bluuebunny/crossref_metadata_2025 huggingface dataset:
Life History, Reproductive Morphology and Development of the Antarctic Brown Alga Desmarestia menziesii J. Agardh*
Authors: Wiencke C. , Clayton M. N. , Schulz D.
Published: February 2014

The life history, reproduction and development of Desmarestia menziesii J. Agardh from Antarctica is described. Unilocular sporangia occur singly or in small groups in the outermost cortical layer of the sporophyte. They are formed by periclinal division of cortex cells into a stalk cell and the sporangium initial. Meiospores germinate into dioecious microscopic filamentous gametophytes. As in other perennial Antarctic species of the Desmarestiales, gametangia are formed in culture under short‐day conditions or in darkness. In nature, juvenile sporophytes should therefore be formed in winter. They develop only attached to the oogonium. At first they are uniseriate and elongate by means of an intercalary meristem located in their middle part. Laterals are formed predominantly in this region, and they subsequently give rise to secondary laterals. The branching pattern is opposite to alternate in both young and adult plants. Cortication of the main axis is initiated by filaments growing out from the lowermost cells of the primary laterals. In sporophytes of this developmental stage the meristem of the main axis is confined to a small region where cortication starts and above. Lateral branches elongate and become corticated in the same way as the main axis. In mature plants, cells of the inner cortex can become meristematic again and form a meristoderm which contributes to axis thickness by periclinal and anticlinal divisions. The observations are discussed in relation to possible evolutionary relationships in the genus Desmarestia and in the order Desmarestiales.
Epilithic and Cryptoendolithic Cyanobacteria of Clarens Sandstone Cliffs in the Golden Gate Highlands National Park, South Africa
Authors: Wessels D. C. J. , Büdel B.
Published: February 2014

A cryptoendolithic cyanobacterial community is described from Clarens sandstone in a montane ecosystem of the north‐eastern Orange Free State, South Africa. The community is dominated by a species of the unicellular cyanobacterial genus Chroococcidiopsis. Chlorophylla content of the colonised sandstone ranged between 44.3 and 51.8mg m−2. The establishment and species composition of an artificially created tintenstrich cyanobacterial community is documented. The possible contribution of cryptoendolithic cyanobacterial communities in the biological formation of hollows and caves in Clarens sandstone cliffs is discussed.
Adverse Effects of Epiphytic Crustose Lichens upon Stem Photosynthesis and Chlorophyll of Populus tremula L.
Authors: Solhaug K. A. , Gauslaa Y. , Haugen J.
Published: February 2014

Dry cork layer (phellem) in stems of Populus tremula transmitted 35–55 percent of incident irradiation, depending upon moisture content. A cover of crustose Lecanora lichens reduced transmission through phellem to 10 percent or less of incident irradiation. The bark contains photosynthetically active cells. Apparent quantum yield for photosynthetic O2‐evolution was 0.017 in bark covered with dry Lecanora compared with 0.070 in naked bark. The capacity for gross photosynthesis in high light (1090 μmol photons m−2 s−1) was reduced by 50 percent in Lecanora‐covered bark. Lecanora did not reduce the ratio between variable and maximal chlorophyll a fluorescence (Fv/Fm). Chlorophyll content per unit area was similar in leaves and naked bark of Populus tremula. The chlorophyll content in the bark decreased with increasing chlorophyll content in Lecanora. Chlorophyll a/b ratio was 2.5 in the bark compared with 4.0 in leaves and in Lecanora, and the ratio decreased down the stems. The a/b ratio was 2.3 in Lecanora covered bark compared with 2.6 in naked bark. The changes in bark photosynthesis below a Lecanora crust were probably due to acclimation of bark photosynthesis to shade, since the lichen acids in the measured lichens neither suppressed photosynthetic O2‐evolution nor changed the Fv/Fm in bark disks.
Differential Effects of Abscisic Acid on Phosphoenolpyruvate Carboxylase and CAM Operation in Kalanchoë blossfeldiana
Authors: Taybi T. , Sotta B. , Gehrig H. , Güçlü S. , Kluge M. , Brulfert J.
Published: February 2014

Photoperiodism or water stress can shift young leaves of Kalanchoë blossfeldiana from C3‐type photosynthesis to Crassulacean acid metabolism (CAM). CAM induction implies synthesis of phosphoenolpyruvate carboxylase (EC 4.1.1.31, PEPC). Present results show that, in plants as well as in isolated leaves, an increase in endogenous levels of abscisic acid (ABA) preceded PEPC increase, independently of the nature of the CAM inductive parameter.

