PHLOEM ANATOMY OF THE CARBONIFEROUS COENOPTERID FERNS ANACHOROPTERIS AND ANKYROPTERIS

Phloem histology in the petioles of two genera of Pennsylvanian ferns is detailed from coal balls collected at various localities in North America. Both Ankyropteris and Anachoropteris have primary phloem that completely surrounds the central xylem trace and is separated from it by a parenchymatous sheath. Ankyropteris contains very narrow (about 13.5 μm diam) sieve elements and a few strands of phloem parenchyma. End walls are either horizontal or slightly oblique and sieve areas as well as scattered individual pores have been observed. Anachoropteris phloem contains two different sizes of sieve elements. Small sieve elements that surround the C-shaped trace are similar to those seen in Ankyropteris. Larger elements (approximately 50–120 μm in diam) are present only within the C-shaped trace, and are elongate (up to 2.5 mm) with very oblique end walls. Sieve areas on these large cells are conspicuous, 5–8.5 μm in diam and aggregated into groups. The cell wall within each sieve area appears to be composed of criss-crossed fibrillar material. Phloem anatomy in these two ferns is compared to that previously described in other Carboniferous vascular cryptogams, as well as that known from extant plants.     

THE PHLOEM OF ETAPTERIS LECLERCQII AND BOTRYOPTERIS TRIDENTATA

The phloem of Etapteris leclercqii and Botryopteris tridentata petioles is described from Lower Pennsylvanian coal balls. Petioles of B. tridentata are characterized in transverse section by an omega-shaped xylem trace, a phloem zone which extends from 2-10 cells in width, and 2-parted cortex. Etapteris leclercqii petioles exhibit a 4–9 cell-wide phloem zone surrounding the central clepsydroid xylem mass, and a 3-parted cortex. In both taxa a 1–2 cell layer parenchyma sheath separates the xylem from the extra-xylary tissues. The phloem of both species consists of sieve elements that average about 20 μm in diam by 200 μm in length in Botryopteris, and 100 μm in length in Etapteris, with horizontal-slightly oblique end walls. In transmitted light, the radial walls of the sieve elements form an irregular reticulate pattern enclosing elliptical lighter areas. With the scanning electron microscope, these areas appear as horizontal-slightly oblique furrows on the cell wall, with many small indentations lining the furrows. These indentations, because of their regular occurrence and size (from a few fractions of a micron up to 1.0 μm in diam), are interpreted as sieve pores, and the elliptical areas that enclose them as sieve areas. The phloem of E. leclercqii and B. tridentata is compared with that described for other fossil genera and with that of extant ferns.     

Ricerche Sull'infrastruttura del Coleottile di Avena

Abstract

Researches on ultrastructure of Avena coleoptile. 3. The sieve elements. — A study on the ultrastructural organization of the mature sieve elements of Avena coleoptile has been carried out. Data suggest that functional phloem tubes are alive and remain alive until they are working. Judging on morphological basis, the metabolic activity of sieve elements should be of peculiar type and low in comparison to that of the companion cells. In fact the cytoplasm is located in a narrow parietal strand, mitochondria, Golgi apparatus and endoplasmic reticulum are present, but they appear very modified; plastids and nucleus are absent. The cytoplasm is bounded externally by a normal plasmalemma, whilst the vacuole has no visible limits: a tonoplast is, therefore not identifiable.

The strands connecting the superimposed sieve elements with one another through the sieve plate result to be made by a double membrane system very similar to the endoplasmic reticulum, which we believe to realize cytoplasmic continuity between phloem tubes.

The data reported are more favorable to the existence in the sieve tubes of an active mechanism of translocation of organic solutes than a passive mass-flow.

The collaboration of companion cells in the translocation mechanism has been discussed.     

Ectoenzymes in Prorocentrum minimum

Ectoenzymes, or enzymes associated with the cell-surface or periplasmic space, play an important role in organic matter cycling by rendering certain forms of dissolved organic matter bioavailable. Ectoenzyme activities may thereby help meet the nutritional demands of harmful algae such as Prorocentrum minimum. The activities of two ectoenzymes; leucine aminopeptidase and alkaline phosphatase, have been studied in axenic cultures of P. minimum. Leucine aminopeptidase releases non-polar amino acids such as leucine from the N-terminus of polypeptides, whereas alkaline phosphatase is an enzyme that is able to hydrolyze phosphate from phosphomonoesters. P. minimum alkaline phosphatase is the better studied of the two ectoenzymes and its characteristics are reviewed herein. Future research on P. minimum physiology will benefit from a growing suite of tools available for assessing the activity of alkaline phosphatase and other ectoenzymes in field populations and ultimately the work done with P. minimum will be useful for studies of other harmful species.     

