Detlef Kramer

Crassulacean acid metabolism in tropical dicotyledonous trees of the genusClusia

SummaryThe performance of crassulacean acid metabolism (CAM) by dicotyledonous trees of the genusClusia sampled at three sites in the state of Falcon in northern Venezuela is characterized.Clusia leaves have a somewhat succulent appearance. Unlike leaves of many other CAM plants, which are uniformly built up of very large isodiametric cells, there are distinct layers of palisade and spongy mesophyll, with individual cells being smaller. There is no specialized water storage tissue. δ13C values indicate thatC. multiflora in the elfin-cloud forest on top of Cerro Santa Ana, at ∼800 m altitude, performs C3 photosynthesis (δ13 −27.1‰). However,C. rosea in the tall cloud forest on Cerro Santa Ana (∼600m altitude), andC. rosea andC. alata in the dry forest on Serrania San Luis (∼900 m altitude) perform CAM (δ13C −14.1 to −19.2‰). InC. alta andC. rosea there were large day-night changes in the levels of malic and citric acids ranging from 63 to 240 mmol 1−1 for malid acid and from 35 to 112 mmol 1−1 for citric acid. The sum of the changes in malate and citrate levels accounts for the changes of titratable protons measured. With a day-night change of titratable protons of 768 mmol 1−1 in one of the analyses,C. rosea showed the highest value yet encountered in a CAM plant. Oscillations of free sugars (fructose, glucose, sucrose) and of starch were also analysed in the CAM performingClusia species. Carbon skeletons of the precursors involved in nocturnal malate and citrate synthesis largely derive from free sugars and not from polyglucan. Unlike some other CAM plants, there is no clear and quantitative correlation between day-night changes of organic acid levels and cell sap osmolality.

Potassium Ion Channels of Chlorella Viruses Cause Rapid Depolarization of Host Cells during Infection

ABSTRACT Previous studies have established that chlorella viruses encode K+ channels with different structural and functional properties. In the current study, we exploit the different sensitivities of these channels to Cs+ to determine if the membrane depolarization observed during virus infection is caused by the activities of these channels. Infection of Chlorella NC64A with four viruses caused rapid membrane depolarization of similar amplitudes, but with different kinetics. Depolarization was fastest after infection with virus SC-1A (half time [t1/2], about 9 min) and slowest with virus NY-2A (t1/2, about 12 min). Cs+ inhibited membrane depolarization only in viruses that encode a Cs+-sensitive K+ channel. Collectively, the results indicate that membrane depolarization is an early event in chlorella virus-host interactions and that it is correlated with viral-channel activity. This suggestion was supported by investigations of thin sections of Chlorella cells, which show that channel blockers inhibit virus DNA release into the host cell. Together, the data indicate that the channel is probably packaged in the virion, presumably in its internal membrane. We hypothesize that fusion of the virus internal membrane with the host plasma membrane results in an increase in K+ conductance and membrane depolarization; this depolarization lowers the energy barrier for DNA release into the host.

Supply and compartmentalization of potassium in mesophyll cells of the needles of spruce, Picea abies (L.) Karst.

SummaryThe water and potassium content and the relative vacuolar volume (α = Vvacuole/Vcell) of mesophyll cells of the needles of healthy 21-yearold spruce trees [Picea abies (L.) Karst.] were determined. In 5-year-old needles α was 0.626 ± 0.178 (ovx ± SD). Potassium concentrations in the bulk tissue water ranged from about 65 to 105 mM. Simulations were made using this information and a simple two-compartmental model of the cell with the bulk cytoplasm and the vacuole and assuming that the minimum cytoplasmic and vacuolar K+ concentrations are 100–150 mM and 10–15 mM respectively. It is shown that a K+ content of needles below 50 mmol/1 tissue water would be precarious for maintenance of normal physiological and metabolic performance.

Preliminary Characterization of a Group of Actinophages of the Thermophilic Actinomycete Genus Saccharomonospora

The comparison of the Saccharomonospora phages phi SaC1, phi SaG1, phi SaV1, phi SaV2, phi SaV3, and Tm1 demonstrated that they all belong to a single group of closely related actinophages: they were similar with regard to host range, virion mophology (B1 type), genome length (43-45 kb), and GC content of their genomes (63, 3% G + C). Furthermore, DNA-DNA hybridization showed that the phage genomes had a high degree of homology to each other. The phages are, therefore, proposed as representatives of a new bacteriophage species in the sense of the ICTV.

Structure and function in absorption and transport of nutrients

The term transfer cell applies to cells that are thought to be particularly active in transport of inorganic or organic solutes across the plasmalemma. Structurally the most significant feature is the differentiation of cell-wall protuberances on the inner surface of the wall. These wall ingrowths — which often form a considerable wall labyrinth — are surrounded by the plasmalemma, which is therefore largely increased. Transfer cells are regarded as analogues of the microvilli in many animal cells, which are specialized in transport processes. It is widely held that in both systems the amplified plasmalemma surface leads to a largely increased number of pumping sites per cell, thus promoting active transport at the symplast/apoplast border [1]. The occurrence of transfer cells has been demonstrated to be common in all plant organs. In roots, transfer cells are common in the xylem parenchyma of leguminous nodules [7] as well as in rhizomes [8]. However, until 1976 no transfer cells had been described that could be directly related to the absorption of nutrients by the root and their transport to the shoot.

Transfer cells in the epidermis of roots: a structural differentiation to overcome nutrient deficiency.

Transfer cell is a term describing cells with an increased plasmalemma surface area due to the formation of a wall labyrinth. It is presumed that this corresponds to the role of such cells in transport processes, either in secretion (e. g., glands) or absorption (e. g., xylem parenchyma cells). Although the main function of root epidermal cells is absorption of nutrients, transfer-cell characteristics have not been reported previously for this tissue.