Source Of Photosynthate Research Articles

Electrical energy production from plant biomass: an analysis model development for Pandanus Amaryllifolius plant microbial fuel cell

Plant microbial fuel cell (P-MFC) is an electrochemical reactor that converts organic compounds to electrical energy through the catalytic reaction from electrochemically active bacteria (EAB). However, there is no sign of an attempt in developing the functional model in predicting the energy conversion and utilization of P-MFC. In this study, an analytic model is proposed to show the whole production process of the organic compound to electrical energy generation. <em>Pandanus Amaryllifolius</em> plant was used as sources of photosynthate, where biomass product from rhizodeposition, acetate was produced, and soil bacteria as the microbial culture, and air as the input to the cathode chamber. The proposed analytical model is able to predict the output of the P-MFC using the parameters from the experiment. The generated data from the model was then compared with the monitored data from the <em>Pandanus Amaryllifolius </em>P-MFC. The results show the electrical power output has a high similarity pattern with the bacterial growth curve model and able to achieve the coulombic efficiency of 95.32%.

English

Flag leaf is the most important source of photosynthate for developing rice grains, and flag leaf thickness is an important morphological trait in rice plant-type breeding programs. In the present study, we carried out association mapping for flag leaf thickness in a local rice population which consisted of 86 cultivars derived from breeding programs and planted in large areas in South China. Phenotyping was conducted in the field using nondestructive leaf thickness measurements. Two hundred and thirty-six SSR markers covering 12 chromosomes were employed to genotype the accessions. The association analysis was carried out using a unified mixed-model approach. The Q+K model was selected for investigating marker-trait associations. A total of eleven marker-trait pairs with significant marker-trait associations were identified which were distributed on eight chromosomes. Four of these loci had already been identified as related to flag leaf thickness in previous studies, while the other seven were novel QTLs. The locus PSM163 had the highest r2-marker value of the seven novel loci, explaining 21.54 and 18.49% of the phenotypic variation in 2008 and 2009, respectively. Three of four QTLs, which were detected in a F2 mapping population in the validation study, could correspond to a significant locus in AM, respectively. The six alleles which had the highest phenotypic values at their respective loci should be considered as favored alleles in breeding programs. Pyramiding the favored alleles for flag leaf thickness identified in the study might be a valuable approach to construct an ideal plant architecture in rice breeding. Key words: Rice, flag leaf thickness, breeding programs, association mapping, mixed linear model.

Physiological Integration Plays Key Role in Cranberry (Ericales: Ericaceae) for Tolerance of Damage byDasineura oxycoccana(Diptera: Cecidomyiidae)

Understanding the mechanisms by which plants tolerate herbivory is important in the study of insect-plant interactions. In cranberry, current season growth has been identified as the main source of photosynthate for the developing fruits. Feeding injury by larvae of cranberry tipworm, Dasineura oxycoccana Johnson, disrupts the apical growth of cranberry shoots or uprights, but does not impact fruit output. To study the effects of experimentally depleting photosynthate available from sources other than the current season growth on fruit output, we girdled tipworm-injured uprights. This technique enabled us to estimate the contribution of current season growth in supplying photosynthate to developing fruits in tipworm-injured uprights. The mean fruit weight declined by >55% in those tipworm-injured uprights that were limited to photosynthate from only the current season growth (girdled uprights). The result was consistent between two phenologically different cultivars of cranberry, one a native selection from wild cranberry stands ('Howes') and the other a hybrid ('Stevens'). In addition, fruit weight was positively correlated to current season leaf area in the girdled uprights only. These results strongly suggest that physiological integration among the different sources of photosynthate plays a key role in the tolerance of tipworm feeding injury for fruit output in cranberry.