OBSERVATIONS ON SIEVE ELEMENTS IN THREE PERENNIAL MONOCOTYLEDONS

Seasonal collections were made of rhizomes of Polygonatum canaliculatum and Typha latifolia and of aerial stems of Smilax hispida. Many metaphloem sieve elements in all three species remain functional for 2 or more years, or for the life of the plant parts in which they occur. Although the protoplasts of mature sieve elements remain similar in appearance from one time of year to the next, the amount of callose associated with the sieve plates and lateral sieve areas of such cells apparently varies with the seasons, being heavier in late fall and winter and lighter in late spring and summer. At maturity the metaphloem sieve elements contain strands derived from the slime bodies of immature cells. It is suggested that in mature sieve elements the slime strands normally occur as a network along the wall. Many mature sieve elements of S. hispida contained normal-appearing nuclei.     

THE LATERAL MERISTEM AND ITS DERIVATIVES IN THE CORM OF ISOETES MURICATA

Corm tissue of Isoetes muricata Dur. was fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. Very young secondary sieve elements can be distinguished from contiguous cambial cells by their distinctive plastids and by the presence of crystalline and/or fibrillar proteinaceous material in dilated cisternae of rough endoplasmic reticulum (ER). At maturity, the sieve elements are lined by the plasmalemma and a parietal, anastomosing network of smooth ER. Degenerate nuclei persist in all mature sieve elements. In addition, mature sieve elments contain plastids and mitochondria. Sieve-area pores are present in all walls. The lateral meristem of I. muricata consists of 2–3 layers of cells year-round. Judging from numerous collections made between October 1972 and July 1975, new sieve-element differentiation precedes cambial activity by about a month. Early in May, 1–2 cells immediately adjacent to already mature sieve elements differentiate directly into sieve elements without prior division. In early June, at about the time sieve-element differentiation is completed, cambial division begins. Division is sporadic, not uniform throughout the meristem. Dormancy callose accumulates in the secondary sieve elements in late October, and is removed in early May, at about the same time new sieve-element differentiation begins. Cells of the dormant cambium are characterized by the presence of numerous small vacuoles and large quantities of storage materials, including lipid droplets, starch grains, and tannin. By contrast, active cambial cells contain few large vacuoles with little or no tannin, and they have little storage material.     

Helmet‐shaped Body of Entodiniomorphid Ciliates (Ciliophora,Entodiniomorphida), a Synapomorphy or a Homoplasy?

Triadinium was created to include Triadinium caudatum. Further, four other species were included, T. minimum, T. galea, T. elongatum, and T. magnum, all sharing a characteristic helmet‐shaped body. Wolska and Grain argued that the inclusion of T. minimum and T. galea into Triadinium was done based on superficial morphological aspects, and established two new genera to accommodate these species: Circodinium and Gassovskiella. Although the phylogenetic relationships within Entodiniomorphida have been investigated by multiple authors, none of them discussed the evolutionary relationship of helmet‐shaped entodiniomorphids. We performed molecular phylogenetics and revisited old literature digging for morphological data to explain our results. According to our analyses, the helmet‐shaped body is homoplastic and may have evolved from at least three different entodiniomorphid ancestors. Circodinium minimum is phylogenetically related to members of Blepharocorythidae, T. caudatum emerged within Spirodiniidae and G. galea within Polydiniellidae. This phylogenetic hypothesis is partially supported by information on infraciliature and ultrastructure of C. minimum and T. caudatum. However, such morphological information is not available for polydiniellids. In order to shed some light into the evolution of the helmet‐shaped ciliates, future works should focus to collect information on the infraciliature and the ultrastructure of Polydiniella mysorea and of other Triadinium species.     

