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Clusia rosea Jacq. is abundant in the moist parts of the Caribbean island of St John (US Virgin Islands, Lesser Antilles) but relatively rare along the dry south coast. Three types of seedlings were encountered, terrestrial seedlings, seedlings growing as humus-epiphytes on other trees, and seedlings growing inside the tanks of the bromeliad Aechmea lingulata (L.) Baker. Free-living trees grow from terrestrial seedlings or from epiphytic seedlings strangling and shading their host trees. Leaf-Na+ levels were always low (1-4 mequiv l-1 tissue water); trees close to the shore were not affected by salinity. In leaves of mature C. rosea trees, levels of Ca2+, Mg2+ and K+ were about 60-90, 40-50, 45-55 mequiv l-1 tissue water, respectively. Epiphytic seedlings tended to contain lower levels of these inorganic cations than seedlings growing terrestrially or in the tanks of Ae. lingulata. Epiphytic seedlings contained significantly less nitrogen than terrestrial seedlings. In the leaves of mature trees N-levels were independent of altitude and location on the island, but shaded leaves had significantly higher N-levels than exposed leaves. Light compensation point of photosynthesis in epiphytic seedlings performing C3-photosynthesis was 17.5 (μmol photons m-2 s-1), photosynthesis was saturated at about 300 μmol photons m-2 s-1 showing a maximum rate of CO2-uptake of 2.3 μmol m-2 s-1. [ABSTRACT FROM AUTHOR]

Measurements were performed on leaves of Clusia rosea Jacq. trees in the moist central mountains (330 to 365 m above sea level) and at the dry south coast of St John Island (US Virgin Islands, Lesser Antilles). Seedlings of C. rosea were also studied in the central hills. During the study period (March 1989) all trees showed crassulacean acid metabolism (CAM), in which net CO2 uptake extended for a remarkably long time in the morning (phase II of CAM: until about 11 to 12 h) and contributed about &frac;13 of total net CO2-uptake. During the night (phase I of CAM) malic acid and citric acid were accumulated concurrently at a molar ratio of malic : citric acid of about 1.6. Internal recycling of respiratory CO2 was 20% of total CO2 fixed during the night. Water-use-efficiency (mol CO2 taken up : mol H2O transpired) was 0.014 to 0.022. The pH of leaf-cell sap at the end of the dark period was 2.85. This would still allow an H+-ATPase at the tonoplast to transport 2H+ into the vacuole per ATP hydrolysed when operating near thermodynamic equilibrium. Free sugars, glucose and fructose, and starch were used as precursors for the CO2-acceptor phosphoenolpyruvate during the dark period; contributions of the two hexoses were about equal and together four-times that of starch. Xylem tensions showed increases of up to 8 bar during day-time. Leaf-sap osmotic pressures did not change significantly; the trend was a small decline during day-time. Among the seedlings, three different modes of photosynthesis were encountered, namely C3-photosynthesis in terrestrial and in epiphytic seedlings, continuous stomatal opening and CO2-uptake day and night in epiphytic seedlings, and CAM in seedlings growing in the tanks of Aechmea lingulata (L.) Baker. [ABSTRACT FROM AUTHOR]

Four different Clusia species showing C3 photosynthesis (C. multiflora) or crassulacean acid metabolism (CAM) (C. rosea, an unidentified Clusia sp. and C. alata) co-occur in the same habitat in the northwest of Venezuela. The aim of this field study was to correlate the adaptive changes in chlorophyll a fluorescence with gas exchange patterns and deacidification of nocturnally accumulated organic acids. The results indicate that in C. rosea and Clusia sp. a lowering of the potential quantum yield, measured as Fv/Fm after 10 min of dark adaptation, is restricted to the early morning hours. With the onset of deacidification there was no further decline in Fv/Fm, although the irradiance upon the leaves remained high. For the C3-plant, C. multiflora, changes in Fv/Fm were correlated with changes in irradiance incident on the leaves before predarkening for 10 min for Fv/Fm measurements. The fast relaxation of Fv/Fm under low light indicates that C. multiflora was not suffering photoinhibitory damage. Effective quantum yield as determined by ΔF/Fm, was low under high irradiances for C. rosea and Clusia sp. and did not change significantly for C. rosea during phase III of CAM. During the time of low incident irradiance C. alata and C. multiflora reached an effective quantum yield that was close to the optimal quantum yield of electron transport. It is noteworthy that apparent electron transport rates through photosystem II (PS II) ((ΔF/F'm) × PPFD) were highest for C. rosea, Clusia sp. and C. alata during phase III of CAM. Electron transport rates in C. multiflora were under high irradiance and did not differ from those in phase II and IV of CAM. The possible role of CO2 evolution from acid decarboxylation with respect to photosynthetic efficiency is discussed. [ABSTRACT FROM AUTHOR]

Leaf-tips of Epidendrum and Laeliocattleya (Orchidaceae) have been cultured in vitro. Epidendrum seedling leaf-tips form calli on Murashige-Skoog medium (MS) or after being transferred to Knudson C agar following prior growth on MS. Plantlets also develop from tips of young leaves of mature Laeliocattleya plants cultured in Heller's medium or in a solution specifically devised for orchid shoot-tip cultures. In Heller's medium plantlet development is preceded by callus formation whereas in the shoot-tip medium protocorm-like bodies are formed first. These tissues when subcultured from Heller's medium or the shoot-tip solution to Knudson C agar also produce plantlets which resemble orchid seedlings. The results are discussed in relation to the components of each medium, the requirements of germinating orchid seeds and protocorms, and the difficulties encountered in attempts to culture tissues of mono-cotyledonous plants. [ABSTRACT FROM AUTHOR]

Presents a correction for the article on different species of Clusia, published in the 1997 issue of the journal "The New Phytologist."