Phytoplasma distribution in coconut palms affected by lethal yellowing disease

Lethal yellowing (LY), the most devastating disease affecting the coconut palm in America, is caused by phytoplasmas known to be distributed in different parts of infected plants. However, no comprehensive reports exist on the phytoplasma distribution. This study refers to the detection of LY phytoplasma DNA using PCR in different coconut plant parts, throughout the development of the disease. Sample analysis of positive palms taken at different stages of disease development (either symptomatic or symptomless) showed differences in the percentage of LY detection between plant parts. Some parts showed a very high level of LY DNA (stem, young leaves, inflorescences, stem apex and root apex), low levels were found in the intermediate leaves and roots without apex, whereas no LY phytoplasma DNA was detected in mature leaves. The detection percentage of LY phytoplasma DNA was lowest in symptomless-infected palms for all parts, except the stem, where phytoplasma accumulations were consistently detected. This pattern of detection among parts is consistent with the hypothesis that phytoplasmas move from photosynthate source tissues to sink tissues via the phloem mass flow process. The accumulations in the (lower) stem, prior to the appearance of symptoms, suggest that this part of the palm is where phytoplasmas first move from leaves after foliar feeding by vectors and in which they probably multiply and distribute to other palm parts, including roots. Embryos from infected palms were analysed by nested-PCR and 28% of 394 embryos were positive. Phytoplasma DNA was detected in embryos from fruit on any of the fruiting bunches regardless the age, but no pattern of quantitative distribution throughout the bunch developmental stages was observed. Germination of seeds from LY-positive symptomatic palms was 58% and from LY-negative symptomless palms were 71%. No phytoplasma was detected in seedlings tested from both symptomatic and non-symptomatic palms. Seedlings tested after 2 years did not develop LY symptoms or eventually died.

The structural and photosynthetic characteristics of the exposed peduncle of wheat (Triticum aestivum L.): an important photosynthate source for grain-filling.

BackgroundIn wheat (Triticum aestivum L), the flag leaf has been thought of as the main source of assimilates for grain growth, whereas the peduncle has commonly been thought of as a transporting organ. The photosynthetic characteristics of the exposed peduncle have therefore been neglected. In this study, we investigated the anatomical traits of the exposed peduncle during wheat grain ontogenesis, and we compared the exposed peduncle to the flag leaf with respect to chloroplast ultrastructure, photosystem II (PSII) quantum yield, and phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31) activity.ResultsTransmission electron microscope observations showed well-developed chloroplasts with numerous granum stacks at grain-filling stages 1, 2 and 3 in both the flag leaf and the exposed peduncle. In the exposed peduncle, the membranes constituting the thylakoids were very distinct and plentiful, but in the flag leaf, there was a sharp breakdown at stage 4 and complete disintegration of the thylakoid membranes at stage 5. PSII quantum yield assays revealed that the photosynthetic efficiency remained constant at stages 1, 2 and 3 and then declined in both organs. However, the decline occurred more dramatically in the flag leaf than in the exposed peduncle. An enzyme assay showed that at stages 1 and 2 the PEPCase activity was lower in the exposed peduncle than in the flag leaf; but at stages 3, 4 and 5 the value was higher in the exposed peduncle, with a particularly significant difference observed at stage 5. Subjecting the exposed part of the peduncle to darkness following anthesis reduced the rate of grain growth.ConclusionOur results suggest that the exposed peduncle is a photosynthetically active organ that produces photosynthates and thereby makes a crucial contribution to grain growth, particularly during the late stages of grain-filling.

Leaf miner activity and its effects on leaf chemistry in adult beech under elevated CO2

Using the Swiss Canopy Crane CO2 enrichment facility, the beech weevil's host choice in a CO2-enriched atmosphere and the in situ effect of its infestation on the chemistry of host leaves were investigated. The fraction of infested leaves was larger on CO2-enriched trees, suggesting that weevil impact on beech may increase as atmospheric CO2 concentration keeps rising. Egg insertion in the central leaf vein partially interrupts phloem and xylem transport. Because of this separation between the source of photosynthates, the leaf tip, and the rest of the plant, the leaf tip becomes enriched in non-structural carbohydrates and depleted in nitrogen. Elevated CO2 slightly enhanced non-structural carbohydrates in uninfested leaves, but exerted no further increase in infested leaf part, suggesting a saturation effect. Mit Hilfe der, Swiss Canopy Crane’ CO2-Anreicherungsanlage haben wir in situ die Präferenzen der Buchenspringrüssler bei der Wahl ihrer Wirtsbäume nach CO2-Exposition und den Einfluss ihres Befalls auf die Chemie von Buchenblättern untersucht. An CO2-behandelten Bäumen war der Befall höher als an Kontrollbäumen. Mit ansteigender atmosphärischer CO2-Konzentration könnte sich daher die Schadwirkung des Buchenspringrüsslers auf die Rotbuche verstärken. Die Eiablage in der Hauptblattader hat zur Folge, dass Phloem- und Xylemtransport teilweise unterbrochen werden. Diese Unterbrechung zwischen einer Assimilatquelle, der Blattspitze, und dem Rest der Pflanze, führt zu einer Anreicherung nicht-strukturgebundener Kohlenhydrate (NSC) und einer Abnahme der Stickstoff Konzentration in der Blattspitze. Die NSC-Konzentration in nicht befallenen, CO2-behandelten Blättern zeigte zwar eine leichte Zunahme, stieg aber in den befallenen, CO2 behandelte Blattspitzen nicht weiter an, was auf einen Sättigungseffekt hindeutet.

