Quantifying sink and source limitations on dry matter partitioning to fruit growth in peach trees

We describe an approach for determining the degree of sink and source limitations on peach ( Prunus persica L. Batsch) fruit growth during several growth periods. Source limitations on fruit growth may be due to either a shortfall in assimilate supply within the tree (supply limitation) or to a deficiency in the capacity of the translocation system to deliver assimilates in sufficient quantity to support the maximum fruit growth rate (transport/competition limitation). To ascertain the potential maximum rate of fruit growth, fruit thinning treatments were used. One month after bloom, the number of fruits per tree was adjusted to between 50 and 700 on an early and a late maturing peach cultivar (cvs Spring Lady and Cal Red, respectively). Rates of potential sink demand, potential source supply and actual fruit growth were estimated from sequential harvests of all fruits on 42 trees on two (Spring Lady) and three (Cal Red) dates. These values were used to estimate the proportion of potential growth achieved, and the supply and transport/competition limitations on fruit growth. The results indicated that source limitations were significant on trees with moderate to high fruit numbers. These source limitations were due to supply limitations during all harvest intervals and to transport/competition limitations during the early harvest intervals. Sink limitations occurred to the greatest extent during the mid-period of fruit growth on the later maturing cultivar.     

Manipulation of sucrose phloem and embryo loading affects pea leaf metabolism,carbon and nitrogen partitioning to sinks as well as seed storage pools

Seed development largely depends on the long‐distance transport of sucrose from photosynthetically active source leaves to seed sinks. This source‐to‐sink carbon allocation occurs in the phloem and requires the loading of sucrose into the leaf phloem and, at the sink end, its import into the growing embryo. Both tasks are achieved through the function of SUT sucrose transporters. In this study, we used vegetable peas (Pisum sativum L.), harvested for human consumption as immature seeds, as our model crop and simultaneously overexpressed the endogenous SUT1 transporter in the leaf phloem and in cotyledon epidermal cells where import into the embryo occurs. Using this ‘Push‐and‐Pull’ approach, the transgenic SUT1 plants displayed increased sucrose phloem loading and carbon movement from source to sink causing higher sucrose levels in developing pea seeds. The enhanced sucrose partitioning further led to improved photosynthesis rates, increased leaf nitrogen assimilation, and enhanced source‐to‐sink transport of amino acids. Embryo loading with amino acids was also increased in SUT1‐overexpressors resulting in higher protein levels in immature seeds. Further, transgenic plants grown until desiccation produced more seed protein and starch, as well as higher seed yields than the wild‐type plants. Together, the results demonstrate that the SUT1‐overexpressing plants with enhanced sucrose allocation to sinks adjust leaf carbon and nitrogen metabolism, and amino acid partitioning in order to accommodate the increased assimilate demand of growing seeds. We further provide evidence that the combined Push‐and‐Pull approach for enhancing carbon transport is a successful strategy for improving seed yields and nutritional quality in legumes.     

Enhanced leaf photosynthesis as a target to increase grain yield: insights from transgenic rice lines with variable Rieske FeS protein content in the cytochrome b6/f complex

Although photosynthesis is the most important source for biomass and grain yield, a lack of correlation between photosynthesis and plant yield among different genotypes of various crop species has been frequently observed. Such observations contribute to the ongoing debate whether enhancing leaf photosynthesis can improve yield potential. Here, transgenic rice plants that contain variable amounts of the Rieske FeS protein _in the cytochrome (cyt) b₆/f complex between 10 and 100% of wild‐type levels have been used to investigate the effect of reductions of these proteins on photosynthesis, plant growth and yield. Reductions of the cyt b₆/f complex did not affect the electron transport rates through photosystem I but decreased electron transport rates through photosystem II, leading to concomitant decreases in CO₂ assimilation rates. There was a strong control of plant growth and grain yield by the rate of leaf photosynthesis, leading to the conclusion that enhancing photosynthesis at the single‐leaf level would be a useful target for improving crop productivity and yield both via conventional breeding and biotechnology. The data here also suggest that changing photosynthetic electron transport rates via manipulation of the cyt b₆/f complex could be a potential target for enhancing photosynthetic capacity in higher plants.     

