Sediment accumulation rate and radiological characterisation of the sediment of Palmones River estuary (southern of Spain).

Chemical analyses and radioecological methods were combined in order to estimate the sediment accumulation rate in the upper 20 cm depth of the Palmones River estuary. Organic matter, total carbon, C:N and (137)Cs vertical profiles showed changes at 13 cm depth. These changes could be associated with the decrease in river input since 1987 when a dam situated in the upper part of the estuary started to store water. Using 1987 as reference to date the sediment, accumulation rate was 1.2 cm yr(-1). As alternative method, two layer model of (210)Pb(xs) vertical distribution showed a sedimentation rate of 0.7 cm yr(-1) with a surface mixing layer of 7 cm thickness. The high ammonium, potassium and sodium content in pore water and the strong correlation between (137)Cs activities and organic matter in dry sediment suggests that (137)Cs (the only anthropogenic product detected) is mainly accumulated in the estuary associated with the particulate organic material from the catchment area.

Non-photosynthetic enhancement of growth by high CO2 level in the nitrophilic seaweed Ulva rigida C. Agardh (Chlorophyta).

The effects of increased CO2 levels (10,000 microl l(-1)) in cultures of the green nitrophilic macroalga Ulva rigida C. Agardh were tested under conditions of N saturation and N limitation, using nitrate as the only N source. Enrichment with CO2 enhanced growth, while net photosynthesis, gross photosynthesis, dark respiration rates and soluble protein content decreased. The internal C pool remained constant at high CO2, while the assimilated C that was released to the external medium was less than half the values obtained under ambient CO2 levels. This higher retention of C provided the source for extra biomass production under N saturation. In N-sufficient thalli, nitrate-uptake rate and the activity of nitrate reductase (EC 1.6.6.1) increased under high CO2 levels. This did not affect the N content or the internal C:N balance, implying that the extra N-assimilation capacity led to the production of new biomass in proportion to C. Growth enhancement by increased level of CO2 was entirely dependent on the enhancement effect of CO2 on N-assimilation rates. The increase in nitrate reductase activity at high CO2 was not related to soluble carbohydrates or internal C. This indicates that the regulation of N assimilation by CO2 in U. rigida might involve a different pathway from that proposed for higher plants. The role of organic C release as an effective regulatory mechanism maintaining the internal C:N balance in response to different CO2 levels is discussed.

Affinity for inorganic carbon of Gracilaria tenuistipitata cultured at low and high irradiance.

Regulation by irradiance level of the mechanism for dissolved inorganic carbon (DIC) acquisition was examined in the red macroalga Gracilaria tenuistipitata Zhang et Xia. For this purpose, affinity for external DIC, carbonic anhydrase (CA; EC 4.2.1.1) activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were determined in thalli grown at 45 and 500 micromol photons m(-2) s(-1). Oxygen evolution rates declined by 50% when the medium pH was changed from 8.1 to 8.7, and the pH compensation point attained was ca. 9.2. These characteristics were unaffected by the light treatments. In contrast, photosynthetic conductance for DIC at pH 8.7 was doubled in thalli grown at high irradiance compared with those grown at low irradiance (to 0.74 x 10(-6) from 0.33 x 10(-6) m s(-1)). Photosynthetic rates at saturating DIC concentration were also higher by 60% in thalli grown at high irradiance. These differences could not be attributed to changes in the use of external DIC, since external CA activity did not vary. Although the irradiance level did not modify the pool size of Rubisco, Rubisco content expressed on a chlorophyll a basis was almost doubled at high irradiance. These results likely indicate that the internal transport of DIC towards the active-site of Rubisco, rather than the external use of DIC, is enhanced in the thalli grown at high irradiance.

Regulation of the mechanism for HCO (3) (-) use by the inorganic carbon level in Porphyra leucosticta Thur. in Le Jolis (Rhodophyta).

