vitro rooting and acclimatization of micropropagated Spathiphyllum ‘Petite’ plantlets were studied to uncover in what way photosynthesis and carbohydrate reserves, accumulated during tissue culture, sustain plantlets regrowth and root formation. We followed carbon partitioning between sugars (sucrose, glucose and fructose) and starch and the changes in the activities of the key enzymes involved, including sucrose- P-synthase, sucrose synthase, acid invertase and ADPG pyrophosphorylase. It was concluded that during acclimatization of tissue cultured Spathiphyllum plantlets, photoassimilates accumulate before root emergence. Afterwards, carbohydrates were mainly translocated to these growing sinks. This was supported by the elevated levels of sucrose metabolising enzymes. Sink demands at the end of the light period gradually became saturated when plants were fully acclimatized. This resulted in a down regulation of sucrose- P-synthase and an activation of ADPG pyrophosphorylase, and at that moment a further starch accumulation started.

Plant Size Influences Bell Pepper Seed Quality and Yield

This study investigated the influence of plant size, as determined by plant density, and fruit load variation on the production and quality of bell pepper (Capsicum annuum L.) seeds. Six-week-old `Resistant Giant no. 4' bell pepper seedlings were transplanted 15, 30, 45, and 60 cm apart. Plants spaced 45 cm apart were not thinned or were thinned to one or three fruit per plant. Pepper plants grown at low plant densities produced larger fruit and seeds that germinated faster and at higher percentages than plants grown at higher densities. Assimilate export rate (AER) increased linearly with plant spacing. At harvest, C exchange rate (CER) and AER of plants with nonthinned fruit loads were ≈ 300% and 500% higher, respectively, than those of plants with one or three fruit. Fruit thinning decreased CER and AER; however, seeds produced by plants with one or three fruit had significantly higher germination percentages than plants with full fruit loads. These observations suggest that the high CERS of smaller plants with nonthinned fruit loads may have been insufficient to compensate completely for the higher sink demands. Therefore, crop cultural practices that increase the ratio of pepper plant size to total fruit count may increase the quality of seeds produced by those plants.

Phloem Translocation from a Leaf to Its Nodal Region and Axillary Branch in Populus deltoides

Microautoradiography was used to follow the movement of 14C through the nodal regions and in the stems of young Populus deltoides Bartr ex Marsh plants when either entire laminae were photosynthetically fed 14CO2 or cut petioles were fed 14C-labeled amino compounds The leaf/branch gap of the central (C) leaf trace is filled with both thick- and thin-walled, heavily pitted parenchymatous cells that retain their protoplasts. The C-trace translocates little 14C to mature cells of the gap region because it lacks differentiated rays at this level in the stem However, the C-trace contributes 14C to the cambium-like region that adds cells to the gap. The C-trace also transfers 14C laterally to phloem of the branch traces in the nodal region. The branch traces in turn translocate 14C according to sink demands acropetally in the branch, or basipetally in the stem, or laterally to adjacent stem traces, or inward to the gap region The 14C translocated inward via the rays is presumably deposited in the gap cells, where it accumulates as stored starch during predormancy No evidence was found that gap cells functioned as transfer cells. Little cross transfer occurred between unrelated leaf traces in the stem Thus, gap cells at nodes other than the treated node received 14C only when a labeled trace lay immediately contiguous to branch traces at that node For example, the left trace of the treated leaf contributed 14C to the branch traces and nodal region but not to the leaf trace situated three nodes below Amino compounds fed through cut petioles transported 14C primarily upward in the transpiration stream. Xylem-to-phloem transfer via the rays occurred at all levels in the stem, but it was particularly pronounced at nodal junctures No labeled amino acids were transported into the gap region