Refat Abdel-Basset

Membrane stabilization and survival of dehydratedChlorella fusca cells induced by calcium

Chlorella fusca was subjected to evaporative dehydration under air humidity of 72%. Ca2+ pretreated cultures lost water as rapidly as untreated cultures. Nevertheless, an ameliorative effect of Ca2+ pretreatment in droughted cells was found as membrane stability index was improved and K+ leakage was reduced. In addition, higher chlorophyll content and stability was observed. These parameters enabled droughted cells to recommence growth upon rewatering. Thus Ca2+ might increase survival ofC. fusca cells subjected to drought through membrane stabilization.

Aluminium reduces sugar uptake in tobacco cell cultures: a potential cause of inhibited elongation but not of toxicity

Aluminium is well known to inhibit plant elongation, but the role in this inhibition played by water relations remains unclear. To investigate this, tobacco (Nicotiana tabacum L.) suspension-cultured cells (line SL) was used, treating them with aluminium (50 microM) in a medium containing calcium, sucrose, and MES (pH 5.0). Over an 18 h treatment period, aluminium inhibited the increase in fresh weight almost completely and decreased cellular osmolality and internal soluble sugar content substantially; however, aluminium did not affect the concentrations of major inorganic ions. In aluminium-treated cultures, fresh weight, soluble sugar content, and osmolality decreased over the first 6 h and remained constant thereafter, contrasting with their continued increases in the untreated cultures. The rate of sucrose uptake, measured by radio-tracer, was reduced by approximately 60% within 3 h of treatment. Aluminium also inhibited glucose uptake. In an aluminium-tolerant cell line (ALT301) isogenic to SL, all of the above-mentioned changes in water relations occurred and tolerance emerged only after 6 h and appeared to involve the suppression of reactive oxygen species. Further separating the effects of aluminium on elongation and cell survival, sucrose starvation for 18 h inhibited elongation and caused similar changes in cellular osmolality but stimulated the production of neither reactive oxygen species nor callose and did not cause cell death. We propose that the inhibition of sucrose uptake is a mechanism whereby aluminium inhibits elongation, but does not account for the induction of cell death.

CHARACTERIZATION OF HYDROGEN PHOTOEVOLUTION IN OSCILLATORIA CHALYBEA DETECTED BY MEANS OF MASS SPECTROMETRY

Abstract The filamentous non-heterocystous cyanobacterium Oscillatoria chalybea is capable to photoevolve molecular hydrogen when the cells are flushed to anaerobiosis with nitrogen or argon and exposed to short light flashes or continuous light. The light-induced hydrogen gas exchange of Oscillatoria chalybea has been investigated by direct determination of dynamic changes in the hydrogen partial pressure at m/e=2 in the H/D collector of a mass spectrometric set-up. By means of this technique also the time curves of the light-induced hydrogen gas exchange could be directly recorded. Depending on the chlorophyll concentration in the measuring cell we observed an increasing hydrogen content of the aqueous Oscillatoria suspension i.e. a dark evolution of molecular hydrogen. Upon the onset of light an initial rise of the H 2-signal was observed which was increasingly mixed or followed by a hydrogen uptake. The capability to photoevolve molecular hydrogen was maximal with young cultures and decreased with increasing age. The hydrogen evolution signals require relatively short dark adaptation to get pronounced; few seconds suffice for 2/3 of the hydrogen evolution amplitude. Prolonged dark adaptation maximizes the flash amplitudes. The hydrogen evolution signals do not deactivate by low flash frequency Oscillatoria chalybea evolves molecular hydrogen following growth on nitrogen free or nitrate containing medium. Increase of the oxygen partial pressure of the assays completely abolishes the hydrogen evolution signals with an I50-value of 6 μm.

