An Experimental Evaluation of Different Methods of Restoring Phyllospadix torreyi (Surfgrass)

The surfgrass Phyllospadix torreyi is an abundant seagrass found on rocky exposed shores of the Pacific coast of North America. In southern California surfgrass populations are adversely affected by a range of natural events and anthropogenic activities. Few attempts have been made to develop restoration methods for surfgrass, and none have investigated the efficacy of using different life stages. We evaluated several techniques for restoration in intertidal and subtidal habitats using: (1) laboratory‐reared seedlings transplanted to the field (2) sprigs (short lengths of rhizome containing a few shoots) transplanted from undisturbed populations, and (3) plugs (a cohesive clump of shoots and rhizomes) transplanted from undisturbed populations. We calculated the net change in the aerial coverage of surfgrass after 6 months, taking into account the recovery or additional losses from the donor population, and amount of effort involved in transplanting. Transplanted seedlings survived poorly and had minimal rhizome growth at both the intertidal and the subtidal sites, yet the individuals that did survive showed a 275% increase in leaf number. Survivorship of transplanted plugs was high in both habitats; however, physical disturbances to the donor populations exacerbated damage sustained at the time of collecting, yielding a substantial net loss in surfgrass. Sprigs transplanted to the subtidal had higher survivorship (71 versus 48%) and a greater increase in the aerial coverage of rhizome (86 versus 42%) than those transplanted to the intertidal. Of the three techniques, transplanted sprigs had the greatest overall increase in aerial coverage per unit effort, suggesting that this method may be the most effective approach for restoring P. torreyi.     

Stasis or kinesis? Hidden dynamics of a rocky intertidal macrophyte mosaic revealed by a spatially explicit approach

Macrophyte mosaics, or tile-like assemblages of turfy marine macroalgae and surfgrass (Phyllospadix scouleri), are persistent and highly diverse along the central Oregon coast. To test the hypothesis that spatial pattern and species abundances are relatively invariant in this system, we studied community structure, disturbance, and species interactions from 1985 to 1990. Abundances and disturbance in permanently marked plots at each of five sites spanning wave-exposed to wave-protected areas were monitored photographically each year. The analysis was spatially explicit, incorporated position effects, and allowed determination of species displacements. To interpret the potential influence of substratum on disturbance, we quantified rock hardness and sediment depth at each site. Field experiments tested the role of grazers and spatial interactions on maintenance of between-patch boundaries.Mosaic dynamics varied with wave exposure. At wave-exposed and wave-protected sites, average patterns of abundance and assemblage structure were relatively constant through time, but analysis of transition probabilities showed high rates of change among mosaic elements at wave-exposed sites and low rates of change at wave-protected sites. At wave-exposed sites, most changes involved Phyllospadix displacing neighboring macroalgal turfs but rarely the reverse. At all wave-exposures, surfgrass was the most frequently disturbed mosaic element. Disturbed areas were quickly colonized by macroalgae. At wave-exposed sites, disturbances were closed by regrowth of surfgrass. Disturbance rates were similar across wave-exposures, with wave forces causing most loss at wave-exposed sites and a combination of substratum failure and sediment burial causing most loss at wave-protected sites. At wave-exposed sites, disturbances tended to be larger (436.7 vs. 278.6 cm²) but less numerous (228 vs. 484 total disturbances) than at wave-protected sites.At wave-exposed sites, surfgrass overgrew all other species except the kelp Lessoniopsis littoralis, which was competitively equivalent to surfgrass. Grazing had no effect on spatial interactions. Disturbance prevented surfgrass monocultures, and with variable dispersal and patchy recruitment, maintained mosaic structure. At wave-protected sites, standoffs were the usual outcome of interactions, and patchiness resulted primarily from colonization of disturbances and subsequent succession. Like mussels, Phyllospadix are simultaneously dominant competitors, the most disturbance-susceptible species, and poor colonizers. These features are shared by theoretical models exploring the processes underlying spatially structured assemblages, and may characterize spatially structured systems in general.     

