Carbon Metabolism in Seagrasses: III. ACTIVITIES OF CARBON-FIXING ENZYMES IN RELATION TO INTERNAL SALT CONCENTRATIONS

The internal salt content and distribution in photosynthetictissues as well as the effect of NaCl on photosynthetic carbonfixation enzymes was investigated in two seagrass species fromthe Red Sea. Concentrations of both Na⁺ and Cl^– were lower in the chloroplast-richepidermis than in underlying cell layers in Halophila stipulacea.In Halodule uninervis, the concentration of Na⁺ was lower inthe epidermis than in the underlying cells, while K⁺ was evenlydistributed between cell layers. The epidermal concentrationsof Na+ were estimated to be 0.17 and 0.10 M for Halophila stipulaceaand Halodule uninervis, respectively, which were about to the average leaf concentrations. Epidermal Cl^– concentrationof Halophila stipulacea was estimated to be 0.08 M, a valueonly about of the overall leaf concentration. Phosphoenolpyruvate carboxylase (PEPcase) extracted from leavesof these seagrasses showed increased activity at 0.05–0.3M NaCl in vitro. Ribulose-l, 5-bisphosphate carboxylase (RuBPcase)activity, on the other hand, was inhibited by NaCl at all testedconcentrations. At epidermal NaCl concentrations, PEPcase activitywas thus stimulated while RuBPcase was inhibited. The reducedRuBPcase activity at such concentrations compared to salt-freeconditions was still sufficient to account for observed photosyntheticrates. We conclude that these seagrasses have adapted to a saline environmentboth by maintaining relatively low ion concentrations in theepidermis where photosynthesis occurs and by having carbon-fixingenzymes capable of functioning in the presence of salt.     

RAPID SYNCYTIUM FORMATION BETWEEN HUMAN T-CELL LEUKAEMIA VIRUS TYPE-I (HTLV-I)-INFECTED T-CELLS AND HUMAN NERVOUS SYSTEM CELLS: A POSSIBLE IMPLICATION FOR TROPICAL SPASTIC PARAPARESIS/HTLV-I ASSOCIATED MYELOPATHY

Tropical spastic paraparesis/HTLV-I associated myelopathy (TSP/HAM), is characterized by infiltration of human T cell leukaemia virus type-I (HTLV-I)-infected T-cells, anti-HTLV-I cytotoxic T cells and macrophages into the patients’ cerebrospinal fluid and by intrathecally formed anti-HTLV-I antibodies. This implies that the disease involves a breakdown of the blood—brain barrier. Since astrocytes play a central role in establishing this barrier, the authors investigated the hypothesis that the HTLV-I infected T cells disrupt this barrier by damaging the astrocytes. The present study revealed the HTLV-I-producing T cells conferred a severe cytopatic effect upon monolayers of astrocytoma cell line in co-cultures. Following co-cultivation, HTLV-I DNA and proteins appeared in the monolayer cells, but after reaching a peak their level gradually declined. This appearance of the viral components was proved to result from a fusion of the astrocytic cells with the virus-producing T cells, whereas their subsequent decline reflected the destruction of the resulting syncytia. This fusion could be specifically blocked by anti HTLV-I Env antibodies, indicating that it was mediated by the viral Env proteins expressed on the surface of the virus-producing cells. Similar fusion was observed between the HTLV-I-producing cells and certain other human nervous system cell lines. If such fusion of HTLV-I-infected T cells occurs also with astrocytes and other nervous system cells in TSP/HAM patients, it may account, at least partially, for the blood—brain barrier breakdown and some of the neural lesions in this syndrome.     

Effect of salt and soil water status on transpiration of Salsola kali L.

Abstract Transpiration of Salsola kali L. plants, grown in small pots under controlled environmental conditions, was followed through a drying cycle of the soil. Three different nutrient solutions were used during the preconditioning growth period: control (C), half-strength Hoagland's nutrient solution; C plus 150mol m⁻³ NaCl; and C plus 150mol m⁻³ KCl. Soil water content at saturation at the beginning of the drying cycle was 20% (w/w). Both NaCl and KCl treatments modified the plants' response to changes in soil water status. The control plants transpired twice as much (per unit leaf dry weight) as the salt-treated plants, even when the soil was at maximal water capacity. Transpiration of the control plants remained high, until the soil water content declined to 5%. After that stage the stomata of these plants closed abruptly. Transpiration of the salt-treated plants started decreasing when the soil water content was approximately 16%, and did so gradually until all the available water was depleted. When transpiration was plotted against soil water potential a sharp decline in the transpiration of control plants was observed with the soil water potential decreasing from -0.04 to -1.2MPa. Transpiration of the salt-treated plants decreased gradually over a wide range of soil water potential (−0.8 to −7.0MPa).