Matrix-assisted laser desorption/ionization time of flight mass spectrometry peptide mass fingerprints and post source decay: a tool for the identification and analysis of phloem proteins from Cucurbita maxima Duch. separated by two-dimensional polyacrylamide gel electrophoresis

A combination of gel electrophoresis and mass spectrometry was used to analyze the soluble proteins from phloem sap of Cucurbita maxima Duch. Phloem proteins were separated using two-dimensional gel electrophoresis. Coomassie-stained spots were cut out and subjected to tryptic digestion. To identify proteins, peptide mass fingerprints were determined by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry. In addition, MALDI-TOF post source decay measurements were used to obtain partial sequence information for the proteins. Results from both approaches were used for database searches. In this study, 17 proteins in the mass range 5-50 kDa were analyzed. Of these proteins six could be clearly identified, seven showed significant homologies to known plant proteins, and four were not significantly homologous to database entries. The present study suggests that the applied method is feasible for a large-scale analysis and identification of phloem proteins derived from different organs or from plants kept under various physiological conditions.     

The potential of lentil (Lens culinaris) as a grain legume crop in the UK: an assessment based on a crop growth model

A crop growth model developed in Canterbury, New Zealand was used to assess the potential of lentil (Lens culinaris) as a grain legume crop in the UK. The model was validated using five sowing dates at Durham (54.77°N, 1.58°W) in 1999. Predicted time to flowering was within 7 days of actual time to flowering and predicted seed yields were within 9% of actual yields. Actual yields ranged from 1.40 to 1.65 t ha‐¹. Seed was of high quality. The model was used to predict rate of development and yields of spring and autumn sown lentils at eight sites along a transect from NW Scotland (Stornoway, 58.22°N, 6.32°W) to SE England (East Mailing, 51.28°N, 0.45°E) chosen to encompass important environmental gradients in the UK. In general, for a 1 May sowing with 150 or 250 mm plant available water (PAW) and a 1 October sowing with 150 mm PAW, predicted mean values over the period 1987–95 for maximum crop growth rate, maximum leaf area index, radiation intercepted, total dry matter produced and seed yield were closely positively related to monthly mean values for mean daily air temperature and increased along the transect from NW to SE UK. Time to flowering generally decreased along the transect from NW to SE UK ranging from 28 June to 9 July and from 20 May to 14 June with the May and October sowings respectively. For the 1 May sowing with 250 mm PAW, predicted mean seed yield ranged from 1.00 to 1.90 t ha‐1. For all sites, yield was very stable over the 9 yr period. For the 1 May sowing with 150 mm PAW, predicted mean seed yield ranged from 0.97–1.23 t ha‐1. Yields for the four more southerly sites were more variable at the lower PAW and, in exceptionally dry years, were substantially lower than average. For these sites, autumn sowing increased seed yields in exceptionally dry years and gave similar or greater mean seed yields to spring sowing with 250 mm PAW. For East Mailing, predicted yields for autumn sowing were on average 2.78 t ha‐1. Also, for Stornoway, because of its relatively high overwinter temperatures, the model predicted substantial increases in yield with autumn sowing. It is concluded that lentil has considerable potential as a grain legume crop in the UK.     

Evolution of ontogenetic allometry shaping giant species: a case study from the damselfish genus Dascyllus (Pomacentridae)

The evolution of body size, the paired phenomena of giantism and dwarfism, has long been studied by biologists and paleontologists. However, detailed investigations devoted to the study of the evolution of ontogenetic patterns shaping giant species are scarce. The damselfishes of the genus Dascyllus appear as an excellent model for such a study. Their well understood phylogeny reveals that large‐bodied species have evolved in two different clades. Geometric morphometric methods were used to compare the ontogenetic trajectories of the neurocranium and the mandible in both small‐bodied (Dascyllus aruanus and Dascyllus carneus; maximum size: 50–65 mm standard length) and giant (Dascyllus trimaculatus and Dascyllus flavicaudus; maximum size: 90–110 mm standard length) Dascyllus species. At their respective maximum body size, the neurocranium of the giant species is significantly shorter and have a higher supraoccipital crest relative to the small‐bodied species, whereas mandible shape variation is more limited and is not related to the ‘giant’ trait. The hypothesis of ontogenetic scaling whereby the giant species evolved by extending the allometric trajectory of the small‐bodied ones (i.e. hypermorphosis) is rejected. Instead, the allometric trajectories vary among species by lateral transpositions. The rate of shape changes and the type of lateral transposition also differ according to the skeletal unit among Dascyllus species. Differences seen between the two giant species in the present study demonstrate that giant species may appear by varied alterations of the ancestor allometric pattern. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 99–117.     