Partitioning of photosynthates originating from bent shoots in the arching and high-rack culture systems of cut rose production

The arching and high-rack culture systems were developed and patented by Japanese rose growers. Both culture systems have bent canopies (lower bent shoots). In the arching culture system, shoots sprouting from the crown are harvested as cut flowers. However, the high-rack culture system also has a bent canopy originating from the mother stem (upper bent shoots) and flower stems sprout and is harvested at the top of each mother stem. Partitioning of photosynthates originating from bent shoots in arching and high-rack culture systems of rose production was investigated to elucidate how carbohydrates are re-allocated from the bent shoots in different culture systems of roses. At the flowering stage in both culture systems, 50–70% of 13C-photosynthates originated from bent shoots were exported to other parts within 72 h after 13CO 2 feeding to the bent shoot. In the arching culture system, photosynthates from lower bent shoots were partitioned mainly to the roots and crown. Similarly, in the high-rack culture system, between 71 and 86% of the exported carbon from the bent shoots were allocated to below the point of bending (roots + crown + mother stems) and only 9–28% was allocated to flowering shoots above the point of bending. In both culture systems, photosynthate translocation from the lower bent shoot directly to flowers was low. Accordingly, bent shoots in rose plants acted as a source of photosynthates, independent of culture system. The height of the bent shoots determined for a great deal in the re-allocation of the photosynthates, and provides a partial explanation for difference in production of cut roses.

Carbon dioxide exchange of larch (Larix gmelinii) cones during development

Larch (Larix gmelinii (Rupr.) Rupr.) cone scales are green, but little is known of their photosynthetic role in cone development or about how they differ in gas exchange characteristics from needle leaves. In contrast to leaf photosynthesis (Pleaf), we found that stomatal regulation of cone photosynthetic rate (Pcone) was marginal because the photosynthetic carbon came from internal recycling of respiratory carbon dioxide (CO2). Photosynthetic recycling of respired CO2 was confirmed by the finding that the intercellular CO2 concentration (Ci) in cone scales was much higher than ambient [CO2]; also, there was a positive correlation between Pcone and Ci, whereas Pleaf was almost constant as Ci varied. Low chlorophyll (Chl) concentration was a limiting factor for Pcone, but not for Pleaf, as indicated by the correlation between Pcone and chlorophyll concentration. Moreover, chlorophyll utilization efficiency (Psat/Chl a+b) for cone scales was lower than that for leaves. In both cones and leaves, nitrogen (N) was positively correlated with photosynthetic capacity (P), but the P/N value was much lower for cones than for leaves. For both organs, the ratio of respiration to N was broadly similar. Although mature cones have no photosynthetic capacity, Pcone of young cones was as high as 5.3 micromol m(-2) s(-1), about 1.26 times the value of Pleaf, and accounted for the refixation of 30-40% of the respiratory CO2 produced by cones, equivalent to the photosynthetic capacity of a bundle of short shoots near each cone. Thus, Pcone may be an important additional source of photosynthate for cones, given the weak assimilating capacity of leaves that are not fully expanded during cone development.