Long-distance dispersal of the beach strawberry,Fragaria chiloensis,from North America to Chile and Hawaii

Background and AimsThe beach strawberry, Fragaria chiloensis, is found in a narrow coastal band from the Aleutian Islands to central California and then jumps thousands of kilometres all the way to Hawaii and Chile. As it probably had a North American origin, it must have been introduced to the other locations by long-distance dispersal. The aim of this study was to determine which agent carried the beach strawberry to its Pacific and South American locations.MethodsA deductive framework was constructed to separate between the possible modes of long-distance dispersal involving animals, wind and ocean currents. Bird migration was subsequently identified as the most likely scenario, and then the routes, habitats, feeding preferences and flight distances of all the shorebird species were evaluated to determine the most likely carrier.Key ResultsSix species migrate between North America and Chile and feed on the beaches and rocky shores where F. chiloensis grows naturally: Black-bellied Plovers, Greater Yellowlegs, Ruddy Turnstones, Sanderlings, Whimbrels and Willets. Of these, only two eat fruit and migrate in long continuous flight: Ruddy Turnstones and Whimbrels. Two species travel between North America and Hawaii, eat fruit and forage on the beaches and rocky shores where F. chiloensis grows naturally: Pacific Golden-plovers and Ruddy Turnstones. Ruddy Turnstones eat far less fruit than Pacific Golden-plovers and Whimbrels, making them less likely to have introduced the beach strawberry to either location.ConclusionsWe provide evidence that F. chiloesis seeds were probably dispersed to Hawaii by Pacific Golden-plovers and to Chile by Whimbrels.     

Stable carbon isotope ratio variations in marine macrophytes along intertidal gradients

Summary The hypothesis that relative water motion and boundary layer diffusion processes affect carbon isotope ratios of aquatic plants was tested in tidal pool and surge zone comparisons of the surfgrass Phyllospadix spp. No evidence was found that submerged plants growing in still upper tidal pools were isotopically different from those growing submerged in lower tidal surge zones. Significant decreases in ¹³C/¹²C ratios for plants growing emersed in the intertidal may have been caused by uptake of atmospheric carbon dioxide. Marine algae (Egregia menziesii and Halosaccion americanum) growing at the same location and tidal elevations as the seagrasses showed somewhat different isotopic fractionation patterns, suggesting that causes of isotopic variability in the seagrasses were not necessarily the same as those in the two marine algae.     

Invading Monotypic Stands of Phalaris arundinacea: A Test of Fire, Herbicide, and Woody and Herbaceous Native Plant Groups

Phalaris arundinacea L. is an aggressive species that can dominate wetlands by producing monotypic stands that suppress native vegetation. In this study invasion windows were created for native species in monotypic stands of P. arundinacea with either fire or herbicide. Three native species groups, herbaceous plants, herbaceous seeds, and woody shrubs, were planted into plots burned or treated with herbicide in the early spring. Fire did not create an effective invasion window for native species; there was no difference in P. arundinacea root and shoot biomass or cover between burned and control plots (p≥ 0.998). Herbicide treatment created an invasion window for native species by reducing P. arundinacea root and shoot biomass for two growing seasons, but that invasion window was fast closing by the end of the second growing season because P. arundinacea shoot biomass had nearly reached the shoot biomass levels in the control plots (p= 0.053). Transplant mortality, frost, and animal herbivory prevented the herbaceous species and woody seedlings from becoming fully established in the plots treated with herbicide during the first year of the experiment. Transplanted monocots had a greater survival than dicots. By the second growing season the herbaceous group had the greatest mean areal cover (5%), compared to the woody seedlings (3%) and seed group (0%). Long‐term monitoring of the plots will determine whether the herbaceous transplants will compete effectively with P. arundinacea and whether the woody species will survive, shade the P. arundinacea, and accelerate forest succession.     

Food supply, grazing activity and growth rate in the limpet Patella vulgata L.: a comparison between exposed and sheltered shores

The limpet Patella vulgata L. is an important microphagous grazer on intertidal rocky shores of north-west Europe, occurring across the wave exposure gradient. Groups of P. vulgata were selected at mid-tide level of two exposed shores and two sheltered, fucoid dominated shores on the Isle of Man, British Isles, and manipulated to equivalent densities and population structure. The level of grazing activity and growth rate were determined over a 1-year period. At the same time, the abundance of epilithic microalgae, measured as the concentration of chlorophyll a, was determined as an estimate of food supply. Microagal abundance showed a seasonal pattern in both exposed and sheltered conditions, with higher levels in winter compared to summer. In both seasons, the microalgal resource was more abundant on the sheltered shore studied. The level of grazing activity in P. vulgata showed a seasonal pattern on the exposed but not the sheltered shores. Averaged over the year, grazing activity on the exposed shores was over double that on sheltered shores. Thus, in sheltered conditions, food supply for limpets was high and grazing activity low; in exposed conditions, food supply was low and grazing activity high. The growth rate of P. vulgata, measured as increase in shell length, showed no significant difference between exposed and sheltered shores. Growth rate was also determined in P. vulgata at natural densities. Although the overall density declined with decreasing exposure to wave action, the density per unit area of grazeable substance was higher in shelter. In these populations, the mean growth rate was over twice as high on exposed compared to sheltered shores.     