Exogenously applied ABA was taken up and accumulated by isolated leaves to a level similar to the internal ABA concentration in the leaf tissues. Both in entire plants and in isolated leaves, exogenous ABA mimicked the effects of water stress or short days in triggering PEPC capacity. Using a heterologous cDNA probe (derived from Sorghum leaf PEPC gene) it could be shown that an early step of the leaf response to drought or ABA treatment consisted in an increase in the amount of PEPC transcripts. Depending on the duration of ABA application, C3 photosynthesis, typical CAM or CAM‐idling could be triggered in isolated leaves. In each case, similar increases in PEPC capacity (maximum extractable activity) were obtained, suggesting that the type of photosynthesis performed by the leaves is not controlled by the level of the PEPC capacity. The results suggest that the photosynthetic behaviour of the leaves is primarily governed by the progressive drop in availability of external carbon caused by the ABA‐controlled closure of the stomata. Effects of ABA on PEPC synthesis proceed independently of CAM performance.
Mobilization of Starch after Submergence of Air‐Grown Rice Coleoptiles. Implications for Growth and Gravitropism
Authors: Kutschera U. , Hoss R.
Published: February 2014

Submergence of air‐grown rice seedlings (Oryza sativa L. var. Sasanishiki) induces elongation of the coleoptile. We investigated whether rapid underwater extension is associated with a loss of starch. After 1 d of submergence the starch content was reduced by 70%. This loss of reserve carbohydrate was accompanied by a 38% increase in the concentration of glucose in the cell sap of the coleoptiles. The submerged (starch‐depleted) coleoptiles had a slower negative gravitropism than the air‐grown controls, although the rate of elongation in the horizontal position was not impaired. We conclude that the submergence‐induced mobilization of starch provides substrates and osmotica for the rapidly growing cells. In addition, our results indicate that a full complement of starch is necessary for normal gravitropism in the rice coleoptile.
Further Studies of the Phloem Loading Process in Leaves of Barley and Spinach. The Comparison of Metabolite Concentrations in the Apoplastic Compartment with those in the Cytosolic Compartment and in the Sieve Tubes1
Authors: Lohaus Gertrud , Winter Heike , Riens Burgi , Heldt H. W.
Published: February 2014

The concentrations of sucrose, amino acids, nitrate and malate in the apoplastic compartment of illuminated leaves of barley and spinach were determined and compared with the corresponding concentrations in the cytosolic compartment of mesophyll cells and in the phloem sap, as measured previously with plants grown under identical conditions. The concentrations of sucrose and amino acids in the apoplast are found to be much lower than in the cytosol and in the phloem sap, indicating that not only the uptake into the phloem of sucrose, but also of amino acids, requires transport against a concentration gradient. The gradient of sucrose and amino acids between the cytosol and the apoplast was maintained when phloem transport had been blocked by cold girdling. Apparently, the efflux of sucrose and amino acids from the source cells to the apoplast is regulated in such a way that it meets the requirements of phloem transport. The percentages of the single amino acids as part of the total amino acids are quite similar in the cytosol, apoplast and phloem sap. The ratio of sucrose to the total amino acids in the cytosol is similar to that in the apoplast but about five times higher in the phloem sap. It appears from these results that the preferential extraction of sucrose over amino acids from the source cells to the phloem is due to the uptake from the apoplast into the phloem.
Different Patterns of Intercellular Transport of Lucifer Yellow in Young and Mature Antheridia of Chara vulgaris L.
Authors: Maszewski J. , van Bel A. J. E.
Published: February 2014

Intra‐ and intercellular movement of the fluorochrome Lucifer Yellow (LY), microinjected into the shield cells of male sex organs, was examined at different stages of spermatogenesis in Chara vulgaris L. Two distinct stage‐associated types of probe movement were noted: (I) a fast and uniform spreading of fluorescence within the shield cell injected, followed by centripetal transport of LY into the adjoining manubrium and the capitular cells, and subsequent redistribution into the other manubria and shield cells in young antheridia (up to the stage of 4‐cellular filaments), and (II) limited spreading of fluorescence, restricted to the triangle‐shaped area of the impaled shield cell in more mature antheridia with multicellular filaments. These results confirm earlier electron microscopic observations on plasmodesmatal connections indicating an intensive solute movement between all cell types in young antheridia of Chara. Developmental changes appearing at later stages, during differentiation of sperm cells, strongly reduce the capacity for intercellular symplasmic transport.
Oxidative Stress Responses Accompanying Photoinactivation of Catalase in NaCI‐treated Rye Leaves
Authors: Streb P. , Feierabend J.
Published: February 2014

When segments of rye leaves (Secale cereale L.) grown at 90 μmol m−2 s−1 PAR were incubated at a higher photon flux of 400–500 μ mol m−2 s−1 PAR in the presence of 0.2‐0.6 M NaCl, a preferential loss of catalase activity was induced. The extent of this decline increased with the concentration of NaCl. In addition, the accumulation of alternative antioxidative components, such as ascorbate, glutathione, glutathione reductase, or peroxidase, was inhibited. The total content of H2O2 was, however, lower in catalase‐depleted than in untreated control leaves. The occurrence of strong oxidative stress in NaCl‐treated leaves was indicated by marked declines in the ratios of reduced to oxidized ascorbate and glutathione and by the degradation of chlorophyll in light. The specific elimination of catalase activity by the inhibitor aminotriazole was also accompanied by a rapid decline in the ratio of reduced to oxidized glutathione but other symptoms of oxidative stress were much less severe than in the presence of NaCl. However, all symptoms of photooxidative damage seen in NaCl‐treated leaves were closely mimicked by treatment with the translation inhibitor, cycloheximlde, in light. The results suggest that NaCl‐induced oxidative damage in light was predominantly mediated by the inhibition of protein synthesis. By this inhibition the resynthesis of catalase, which has a high turnover in light, was blocked and the leaves were thus depleted of catalase activity and, in addition, the intensification of alternative antioxidative systems was also prevented.
Phylogenetic Relationships between some Members of the Subfamily Lamioideae (Family Labiatae) Inferred from Nucleotide Sequences of the rbcL Gene*
Authors: Wink M. , Kaufmann Martina
Published: February 2014

