Decline In Chlorophyll Research Articles

Shifting nutrient-mediated interactions between algae and bacteria in a microcosm: Evidence from alkaline phosphatase assay

The impacts of different nutrient additions (N+P, N+P+C, 4N+P, 4N+P+C, N+2P) on the growth of algae and bacteria were studied in a microcosm experiment. Since alkaline phosphatase activity (APA) provides an indication of phosphorus deficiency, the higher value for algal APA in the treatments with excess nitrogen and for bacterial APA in the treatments with excess carbon suggested that, algal and bacterial phosphorus-limited status were induced by abundant nitrogen and carbon input, respectively. Bacterial phosphorus-limited status was weakened due to higher bacterial competition for phosphorus, compared to algae. In comparison with the bacterial and specific bacterial APA, higher values of algal and specific algal APA were found, which showed a gradual increase that coincided with the increase of chlorophyll a concentration. This fact indicated not only a stronger phosphorus demand by algae than by bacteria, but also a complementary relationship for phosphorus demand between algae and bacteria. However, this commensalism could be interfered by glucose input resulting in the decline of chlorophyll a concentration. Furthermore, the correlation between bacterial numbers and chlorophyll a concentration was positive in treatments without carbon and blurry in treatments with carbon. These observations validate a hypothesis that carbon addition can stimulate bacterial growth justifying bacterial nutrient demand, which decreases the availability of nutrients to algae and affects nutrient relationship between algae and bacteria. However, this interference would terminate after algal and bacterial adaption to carbon input.

Relationship between electrical conductivity, softening and color of Fuerte avocado fruits during ripening

To identify the most important ripening parameters of Fuerte avocado fruits, and to quantify the relationship between color changes, electrical conductivity and softening of avocado fruits, the ripening process was investigated to fulfill the consumer and market demands. Mature and high quality avocado fruits (Persea Americana Mill.) were held to ripe at 20C in controlled temperature rooms with 90-95% relative humidity for two weeks. Fruit quality characteristics (respiration rate, soluble solids content (SSC), total acidity (TA), ascorbic acid and oil content) during ripening period at 20C were evaluated. Moreover, ripening parameters as color changes, chlorophyll contents, fruit firmness and electrical conductivity and ripening enzymes (CX and PME) were also investigated throughout ripening process. During ripening period for 2 weeks at 20C, fruit quality criteria showed that respiration rate and oil content had a noticeable significant increase with the ripening increase. While, acidity (TA), soluble solids (SSC) and ascorbic acid content cleared a slight and significant decrease. Throughout color development, the three parameters lightness (L*), hue (h◦) and chroma (C*) changed significantly, hue decreased little, lightness moderately, while chroma changed more quickly. Moreover, an significant decline in chlorophyll a and b concentration occurred and reflected to color changes during ripening process. For ripening enzyme activities, Fuerte avocado fruits showed a great increase in cellulase activity compared with gradual decrease in Pectinmethylesterase activity after ripening. Avocado fruit firmness markedly reduced gradually after harvest till ripening at 20C, and this decline was positively correlated with an increase of electrical conductivity of the fruit tissue suggesting a gradual loss of cell membrane integrity. This increase in conductivity was promoted by ripening process. These results have allowed us to set that ripening process had some parameters were simple and rapid to measure as ripening indices. We conclude that in Fuerte avocado fruits, electrical conductivity (EC) can serve as a good indicator of membrane permeability and that it is highly correlated with ethylene production, softening and also demonstrates a relationship between firmness and EC.

Longitudinal trends and discontinuities in nutrients, chlorophyll, and suspended solids in the Upper Mississippi River: implications for transport, processing, and export by large rivers