Dark preincubation improves shoot organogenesis from Rhodiola crenulata leaf explants

An efficient in vitro plant regeneration system has been developed using dark preincubated leaf explants of Rhodiola crenulata, a traditional Tibetan medicinal plant. The leaf explants, preincubated in the dark for 5 d, developed an average of 9.1 shoots per explant on a medium containing 15 μM N ⁶-benzyladenine (BA) and 2.5 μM gibberellic acid (GA₃). The biochemical mechanism underlying dark-induced shoot organogenesis was investigated by measuring polyphenol oxidase (PPO) activity. Dark preincubation significantly reduced PPO activity in leaf explants during the initial period of shoot organogenesis and reduced browning compared to explants cultured in the light. Up to 88.4 % of the regenerated shoots formed roots and developed into complete plantlets on a medium containing 5 μM indoleacetic acid (IAA) within 25 d. Approximately 82 % of the regenerated plantlets survived transplantation and grew vigorously in the greenhouse.     

Effects of grazer identity on the probability of escapes by a canopy-forming macroalga

Through their grazing activities limpets have an important role in controlling macroalgal abundance and as a result the structure and dynamics of rocky shore assemblages. Using two congeneric limpet species, with different biogeographic distributions, and whose ranges are expected to alter with climatic warming, we separated the magnitude of their grazing activity over time and the subsequent consequence for macroalgal growth.The northern/boreal limpet, Patella vulgata (L.), consistently grazed more than the southern/lusitanian limpet, P. depressa (Pennant), particularly during spring and summer when P. depressa was reproductively active. Individuals of Fucus vesiculosus (L.) that settled during this time were able to grow to a size where they escaped the grazing activities of P. depressa, resulting in mature F. vesiculosus being present in all P. depressa treatments. In contrast, P. vulgata, which was not reproductively active during this period, exhibited no reduction in its grazing activity and prevented macroalgae from growing in experimental treatments. It therefore appears that P. vulgata has a stronger role, than P. depressa, in controlling macroalgal abundance on shores of southwest Britain.We present a conceptual model highlighting the direct and indirect interactions between these two limpet species and F. vesiculosis. If as predicted, under current warming scenarios, P. depressa becomes the dominant limpet on shores of southwest Britain there will be subsequent changes in rocky shore community structure and ecosystem functioning. Our research emphasises that even closely related species with similar ecological niches can exhibit different behaviours that fundamentally alter their biological interactions with other organisms leading to idiosyncratic responses to predicted changes in climate.     

Seasonal variation in short-term survival of Zostera noltii transplants in a declining meadow in Portugal

In one decade (from 1986 to 1997), the area occupied by Zostera noltii in the Mondego estuary (western coast of Portugal) decreased from 150,000 to 200 m². Our purpose was to identify the most suitable season for transplantation of Z. noltii, as one of the methodologies included in a broader restoration plan of the local Z. noltii meadows. Each month a short-term transplantation experiment (20 days) was undertaken, where the net growth rate of transplants, the number of lost shoots and the number of surviving shoots was estimated. Transplant loss variation was markedly seasonal (ANOVA, F_1,12 = 13.11, p < 0.01). From spring to middle autumn (April–October), the amount of lost shoots was significantly higher (average = 63%) than during late autumn and winter (average = 26%). Multiple regression results suggest that the number of surviving shoots was negatively related with insolation and NH₄-N concentration. Additionally, the net growth rate of the transplants was negatively related with salinity.In conclusion, we recommend that at southern European latitudes, Z. noltii transplantation be undertaken during late autumn and winter. The success of transplantation at this time of the year seems to be related with the prevailing external conditions, namely, low temperatures and low photon flux densities. Furthermore, we hypothesise that the proportion of aboveground to belowground biomass in Z. noltii may also influence transplant survival. Transplantation success was higher whenever belowground biomass was higher than aboveground biomass. In the Mondego estuary, in autumn and winter, the belowground biomass of Z. noltii represents about 51% of the total plant biomass, while in spring and summer, this value decreases to 31% of the total biomass.     