Dry-matter partitioning and radiation-use efficiency in cowpea cultivars (Vigna unguiculata (L.) Walp. cvs TC-9-6 and M-28-6-6) during consecutive seasonal courses in the Orinoco llanos

Field work on rainfed cowpea (Vigna unguiculata (L.) Walp. cvs TC-9-6 and M-28-6-6) was conducted in the Orinoco lowlands to explain the changes in dry-mass partitioning and radiation-use efficiency (RUE) as compared with other cultivars over four consecutive seasons. Growth features were assessed in early-maturing, prostrate-canopy (TC-9-6), and medium-maturing, erect-canopy (M-28-6-6) cowpeas. These cultivars were sown in consecutive middle-wet and late-wet seasons in double peak rainfall conditions. Dry mass accumulation by cultivars was assessed as a function of leaf-area duration and the efficiency with which radiation was converted into dry mass throughout the season (i.e. radiation-use efficiency). Cultivar differences in canopy architecture and duration of leaf area had a minor effect on the total dry mass production. In the early-maturing TC-9-6, RUE for a middle-wet and a late-wet season was 0·90±0·04 and 0·65±0·05 g/MJ, respectively. In the medium-maturing M-28-6-6, the values were 0·97±0·05 and 0·72±0·03 g/MJ, respectively. A season with rainfall below 100 mm had a negative effect on phenology and RUE. When average rainfall was above 100 mm, the total dry mass accumulation was not affected by differences in cultivars and seasons. The rate of harvest index (HI) changes was negatively related to pod-filling duration. The changes in assimilation distribution depended on the process of partitioning as modulated by the limited pod-sink and the photosynthate supply. However, the photosynthate source was not depressed by the sink activity of the pod-filling. Partitioning to non-reproductive sinks was maintained. M-28-6-6 with high dry-mass production and delayed senescence did not effectively divert a large amount of assimilate to pod-filling. Pod sink activity in cowpea was limited by genotype. Harvest index in M-28-6-6 decreased with the increasing dry mass. The final HI and rate of linear increase in HI differed between cultivars and were lower in M-28-6-6. The results of the present work in the Orinoco lowlands are relevant for a wide range of savannahs with a late wet season.

Photosynthate and Dry Matter Partitioning in Short‐ and Long‐Season Cotton Cultivars

Differences in source‐sink relationships between short‐ and long‐season cotton (Gossypium hirsutum L.) cultivars, the contribution of main stem leaves to boll growth, and the distribution of nonstructural carbohydrates late in the season are not well understood. This study compared the cultivars Tamcot CAMD‐E (a short‐season type) and Stoneville 213 (a long‐season type) for two seasons in the field. To study photosynthate partitioning, the uppermost fully expanded leaf on the main stem subtending a reproductive axillary branch was pulsed with 14CO2 at the onset of reproductive growth (ORG) and at early reproductive growth (ERG), and sampled 48 h later. To study nonstructural carbohydrate partitioning, 14C‐starch was injected into the base of the main stem just above the soil surface durifig late reproductive growth (LRG). At ORG in 2 yr and ERG in the year with poor growing conditions, there were no cultivar differences in partitioning of accumulated dry matter throughout the plant or recent 14C‐photosynthate. However, at ERG in a year with good growing conditions, Tamcot CAMD‐E distributed a greater percentage (45%) of its dry matter to reproductive growth than did Stoneviile‐213 (30%). Tamcot CAMD‐E also partitioned 85% of its 14C‐photosynthate to the reproductive structures compared with only 60% in Stoneville‐213. Main stem leaves were an important source of photosynthate to the developing bolls in both cultivars and years. The total nonstructural carbohydrates of the main stem and root contained from 20 to 90% of the 14C‐photosynthate from the main stem leaves partitioned to the main stem or root at ORG and ERG. Both cultivars partitioned more than one‐half of the injected 14C‐starch to the main stem and its vegetative branches in both years at LRG. At this later stage of reproductive growth, cotton production could benefit from a different pattern of partitioning that favored the distribution of stored carbohydrates to reproductive structures.

Remobilization of Pre‐Anthesis Assimilates to the Grain for Grain Only and Dual‐Purpose (Forage and Grain) Triticale