Total DNA was extracted from 25 species (8 genera) of the subfamily Lamioideae sensu Erdtman (family Labiatae). Using rbcL‐specific primers, the rbcL gene was amplified by polymerase chain reaction (PCR) and 1420 bp were sequenced directly, or after cloning. RbcL sequences were evaluated with character‐state (maximum parsimony; PAUP) and distance methods (neighbour‐joining; MEGA). In agreement with classical systematics all taxa studied cluster outside the Nepetoideae. The following clades are apparent: I ‐ Westringia/Prostanthera, II ‐ Ajuga/Teucrium and III ‐ Scutellaria, Stachys, Lamium and Marrubium. Lamium album, L. amplexicaule and L. garganicum appear as a sister clade to Marrubium. Both share a common ancestor with a second Lamium clade (including L. purpureum, L. maculatum and L. galeobdolon). The phylogenetic relationships are discussed with regard to the systematic classification of the subfamilies Lamioideae and Nepetoideae (sensu Erdtman).
Ecology and Morphology of Blossfeldia liliputana (Cactaceae): a Poikilohydric and almost Astomate Succulent*
Authors: Barthlott W. , Porembski St.
Published: February 2014

Plants of the monotypic Blossfeldia liliputana have the smallest bodies of all Cactaceae. The button‐like plants with a diameter of usually some 10 mm occur in rock crevices in arid regions between S Bolivia and N Argentina. Based on observations and experiments in the field and in cultivation, morphology, anatomy, reproductive biology, certain aspects of ecophysiology, and behaviour under water stress are described. The very small flowers are autogamous; the arillate hairy seeds are unique within the family and represent a particular adaptation to ant dispersal. These CAM‐plants virtually lack stomata: 0.6 stomata/mm2 represents the lowest number in terrestrial autotrophic vascular plants. However, all other xeromorphic features characteristic for globular cacti are absent (e.g. no thickened cuticle, no thickended outer cell walls, no thickened hypodermal layers). These features allow a high degree of desiccation: under water stress the plants lose up to 80% of their weight within one year and can withstand an additional drought of at least another year. Thus Blossfeldia is poikilohydric like many lichens and mosses and represents the unique life form of a succulent resurrection plant.
Functional Morphology of Aztekium ritteri (Cactaceae)
Authors: Porembski St.
Published: February 2014

The dwarf globular cactus Aztekium ritteri shows a high degree of surface differentiation. The stem consists of 8–15 ribs, these in turn being sculptured by transverse furrows: compared with a sphere of equal size, the surface/volume ratio is increased by more than 10‐fold. At the same time, only 20% of the stem surface is exposed to direct sunlight, 80% lying in the shade of its own body, in a system of furrows and crypts. The exposed areas have few stomata and the epidermal cell walls are notably thickened and cutinised. In addition, these form an exoskeleton by means of a hypodermis containing calcium oxalate crystals while the unexposed cell surface regions, hidden in the furrows, lack xeromorphic characters and calcium oxalate crystals. By far the greatest number of stomata are found in the furrows mostly in deep crypts. When dehydration occurs as a consequence of longer periods of drought, the furrows and crypts close together, thereby reducing transpiration losses. The complicated interlocking nature of the surface architecture of Aztekium is discussed in terms of the functional aspects as an adaptation to an extreme habitat (vertical shale cliffs in Nuevo León, Mexico).
Field Studies on Growth and Regenerative Capacity in the Foliose Macrolichen Xanthoria parietina (Teloschistales, Ascomycotina)
Authors: Honegger Rosmarie , Conconiy S. , Kutasi Verena
Published: February 2014

Growth and development of the foliose macrolichen Xanthoria parietina and adjacent lichen and bryophyte spp. was photographically monitored over a period of five years. This association developed on a plane quadrangle on the top surface of a sandstone block in the botanical garden of the University of Zürich. Line tracings of the thalline outlines were used for a quantitative estimation of laminal growth by means of gravimetric morphometry. Average radial growth of approximately 6 mm yr−1 was recorded, with maxima around 7 mm yr−1. The oldest, apothecia‐covered central parts of the thalli lost contact with the substratum and broke off along stress cracks but the blank substratum was rapidly re‐colonized by new thallus lobes which regenerated along the wound margins, to our present knowledge a peculiarity of X. parietina and few related species among the Teloschistales. Approximately 50% of the surface area of the experimental plot was covered by X. parietina at the beginning and again at the end of this five years period, with significant fluctuations in the time between. New growth in the range of 87% of the total surface area almost compensated the losses of approximately 90% per surface area in five years. New growth and losses within these five years accounted for more than 170% of the initial coverage. X. parietina gains a significant ecological advantage from its very remarkable regenerative capacity.
Pigment Accumulation and Photosynthesis in Developing Rye Coleoptiles
Authors: Bette A. , Kutschera U.
Published: February 2014