Across the distances spanned by large rivers, there are important differences in catchment characteristics, tributary inputs, and river morphology that may cause longitudinal changes in nutrient, chlorophyll, and suspended solids concentrations. We investigated longitudinal and seasonal patterns in the Upper Mississippi River (UMR) using long-term data (1994–2005) from five study reaches that spanned 1300 km of the UMR. Lake Pepin, a natural lake in the most upstream study reach, had a clear effect on suspended material in the river. Suspended solids and total phosphorus (TP) concentrations were substantially lower downstream of the lake and percent organic material (OM%) in suspension was higher. Below L. Pepin, mean total and organic suspended solids (TSS, OSS) and TP increased downriver and exhibited approximately log-linear relationships with catchment area, whereas OM% declined substantially downriver. Despite the downriver increase in TSS and OSS, concentrations similar to those above L. Pepin do not occur until ~370 km downriver indicating the extent of the influence of L. Pepin on the UMR. Chlorophyll concentrations were lower in the most downstream study reach, likely reflecting the shorter residence time and poor light climate, but there was not a consistent longitudinal decline in chlorophyll across the study reaches. Dissolved silica (DSi), DSi:TN, and DSi:TP declined downriver suggesting that DSi uptake and sedimentation by river phytoplankton may be reducing DSi transport in the river, and indicating that the eutrophication of the river may contribute to a reduction of DSi export to the Gulf of Mexico.

Impacts of two biomanipulation fishes stocked in a large pen on the plankton abundance and water quality during a period of phytoplankton seasonal succession

Silver and bighead carp were stocked in a large pen to control the nuisance cyanobacterial blooms in Meiliang Bay of Lake Taihu. Plankton abundance and water quality were investigated about once a week from 9 May to 7 July in 2005. Biomass of both total crustacean zooplankton and cladocerans was significantly suppressed by the predation of pen-cultured fishes. There was a significant negative correlation between the N:P weight ratio and phytoplankton biomass. The size-selective predation by the two carps had no effect on the biomass of green alga Ulothrix sp. It may be attributed to the low fish stocking density (less than 40 g m −3) before June. When Microcystis dominated in the water of fish pen, the pen-cultured carps effectively suppressed the biomass of Microcystis, as indicated by the significant decline of chlorophyll a in the >38 μm fractions of the fish pen. Based on the results of our experiment and previous other studies, we conclude that silver and bighead carp are two efficient biomanipulation tools to control cyanobacterial ( Microcystis) blooms in the tropical/subtropical eutrophic waters. Moreover, we should maintain an enough stocking density for an effective control of phytoplankton biomass.

Variance in Leaf Chlorophyll Decline Induced by Elevated-ozone in Four Chinese Rice Cultivars under Fully Open-air Field Conditions

Variance in Leaf Chlorophyll Decline Induced by Elevated-ozone in Four Chinese Rice Cultivars under Fully Open-air Field Conditions

Ecophysiological tolerance of duckweeds exposed to copper

Although essential for plants, copper can be toxic when present in supra-optimal concentrations. Metal polluted sites, due to their extreme conditions, can harbour tolerant species and/or ecotypes. In this work we aimed to compare the physiological responses to copper exposure and the uptake capacities of two species of duckweed, Lemna minor (Lm(EC1)) and Spirodela polyrrhiza (SP), from an abandoned uranium mine with an ecotype of L. minor (Lm(EC2)) from a non-contaminated pond. From the lowest Cu concentration exposure (25 μM) to the highest (100 μM), Lm(EC2) accumulated higher amounts of copper than Lm(EC1) and SP. Dose–response curves showed that Cu content accumulated by Lm(EC2) increases linearly with Cu treatment concentrations ( r 2 = 0.998) whereas quadratic models were more suitable for Lm(EC1) and SP ( r 2 = 0.999 and r 2 = 0.998 for Lm(EC1) and SP, respectively). A significant concentration-dependent decline of chlorophyll a (chl a) and carotenoid occurred as a consequence of Cu exposure. These declines were significant for Lm(EC2) exposed to the lowest Cu concentration (25 μM) whereas for Lm(EC1) and SP a significant decrease in chl a and carotenoids was observed only at 50 and 100 μM-Cu. Electric conductivity (EC) and malondialdehyde (MDA) content increased after Cu exposure, indicating oxidative stress. Significant increase of EC was observed in Lm(EC2) for all Cu concentrations whereas the increase for Lm(EC1) and SP became significant only after an exposure to 50 μM-Cu. On the contrary, for Lm(EC1), SP, and Lm(EC2), MDA content significantly increased even at the lowest concentration. Protein content and catalase (CAT) activity showed a decrease with an increase in Cu concentration. For the species Lm(EC1) and SP, a significant effect of copper on CAT activity was observed only at the highest concentration (100 μM-Cu) whereas, for Lm(EC2), this effect started to be significant after an exposure to 50 μM-Cu. Superoxide dismutase (SOD) activity increased with increasing concentrations of Cu, with a very similar trend between the three populations of duckweed. However, due to the facts that enzyme activity is expressed as units of activity per gram of protein and that protein content decreased with Cu exposure, the increase in SOD activity might partly result from a relative increase of this enzyme inside the pool of proteins. Consequently, the results obtained in our experimental conditions strongly suggest that duckweed species from the uranium-polluted area have developed mechanisms to cope with metal toxicity and that this tolerance is based on the existence of protective mechanism to limit the metal uptake rather than on an enhancement of the antioxidative metabolism.