Proliferating sieve elements present in bud phloem anastomoses connect sieve tubes of axillary bud traces to stelar vascular bundles in the aquatic monocotyledonPotamogeton natans L. (Potamogetonaceae)

Summary The stem ofPotamogeton natans is characterized by a central stelar vascular system with reduced xylem and abundant phloem. Wide sieve tubes composed of short sieve-tube members joined by simple sieve plates and associated with companion cells establish an effective conduit for assimilates. At each node the phloem forms a network of parallel sieve elements connecting the stem phloem to leaf and bud traces. InP. natans an axillary bud rarely develops into a side branch, its procambial vascular bundles are each connected to the nodal complex via separate anastomoses. Their most unusual components are the anastomosai sieve elements (ANSE), characterized by thin cell walls pitted all over by tiny callose-lined pores resembling plasmodesmata, which can be detected as bright areas by fluorescence microscopy after staining with aniline blue. Several layers of ANSE make up the centre of an anastomosis and link to both the nodal and bud stelar sieve tubes via mediating (MSE) and connecting sieve elements (CSE). The ultrastructural differentiation of ANSE, MSE, and CSE corresponds to that of normal sieve elements, i.e., in the mature stage they are enucleate, evacuolate, and have lost most of their cytoplasm. Their plastids are of form-P2c, containing many cuneate protein crystals, typical of monocotyledonous sieve elements. Quantitative aspects of the pore areas are discussed in relation to the functional significance of bud anastomoses.Abbreviations ANSE anastomosai sieve elements - CSE connecting sieve elements - FM fluorescence microscopy - LM light microscopy - MSE mediating sieve elements - TEM transmission electron microscopy Dedicated to Professor Dr. Rainer Kollmann on the occasion of his retirement     

Das Phloem der Haustorien vonCuscuta

Summary Haustoria ofCuscuta odorata R. & P. andC. grandiflora H.B.K. show continuous traces of sieve elements, connecting the phloem of the host with that of theCuscuta shoot. The continuity of this haustorial phloem is discernible by callose fluorescence after staining with aniline blue. The fine structural criteria for sieve tubes are analyzed electronmicroscopically, with special respect to sieve pores, P-protein, and a distinct wall-standing smooth surfaced ER. Within the central part of the haustorium sieve tubes are elongated, while the elements abutting the phloem of theCuscuta shoot are nearly isodiametric in shape. Both elements are associated with rather large companion cells, derived from an unequal division.

     

Occurrence of Mycoplasma-like Organisms in Parenchyma Cells of Cuscuta odorata (Ruiz et Pav.)

In shoots of the dodder Cuscuta odorata mycoplasma-like organisms (MLO) were observed to occur in nearly all mature sieve elements. Their frequency within the sieve elements varied from a few organisms to high concentrations. In addition, MLO, were found in other cell types. By identifying these cells and investigating the location in the vascular tissue three different types of cells infected with MLO could be distinguished: (1) phloem parenchyma cells, (2) parenchyma cells separating the five vascular bundles of C. odorata and (3) cells in the outer region of the vascular system next to the cells looking like an endodermis. Within the cells of the types 2 and 3, MLO occurred in large numbers and at different morphological structures., Therefore, we assume that the MLO multiply in these cells.     

Effects of natural and field-simulated blooms of the dinoflagellate Prorocentrum minimum upon hemocytes of eastern oysters, Crassostrea virginica, from two different populations

Oysters, Crassostrea virginica, from two populations, one from a coastal pond experiencing repeated dinoflagellate blooms (native), and the other from another site where blooms have not been observed (non-native), were analyzed for cellular immune system profiles before and during natural and simulated (by adding cultured algae to natural plankton) blooms of the dinoflagellate Prorocentrum minimum. Significant differences in hemocytes between the two oyster populations, before and after the blooms, were found with ANOVA, principal components analysis (PCA) and ANOVA applied to PCA components. Stress associated with blooms of P. minimum included an increase in hemocyte number, especially granulocytes and small granulocytes, and an increase in phagocytosis associated with a decrease in aggregation and mortality of the hemocytes, as compared with oysters in pre-bloom analyses. Non-native oysters constitutively had a hemocyte profile more similar to that induced by P. minimum than that of native oysters, but this profile did not impart increased resistance. The effect of P. minimum on respiratory burst was different according to the origin of the oysters, with the dinoflagellate causing a 35% increase in the respiratory burst of the native oysters but having no effect on that of the non-native oysters. Increased respiratory burst in hemocytes of native oysters exposed to P. minimum in both simulated and natural blooms may represent an adaptation to annual blooms whereby surviving native oysters protect themselves against tissue damage from ingested P. minimum.     