Short-term variation in the isotopic composition of organic matter allocated from the leaves to the stem of Pinus sylvestris: effects of photosynthetic and postphotosynthetic carbon isotope fractionation

We aimed to quantify the separate effects of photosynthetic and postphotosynthetic carbon isotope discrimination on δ¹³C of the fast‐turn‐over carbon pool (water soluble organic carbon and CO₂ emitted from heterotrophic tissues), including their diel variation, along the pathway of carbon transport from the foliage to the base of the stem. For that purpose, we determined δ¹³C in total and water‐soluble organic matter of the foliage plus δ¹³C and δ¹⁸O in phloem organic matter of twigs and at three heights along the stem of Pinus sylvestris over a nine‐day period, including four measurements per day. These data were related to meteorological and photosynthesis parameters and to the δ¹³C of stem‐emitted CO₂. In the canopy (foliage and twigs), the δ¹³C of soluble organic matter varied diurnally with amplitudes of up to 1.9‰. The greatest ¹³C enrichment was recorded during the night/early morning, indicating a strong influence of starch storage and remobilization on the carbon isotope signatures of sugars exported from the leaves. ¹³C enrichment of soluble organic matter from the leaves to the twig phloem and further on to the phloem of the stem was supposed to be a result of carbon isotope fractionation associated with metabolic processes in the source and sink tissues. CO₂ emitted from the stem was enriched by 2.3–5.2‰ compared with phloem organic matter. When day‐to‐day variation was addressed, water‐soluble leaf δ¹³C and twig phloem δ¹⁸O were strongly influenced by c_i/c_a and stomatal conductance (G_s), respectively. These results show that both photosynthetic and postphotosynthetic carbon isotope fractionation influence δ¹³C of organic matter over time, and over the length of the basipetal transport pathway. Clearly, these influences on the δ¹³C of respired CO₂ must be considered when using the latter for partitioning of ecosystem CO₂ fluxes or when the assessment of δ¹³C in organic matter is applied to estimate environmental effects in c_i/c_a.     

The effect of temperature and somatic growth on otolith growth: the discrepancy between two clupeid species from a similar environment

Otolith growth rates of the early life stages of herring Clupea harengus ( n = 472) and smelt Osmerus eperlanus ( n = 348) collected in the Vistula Lagoon (Baltic Sea) during 1997–1999 were analysed. The larvae and early juveniles were not only collected in the same geographical area they were also of the same size (range 15–43 mm standard length, L _S), similar ages and were collected during the same seasons (May to July). Although the two clupeid species experienced very similar environmental conditions, there were significant discrepancies in the analysed relationships. The otolith growth of larval and juvenile smelt was very strongly related to somatic growth while temperature had a minor effect. In herring, the effect of somatic growth, although clearly visible and statistically highly significant, was of less importance than temperature. Furthermore, variation in the otolith size and L _S relationship was affected by temperature and somatic growth in both species, but the variance of otolith size at L _S was higher for herring than for smelt. Although growth backcalculation from otoliths can presently be recommended as an appropriate method for use with both smelt and herring (despite possibly lower precision and accuracy with the latter), other methods referring directly to short-term increment width changes ( e.g. marginal increment analysis) are recommended for smelt but not for herring.     