Amino Acid Substitutions in Homologs of the STAY-GREEN Protein Are Responsible for thegreen-fleshandchlorophyll retainerMutations of Tomato and Pepper

Color changes often accompany the onset of ripening, leading to brightly colored fruits that serve as attractants to seed-dispersing organisms. In many fruits, including tomato (Solanum lycopersicum) and pepper (Capsicum annuum), there is a sharp decrease in chlorophyll content and a concomitant increase in the synthesis of carotenoids as a result of the conversion of chloroplasts into chromoplasts. The green-flesh (gf) and chlorophyll retainer (cl) mutations of tomato and pepper, respectively, are inhibited in their ability to degrade chlorophyll during ripening, leading to the production of ripe fruits characterized by both chlorophyll and carotenoid accumulation and are thus brown in color. Using a positional cloning approach, we have identified a point mutation at the gf locus that causes an amino acid substitution in an invariant residue of a tomato homolog of the STAY-GREEN (SGR) protein of rice (Oryza sativa). Similarly, the cl mutation also carries an amino acid substitution at an invariant residue in a pepper homolog of SGR. Both GF and CL expression are highly induced at the onset of fruit ripening, coincident with the ripening-associated decline in chlorophyll. Phylogenetic analysis indicates that there are two distinct groups of SGR proteins in plants. The SGR subfamily is required for chlorophyll degradation and operates through an unknown mechanism. A second subfamily, which we have termed SGR-like, has an as-yet undefined function.

Stoichiometric relationships in vernal pond plankton communities

Summary1. The light‐nutrient hypothesis (LNH) predicts that changes in light supply can alter the balance of nutrient and energy limitation in primary producers. We tested this prediction by examining temporal changes in vernal forest ponds, which are highly dynamic systems with respect to seasonal change in light and nutrient supply. In three vernal ponds that differ in productivity, we measured changes in light, total and seston nitrogen and phosphorus, and seston carbon and chlorophyll during the spring, before and after tree leaf‐out. We also quantified changes in the population dynamics of the major zooplankton grazers in these systems.2. In each pond, nutrient levels increased and light levels declined, creating a temporal shift in light‐nutrient supply to the plankton. Results generally supported predictions of stoichiometric theory and the LNH, but there were notable exceptions.3. Seston C : N : P ratios rapidly changed in response to dramatic increases in N and P supply rates. However, seston N : P was typically lower than values for total N : P in the water. Furthermore, as predicted, we observed a decline in seston C : P as the light : nutrient ratio declined, but seston C : N simultaneously increased. These results suggest an unexpected shift towards potential nitrogen limitation. Alternatively, this change in nutrient ratios may be driven by a seasonal change in phytoplankton composition or nutritional mode.4. Seston carbon concentrations remained stable despite seasonal changes in grazing intensity associated with the phenology of large‐bodied Daphnia grazers. However, chlorophyll concentrations declined dramatically as the season progressed, resulting in a simultaneous decline in the C : Chlorophyll ratio of seston. Both pond shading and increased grazing probably contributed to the decline in chlorophyll.