AbstractIn Mediterranean environments, translocation of pre‐anthesis assimilates to the grain is an important source of photosynthates. In this work, the effect of forage removal at the beginning of jointing on the amount of dry matter (DM) accumulated before anthesis and remobilized during grain filling was studied in five spring and five winter triticale genotypes (×Triticosecale Wittmack). Field experiments were conducted in 1992 and 1993 in northeastern Spain. Two harvesting treatments were used: (i) grain production only and (ii) cutting the crop for forage at the beginning of jointing and harvesting the grain produced after regrowth. Pre‐anthesis storage of carbohydrates was very important to grain filling in triticale, both for grain and for dual‐purpose. Contribution of pre‐anthesis assimilates to grain yield in the uncut plots was 46% in spring triticale genotypes and 65% in winter genotypes, as the later‐maturity winter triticale genotypes were more affected by terminal abiotic stresses. Reductions in DM accumulated at anthesis after forage removal were more pronounced in winter genotypes (39%) than in spring genotypes (20%), where an earlier development allowed for a longer recovery period after cutting; DM reductions were similar to grain yield decreases. The effect of forage removal on translocation depended on the growth hbit of the genotype and environmental conditions. Most differences were associated with changes in crop phenology. In spring types, with early jointing, DM translocation and the contribution of pre‐anthesis assimilates to grain were not affected by forage removal, whereas both traits were drastically reduced in winter triticale. Most differences in 13C/12C carbon isotope discrimination (Δ) in grains were also phenology driven.

Responses of Pinus sylvestris branches to simulated herbivory are modified by tree sink/source dynamics and by external resources

1. It is claimed that the quality of foliage following defoliation depends on carbon/nutrient balance of the tree. To study the importance of sink/source regulation for the quality of foliage, as well as for its quantity, Pinus sylvestris trees were defoliated and fertilized both in southern Finland and at the tree line in northern Finland. 2. The pattern of defoliation in a shoot was more decisive for quantitative changes in new foliage than its extent: removal of similar amounts of foliage from different branch parts led to different outcomes. 3. Defoliation of 50% spread evenly within a shoot, or applied to the basal part of a shoot only, did not alter production of new foliage, whereas defoliation applied to the apical part of a shoot decreased the mass and length of needles in the new shoot. Defoliation of apically located 1‐year‐old needles of the branch leader shoot, but not of 2‐year‐old ones, significantly reduced the mass and length of needles in new shoots. 4. These results are consistent with the explanation that damage alters the ability of shoots and branches to form strong meristematic sinks and that sink strength determines the ability of these meristems to draw resources from the common pool of the tree. 5. Defoliation of the main photosynthate source lowered concentrations of the fructose and glucose, indicating shortage of carbon. However, whole‐tree defoliation did not affect the concentrations of individual foliar sugars. 6. Traits describing pine shoot growth correlated negatively with foliar phenolic concentrations but not with concentrations of other secondary compounds. Concentrations of foliage phenolics consistently increased after defoliation, while terpenoids, putatively the main class of defensive compounds in Scots Pine, did not respond to defoliation. Defoliation of a branch or a whole tree had only slight effects on the concentrations of fibre, mono‐ and sesquiterpenes, resin acids or nitrogen. 7. Likewise, fertilization significantly increased the concentration of some sesquiterpenes only in pine foliage. Whole‐branch defoliation and fertilization together had no effect on the concentration of fibre or nitrogen in pine foliage. 8. Altogether, the amount of foliar biomass removed, nutrients or carbon did not explain in any consistent way the qualitative changes in the pine foliage. Instead, results were consistent with simple physiological dependence of foliar traits on sink strength. Production of terpenoids reflected increased sink strength, but the production of phenolics was negatively correlated with sink strength. 9. The difference between shoot growth characteristics and foliage concentrations of phenolics and, on the other hand, terpenoids, may have a biosynthetic, instead of an ecological or evolutionary explanation. Protein synthesis, and thereby possibilities for growth, competes with phenolic synthesis (via phenylalanine) but not with terpenoid synthesis. 10. These results indicate that in Scots Pine the predicted trade‐off between growth and production of pooled carbon‐rich secondary compounds was found in phenolics but presumably for reasons external to the carbon/nutrient balance and growth/differentiation balance hypotheses. Instead, terpenoids did not behave as predicted by these theories.

Modeling Carbohydrate Production, Storage, and Export in Leafy and Normal Maize (Zea mays L.)