The response of potatoes (Solunum tuberosum L.) to salinity: plant growth and tuber yields in the arid desert of Israel

The response of potato cultivars to water salinity was studied under field conditions in sandy loessial soil in the arid desert of Southern Israel. The potatoes were drip-irrigated with water of three different salinities: water commonly used for irrigation (1.0–1.4 dS m^-1); saline water from a local well (6.1–6.9 dS m^-1); and a mixture of the two (3.84.3 dS m^-1). Salinity retarded plant emergence, enhanced haulm senescence and reduced growth of both haulms and tubers. Increasing the salinity progressively reduced tuber yields. Application of the saline water well after plant establishment (Expt A) decreased tuber yields by 615% and 22–31% in the intermediate and the high salinities, respectively. When irrigation with saline water was started soon after planting (Expt B), tuber yields were decreased by 0–17% and 21–79% in the intermediate and the high salinities, respectively. When the tubers emerged in salinised soil, tuber yields were decreased by 21–54% and 42–59% in the intermediate and the high salinities, respectively. A differential response of various cultivars to salinity was observed. None of the potato cultivars or clones exhibited exceptional tolerance to severe salinity. The earlier maturing cvs Atica and Désirée were the least susceptible to the moderate salinity imposed throughout the entire growing season; however, no association was noted between maturation time and the response to salinity.     

The long way from Kyoto to Marrakesh: Implications of the Kyoto Protocol negotiations for global ecology

The Sixth and Seventh Conference of the Parties (COP 6 and 7) at The Hague, Bonn and Marrakesh came to a final Agreement on the Kyoto Protocol, which is thus ready for ratification by the individual nations. The Agreement was only achieved by allowing countries to offset their fossil fuel emission targets (on average 95% of the 1990 emissions) by increasing biological carbon sequestration, and by trading carbon credits. Activities that would count as increasing biological carbon sequestration include afforestation and reforestation, and changes in management of agriculture and forestry. According to the Agreement reached in Marrakesh, biological carbon sequestration may reach an offset of up to 80% of the required reduction in fossil fuel emissions (4% of the 5% reduction commitment). We explain why the allowable offset rose as high during the course of the negotiations. It is highlighted that major unintended consequences may be a result of the policy as it stands in the Marrakesh Accord. Major losses of biodiversity and primary forest are expected. We present scientific concerns regarding verification, which lead to scientific doubts that the practices encouraged by the Agreement can actually increase sequestration under a full carbon accounting scheme. We explain that there is a ‘win‐win’ option that would protect high carbon pools and biodiversity in an economically efficient way. But, this is not supported by the Agreement. Despite the very positive signal that most nations of the United Nations will devote major efforts towards climate protection, there remains a most urgent need to develop additional rules to avoid unintended outcomes, and to promote the ‘win‐win’ options that we explain.     

The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant

The location and timing of domestication of the olive tree, a key crop in Early Mediterranean societies, remain hotly debated. Here, we unravel the history of wild olives (oleasters), and then infer the primary origins of the domesticated olive. Phylogeography and Bayesian molecular dating analyses based on plastid genome profiling of 1263 oleasters and 534 cultivated genotypes reveal three main lineages of pre-Quaternary origin. Regional hotspots of plastid diversity, species distribution modelling and macrofossils support the existence of three long-term refugia; namely the Near East (including Cyprus), the Aegean area and the Strait of Gibraltar. These ancestral wild gene pools have provided the essential foundations for cultivated olive breeding. Comparison of the geographical pattern of plastid diversity between wild and cultivated olives indicates the cradle of first domestication in the northern Levant followed by dispersals across the Mediterranean basin in parallel with the expansion of civilizations and human exchanges in this part of the world.     

The silvering process of Anguilla anguilla: a new classification from the yellow resident to the silver migrating stage

The identification of five stages for female and two stages for male eels Anguilla anguilla using multivariate analysis was carried out on a large sample of individuals collected at six different locations in France. Stages corresponded to a growth phase (stages I and II), a pre‐migrant phase (III) and two migrating phases (IV and V). It is likely that an important period of growth triggered silvering through the production of growth hormone (GH) in stage III eels. In migrating eels gonad development, gonadotropin hormone (GTH‐II) production and increase of eye surface were similar at all sites. Differences among locations were found in gut regression and pectoral fin length. As variability for these increased with the size of the watershed and values were highest for the most downstream locations, fin length and gut regression may indicate the time since an eel started its migration.     