Rye seedlings (Secale cereale L.) were grown in darkness or irradiated with white light (WL) of medium intensity (100 μmol quanta . m−2 . s−1). In the coleoptile and primary leaf of irradiated plants synthesis of chlorophylls a and b with average ratios of 2.4 and 2.7, respectively, were measured. The chlorophyll content of the fully green primary leaf was about 10‐fold larger than that of the pale green coleoptile. In darkness a large increase in carotenoid content occurred in the primary leaf, but in the coleoptile the level of carotenoids remained very low. In both organs a WL‐induced increase in carotenoid synthesis was observed. The level of anthocyanin was likewise enhanced by WL. In the coleoptile and primary leaf of irradiated seedlings light‐dependent oxygen evolution was measured. The specific activity of the enzyme ribulose‐1,5‐bisphosphate carboxylase/oxygenase was enhanced after WL treatment. The results indicate that the mature rye coleoptile is a photosynthetically active plant organ.
Inhibition of Photosystem II by UV‐B Radiation and the Conditions for Recovery in the Liverwort Conocephalum conicum Dum.
Authors: Ihle Carolin , Laasch H.
Published: February 2014

Inhibition of photosynthesis by UV‐B was investigated in the thalloid liverwort Conocephalum conicum Dum. UV‐B irradiance was adjusted to a strength producing 50% inhibition of the rate of photosynthesis during 10 min of irradiation. A linear relationship of the fluorescence terms Fv/Fm of photosystem (PS) II and JP was observed following a UV‐B irradiation. This suggested that PS II was a major site of UV‐B‐induced damage of photosynthesis. The apparent inhibition of Fv/Fm was much smaller when electron flow to the secondary PS II acceptor QB was inhibited by DCMU or when Fv/Fm was measured at 77 K. Apparently, the major target of UV‐B effects was electron donation to the PS II reaction center, rather than electron transfer reactions at the PS II acceptor side. The time required for repair of PS II from UV‐B‐induced damage was light‐dependent and minimal at a flux density of 5 μE m−2 s−1. Low temperatures and the presence of streptomycin inhibited the repair processes of PS II, indicating that protein synthesis may be involved in the recovery of PS II. The data indicate that UV‐B irradiation on bright and cool winter days may be most harmful for photosynthesis of C. conicum. A repeated irradiation of the thalli with UV‐B induced tolerance of photosynthesis which was related to an accumulation of pigments with a maximum of absorption around 315 nm.
Mercury Increases Light Susceptibility in the Green Alga Haematococcus lacustris
Authors: Xyländer M. , Hagen Ch. , Braune W.
Published: February 2014

The influence of mercury ions (Hg2+, 10 μM) on photosynthesis was investigated in flagellates and aplanospores of Haematococcus lacustris. Hg2+ stress resulted in a fast decrease of chlorophyll fluorescence yield. This was initially caused by an increase in reversible non‐photochemical quenching of chlorophyll fluorescence. During further exposure to Hg2+, an increasing contribution of pH independent non‐photochemical quenching and a parallel rise in the content of the xanthophyll cycle pigment zeaxanthin was detected. An increase of the initial chlorophyll fluorescence as a final sign of Hg2+ induced adverse effects on photosynthesis supports our hypothesis that mercury ions predispose to non‐reversible, “chronic” photoinhibition.
Scale and Bristle Morphology of Mallomonas tonsurata (Synurophyceae) in Cultures with Varied Nutrient Supply*
Authors: Hahn A. , Gutowski A. , Geißler U.
Published: February 2014

Scale‐bearing taxa of the chrysophytes are important paleoindicators because of their often restricted ecological requirements and their highly preserved extracellular siliceous structures. The diagnostic features can usually only be resolved using electron microscopy and, since these features are often shared between closely related taxa, identification in field studies remain uncertain in most cases. As the respective influences of genetics and environmental factors upon morphological variation cannot be evaluated in field studies, examinations were conducted by growing a clonal culture of Mallomonas tonsurata in different media with varying silicon, nitrogen and phosphorus supply, followed by micromorphological analyses of scales and bristles. Increased silica content resulted in significant elongation of scales with a corresponding tendency to build slender scales. In experiments with varied ratios of nitrogen and phosphorus in the media the most pronounced changes were observed under phosphorus enrichment leading to significantly larger scales and more needle‐like bristle tips. These bristles resemble those of M. areolata. This shows that bristles are more variable than scales and thus must be regarded as of little value for taxonomical description. However, the above‐mentioned changes are not sufficiently pronounced to result in a sharp distinction between two different species. This confirms that siliceous structures of chrysophytes are, in principle, a most valuable tool for taxonomic differentiation although in field studies morphological variability of taxonomically relevant characters should still be considered.
Field Measurements of Photosynthesis of Umbilicarious Lichens in Winter
Authors: Kappen L. , Schroeter B. , Hestmark G. , Winkler J. B.
Published: February 2014

The photosynthetic performance of Lasallia pustulata and Umbilicaria spodochroa was measured both in the field on granitic rock in southern Norway and in the laboratory under controlled conditions of light and temperature. In the field thallus temperatures varied between − 2 and + 5 °C during the daylight period in January 1994. In situ water contents were between 50 and 400% d.wt. in L. pustulata and between 100 and 500% d.wt. in U. spodochroa. The lichens were active during the whole period of investigation. Photosynthetic rates reached 13.03 μmol CO2 g Chl−1 s−1 in L. pustulata and 5.56 μmol CO2 g Chl−1 s−1 in U. spodochroa. Ice formation on the thallus surface did not impede CO2 exchange. Light was mainly the limiting factor, as could be confirmed by the laboratory experiments. In general, habitat conditions never provided optimum photosynthetic rates but photosynthetic carbon balance was positive during 4 of the 5 days investigated. The coldest day was photosynthetically almost as efficient as the warmest day during this period.
Reproduction and Pollination in Central European Populations of Silene and Saponaria Species
Authors: Jürgens A. , Witt Taina , Gottsberger G.
Published: February 2014