Increase in activity, glycosylation and expression of cytokinin oxidase/dehydrogenase during the senescence of barley leaf segments in the dark

The aim of the study was to elucidate relations between senescence and cytokinin oxidase/dehydrogenase (CKX, EC 1.4.3.18/1.5.99.12). Segments derived from first foliage leaves of Hordeum vulgare L. cv. Alexis were put with their bases into water and kept in darkness. Their senescence was characterized, e.g. by a 60% decline in chlorophyll within 5 days. During this time, the in vitro activity of CKX increased fast and markedly, e.g. 14‐fold. Application of 10−4M kinetin (Kin), which slightly retarded the loss of chlorophyll, multiplied the enhancement of CKX activity strongly. Both in the presence and in the absence of Kin, the proportion of glycosylated to non‐glycosylated CKX increased during senescence. By hybridization with an antisense RNA probe derived from a fragment of the CKX gene Zmckx1 of maize, an increase of the corresponding transcript of the barley gene Hvckx1 in segments incubated without Kin was shown. The content of base and riboside cytokinins slowly declined in such segments, which argues against triggering but for facilitating senescence processes by CKX.

Matricaria chamomilla is not a hyperaccumulator, but tolerant to cadmium stress

The influence of low (3 µM) and high (60 and 120 µM) cadmium (Cd) concentrations were studied on selected aspects of metabolism in 4-week-old chamomile (Matricaria chamomilla L.) plants. After 10 days’ exposure, dry mass accumulation and nitrogen content were not significantly altered under any of the levels of Cd. However, there was a significant decline in chlorophyll and water content in the leaves. Among coumarin-related compounds, herniarin was not affected by Cd, while its precursors (Z)- and (E)-2-β-d-glucopyranosyloxy-4-methoxycinnamic acids (GMCAs) increased significantly at all the levels of Cd tested. Cd did not have any effect on umbelliferone, a stress metabolite of chamomile. Lipid peroxidation was also not affected by even 120 µM Cd. Cd accumulation was approximately seven- (60 µM Cd treatment) to eleven- (120 µM Cd treatment) fold higher in the roots than that in the leaves. At high concentrations, it stimulated potassium leakage from the roots, while at the lowest concentration it could stimulate potassium uptake. The results supported the hypothesis that metabolism was altered only slightly under high Cd stress, indicating that chamomile is tolerant to this metal. Preferential Cd accumulation in the roots indicated that chamomile could not be classified as a hyperaccumulator and, therefore, it is unsuitable for phytoremediation.

Nutrient and phytoplankton dynamics during the stationary and declining phases of a phytoplankton bloom induced by iron-enrichment in the eastern subarctic Pacific

Abstract This paper reports on the variations in nutrient concentrations and phytoplankton dynamics during the stationary and declining phases of a phytoplankton bloom induced by a mesoscale iron-enrichment conducted in the high-nutrient low-chlorophyll (HNLC) eastern subarctic Pacific. During the 26-d sampling period, the main pycnocline was located between 30 and 45 m with a shallow pycnocline developing at 10 m, 19 d after the first iron-enrichment. The iron-induced bloom dominated by diatoms peaked during days 15 and 18, a period of high chlorophyll a concentrations (ca. 5 mg m−3), and declined thereafter. Nitrogenous nutrients and phosphate were not depleted during the whole experiment. In contrast, silicic acid and iron concentrations became very low during the stationary phase of the diatom bloom (days 15–18) and Fv/Fm declined. These observations suggest that silicic acid and iron limitation probably prevented further development of the diatom bloom. The decline in chlorophyll a concentrations during days 19–24 was mostly due to the decrease in diatom abundance. On the other hand, cell abundances of pico- and nanophytoplankton exhibited little change until day 24. In the layer located between the main and the shallow pycnocline (10–30 m), ammonium and silicic acid concentration increased during days 19–26, suggesting recycling of these nutrients. The amount of silicic acid recycled during that period was estimated at 71.3–99.2 mmol m−2, while the dissolution rate of biogenic silica (BSi) was estimated to be 5.9–9.2% d−1 in the upper 50 m of the water column. These results show that the development of a shallow pycnocline during the experiment accelerated the iron and silicic acid depletion in the upper mixed layer and influenced the recycling of the organic matter assimilated during the iron-induced bloom in the ocean surface.