The capacity for HCO (3) (-) use by Porphyra leucosticta Thur. in Le Jolis grown at different concentrations of inorganic carbon (C(i)) was investigated. The use of HCO (3) (-) at alkaline pH by P. leucosticta was demonstrated by comparing the O(2) evolution rates measured with the O(2) evolution rates theoretically supported by the CO(2) spontaneously formed from HCO (3) (-) . Both external and internal carbonic anhydrase (CA; EC 4.2.1.1) were implied in HCO (3) (-) use during photosynthesis because O(2) evolution rates and the increasing pH during photosynthesis were inhibited in the presence of azetazolamide and ethoxyzolamide (inhibitors for external and total CA respectively). Both external and internal CA were regulated by the C(i) level at which the algae were grown. A high C(i) level produced a reduction in total CA activity and a low C(i) level produced an increase in total CA activity. In contrast, external CA was increased at low C(i) although it was not affected at high C(i). Parallel to the reduction in total CA activity at high C(i) is a reduction in the affinity for C(i), as estimated from photosynthesis versus C(i) curves, was found. However, there was no evident relationship between external CA activity and the capacity for HCO (3) (-) use because the presence of external CA became redundant when P. leucosticta was cultivated at high C(i). Our results suggest that the system for HCO (3) (-) use in P. leucosticta is composed of different elements that can be activated or inactivated separately. Two complementary hypotheses are postulated: (i) internal CA is an absolute requirement for a functioning C(i)-accumulation mechanism; (ii) there is a CO(2) transporter that works in association with external CA.

Biochemical and physiological responses of Gracilaria tenuistipitata uuder two different nitrogen treatments.

The influence of nitrogen on ribulose-1.5-bisphosphate carboxylase/oxygenase (Rubisco. EC 4.1.1.39) content is poorly understood in macroalgae. N-deficient Gracilaria tenuistipitata Zhang et Xia var. liui was cultivated in the laboratory under constant light intensity and temperature. Biochemical and physiological variables were monitored after a high (1 mM) or low (o. 1 mM) nitrate pulse. Rubisco content in crude extracts was estimated by SDS-PAGE with the Coomassie Blue Staining procedure. Nitrate was consumed immediately in the low-N treatment, but there was always an external nitrate source in the high-N treatment. Total soluble proteins and phycobiliproteins decreased as internal nitrogen diminished in the low-N treatment, but kept fairly constant in N-sufficient conditions. However, Rubisco content increased until the 7th day and then started to decrease in both cases. Fresh weight increment showed a better correlation with Rubisco than with pigment content.

[Photocontrol of the synthesis of chlorophyll a and phycocyanin in the cyanobacterium Calothrix crustacea Schousboe]. / Fotocontrol de la síntesis de clorofila a y de ficocianina en la cianobacteria Calothrix crustacea Schousboe.

Chlorophyll a and phycocyanin synthesis in the cyanobacterium Calothrix crustacea Schousboe (ecophene Rivularia bullata) have been studied in white light after the application of red and green light pulses. The light quality produces a complementary pattern in the pigment synthesis. Chlorophyll synthesis is stimulated by red light pulses whereas phycocyanin synthesis is by green light pulses. Because the effect of red light on chlorophyll synthesis shows some far-red photoreversibility, the action of phytochrome is proposed. The green light effect on phycocyanin synthesis is only partially reversed by far-red light. This reversion is lost after incubation in white light for two hours. The effect of green light on phycocyanin synthesis could not only be due to phytochrome since theoretically in green light the level of the active form of phytochrome is lower than in red light. Thus, the action of a specific green light photoreceptor is proposed.

[Control of chlorophyll a synthesis by phytochrome and cryptochrome in the red alga Corallina elongata Ellis et Soland]. / Control de la síntesis de clorofila a por el fitocromo y criptocromo en la rodofícea Corallina elongata Ellis et Soland.

Chlorophyll a synthesis in the red alga Corallina elongata is controlled by phytochrome and by a specific blue light photoreceptor. Although the estimated photoequilibrium of phytochrome is similar in blue and red light, the amount of chlorophyll accumulated is greater in blue light, which implies the action of cryptochrome, according to the criteria for the specific blue light photoreceptor involvement. The amount of chlorophyll synthesized is greater when the level of photoequilibrium approaches 65% (in blue and red light) than with higher levels (72.7% in white light and 70.8% in green light). The action of phytochrome is demonstrated by the induction of chlorophyll synthesis after red pulses and the reversion after far red pulses. The reversion is not complete but the percentage of reversibility is high (85-90%). The amount of chlorophyll accumulated is greater in darkness after the application of red light pulses than in white light after the same light pulses. The induction of chlorophyll synthesis is greater after red pulses than after continuous red light. The existence of a fast destruction of chlorophyll in continuous light is observed. This destruction is greater in the high photoequilibrium of phytochrome (70-72%). The turnover times and the induction mechanism of chlorophyll synthesis must be very fast. This indicates the existence of a possible rapid adaptation to the change in light quality and intensity in the marine system.