Vegetation shift from deciduous to evergreen dwarf shrubs in response to selective herbivory offsets carbon losses: evidence from 19 years of warming and simulated herbivory in the subarctic tundra

Selective herbivory of palatable plant species provides a competitive advantage for unpalatable plant species, which often have slow growth rates and produce slowly decomposable litter. We hypothesized that through a shift in the vegetation community from palatable, deciduous dwarf shrubs to unpalatable, evergreen dwarf shrubs, selective herbivory may counteract the increased shrub abundance that is otherwise found in tundra ecosystems, in turn interacting with the responses of ecosystem carbon (C) stocks and CO₂ balance to climatic warming. We tested this hypothesis in a 19‐year field experiment with factorial treatments of warming and simulated herbivory on the dominant deciduous dwarf shrub Vaccinium myrtillus. Warming was associated with a significantly increased vegetation abundance, with the strongest effect on deciduous dwarf shrubs, resulting in greater rates of both gross ecosystem production (GEP) and ecosystem respiration (ER) as well as increased C stocks. Simulated herbivory increased the abundance of evergreen dwarf shrubs, most importantly Empetrum nigrum ssp. hermaphroditum, which led to a recent shift in the dominant vegetation from deciduous to evergreen dwarf shrubs. Simulated herbivory caused no effect on GEP and ER or the total ecosystem C stocks, indicating that the vegetation shift counteracted the herbivore‐induced C loss from the system. A larger proportion of the total ecosystem C stock was found aboveground, rather than belowground, in plots treated with simulated herbivory. We conclude that by providing a competitive advantage to unpalatable plant species with slow growth rates and long life spans, selective herbivory may promote aboveground C stocks in a warming tundra ecosystem and, through this mechanism, counteract C losses that result from plant biomass consumption.     

The transformation of male sex cells of Tetranychus urticae K. (Acari,Tetranychidae) during passage from the testis to the oocytes: an electron microscopic study

The fine structure of the spermatozoon of Tetranychus urticae is described during passage from the testis to the site of insemination in the ovary. The male sex cells differentiate from a cytoplasmic mass which is characterised by nuclei bearing tubule-like structures. Infoldings appear in peripheral membrane of the germ cells at the beginning of spermiogenesis, chromatin condenses, and the nuclear membrane is reduced. The spermatozoon is surrounded by a double membrane: the inner one is the sperm membrane and the outer one is of somatic origin. The sperm reach the glanular region of the testis where they are transformed into amoeboid cell and are next collected in the seminal vesicle.

After copulation, the sperm can be observed in the lumen of the receptaculum seminis of the female from which they soon enter the epithelial cells. Still surrounded by a double membrane, the sperm, which are now packed in clusters, develop microtubules immediately beneath the inner membrane and enlarge by decondensation of chromatin and by infiltration of cytoplasmic material. Insemination takes place in the vitellogenic region of the ovary just before the eggs close their pores; the sperm have now reached ten times their original size.     

The Utility of Carbon and Nitrogen Isotope Analyses to Trace Contributions from Fish Farms to the Receiving Communities of Freshwater Lakes: a Pilot Study in Esthwaite Water,UK

A pilot study was conducted to assess the potential for stable isotope analyses to reveal the fate of waste pelleted food material from fish farms in freshwater food webs. Esthwaite Water (Cumbria, UK) was selected as the study site, as it hosts an established salmonid farm, and a wealth of complementary limnological data exists. Salmonid pellet feed consists of primarily marine-derived material and thus exhibits carbon and nitrogen stable isotopic compositions distinct to most freshwater organic material. Comparison of the isotopic ratios of organisms at the cage site with an unaffected control site, supports incorporation of pellet-derived material to the diet of planktonic and benthic communities. Moreover, after allowing for a number of trophic transfers, stable isotope analyses revealed the predatory cladoceran Leptodora kindti also utilised pellet material, while roach were probably short-circuiting the food chain by directly consuming particulate pellet material, as well as via ingestion of their zooplankton prey. Isotope data substituted into a simple two-source mixing model suggested that approximately 65% of Daphnia, and >80% of roach body carbon may be derived from pellet material in the plankton, and that chironomid larvae may incorporate >50% in the sediment environs. However, contributions calculated from both ¹³C and ¹⁵N values were inconsistent, which may simply be due to the constraints of the model and parameters used, but may also reflect different routing of isotopes from the original pellet source, via soluble or particulate routes.