Effects of pre‐processing of Raman spectra on in vivo classification of nutrient status of microalgal cells

AbstractRaman spectra were obtained from cells of the chlorophyte unicellular eukaryotic alga Dunaliella tertiolecta, which had been grown either under nutrient‐replete conditions or starved of nitrogen for 4 days. Spectra were rich in bands which could all be attributed to either chlorophyll a or β‐carotene. A cursory examination of the differences between the spectra of replete and starved cells indicated a decline in chlorophyll a and an increase in β‐carotene in chlorophytes. Unprocessed spectra showed pronounced baseline effects. A variety of pre‐processing techniques were used in an attempt to visualise the spectral, and hence chemical, differences in the transformed data and perform classification based upon these differences. Six types of spectral pre‐processing were compared: baseline correction with vector normalisation; Multiplicative Scatter Correction (MSC), Extended Multiplicative Signal Correction (EMSC); Standard Normal Variate (SNV); and vector normalised 1st and 2nd derivative spectra. Results for Soft Independent Modelling of Class Analogy (SIMCA) and Partial Least Squares (PLS) discriminant analysis were compared. All pre‐processing methods allowed spectral differences between N‐replete and N‐starved spectra to be visualised, with derivatives and EMSC scoring the lowest RMSEC and RMSEV values with PLS and also the best overall classification results. SIMCA was not suited to classifying the nutrient classes under any of the pre‐treatments, due to the small model distances involved. Copyright © 2006 John Wiley & Sons, Ltd.

Photosynthetic activity, pigment composition and antioxidative response of two mustard ( Brassica juncea) cultivars differing in photosynthetic capacity subjected to cadmium stress

Photosynthetic performance, contents of chlorophyll and associated pigments, cellular damage and activities of antioxidative enzymes were investigated in two mustard (Brassica juncea L.) cultivars differing in photosynthetic capacity subjected to cadmium (Cd) stress. Exposure to Cd severely restricted the net photosynthetic rate (P(N)) of RH-30 compared to Varuna. This corresponded to the reductions in the activities of carbonic anhydrase (CA) and ribulose-1,5-bisphosphate carboxylase (Rubisco) in both the cultivars. Decline in chlorophyll (Chl) (a+b) and Chl a content was observed but decrease in Chl b was more conspicuous in Varuna under Cd treatments, which was responsible for higher Chl a:b ratio. Additionally, the relative amount of anthocyanin remained higher in Varuna compared to RH-30 even in the presence of high Cd concentration, while percent pheophytin content increased in RH-30 at low Cd concentration. A higher concentration of Cd (100 mg Cd kg(-1) soil) resulted in elevated hydrogen peroxide (H(2)O(2)) content in both the cultivars. However, Varuna exhibited lower content of H(2)O(2) in comparison to RH-30. This was reflected in the increased cellular damage in RH-30, expressed by greater thiobarbituric acid reactive substances (TBARS) content and electrolyte leakage. The enhanced activities of antioxidative enzymes, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) and also lower activity of superoxide dismutase (SOD) in Varuna alleviated Cd stress and protected the photosynthetic activity.

Elevated sunlight promotes ripening-associated pigment changes in apple fruit

Content and composition of chlorophylls and carotenoids were studied with non-destructive reflectance measurements and HPLC in sun- and shade-adapted skins of apple fruit ripening on and off the tree. In on-tree ripening fruit elevated sunlight brought about a decline in chlorophyll and retention or an increase in total carotenoid content. In later harvested fruit the molar ratio between the pigments was high and exceeded unity in sunlit (but not in shaded) skin on the tree. Postharvest, apples with a chlorophyll content lower than 2 nmol cm −2 displayed a rapid decrease in chlorophyll and a remarkable induction of carotenoids, much more pronounced in sunlit skin. In the progress of ripening, the carotenoid pattern underwent considerable changes: a decline in lutein and β-carotene and a build up of violaxanthin and fatty acid xanthophyll esters, the latter dominating at advanced stages of ripening. The results suggest that the differences in pigment dynamics between sunlit and shaded skins both on- and off-tree could be regarded as acceleration and enhancement of ripening-specific changes. Since promotion of ripening in sunlit fruit surfaces might be considerable in apples growing under contrasting illumination this should be taken into account in planning of harvest time and selection of storage conditions for apple fruit.