Flower morphology, flowering phenology, flower visitors, reproductive systems, and stigmatic receptivity of six species of Silene and Saponaria (Silene alba, S. dioica, S. vulgaris, S. nutans, S. noctiflora. Saponaria officinalis) were studied from April to October 1993 and from April to June 1994 in natural populations around Giessen in Hessen/Central Germany and, additionally, in individuals grown from seeds in the Botanical Garden of the University of Giessen. With the exception of Saponaria officinalis and S. noctiflora, all species were regularly visited and pollinated by crepuscular and nocturnal moths and hawkmoths, but only one species, S. alba, was exclusively pollinated by these night‐active insects. The other species showed mixed pollination syndromes in which nocturnal and diurnal insects both promoted pollen transfer. Geitonogamy or even autogamy occurred in the gynodioecious and hermaphrodite species S. vulgaris, S. nutans, S. noctiflora, and Saponaria officinalis. Silene noctiflora, the only annual species, is pseudocleistogamous; the majority of its flowers did not open, and fruit set occurred after selfing in bud.
Pollen Tubes: a Model System for Plant Cell Growth*
Authors: Derksen J.
Published: February 2014

Recent observations of pollen tubes show that these tubes may grow in a pulsatory fashion (Pierson et al., 1995; Plyushch et al., 1995; Li et al., 1996; Geitmann et al., 1996a, 1996b), in which phases of fast and slow growth alternate regularly. The occurrence of pulsatory growth has been used by Geitmann and coworkers (1996b) to study factors that might control growth. Their results emphasize the role of the cell wall and secretory events in regulating pollen tube growth. Here we will briefly review recent results related to the role of exocytosis, cytoskeleton, calcium and the cell wall in pollen tube growth.
Pigment Evolution in the Caryophyllales: a Systematic Overview*
Authors: Clement J. S. , Mabry T. J.
Published: February 2014

While the apparent mutual exclusiveness of anthocyanins and betalains in the Caryophyllales has given rise to considerable taxonomic debate, historical factors affecting the present distribution of these compounds have rarely been discussed. An understanding of pigment evolution in the order is hindered by a number of unresolved systematic issues and a lack of knowledge of the importance of anthocyanins and betalains beyond their roles in pollination and seed dispersal. The hypothesis that betalains arose in an unpigmented ancestor of the Chenopodiinae in response to selection from pollinators cannot be rejected, but scant evidence exists in favor of it. Questions persist regarding whether the most recent ancestor to the Chenopodiinae presented a pigmented floral display and whether the appropriate pollinators were present at this time to select for floral pigmentation. In view of these ambiguities and the possible non‐monophyly of the Chenopodiinae we consider some alternative scenarios and suggest potentially rewarding avenues for future research. We discuss roles for anthocyanins and betalains beyond their use as optical attractants, possible costs and benefits associated with producing each pigment type, and the possibility that they may have co‐occurred in an ancestor for some period of time.
Inhibition of Intracellular Pectin Transport in Pollen Tubes by Monensin, Brefeldin A and Cytochalasin D*
Authors: Geitmann Anja , Wojciechowicz Kasia , Cresti M.
Published: February 2014

Specific inhibitors of the secretory pathway represent important tools for investigation of cell wall synthesis and tip growth in pollen tubes. Brefeldin A completely inhibits germination of Nicotiana tabacum pollen tubes at 2.2 μM. Ultrastructural investigation of pollen tube cytoplasm showed that brefeldin A caused the appearance of reticular structures and “brefeldin A compartments” containing unesterified pectins. Monensin caused inhibition of pollen tube germination at 80 nM. The drug induced swelling of the Golgi cisternae, many of which contained methyl‐esterified pectins. Cytochalasin D was effective at 1 μg/ml, the inhibition of germination being fully reversible. Application of the drug caused accumulation of secretory vesicles containing methyl‐esterified pectin around the dictyosomes. In contrast to brefeldin A and monensin, cytochalasin D caused a slowdown of cytoplasmic streaming. Monensin, but not the other drugs, caused a considerable decrease in pollen tube diameter. The characterization and quantification of the effects of the drugs on pollen tubes represents a necessary prerequisite for their application in physiological studies.
Distribution of Plasma Membrane H+‐ATPase and Polar Current Patterns in Leaves and Stems of Elodea canadensis*
Authors: Baur Marion , Meyer A.J. , Heumann H.‐G. , Lützelschwab M. , Michalke W.
Published: February 2014