Selective Control of the Prorocentrum minimum Harmful Algal Blooms by a Novel Algal-Lytic Bacterium Pseudoalteromonas haloplanktis AFMB-008041

In this study, we examined the algal-lytic activities and biological control mechanisms of Pseudoalteromonas haloplanktis AFMB-08041, which was isolated from surface seawater obtained at Masan Bay in Korea. In addition, we assessed whether AFMB-08041 could be used as a biocontrol agent to regulate harmful dinoflagellate Prorocentrum minimum. From these experiments, we found that the inoculation of AFMB-08041 at a final density of 2.5 × 10⁴ cfu ml⁻¹ caused P. minimum cells to degrade (>90%) within 5 days. The algal cells were lysed through an indirect attack by the AFMB-08041 bacterial strain. Our results also suggest that the algal-lytic compounds produced by AFMB-08041 may have β-glucosidase activity. However, P. haloplanktis AFMB-08041 was not able to suppress the growth of other alga such as Alexandrium tamarense, Akashiwo sanguinea, Cochlodinium polykrikoides, Gymnodinium catenatum, and Heterosigma akashiwo. Moreover, we observed that the growth of Prorocentrum dentatum, which has a very similar morphological structure to P. minimum, was also effectively suppressed by P. haloplanktis AFMB-08041. Therefore, the effect of AFMB-08041 on P. minimum degradation appears to be species specific. When testing in an indoor mesocosms, P. haloplanktis AFMB-08041 reduced the amount of viable P. minimum cells by 94.5% within 5 days after inoculation. The combined results of this study clearly demonstrate that this bacterium is capable of regulating the harmful algal blooms of P. minimum. In addition, these results will enable us to develop a new strategy for the anthropogenic control of harmful algal bloom-forming species in nature.     

FACTS AND MECHANISMS: A COMPARATIVE SURVEY

1. This review aims to survey the process of translocation of solutes in the phloem, including the experimental observations of the process, hypothetical mechanisms with their consequences, and the compatibility of these mechanisms with the experimental information. 2. Some properties of the sieve elements are summarized. The characteristic constituent of the sieve elements is a fibrillar protein, P-protein, of 60–120 A. filaments, whose function and distribution in intact sieve elements are still the subject of debate. 3. Apart from the very high levels of sucrose (0.3–0.9 m) and of specific amino acids and amides (10–100 mm), the contents of the sieve elements are characterized by close regulation of the ionic content; thus K (20–85 ^mM) and Mg (2.3–23 mM) are very high relative to Na (0.06–0.3 mM) and Ca (0.25–0.5 mM) respectively; the pH is also very high. 4. Convective movement (mass flow) is demanded by the very high rates of mass transfer. The longitudinal sucrose flux is about 2.5 times 10⁶ pmoles cm.^-2 sec.^-1 in petioles, and several times higher in fruits or trees; this is about 10⁵ times any reasonable transmembrane flux, and demands very large loading areas for each file of sieve elements. It also renders unlikely any mechanism demanding an associated trans-membrane flux of any solute which approaches within several orders of magnitude of the sucrose flow. 5. The evidence from tracer measurements (of ¹⁴C or of heat) favour a mass flow of some kind in the sieve tube, with only restricted exchange between the flowing stream and other sucrose pools in the phloem (or out of it). It is not consistent with ready equilibration with a large stationary reservoir of sucrose, or with reverse flows. There is close correspondence between the input and output kinetics of a length of the trans-location path, or of build-up curves at different distances; hence lateral exchange from the moving stream is relatively minor. 6. Tracer measurements show that loading into the translocation stream is relatively slow, and is the main determining factor in the time course of appearance of tracer down the stem, or in the profile of radioactivity against distance in the stem. This applies not only to the initial steep front of radioactivity in the stem, but also to the error function profiles found at longer times in some plants; those do not arise as has been suggested, by exchange in a two-way system of transcellular strands, but are a reflexion of the loading kinetics. 7. The evidence for or against bidirectional movement is equivocal. In conditions in which there is a strong source/sink gradient imposed, the movement of both labelled carbon and heat is consistent with a one-way system, and is difficult to reconcile with two-way movement. However, in the absence of any strong gradient there is evidence for bidirectional movement. It is suggested that the pattern of flow, as well as the direction and rate of flow, may be controlled by the source/sink relations along the path. 8. Electro-osmosis as a mechanism for translocation seems to be ruled out by a number of theoretical difficulties. The most basic of these is the fact that an electro-osmotic mechanism is inherently incapable of the transport of both anions and cations, whereas the phloem can do both. There are further quantitative difficulties. The ratio of sucrose to potassium in the sieve elements is about 10, and if potassium provides the current a longitudinal potassium flux of about 2.5 times 10⁶ pmoles cm.^-2 sec.^-l would therefore be required in petioles, and considerably more in fruits or trees. This raises very great difficulties of potassium circulation to provide a complete current loop, in the path of recirculation, the size of the transmembrane fluxes required, and the energetics of pumping enough potassium to maintain the driving force for electro-osmosis. 9. Possibilities of activated mass flow, by a mechanism similar to that involved in protoplasmic streaming are discussed. Experimental work on streaming in Nitella and in the slime mould Physarum is reviewed, including the evidence that in both these systems, fibrils, made up of 50–70 Å. filaments, are responsible for the production of the motive force, and that these fibrils are akin to actomyosin. 10. Possible ways in which fibrillar P-protein might be organized in the sieve elements to produce translocation are discussed. The force generated by Nitella-type filaments at the density of P-protein in phloem exudate would be more than adequate for the observed rates of flow. Alternatively the fibrillar arrangement in the slime mould is capable of producing volume flows as large as those in phloem. This hypothesis provides a function for P-protein, and is also consistent with the curious ionic concentrations characteristic of sieve elements. 11. It is suggested that the control by the source/sink relations of the pattern, rate and direction of flow in the phloem might be achieved by the orientation of force-generating microfilaments by a Münch-type flow. Such a flow is inevitable if sucrose is pumped in at one end of the path and removed at the other; it seems to be inadequate to explain the rates of mass transfer, but it might be responsible for inducing the correct orientation and polarity in the motive force.     