Nature of Phosphorus Limitation in the Ultraoligotrophic Eastern Mediterranean

Phosphate addition to surface waters of the ultraoligotrophic, phosphorus-starved eastern Mediterranean in a Lagrangian experiment caused unexpected ecosystem responses. The system exhibited a decline in chlorophyll and an increase in bacterial production and copepod egg abundance. Although nitrogen and phosphorus colimitation hindered phytoplankton growth, phosphorous may have been transferred through the microbial food web to copepods via two, not mutually exclusive, pathways: (i) bypass of the phytoplankton compartment by phosphorus uptake in heterotrophic bacteria and (ii) tunnelling, whereby phosphate luxury consumption rapidly shifts the stoichiometric composition of copepod prey. Copepods may thus be coupled to lower trophic levels through interactions not usually considered.

PHYSIOLOGICAL IMPACTS OF DICHLOROPHYNYLDIMETHYL UREA ON SOME GREEN ALGAE SPECIES

Three algae species belonging to Chlorophyta; i.e Chlorella sp ., Scenedesmus sp . and Haematococcus pluvialis, were incubated under different concentrations of the photosynthetic inhibitor dichlorophynyldimethylurea (DCMU). Algae were treated with 0, 1, 2, 4 and 8x10-5M DCMU added to N8 macronutrient solution containing ammonium acetate instead of potassium nitrate. The measured parameters were optical density, cell count, medium reaction (pH), total chlorophyll, total carotenoids, crude protein and lipids as ether extract. Results showed that DCMU inhibited growth as optical density for both Scenedesmus sp. and Chlorella sp. H. pluvialis exhibited more resistance against all given concentrations. Chlorophyll reached the maximum with lower and moderate levels of DCMU with Scenedesmus sp. and Chlorella sp. As for H. pluvialis, all used concentrations inhibited chlorophyll accumulation. A different manner was observed on carotenoids accumulation, where the decline of chlorophyll was associated with the decomposition of crude protein and rise in carotenoids and lipids content especially with H. pluvialis.

Growth and Pigment Content of Container-grown Impatiens and Petunia in Relation to Root Substrate pH and Applied Micronutrient Concentration

The objective was to quantify the effect of substrate pH and micronutrient concentration on growth and pigment content for two floricultural crop species, Petunia ×hybrida `Priscilla' and Impatiens wallerana `Rosebud Purple Magic'. A 70% peat: 30% perlite medium was amended with dolomitic hydrated lime to achieve five substrate pH's ranging from pH 4.4 to 7.0. Plants were grown in 10-cm-diameter pots in a greenhouse for 4 weeks, and irrigated with a fertilizer containing (in mg·L-1) 210N-31P-235K-200Ca-49Mg. Micronutrients were applied using an EDTA (ethylenedinitrilotetraacetic acid) chelated micronutrient blend (C111), at 1×, 2×, and 4× concentrations (in mg·L-1) of 0.50Fe-0.25Mn-0.025Zn-0.04Cu-0.075B-0.01Mo. Petunia shoot dry mass and stem caliper decreased as substrate pH increased, whereas leaf length and width remained unchanged. The highest level of C111 resulted in higher dry mass and smaller leaf area compared with other C111 levels. Overall, substrate pH and C111 had little effect on plant size or mass for impatiens. For both species, increasing substrate pH above 5.3 resulted in a decline in chlorophyll, carotenoids, and the SPAD chlorophyll index (measured with a Minolta-502 SPAD meter) compared with the lowest three pH levels. Chlorosis was observed at pH 7 after 2 weeks of growth. Increasing C111 concentration had no effect on pigment content below pH 5.3, but increased pigment content at higher pH levels. The SPAD index was highly correlated with chlorophyll content. This research emphasizes that an acceptable range in substrate pH can vary depending on fertilizer practices, with higher micronutrient concentration compensating for lower solubility at high substrate pH.

Hydrophytes lack potential to exhibit cadmium stress induced enhancement in lipid peroxidation and accumulation of proline