The proton pumping ATPase in the plasma membrane of Elodea canadensis is believed to play a major role in inorganic carbon acquisition. To investigate potentially different carbon uptake strategies within the same plant, plasma membrane H+‐ATPase distribution and polar current patterns were investigated in Elodea leaves and stems. Specific activity of plasma membrane H+‐ATPase in leaf microsomal fractions was tenfold higher than in stem derived microsomes. Probing western blots with a monoclonal antibody specific for plasma membrane H+‐ATPase, yielded strongly visible double bands at 100 kDa in leaf microsome preparations, whereas little antigen was detected in analogous stem microsome preparations. Using the same plasma membrane H+‐ATPase specific antibody on tissue sections, the enzyme was found almost exclusively localized at the border of cells at the lower leaf surface. A positive ion current leaving the lower leaf surface was measured, using a vibrating probe device. Part of this current entered the upper leaf surface and part of it the internodes of the stem. The experimental results support the view, that Elodea leaves have different means of inorganic carbon uptake than stem internodes.
Influence of the Shoot Tip and Leaves on Circumnutation in Green Pea Seedlings
Authors: Tepper H. B. , Yang R. L.
Published: February 2014

Portions of the shoot system from young light‐grown pea (Pisum sativum L.) seedlings were excised and circumnutation studied using time‐lapse cinematography. Removal of the youngest leaf or shoot tip as well as ringing the stem with 20 mM triiodobenzoic acid severely restricted circumnutation. Treating the stump of the excised leaf with lanolin containing 10−4 M indole‐3‐acetic acid or replacing the leaf with an artificial aluminum leaf both partially restored circumnutation. When the leaf was replaced with both auxin and an artificial leaf circumnutation continued at approximately the rate of the intact plant. This graphically shows the involvement of both auxin and gravitropism in circumnutation.
Significance of Thiol‐Disulfide Exchange in Resting Stages of Plant Development
Authors: Kranner Ilse , Grill D.
Published: February 2014

Abstract: Desiccation tolerance is a fundamental principle for resting stages of plant development which include the dormancy of seeds and the quiescent stages of resurrection plants. To prevent the deleterious effects of cellular desiccation, a complex interplay of several adaption mechanisms is required. The ability to cope with free radicals, the formation of which is well documented in desiccated tissues, is one of these basic requirements. Detoxification of free radicals by several antioxidants and scavenging enzymes include reactions of reduced glutathione (GSH) resulting in the formation of glutathione disulfide (GSSG). In free radical processing pathways GSSG is considered to be immediately reduced back to GSH by the action of glutathione reductase (EC 1.6.4.2.). However, in desiccated tissues GSSG accumulates. Protein‐glutathione mixed disulfides (PSSG) are also reported to increase in plants under drought leading to the hypothesis that glutathione protects protein thiol groups from auto‐oxidation. The irreversible formation of intramolecular disulfides resulting in denaturation of proteins would be one of the primary sites of desiccation injury. We suggest that PSSG is formed by the reaction of GSSG with high molecular weight thiols and introduce a thiol‐disulfide cycle that involves reduction/oxidation processes of glutathione and protein thiol groups during the dehydration/rehydration processes in desiccation tolerant tissues.
Root Cap Mucilage and Extracellular Calcium as Modulators of Cellular Growth in Postmitotic Growth Zones of the Maize Root Apex*
Authors: Baluška F. , Volkmann D. , Hauskrecht M. , Barlow P. W.
Published: February 2014

Abstract: The control of maize root growth by root cap mucilage and extracellular calcium (Ca) was examined. Special attention was paid to the influence of these factors on cellular aspects of root growth, such as cell shape and organization of the microtubular (MT) cytoskeleton. Externally supplied Ca impaired the transition of early post‐mitotic cells from a more‐or‐less apolar mode of expansion to a strictly anisotropic mode of elongation accompanied by their more rapid growth. However, this inhibitory effect of Ca was not associated with any re‐arrangement of the cortical MTs, their transverse arrays, with respect to the root axis, being maintained under these conditions. Root mucilage, collected from donor root caps and placed around root tips, exerted a similar effect on cell shapes as did externally supplied Ca. In contrast, roots grown in a medium of low Ca content, or from which the root cap mucilage was continually removed, had more elongated cell shapes in their post‐mitotic growth regions when compared to the control roots. These findings are consistent with a notion that Ca is present in the root cap mucilage in physiologically relevant amounts and can mediate growth responses in both the PIG region and the apical part of the elongation zone.

Integrating several known effects of Ca ions on growth at the root apex, a hypothesis is proposed that a Ca‐mediated and MT‐independent control of cell growth in the PIG region might be involved in morphogenetic root movements (e.g. gravitropism), and that root growth responses could be initiated by an asymmetric distribution of extracellular calcium, or root cap slime, around the growing root tip.
Effect of UV Irradiance on Utilization of Inorganic Nitrogen by the Antarctic Diatom Odontella weissflogii (Janisch) Grunow
Authors: Döhler C.
Published: February 2014