The structure of maize (Zea mays L.) canopies influences light interception, photosynthesis, and yield. A recently developed corn phenotype termed Leafy, which has additional leaves above the ear compared with normal phenotypes of the same maturity, is thought to provide a greater source of photosynthates. The objective of this study was to develop a mathematical model to compare hybrid light interception, photosynthesis, carbohydrate storage, and export of carbohydrates from the leaves, based on measured leaf area distribution, leaf photosynthesis, and diurnal changes in leaf sugars and starches. Model simulations were run for two Leafy hybrids and a normal check hybrid, all grown at 6.5 and 3.25 plants m−2. A series of differential equations described how photosynthate was stored as leaf sugar and starch and then exported to stems. Rate coefficients were used to characterize diurnal changes in leaf carbohydrate concentration during early grain filling for different hybrids and planting densities. Model fits to leaf sugar and starch data were good (0.64 ≤ r ≤ 0.89). Model calculations showed that storage of carbohydrates in leaves was relatively small compared with the total amount of leaf photosynthate produced; more than 90% of the photosynthate was exported directly to the stem. Hybrid and planting density comparisons indicated that rate coefficients for the export of photosynthate from leaves increased with total plant dry matter. Leafy hybrids and hybrids grown at the lower plant density had greater plant dry weights, photosynthetic rates, and leaf export rates than the check or hybrids grown at the higher plant density.

Movement Patterns of Carbon from Source to Sink in Cranberry

The source of photosynthate for developing cranberry (Vaccinium macrocarpon Ait.) fruit can be partitioned spatially among new growth acropetal to fruit, 1-year-old leaves basipetal to fruit, and adjacent uprights along the same runner. Cranberry uprights were labeled with 14CO2 in an open system with constant activity during flowering or fruit development. When new growth acropetal to fruit was labeled, substantial activity was found in flowers or fruit. Little activity was found in basipetal tissues. When 1-year-old basipetal leaves were labeled, most of the activity remained in the labeled leaves, with some activity in flowers or fruit. Almost no labeled C moved into acropetal tissues. When new growth of adjacent nonfruiting uprights on the same runner were labeled, almost no activity moved into the fruiting upright. These data confirm that new growth acropetal to developing flowers and fruit is the primary source of photosynthate for fruit development. Furthermore, they show that during the short time studied in our experiment, almost no C moved from one upright to another.

Physiological activity in persistent bulbils of Agave vilmoriniana (Agavaceae)

Plants of Agave vilmoriniana are unique members of a reproductively diverse genus since they produce prolific numbers of both bulbils and viable seeds. Bulbils were observed to remain attached to the flowering stalk into a second summer, instead of abscising in the year they developed. Hence, a number of hypotheses were tested to establish the physiological basis for their longevity and evaluate their influence upon the plant's reproductive biology. Bulbils produced following anthesis were abundant (>2000 bulbils), large (0.44 g dry mass per individual), and their combined leaf surface area (one side) could exceed 3 m2. Thus, the current‐year inflorescence may act as a photosynthate source. Second‐year, attached bulbils are healthy‐looking, even after leaves of the parent plant have senesced, since maternal roots continue to absorb rain water. Rehydrated 2nd‐yr bulbils resume Crassulacean acid metabolism, sometimes demonstrating net daytime tissue acidification. Water conservation by bulbils is very efficient, exhibiting very low cuticular conductances (0.016‐0.0035 mm/s). Bulbils detach over all climatic seasons after having formed >3 and >18 root primordia in their 1st and 2nd year, respectively. About one‐third of bulbils are capable of forming roots after a 1‐yr storage at 35°C, when their water contents averaged 37%. Irrigated bulbils produce water‐absorbing roots within 2 d, with de novo chlorophyll synthesis and nocturnal acidification commencing within 4 d. Two bulbils were observed to root and become established in shaded microhabitats during this 2‐yr study of 29 plants.

Growth and carbohydrate status of coppice shoots of hybrid poplar following shoot pruning.

Fifteen, 1-year-old Populus maximowiczii Henry x P. nigra L. 'MN9' trees were decapitated and allowed to sprout. After 8 weeks, all had 6 to 10 coppice shoots. All shoots, except the tallest (dominant) shoot, were removed from five of the trees (pruned treatment), and shoot growth, gas exchange and carbohydrate status were compared in the pruned and unpruned trees. Although photosynthetic rate of recently mature leaves of pruned trees was approximately 50% greater than that of leaves on the dominant shoot of unpruned trees, and the dry weight of leaves of pruned trees was 37% greater than that of the leaves on the dominant shoot of unpruned trees, the shoot dry matter relative growth rate did not differ between treatments. Concentrations of water-soluble carbohydrates and starch in the uppper stem and leaves of the dominant shoot were similar in pruned and unpruned trees. However, relative to that of the dominant shoot in unpruned trees, the lower stem in pruned trees was depleted in both soluble carbohydrates and starch. Starch deposition, assessed as the quantity of (14)C-starch in tissues 24 h after a fully expanded source leaf was labeled with (14)CO(2), was 3.9 times greater in roots of pruned trees than in roots of unpruned trees. We conclude that early removal of all but the dominant shoot reduces the carbohydrate status of the roots and the lower portion of the stem by eliminating the excised shoots as a source of photosynthate.