Investigations were carried out to evaluate if hydrophytes (viz. Ceratophyllum, Wolffia, and Hydrilla) can be used as markers to assess the level of heavy metal pollution in aquatic bodies. The potential of these hydrophytes for lipid peroxidation and accumulation of proline in response to cadmium (Cd 2+) pollution was studied. Hydrophytes were raised in artificial pond water (APW) supplemented with various levels of Cd 2+. Interestingly, unlike mesophytes none of the hydrophytes showed ability to accumulate proline. Infact, in response to Cd 2+ pollution hydrophytes exhibited a decline in proline levels in comparison to controls but mesophytes (viz. Brassica juncea, Vigna radiata and Triticum aestivum) showed progressive increase in the level of proline with increase in the extent of Cd 2+ pollution. Mesophytes showed six to nine-fold increase in the level of proline in response to 1 mM Cd 2+. The potential of the above hydrophytes for lipid peroxidation was also low under Cd 2+ stress. In contrast, as expected a significant enhancement in the lipid peroxidation was observed in all three mesophytes in response to their exposure to Cd 2+. About two-fold increase in production of malondialdehyde (a cytotoxic product of lipid peroxidation) was recorded in mesophytes exposed to 1 mM Cd 2+. However, a decline in chlorophyll (Chl a and Chl b) levels was recorded in response to Cd 2+pollution both in hydrophytes as well as mesophytes. In summary, hydrophytes neither have potential to accumulate proline nor have ability to accelerate lipid peroxidation under heavy metal stress. This suggests that the adaptive mechanism(s) existing in hydrophytes to tackle heavy metal stress is distinct from that in mesophytes.

Limnological features in Tapacurá reservoir (northeast Brazil) during a severe drought

The drastic interactions of weather as El Nino events with catchment and hydrological processes can cause unexpected changes in physical, chemical and biological properties of freshwater aquatic ecosystems. The severe drought during 1998–1999 in the northeastern region of Brazil induced ecological changes in numerous reservoirs as in Tapacura reservoir, one of the biggest drinking-water suppliers in Pernambuco state. Investigations were based on monthly sampling over 2 years (May 1998–May 2000) conducted at 3 representative stations with 3 sampled depths through the water column (0.5 m, middle and 0.5 m above the bottom). Temporal changes in ecological processes, especially stratification, were driven by two major precipitation patterns, with an initial marked dry period (period 1) followed by a rainy season (period 2). Dissolved oxygen and pH variations, higher conductivity and alkalinity values, higher concentrations of particulate organic material (carbon, nitrogen and phosphorus) and higher levels of algal biomass (chlorophyll a) characterized the dry period (May 1998–May 1999). During this phase of low water level when the reservoir storage capacity reached a minimum of 3.9%, the concentrations of chlorophyll a gradually increased with a cyanobacterial bloom (Cylindrospermopsis raciborskii) noted in April 1999. The decline in chlorophyll a and particulate organic matter were observed as a result of the first rains in May–June 1999, with the drastic changes of quality of matter (higher particulate C/N ratio). After a phase characterized by the entire water column turning anoxic, a second phase in the stratification process could be identified from June 1999 with the pronounced rainfalls accompanied by an overturn event. Annual rainfall deficit and lack of reservoir water renewal in 1998–1999 linked to the 1997 El Nino consequences were important determinants of high eutrophication levels and drastic ecological modifications in Tapacura reservoir.

Effects of nitrogen availability on pigmentation and carbon assimilation in the cyanobacterium Synechococcus sp. strain SH-94-5

Because pigments of phototrophs can be involved either in photosynthesis or photoprotection, pigmentation changes in response to nutrient availability can affect how cells interact with their solar environment. We investigated the impact of nitrogen availability both on pigmentation of the cyanobacterium Synechococcus sp. strain SH-94-5 and on carbon assimilation by this strain in the presence or absence of UV radiation. Pigmentation changes in strain SH-94-5 due to ammonium exhaustion included phycobiliprotein degradation, an exponential decline in chlorophyll a content, and a net increase in beta-carotene. Following its replenishment, ammonium stimulated non-photosynthetic carbon assimilation for several hours prior to the resumption of photosynthesis and growth. Carbon fixation during this lag phase was concurrent with the metabolism of glycogen reserves, and it is likely that inorganic carbon was incorporated into glycogen-derived carbon skeletons primarily for amino acid synthesis. In contrast, carbon fixation was almost exclusively photosynthetic during exponential growth. UV-A radiation (320-400 nm) inhibited photosynthetic but not non-photosynthetic carbon assimilation. Only growing cells were inhibited, and the disappearance of inhibition following nitrogen depletion appeared to result from the reduction of cellular photosensitizing targets below a threshold level rather than from the inactivation of photosynthesis.