Apoplastic and symplastic pathways of atrazine and glyphosate transport in shoots of seedling sunflower

[¹⁴C]Atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-s-triazine) and [¹⁴C]glyphosate (N-[phosphonomethyl]glycine) were xylem fed to sunflower shoots at 100 micromolar for 1 hour in the light, then placed in the dark at 100% relative humidity for 1, 4, 7, or 10 hours. The distribution of atrazine and glyphosate between shoot parts, in the leaves, and between the aoplast and symplast of the leaf was determined. The apoplastic concentrations and distribution patterns of atrazine and glyphosate in the leaves were evaluated using a pressure dehydration technique, our results were compared to the previously reported distribution patterns of the naturally occurring apoplastic leaf solutes, and the apoplastic dye PTS (trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate). The pattern of atrazine and glyphosate distribution in the shoot, and between the leaf apoplast and symplast, was found to reflect the potential of these herbicides to enter the shoot symplast. The results of this study are discussed with respect to current theories of xenobiotic transport in plants, and have been found to be consistent with the intermediate permeability hypothesis for xenobiotic transport.     

The effect of sewage sludge flooding on growth and morphometric parameters of Phragmites australis (Cav.) Trin. ex Steudel

Phragmites australis is the most frequently used species in constructed wetlands (CW) for dewatering and mineralization of sludge. Such CW create a very hostile environment for plants because their roots are exposed to permanently anaerobic conditions. Our working hypothesis assumed a simple relationship between the success of reed in colonising sludge flood stands and maximalisation of shoot oxygen production and transport to rhizomes and roots. Morphometric parameters and density of common reed shoots growing in reed bed systems inundated with sewage sludge were investigated. It was proved that flooding with sewage sludge significantly influenced characteristics of common reed populations. In comparison with natural stands, on stands treated with sewage sludge, maximal density of shoots was higher, biomass was twice as high, shoot diameter was significantly greater, and leaf weight ratio of an individual shoot was also significantly higher. Tendency to shorten shoots was noted. Growing period was longer for reed shoots treated with sewage sludge than on natural stands.     

Transplant Survivorship of Bryophyte Soil Crusts in the Mojave Desert

Patches of the dominant biological soil crust moss (Syntrichia caninervis) in the Mojave Desert were subjected to transplant experiments to test the survivability of crustal transplantation due to source or destination microhabitat. After a period of 27 months, all the reciprocally transplanted and replanted sections had survived. However, percent cover of the reciprocally transplanted patches declined 20–50% relative to initial cover compared to a decline in cover of 36–52% for the replanted patches. Similarly, shoot density declined an average of 26% in the transplants and replants. Shoot mortality was essentially negligible through the first 21 months of the study and then declining across all treatments to approximately 5–10 dead shoots/cm². However, this shoot death was also observed in equivalent densities in the host patches, indicative of a community‐wide decline in plant health that was probably related to a regional rainfall deficit over this period. A tendency existed for plants moved from a shaded site to have reduced shoot density in the new site, and plants moved into exposed sites lost significantly more cover than plants moved into shaded sites. These seemingly conflicting trends result from one of the transplant treatments, the shaded to exposed, exhibiting a greater loss in shoot density and decline in cover than its reciprocal transplant, exposed to shaded. For soil restoration of disturbed bryophyte crusts, we recommend using as source material both the exposed and the shaded portions of the crust but avoiding moving Syntrichia from a shaded site into an exposed site.     

Estimation of dieback process caused by herbivory in an endangered root-sprouting shrub species,Paliurus ramosissimus (Lour.) Poir., using a shoot-dynamics matrix model

Mortality, a critical parameter for population dynamics, is difficult to measure in long-lived trees or clonal herbaceous species because of the extremely low frequency of deaths. A model based on shoot recruitment would be helpful to estimate the population fate of species without a sufficient number of observed deaths. Existing matrix models are applicable to the dynamics of physiologically independent shoots, but not to physiologically dependent ones. We developed a shoot-dynamics model for plants with physiologically-dependent shoots, and used the model to estimate the effects of herbivory and conservation measures on the dynamics of a long-lived, shoot-sprouting shrub species, Paliurus ramosissimus (Rhamnaceae). Two populations of the endangered shrub have been severely damaged by herbivory by sika deer. The damage was mainly to new sprouting shoots. No deaths of individual plants were observed during an 8-year survey, and we could not estimate mortality. Thus, prediction of population dynamics based on births and deaths of individuals was impossible. Because P. ramosissimus is a shoot-sprouting species, we instead estimated the decline of individuals using a shoot-dynamics model. Using this model, we estimated the time to an 80 % decrease in shoot number per individual in the two populations at 37.8 and 37.2 years. These lengths suggest an immediate need for conservation measures to prevent herbivory even though no death of any individual was observed in the field survey. The estimated recovery times from the herbivory damage were 28.7 and 29.2 years if herbivory of new shoots is completely prevented by conservation measure.     