P-Protein in sieve elements

Summary The ultrastructure of P1 and P2 proteins in the sieve elements of Heracleum mantegazzianum is described. P1-protein tubules are closely associated with stacks of membranes, are often linked by short cross-bridges, and occasionally display a hexagonal packing. Incubation with the alkaloids vinblastine and colchicine had no discernible effects on the ultrastructure of the sieve elements at various stages during differentiation. Evidence for and against any similarities between P1-protein tubules and cytoplasmic microtubules is discussed.     

COMPARATIVE LEAF STRUCTURE OF SEVERAL SPECIES OF HOMOSPOROUS LEPTOSPORANGIATE FERNS

The structure of the mature leaves of 13 species from 9 families of homosporous leptosporangiate ferns was examined by light and electron microscopy. In 11 species (Adiantum pedatum L., Athyrium angustum Roth., Cyathea dregei Sm., Lygodium palmatum Sw., Mohria caffrorum (L.) Desv., Oleandra distenta Kuntae, Pellaea calomelanos (Sw.) Link, Pityrogramma calomelanos (L.) Link var. austro-americana (Domn.) Farw., Trichomanes melanotrichum Schlechtend., Vittaria guineensis Desv., and Woodwardia orientalis Sw.) the lamina veins are collateral; in two (Phlebodium aureum and Platycerium bifurcatum), bicollateral as well as collateral veins are present. The vascular bundles in the midribs of C. dregei and those in the petioles and midribs of Phlebodium and Platycerium are concentric. All of the vascular bundles in the homosporous leptosporangiate ferns studied are delimited by a tightly arranged cylinder of endodermal cells with Casparian strips. Within the veins without parenchymatic xylem sheaths, some sieve elements commonly abut tracheary elements with hydrolyzed primary walls. The majority of vascular parenchyma cells contact both sieve elements and tracheary elements, although some parenchyma cells are associated with only one type of conducting cell. Transfer cells (parenchyma cells with wall ingrowths) occur in the veins of 6 species examined. Most of the vascular parenchyma cells, however, have no distinctive structural characteristics. The sieve elements of the homosporous leptosporangiate ferns are very similar structurally and each consists of a plasmalemma, a parietal, anastomosing network of smooth endoplasmic reticulum (ER), and variable numbers of refractive spherules, plastids and mitochondria. The sieve elements of L. palmatum also contain plasmalemma tubules. The parenchymatic cells of the leaf (mesophyll, endodermal and vascular parenchyma cells) are united by desmotubule-containing plasmodesmata. The sieve elements are connected to each other by sieve pores and to parenchymatic cells by pore-plasmodesma connections. The sieve-area pores contain variable amounts of membranous material, apparently ER membranes, but do not occlude them. These membranes commonly are found in continuity with the parietal ER of the lumen. Based upon the relative frequencies of cytoplasmic connections between cell types, the photosynthates may move from the mesophyll to the site of phloem loading via somewhat different pathways in different species of homosporous leptosporangiate ferns.     