Abstract: The impact of UV‐B irradiation on unialgal cultures of the temperate marine diatom Odontella sinensis and of the Antarctic Odontella weissflogii was tested under controlled laboratory conditions. Uptake rates of inorganic nitrogen by Odontella sinensis were more affected by UV‐B radiation than those of Odontella weissflogii. Utilization of 15N‐ammonium was reduced after 3 h of UV‐B exposure. Values of Km from several marine phytoplankton species were estimated from algae not exposed to UV‐B and from those after 3 h of UV‐B radiation. Calculation of Lineweaver‐Burk plot showed, under UV‐B stress, a noncompetitive inhibition for 15NH+4 uptake and a competitive inhibitory effect for 15NO−3 by Odontella weissflogii. The damage to 15NH+4 uptake by UV‐B was more pronounced under red than blue light; a contradictory result was obtained for 15NO−3 utilization by Odontella weissflogii. Reduction of the pigments by UV‐B under white light was dependent on the exposure time; a strong depression of the contents of chlorophyllide a, chlorophyll c, diatoxanthin and the fucoxanthins was found. Contents of the chlorophylls are markedly affected by UV‐B under red light whereas the chlorophyll a concentration is enhanced in blue and green light. UV‐B exposure in conjunction with blue and green light led to a reduction of the protein content and an increase in the amino acid contents. The pattern of pool sizes of free amino acids varied after UV‐B exposure. UV‐A irradiance had no effect. The possible targets of UV‐B irradiation on the uptake system of inorganic nitrogen are discussed in detail. Adaptation to the environmental conditions, e.g. via synthesis of UV stress proteins or mycosporine‐like amino acids, were also considered.
Photosynthetic Depression at High Thallus Water Contents in Lichens: Concurrent Use of Gas Exchange and Fluorescence Techniques with a Cyanobacterial and a Green Algal Peltigera Species
Authors: Lange O. L. , Green T. G. A. , Reichenberger H. , Meyer A.
Published: February 2014

Abstract: Lichens, being poikilohydric, have varying thallus water contents (WC) and show a complex interaction between net photosynthesis (NP) and WC. NP can be depressed at low WC (desiccation effects) and, in some species, also at high WC. In the latter case the depression is normally ascribed to increased CO2 diffusion resistances through water blockage. Recently, an earlier explanation, that the depression at high WC is due to recycling of CO2 from increased dark respiration processes (DR), has been given renewed prominence.

The two explanations were distinguished by the concurrent use of gas exchange and chlorophyll fluorescence techniques to investigate NP: WC relationships in the lichens Peltigera leucophlebia (green algal) and P. neckeri (cyanobacterial). Both species had a distinct optimal WC for NP with depressed values at low and high WC. The maximal quantum yield for both CO2 fixation (initial slope of light response curves of NP) and photosystem II (fluorescence signals of dark‐adapted thalli) was depressed only at low WC and remained high at optimal and greater WC. In contrast, the relative electron transport rate (ETR, derived from fluorescence signals of thalli in the light) tracked NP and was depressed at low and high WC. The depression of both NP and ETR at high WC (not that at low WC) could be prevented by using elevated external CO2 concentrations. A single, linear relationship was found between all values of gross photosynthesis (NP + DR) and ETR regardless of external CO2 concentration or WC.

Our results show that, for these lichens, the depression in NP at high WC is a real fall in photosynthetic rate of the photobionts and is not due to recycling of CO2. The removal of the depression in NP and ETR at high WC by using elevated external CO2 levels allows us to conclude that an additional CO2 diffusion resistance is present.
Water Relations and CO2 Exchange of Tropical Bryophytes in a Lower Montane Rain Forest in Panama
Authors: Zotz G. , Büde B. , Meyer A. , Zellner H. , Lange O. L.
Published: February 2014

For 6 tropical bryophytes, measurements of the diel courses in water status and net CO2 exchange were made in a submontane tropical rain forest in Panama. In addition, the response of gas exchange to changes in photon flux density (PPFD) and thallus water content (WC) was studied under controlled conditions. Diel variation of WC was pronounced, and both low and high WC limited carbon gain considerably. Low PPFD, e.g. during rain storms, was less important in limiting CO2 exchange. More than half of the mean diurnal carbon gain of 2.9 mg C per g thallus carbon was lost during the night as respiration. Assuming that the average 24‐h carbon gain was representative for the entire year, we estimated the net annual primary productivity of the mosses and liverworts to be 45% of the initial plant carbon content.
Seasonal Growth and Photosynthetic Performance of the Antarctic Macroalga Desmarestia menziesii (Phaeophyceae) Cultivated under Fluctuating Antarctic Daylengths
Authors: Gömez I. , Wiencke C.
Published: February 2014

Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d−1 in winter condition (July‐August) to 0.5% d−1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g−1 FW (chlorophyll a), 0.4 mg g−1 FW (chlorophyll c) and 0.9 mg g−1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (Pmax), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O2 g−1 FW h−1 in October and minima close to 9μmol O2 g−1 FW h−1 in April. Dark respiration was high in spring (13μmol O2 g−1 FW h−1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (lk) increased significantly in spring [1.3 μimol O2 g−1 FW h−1 (μmol m−2 s−1)−1 and 26μmol photons m−2 s−1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern.
The Induction of Contractile Root Activity in Sauromatum guttatum (Araceae)
Authors: Pütz N. , Pieper J. , Froebe H. A.
Published: February 2014

Contraction of Sauromatum guttatum roots creates a slow, downward underground corm movement, the corm be‐coming covered by a greater amount of soil, and the geophilous plant surviving the dormancy period at a safer soil position. Corm movement of Sauromatum guttatum is only possible if root contraction results in pulling activity. This pulling activity can be quantified using the lifting technique. Measurements of the pulling activity are shown as working curves over time and as the maximum work of a single contractile root. Our results show that root activity varies in individuals cultivated under different parameter conditions. It can be shown that two factors induce root contraction: first, rapid temperature fluctuations during the preceding growth period; second, illumination of the sheath leaves during the actual growth period. However, light induction is, as found here, more important and hierarchically superior, for the temperature effect is only seen in plants whose sheath leaves are not illuminated. Mobility of S. guttatum plants can thus be described as photo‐movement. If the light effect is not present, the mobility of S. guttatum may become thermo‐movement. However, at present, there is no indication that this movement is oriented to the direction of stimulus.
The Light Harvesting System of the Diatom Cyclotella cryptica. Isolation and Characterization of the Main Light Harvesting Complex and Evidence for the Existence of Minor Pigment Proteins*
Authors: Rhiel E. , Marquardt J. , Eppard M. , Mörschel E. , Krumbein W. E.
Published: February 2014