The importance of back shoots as a source of photoassimilates for growth and flower production inDendrobiumcv. Jashika Pink (Orchidaceae)

SummaryThe contribution of back shoots as a source of photosynthates for growth and flower production in Dendrobium cv. Jashika Pink has been studied using the 14CO2 dosing technique. The leaves of Dendrobium back shoots were active in photosynthesis and translocation of 14C-assimilates. Highest fixation rate, in terms of total 14C-assimilates recovered, was observed in the basal leaf of Dendrobium cv. Jashika Pink plants with an inflorescence and an active vegetative shoot. The test leaf on the back shoots supplied significantly more 14C-assimilates to another shoot bearing an inflorescence than to the other plant parts within the back shoot itself. The inflorescence on the current shoot obtained 14C-assimilates from both the leaves of current shoot and back shoots. The relation of this highly integrated pattern of partitioning of assimilates within multiple shoots is discussed in view of the potential improvement for the harvestable yield of sympodial orchids.

Comparative Growth and Development of Nerine bowdenii W. Watson: Bulbs in Situ versus Replanted

Flowering-size Nerine bowdenii bulbs were sampled from a commercial planting at 2-week intervals from 13 Aug. 1991 to 14 June 1992. They were dissected, and the following variables were recorded: 1) number and dry weight of fully sheathing leaf bases or leaves of each growth unit, 2) length and dry weight of foliage leaves, 3) fresh weight of outermost inflorescence, and 4) dry weight of daughter bulbs. Bulb organs that served as sinks and sources changed as the bulb progressed in its growth and developmental cycle. Before the new foliage provided photosynthates, growth depended on reserves deposited and stored in leaf bases during the preceding seasons. Reserves were used for the development of new leaves (foliage and bases), roots, and daughter bulb enlargement. Once the foliage became the photosynthate source, reserves were stored in old and new leaf bases. The inflorescence became the major sink when elongation of the scape initiated. Thereafter, daughter bulbs became the dominant sinks, receiving photosynthates from the senescence foliage and the reserves stored in leaf bases. The decrease in dry weight of the leaf bases was prominent in bulbs that remained in situ.

Removing New Growth Reduces Fruiting in Cranberry

The sources of photosynthate for fruit growth in cranberry (Vaccinium macrocarpon Ait.) can be spatially partitioned as new growth, old leaves and woody stems, or adjoining uprights. New growth, l-year-old leaves, or both were removed at the time of fruit set and following fruit set. Removing new growth at the time of fruit set reduced fruit set, fruit count, and yield. Removing old leaves at fruit set generally did not reduce fruit set, fruit count, or yield. Removing both often had an additional effect. Removing new leaves after fruit set did not affect fruit set or count, but did reduce fruit size. Removing old leaves after fruit set did not reduce fruit set, fruit count, or size. These data suggest that new growth is an important source of photosynthate for fruit set.

Annual plant life histories and the paradigm of resource allocation

Much of life history theory follows from the idea that natural selection acts on the allocation of resources to competing and independent demographic functions. This paradigm has stimulated much research on the life histories of annual plants. Models of whole-plant resource budgets that use optimal control theory predict periods of 100% vegetative and 100% reproductive growth, sometimes with periods of mixed growth. I show here that this prediction follows from the assumption of independence of the competing ‘vegetative’ and ‘reproductive’ compartments. The prediction is qualitatively unchanged even after relaxing important simplifying assumptions used in most models. Although it follows naturally from the assumptions of the models, this kind of allocation pattern is unlikely to occur in many plants, because it requires that (1) leaf and flower buds can never simultaneously be carbon sinks; and (2) organs that accompany flowers, such as internodes and bracts, can never be net sources of photosynthate. Thus while resources are doubtless important for annual plants, an exclusively resource-based perspective may be inadequate to understand the evolution of their life histories. Progress in research may require models that incorporate, or are at least phenomenologically consistent with, the basic developmental reles of angiosperms.