STRUCTURE AND DEVELOPMENT OF THE SIEVE ELEMENT IN THE STEM OF LYCOPODIUM LUCIDULUM

Stem tissue of Lycopodium lucidulum Michx. was fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. Although their protoplasts contain similar components, immature sieve elements can be distinguished from parenchymatous elements of the phloem at an early stage by their thick walls and correspondingly high population of dictyosomes and dictyosome vesicles. Late in maturation the sieve-element walls undergo a reduction in thickness, apparently due to an “erosion” or hydrolysis of wall material. At maturity, the plasmalemma-lined sieve elements contain plastids with a system of much convoluted inner membranes, mitochondria, and remnants of nuclei. Although the endoplasmic reticulum (ER) in most mature sieve elements was vesiculate, in the better preserved ones the ER formed a tubular network closely appressed to the plasmalemma. The sieve elements lack refractive spherules and P-protein. The protoplasts of contiguous sieve elements are connected with one another by pores of variable diameter, aggregated in sieve areas. As there is no consistent difference between pore size in end and lateral walls these elements are considered as sieve cells.     

A review and new analysis of trophic interactions between Prorocentrum minimum and clams, scallops, and oysters

There has been no consensus on whether Prorocentrum minimum is “toxic,” despite sporadic reports suggesting possible shellfish toxicity and laboratory studies showing harmful effects of this dinoflagellate on molluscan shellfish. Shellfish toxicity outbreaks associated with natural blooms of P. minimum have been confounded by co-occurrence of other toxic phytoplankton. Laboratory studies have demonstrated unequivocally that some P. minimum isolates can produce toxins that kill mice on injection, but the bioactive compound or compounds remain unidentified, and accumulation of toxin in grazing mollusks has not been demonstrated. Laboratory experiments testing the responses of grazing mollusks to P. minimum cultures have yielded variable results, ranging from mortality in scallops and oysters to normal growth of oysters. Effects observed in the laboratory include rejection as pseudofeces by clams, poor larval development in oysters, tissue pathologies (sometimes transient) in oysters and scallops, and systemic immune responses in oysters and scallops. Several recent studies have provided evidence that variation in toxicity of P. minimum is dependent on environmental conditions and their effects on the physiology of this dinoflagellate. Accordingly, seemingly conflicting observations from field and laboratory studies may be explained by transient toxin expression in P. minimum.     

Inducible Mixotrophy in the Dinoflagellate Prorocentrum minimum

Prorocentrum minimum is a neritic dinoflagellate that forms seasonal blooms and red tides in estuarine ecosystems. While known to be mixotrophic, previous attempts to document feeding on algal prey have yielded low grazing rates. In this study, growth and ingestion rates of P. minimum were measured as a function of nitrogen (‐N) and phosphorous (‐P) starvation. A P. minimum isolate from Chesapeake Bay was found to ingest cryptophyte prey when in stationary phase and when starved of N or P. Prorocentrum minimum ingested two strains of Teleaulax amphioxeia at higher rates than six other cryptophyte species. In all cases ‐P treatments resulted in the highest grazing. Ingestion rates of ‐P cells on T. amphioxeia saturated at ~5 prey per predator per day, while ingestion by ‐N cells saturated at 1 prey per predator per day. In the presence of prey, ‐P treated cells reached a maximum mixotrophic growth rate (μ_max) of 0.5 d^?1, while ‐N cells had a μ_max of 0.18 d^?1. Calculations of ingested C, N, and P due to feeding on T. amphioxeia revealed that phagotrophy can be an important source of all three elements. While P. minimum is a proficient phototroph, inducible phagotrophy is an important nutritional source for this dinoflagellate.     

Spatial and temporal regulation of the forisome gene <Emphasis Type="Italic">for1</Emphasis> in the phloem during plant development

Forisomes are protein aggregates found uniquely in the sieve elements of Fabaceaen plants. Upon wounding they undergo a reversible, calcium-dependent conformational switch which enables them to act as cellular stopcocks. Forisomes begin to form in young sieve elements at an early stage of metaphloem differentiation. Genes encoding forisome components could therefore be useful as markers of early sieve element development. Here we present a comprehensive analysis of the developmental expression profile of for1, which encodes such a forisome component. The for1 gene is highly conserved among Fabaceaen species and appears to be unique to this phylogenetic lineage since no orthologous genes have been found in other plants, including Arabidopsis and rice. Even so, transgenic tobacco plants expressing reporter genes under the control of the for1 promoter display reporter activity exclusively in immature sieve elements. This suggests that the regulation of sieve element development is highly conserved even in plants where mature forisomes have not been detected. The promoter system could therefore provide a powerful tool for the detailed analysis of differentiation in metaphloem sieve elements in an unexpectedly broad range of plant species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.