Effect of Ca2+ on the detoxification of Cd2+ byScenedesmus obliquus cells at low or high temperature

Scenedesmus obliquus was incubated with Cd2+ in the presence or absence of calcium at low (10°C) or high (40°C) temperature. The Cd2+ uptake was affected not only by Ca2+ but also by temperature. Growth rate was inhibited by Cd2+ especially at low temperature. In all Ca2+-containing cultures,S. obliquus exhibited higher rates of growth, dry matter and pigment fractions than in those containing Cd2+ alone. Proteins exhibited a similar response. Ca2+ in the presence of Cd2+ was most efficient where protein contents were mostly doubled. On the other hand Ca2+ reduced the solute leakage by the test alga at 10 and 40°C.

Role of calcium and calmodulin antagonist in photosynthesis and salinity tolerance inChlorella vulgaris

To cast light upon the role of Ca1+ and calmodulin on photosynthetic rate (Pn), dark respiration (RD) and amino acid and protein contents in salinity stressed and non-stressedChlorella cultures, the Ca2+ chelator EGTA [ethylene glycol-bis-(2-aminoethyl ether)-N,N- tetraacetate] and the calmodulin antagonist TFP (trifluperazine) were used. TFP markedly inhibited PN while EGTA exerted a slight, if any, effect on PN. NaCl tolerance, on the other side, was markedly abolished by TFP that inhibited PN and lowered rate of proline accumulation. Calmodulin might be involved in osmoregulation and salt tolerance ofChlorella. RD, however, was markedly enhanced by EGTA and Ca2+-free medium and hence the Ca2+ deprivation increased stress severity exerted by NaCl. Combinations of Na+ and Ca2+ enhanced PN, decreased RD and proline content in comparison with an osmotically equivalent reference culture containing only NaCl. Addition of Ca2+ to TFP treated cultures failed to reactivate calmodulin for proline synthesis. However, when Ca2+ was added to EGTA-treated cultures, only relatively reduced proline contents were recorded.

Modulation of the Photosynthetic Source:Sink Relationship in Cultures of the Cyanobacterium Nostoc Rivulare

Nostoc rivulare was grown in batch cultures under controlled CO2 and NO3− concentrations to modulate the photosynthetic source:sink relationship. Increasing CO2 supply accelerated the accumulation of chlorophyll (Chl) a, i.e., supplemental CO2 combined with double concentrations of NO3− more than doubled the amounts of Chl a relative to those of the original medium. Photosynthetic oxygen evolution and respiratory oxygen uptake were both enhanced by elevated CO2 and NO3−. Contents of soluble sugars and starch (total non-structural saccharides) as well as insoluble saccharides (structural fraction) were affected by altering CO2-NO3− combinations. Uptake as well as reduction of either NO3− or NO2− was inhibited by CO2 deprivation. Expanding the sink size via increasing NO3− supply enhanced photosynthesis and thus the sink (NO3−) acted as a feed forward stimulator of the source (photosynthesis). The regulatory role of nitrate on photosynthesis was most influential in CO2-deprived cultures since it could enhance photosynthesis to higher levels than CO2-supplemented, nitrate-free cultures.

Bioenergetics of lactate vs. acetate outside TCA enhanced the hydrogen evolution levels in two newly isolated strains of the photosynthetic bacterium Rhodopseudomonas

Abstract Two local hydrogen-evolving strains of purple nonsulfur bacteria have been isolated, characterized, and identified as Rhodopseudomonas sp. TUT (strains Rh1 and Rh2). Lactate followed by succinate and malate supported the highest amounts of H2 production, growth (O.D.660nm, proteins and bacteriochlorphyll contents), nitrogenase activity, and uptake hydrogenase; the least of which was acetate. Alginate-immobilized cells evolved higher hydrogen amounts than free cell counterparts. Rh1 was more productive than Rh2 at all circumstances. Lactate-dependent hydrogen evolution was more than twice that of acetate, due to ATP productivity (2/–1, respectively), which is limiting to the nitrogenase activity. The preference of lactate over other acids indicates the feasibility of using these two strains in hydrogen production from dairy wastewater.