Growth response of Alstroemeria ‘Parigro Pink’ to phosphate supply in vitro

Rhizome tip explants of Alstroemeria ‘Parigo Pink’ were established on modified Murashige &; Skoog medium with P added as KH₂PO₄ at 0, 0.01, 0.05, 0.25, 1.25 or 2.5 mM. Cultures were transferred to fresh media every 4 weeks. Five explants were harvested from each P treatment after 3, 5, 7, 9 and 11 weeks in culture. Explants were separated into rhizome and shoot, weighed, dried and wet-ashed. Phosphorus content of the ash was determined colorimetrically. Explants supplied 1.25 or 2.5 mM P produced significantly more shoots and growing points, and greater fresh weight of rhizomes and shoots, than those provided with lower P concentrations. Phosphorus accumulation rates in shoots in the two highest P treatments were significantly greater than in the lower P treatments. Shoot tissue P concentrations greater than 7 mmol kg^-1 fwt evidently are required for maximum in vitro growth of Alstroemeria ‘Parigro Pink’. Explants provided the two highest P treatments partitioned a greater proportion of fresh weight and total P to shoots vs rhizomes than lower P treatments.     

Shoot Growth and Mortality Patterns of Urtica dioica, a Clonal Forb

The growth and mortality patterns of the clonal forb Urticadioica were investigated at the level of the individual shootin two growing seasons, 1991 and 1992, in a natural stand. Shootheight and diameter at ground level of each shoot tagged inspring were measured repeatedly five times during the growingseason. Dry weights of these repeatedly measured shoots wereestimated using an allometric relationship between dry weight,height and diameter of harvested shoots. A large decrease inshoot density occurred with stand development from the beginningof the growing season in both the years: (1) shoot survivalrate was about 30% at the end of the growing season; (2) shootmortality rate per 10 x 10 cm subplot between censuses was positivelydependent on shoot density per subplot; (3) the mortality rateof individual shoots was negatively dependent on shoot size(height, diameter and weight) at each growing stage, suggestingone-sided competition between living and dying shoots; (4) shootsize (height, diameter and weight) variability in terms of thecoefficient of variation and skewness decreased in accordancewith shoot mortality. Symmetric competition between living shootswas detected by regression analysis based on a model for individualshoot growth considering the degree of competitive asymmetry.However, the competitive effect on individual shoot growth wasvery small (nearly absent). The mortality pattern of Urticadioica indicates that shoot self-thinning occurred from theearly growing stage as in non-clonal crowded monospecific stands,and contrasts with many clonal plants where shoot self-thinningrarely occurs or, if any, is confined only to a short periodof the later growing stage. The pattern of growth and competitionbetween living shoots of Urtica dioica contrasts with non-clonalcrowded plants undergoing intense competition (usually asymmetric)between individuals, but is a common feature of many clonalplants where shoot competition is supposed to be reduced by'physiological integration' between shoots. These form a newpattern not reported yet for clonal plants. It is pointed outthat clonal plants show a wider spectrum of the growth, competitionand mortality patterns of shoots than non-clonals. Some possiblemechanisms for the pattern of Urtica dioica are discussed.Copyright1995, 1999 Academic Press Shoot competition, diffusion model, individual shoot growth, shoot self-thinning, shoot size variability, Urtica dioica L     

Thidiazuron: an efficient plant growth regulator for enhancing <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation in <Emphasis Type="Italic">Petunia hybrida</Emphasis>

