Microg Chl Research Articles

Seasonal Impacts of Solar UV Radiation on Photosynthesis of Phytoplankton Assemblages in the Coastal Waters of the South China Sea

We carried out experiments to evaluate seasonal changes in the impacts of UV radiation (UVR, 280-400 nm) on photosynthetic carbon fixation of phytoplankton assemblages. Surface water samples were obtained in the coastal area of the South China Sea, where chlorophyll a ranged 0.72-3.82 microg L(-1). Assimilation numbers (photosynthetic carbon fixation rate per chl a) were significantly higher during summer 2005 than those in spring and winter 2004. The mean values obtained under photosynthetically active radiation (PAR) were 2.83 (spring 2004), 4.35 (winter 2004) and 7.29 microg C (microg chl a)(-1) h(-1) (summer 2005), respectively. The assimilation numbers under PAR + UVR were 1.58, 2.71 and 5.28 microg C (microg chl a)(-1) h(-1), for spring, winter and summer, respectively. UVR induced less inhibition of photosynthesis during summer 2005 than during the other seasons, in spite of the higher UVR during summer. The seasonal differences in the productivity and photosynthetic response to UV were mainly due to changes in water temperature, while irradiance and vertical mixing explained >80% of the observed variability. Our data suggest that previous studies in the SCS using UV-opaque vessels might have overestimated the phytoplankton production by about 80% in spring, 61% in winter and 38% in summer.

Hydrogen photoproduction by nutrient‐deprived Chlamydomonas reinhardtii cells immobilized within thin alginate films under aerobic and anaerobic conditions

A new technique for immobilizing H2-photoproducing green algae within a thin (<400 microm) alginate film has been developed. Alginate films with entrapped sulfur/phosphorus-deprived Chlamydomonas reinhardtii, strain cc124, cells demonstrate (a) higher cell density (up to 2,000 microg Chl mL(-1) of matrix), (b) kinetics of H2 photoproduction similar to sulfur-deprived suspension cultures, (c) higher specific rates (up to 12.5 micromol mg(-1) Chl h(-1)) of H2 evolution, (d) light conversion efficiencies to H2 of over 1% and (e) unexpectedly high resistance of the H2-photoproducing system to inactivation by atmospheric O2. The algal cells, entrapped in alginate and then placed in vials containing 21% O2 in the headspace, evolved up to 67% of the H2 gas produced under anaerobic conditions. The results indicate that the lower susceptibility of the immobilized algal H2-producing system to inactivation by O2 depends on two factors: (a) the presence of acetate in the medium, which supports higher rates of respiration and (b) the capability of the alginate polymer itself to effectively separate the entrapped cells from O2 in the liquid and headspace and restrict O2 diffusion into the matrix. The strategy presented for immobilizing algal cells within thin polymeric matrices shows the potential for scale-up and possible future applications.

Physiological characterization and stress-induced metabolic responses of Dunaliella salina isolated from salt pan

A Dunaliella strain was isolated from salt crystals obtained from experimental salt farm of the institute (latitude 21.46 N, longitude 72.11 degrees E). The comparative homology study of amplified molecular signature 18S rRNA, proves the isolated strain as D. salina. The growth pattern and metabolic responses such as proline, glycine betaine, glycerol, total protein and total sugar content to different salinity (from 0.5 to 5.5 M NaCl) were studied. The optimum growth was observed at 1.0 M NaCl and thereafter it started to decline. Maximum growth was obtained on 17th day of inoculation in all salt concentrations except 0.5 M NaCl, whereas maximum growth was observed on 13th day. There were no significant differences (P < 0.01) in chlorophyll a/b contents (1.0-1.16 +/- 0.05 microg chl. a and 0.2-0.29 +/- 0.01 microg chl. b per 10(6) cells) up to 2.0 M NaCl, however at 3.0 M NaCl a significant increase (2.5 +/- 0.12 microg chl. a and 0.84 +/- 0.4 microg chl. b per 10(6) cells) was observed which declined again at 5.5 M NaCl concentration (2.0 +/- 0.1 microg chl. a and 0.52 +/- 0.03 microg chl. b per 10(6) cells). Stress metabolites such as proline, glycine betaine, glycerol and total sugar content increased concomitantly with salt concentration. Maximum increase in proline (1.4 +/- 0.07 microg), glycine betaine (5.7 +/- 0.28 microg), glycerol (3.7 +/- 0.18 ml) and total sugar (250 +/- 12.5 microg) per 10(5) cells was observed in 5.5 M NaCl. A decrease in total protein with reference to 0.5 M NaCl was observed up to 3.0 M NaCl, however, a significant increase (P < 0.01) was observed at 5.5 M NaCl (0.19 +/- 0.01 microg per 10(5) cells). Inductive coupled plasma (ICP) analysis shows that intracellular Na(+) remained unchanged up to 2.0 M NaCl concentration and thereafter a significant increase was observed. No relevant increase in the intracellular level of K(+) and Mg(++) was observed with increasing salt concentration. Evaluation of physiological and metabolic attributes of Dunaliella salina can be used to explore its biotechnological and industrial potential.