The main chlorophyll a/c light harvesting complex of the diatom Cyclotella cryptica was isolated by sucrose density gradient centrifugation. It consisted of two polypeptides of Mrs 18000 and 22000. Both polypeptides and fragments thereof, obtained by formic acid treatment, were blocked at their N‐ter‐mini. An antiserum raised against the two subunits selectively immunolabeled the thylakoid within the chloroplasts. The subunits were nuclear encoded and could be immunoprecipitated from poly (A)+ RNA as precursor proteins in the Mr range of 20000 to 24000. The existence of minor chlorophyll protein complexes and their possible function in light climate adaptation processes was investigated in cells adapted to low light and high light conditions. Low light grown cells contained more fucoxanthin and less β‐carotene relative to chlorophyll a than high light adapted cells. The xanthophyll cycle pigments diatoxanthin and diadinoxanthin increased five‐fold relative to chlorophyll a under high light conditions. Western‐immunoblotting experiments with antisera raised against several chlorophyll a/b and chlorophyll a/c antenna complexes demonstrated that, beside the dominating chlorophyll a/c light harvesting complex, minor antenna complexes might exist, which, in part, seem to react to the light climate applied.
Phototropic Response of the Bean Pulvinus: Movement of Water and Ions
Authors: Irving M. S. , Ritter Sigalit , Tomos A. D. , Koller D.
Published: February 2014

Segmental analysis of the laminar pulvinus of Phaseolus vulgaris L. showed that its phototropic curvature is accompanied by efflux of inorganic ions and water from its contracting sector and a comparable influx into its expanding one. All the major ions, except Na+, contributed to this transport, suggesting that the response to light involves changes in the driving force, or conductivity of a wide range of solutes. During the curvature, K+ and CI− made the greatest and equivalent contributions to efflux, but only Cl− exhibited a matching influx into the expanding sector, while K+ influx was much less. Use of the cell pressure probe showed that, as the laminar angle of elevation changed between −40° to +40°, turgor pressure in the expanding motor cells increased by 0.48 MPa and decreased in the contracting cells by 0.32 MPa. Picoliter osmometry of single‐cell samples showed that during this movement vacuolar osmotic pressure remained constant. Thus, changes in turgor pressure resulted from changes in apoplastic, rather than the protoplastic osmotic pressure. Volumetric modulus of elasticity of pulvinar motor cells is very low, showing that their walls are very elastic. These properties increase the effectiveness of converting osmotic work into the large‐scale, reversible volume changes responsible for leaf movements.
Gradation in Nutrient Composition and Photosynthetic Pathways Across the Restinga Vegetation of Brazil
Authors: Reinert F. , Roberts A. , Wilson J. M. , De Ribas L. , Cardinot G. , Griffiths H.
Published: February 2014

The restinga comprises coastal vegetation formations which dominate the Atlantic seaboard of Brazil. Exposed sand ridges and associated lagoon systems have poorly developed soils subject to pronounced water deficits. Distinct vegetation zones support a high diversity of life forms, and a comparative study has been undertaken to investigate interactions between degree of exposure, nutrient supply and photosynthetic pathway (C3, or CAM) in selected species across the restinga. A number of species occurring throughout the restinga were chosen as representative species of different life forms, comprising C3 pioneer shrubs (Eugenia rotundifolia and Erythroxylum ovalifolium), impounding (tank) terrestrial bromeliad (Neoregelia cruenta: CAM) and the atmospheric epiphyte (Tillandsia stricta: CAM). Comparisons of plant and soil nutrient composition, and airborne deposition were conducted for each zone. Soil nutrient content and organic matter were closely related, reaching a maximum in zone 4, the seaward face of the inner dune. Salt concentration in leaves was independent of atmospheric deposition for the terrestrial species, in contrast to the atmospheric epiphyte T. stricta. In the slack area, vegetation formed characteristic “islands” with the soil beneath enriched in nutrients, suggesting a complex interplay between plants and soil during the development of vegetation succession. Here, two additional trees were investigated, C3 and CAM members of the Clusiaceae, respectively Clusia lanceolata and C. fluminensis. Stable isotope composition of nitrogen (δ15N) was generally more negative (depleted in 15N) in plants with low total nitrogen content. This was exemplified by the atmospheric bromeliad, T. stricta, with an N content of 2.91 g/kg and δ15N of −12.3 per mil. Stable isotopes of carbon (δ13C) were used to identify the distribution of photosynthetic pathways, and while the majority of bromeliads and orchids were CAM, analysis of the soil organic matter suggested that C3 plants made the major contribution in each zone of the restinga. Since δ13C of plant material also suggested that water supply was optimal in zone 4, we conclude that succession and high diversity in the restinga is dependent on exposure, edaphic factors, and perhaps a critical mass of vegetation required to stabilize nutrient relations of the system.