Efficient shoot regeneration and Agrobacterium-mediated genetic transformation systems were developed for Petunia hybrida cv. Mitchell. Leaf explants of petunia were cultured on Murashige and Skoog (MS) medium with different concentrations of thidiazuron (TDZ) without auxin. The highest frequency of shoot regeneration (52.1%) and mean number of shoots per explant (4.1) were obtained on medium containing 2 mg l^?1 TDZ. Leaf explants inoculated with Agrobacterium tumefaciens strain EHA101/pIG121Hm harboring ß-glucuronidase (uidA) and hygromycin resistance genes developed putative transformant shoots. The highest frequency of shoot regeneration (22.5%) and mean number of transformant shoots per explant (2.4) were obtained on a selection medium consisting of the above described regeneration medium and containing 25 mg l^?1 hygromycin as the selection agent. Approximately 95% of putative transformant shoots expressed the uidA gene following histochemical ß-glucuronidase (GUS) assay. These were confirmed to be transgenic by PCR analysis and Southern blot hybridization.     

Factors Influencing the Tissue Culture and the Agrobacterium tumefaciens-Mediated Transformation of Hybrid Aspen and Poplar Clones

Tissue culture conditions and transformation have been established for both aspen and poplar. The use of previously described culture conditions resulted in shoot tip necrosis in the shoot cultures and necrosis of stem and leaf explants. Shoot tip necrosis could be overcome by buffering the medium with 2-(N-morpholino)ethanesulfonic acid and Ca-gluconate and by growing the shoots below 25°C. Necrosis of the explants was probably due to an accumulation of ammonium in the explants and could be overcome by adapting the NO₃⁻/NH₄⁺ ratio of the media. Stem explants of established shoot cultures of the aspen hybrid Populus alba × P. tremula and of the poplar hybrid Populus trichocarpa × P. deltoides were cocultivated with Agrobacterium strains having chimeric bar and neo genes on their disarmed tDNAs. Transformed aspen shoots were obtained from 30 to 40% of the explants, while transformed poplar shoots were obtained from 10% of the explants. Extracts from the transformed trees contained high phosphinotricin acetyltransferase and neomycin phosphotransferase activities, and the trees contained one to three copies of the chimeric genes. The transformed trees were completely resistant to the commercial preparations of the herbicide phosphinotricin (glufosinate), while control trees were not.     

Shoot growth dynamics and the mode of competition of two rhizomatousPolygonum species in the alpine meadow of Mt. Fuji

The growth dynamics of shoot populations and the mode of competition between intra-clonal shoots of two rhizomatous species,Polygonum cuspidatum andPolygonum weyrichii, were investigated at the Houei crater (c. 2380 m a.s.l.) of Mt. Fuji. Three genetic individuals ofP. cuspidatum (large, medium and small) and five genetic individuals ofP. weyrichii were selected for this research. The growth dynamics of shoot populations were analysed using the diffusion model. InP. cuspidatum, linearG(t,x) functions (mean of absolute growth rates of shoots of sizex at timet in the diffusion model) with positive slopes were found in terms of shoot weight in three genetic individuals. The linearG(t,x) functions suggest that smaller-sized shoots were supported by means of physiological integration and not suppressed by larger-sized shoots. As in other clonal plant species, size-independentD(t,x) functions (variance of absolute growth rates of shoots of sizex at timet in the diffusion model) were found inP. cuspidatum. A similar tendency was also found in the five genetic individuals ofP. weyrichii. There was large variance of RGR in terms of shoot weight irrespective of values ofC _r(t,x), defined as (total leaf area of shoots larger thanx at timet/total leaf area of all shoots), in both thePolygonum species. This means that there was a higher probability of growth for smaller shoots, suggesting that competition between shoots was symmetric (two-sided) in bothP. cuspidatum andP. weyrichii.     

Effects of shoot bending of apple trees on accumulation and translocation of14C-labelled assimilates

The translocation of¹⁴C-labelled assimilates from a single leaf in bent and intact apple shoots was studied in varying stages of shoot development. In actively growing shoots¹⁴C-labelled assimilates translocated from the treated leaf and accumulated mainly in the shoot apex. In moderately growing apple shoots radioactive assimilates were translocated from the treated leaf in both directions towards and down the shoot. In apple shoots showing only slight growth activity the¹⁴C-labelled assimilates were transported from the treated leaf mainly to the base of the shoot, stem and roots. Bending shoots changed the pattern of distribution of radioactive assimilates. Bending actively and moderately growing shoots resulted in higher concentration of 14-carbon in the shoot apex than in controls. In slowly growing and non-growing apple shoots bending caused a higher accumulation of radioactive assimilates in the bent section than in an equal section of control shoots.