Short- and long-term effects of solar ultraviolet radiation on the red algae Porphyridium cruentum (S. F. Gray) Nägeli

During spring 2002 and fall 2003 we carried out experiment in tropical southern China to determine the short- and long-term effects of solar ultraviolet radiation (UVR, 280-400 nm) on photosynthesis and growth in the unicellular red alga Porphyridium cruentum. During the experimentation, cells of P. cruentum were exposed to three radiation treatments: (a) samples exposed to PAR (400-700 nm) + UV-A (315-400 nm) + UV-B (280-315 nm)(PAB treatment); (b) samples exposed to PAR + UV-A (PA treatment) and, (c) samples exposed only to PAR (P treatment). To assess the short-term impact of UVR as a function of irradiance, we determined photosynthesis versus irradiance (Pvs.E) curves. From these curves the maximum carbon uptake rate (P(max)) and the light saturation parameter (E(k)) were obtained, with values of approximately 12.8-14.4 microg C (microg chl a)(-1) h(-1), and approximately 250 micromol m(-2) s(-1), respectively. A significant UVR effect on assimilation numbers was observed when samples were exposed at irradiances higher than E(k), with samples exposed to full solar radiation having significant less carbon fixation than those exposed only to PAR. Biological weighting functions of P. cruentum were used to evaluate the UVR impact per unit energy received by the cells; the data indicate that the species is as sensitive as natural phytoplankton from the southern China Sea; however, it is much more resistant than Antarctic assemblages. When evaluating the combined effects of mixing speed and UVR, it was seen that samples rotating fast within the upper mixed layer were less inhibited by UVR as compared to those under slow mixing or in fixed samples. Growth of P. cruentum over a week-long experiment was not affected by neither UVR nor UV-A; additionally, low photoinhibition was found at the end as compared to that at the beginning of this experiment. Our results thus indicate that, although on short-term basis P. cruentum is affected by solar UVR, it can acclimate to minimize UVR-induced effects when given enough time.

Physiological alterations and regulation of heterocyst and nitrogenase formation in Het(-) Fix(-) mutant strain of Anabaena variabilis.

Physiological alterations and regulation of heterocyst and nitrogenase formation have been studied in Het(-) Fix(-) mutant strain of diazotrophic cyanobacterium Anabaena variabilis. Het(-) Fix(-) mutant strain of A. variabilis has been isolated by N-methyl-N'-nitro-N"-nitrosoguanidine (NTG) mutagenesis and was screened with the penicillin enrichment (500 microg ml(-1)). Growth, heterocyst differentiation, nitrogenase and glutamine synthetase (biosynthetic and transferase), (14)CO(2)-fixation, nitrate reductase (NR), nitrite reductase (NiR), glucose-6-phosphate dehydrogenase (G6PDH), and isocitrate dehydrogenase (IDH) activities, and NO(3)(-), NO(2)(-), and NH(4)(+) uptake and whole cell protein profile in different metabolic conditions were studied in the Het(-) Fix(-) mutant strain taking wild-type A. variabilis as reference. Het(-) Fix(-) mutant strain was incapable of assimilating elemental nitrogen (N(2)) due to its inability to form heterocysts and nitrogenase and this was the reason for its inability to grow in BG-11(0) medium (free from combined nitrogen). In contrast, wild-type strain grew reasonably well in the absence of combined nitrogen sources and also showed heterocyst differentiation (8.5%) and nitrogenase activity (10.8 etamol C(2)H(4) formed microg(-1) Chl a h(-1)) in N(2)-medium. Wild-type strain also exhibited higher NR, NiR, and GS activities compared to its Het(-) Fix(-) mutant strain, which may presumably be due to acquisition of high uptake of NO(3)(-), NO(2)(-), and NH(2)(+). Wild-type strain in contrast to its Het(-) Fix(-) mutant strain also exhibited high level of G6PDH, IDH, and (14)CO(2) fixation activities. Low levels of G6PDH and IDH activities in Het(-) Fix(-) mutant strain further confirmed the lack of heterocyst differentiation and nitrogenase activity in the Het(-) Fix(-) mutant strain.NR, NiR, and GS activities in both the strains were energy-dependent and the energy required is mainly derived from photophosphorylation. Furthermore, it was found that de novo protein synthesis is necessarily required for the activities of NR, NiR, and GS in both wild-type and its Het(-) Fix(-) mutant strain.

The relative importance of tryptophan-dependent and tryptophan-independent biosynthesis of indole-3-acetic acid in tobacco during vegetative growth.

A quantitative study of indole-3-acetic acid (IAA) turnover, and the contribution of tryptophan-dependent and tryptophan-independent IAA-biosynthesis pathways, was carried out using protoplast preparations and shoot apices obtained from wild-type and transgenic, IAA-overproducing tobacco (Nicotiana tabacum L.) plants, during a phase of growth when the level of endogenous IAA was stable. Based on the rate of disappearance of [13C6]IAA, the half-life of the IAA pool was calculated to be 1.1 h in wild-type protoplasts and 0.8 h in protoplasts from the IAA-overproducing line, corresponding to metabolic rates of 59 and 160 pg IAA (microg Chl)(-1) h(-1), respectively. The rate of conversion of tryptophan to IAA was 15 pg IAA (microg Chl)(-1) h(-1) in wild-type protoplasts and 101 pg IAA (microg Chl)(-1) h(-1) in protoplasts from IAA-overproducing plants. In both instances, IAA was metabolised more rapidly than it was synthesised from tryptophan. As the endogenous IAA pools were in a steady state, these findings indicate that IAA biosynthesis via the tryptophan-independent pathway was 44 pg IAA (microg Chl)(-1) h(-1) and 59 pg IAA (microg Chl)(-1) h(-1), respectively, in the wild-type and transformed protoplast preparations. In a parallel study with apical shoot tissue, the presumed site of IAA biosynthesis, the rate of tryptophan-dependent IAA biosynthesis exceeded the rate of metabolism of [13C6]IAA despite the steady state of the endogenous IAA pool. The most likely explanation for this anomaly is that, unlike the protoplast system, injection of substrates into the apical tissues did not result in uniform distribution of label, and that at least some of the [2H5]tryptophan was metabolised in compartments not normally active in IAA biosynthesis. This demonstrates the importance of using experimental systems where labelling of the precursor pool can be strictly controlled.