Capsular polysaccharides facilitate enhanced iron acquisition by the colonial cyanobacterium Microcystis sp. isolated from a freshwater lake

Microcystis sp., especially in its colonial form, is a common dominant species during cyanobacterial blooms in many iron‐deficient water bodies. It is still not entirely clear, however, how the colonial forms of Microcystis acclimate to iron‐deficient habitats, and the responses of unicellular and colonial forms to iron‐replete and iron‐deficient conditions were examined here. Growth rates and levels of photosynthetic pigments declined to a greater extent in cultures of unicellular Microcystis than in cultures of the colonial form in response to decreasing iron concentrations, resulting in the impaired photosynthetic performance of unicellular Microcystis as compared to colonial forms as measured by variable fluorescence and photosynthetic oxygen evolution. These results indicate that the light‐harvesting ability and photosynthetic capacity of colonial Microcystis was less affected by iron deficiency than the unicellular form. The carotenoid contents and nonphotochemical quenching of colonial Microcystis were less reduced than those of the unicellular form under decreasing iron concentrations, indicating that the colonial morphology enhanced photoprotection and acclimation to iron‐deficient conditions. Furthermore, large amounts of iron were detected in the capsular polysaccharides (CPS) of the colonies, and more iron was found to be attached to the colonial Microcystis CPS under decreasing iron conditions as compared to unicellular cultures. These results demonstrated that colonial Microcystis can acclimate to iron deficiencies better than the unicellular form, and that CPS plays an important role in their acclimation advantage in iron‐deficient waters.     

Photosynthetic and growth responses of three freshwater algae to phosphorus limitation and daylength

1. Three common species of freshwater phytoplankton, the diatom Nitzschia sp., green alga Sphaerocystis schroeteri and cyanobacterium Phormidium luridum, were grown under contrasting daylengths [18 : 6 h light : dark cycles (LD) versus 6 : 18 h LD] and phosphorus (P) regimes (P‐sufficient versus 1 μm P). The rates of growth and photosynthesis, as well as growth efficiencies and pigment concentrations, were compared among treatments. 2. The growth and photosynthetic parameters of the three species depended on both P status and daylength in a species‐specific way. The responses to P limitation depended on daylength and, conversely, the responses to daylength depended on P status. 3. Growth rates and the maximum rates of photosynthesis (P_max) of all species decreased under P limitation under both light regimes. However, the decrease of P_max because of P limitation was greater under long daylength. The P_max of the green alga S. schroeteri decreased the most (ca. sixfold) under P limitation compared with the other two species. The photosynthesis saturation parameter I_k also decreased under P limitation; the decline was significant in Nitzschia and Sphaerocystis. P‐limitation significantly increased photoinhibition (β) in Nitzschia and Sphaerocystis, but not in Phormidium. The excess photochemical capacity (the ratio of the maximum photosynthesis rate to the photosynthesis rate at the growth irradiance), characterising the ability to utilise fluctuating light, was significantly lower under P limitation. 4. The growth efficiency (growth rate normalised to daylength) declined with increasing daylength in all species. Under short daylength the cyanobacterium Phormidium had the lowest growth efficiency of the three species. 5. The cellular chlorophyll a concentration in both Nitzschia and Sphaerocystis was significantly higher under short daylength, but only under P‐sufficient conditions. In Nitzschia, under short daylength, P‐limitation significantly decreased cellular chlorophyll concentration. In contrast, P‐limitation increased cellular chlorophyll concentration in Sphaerocystis, but under long daylength only. The ratio of chlorophyll a to b in the green alga also declined under short daylength and under P‐limited conditions.     

Iron limitation in the marine cyanobacterium Trichodesmium reveals new insights into regulation of photosynthesis and nitrogen fixation

* As iron (Fe) deficiency is a main limiting factor of ocean productivity, its effects were investigated on interactions between photosynthesis and nitrogen fixation in the marine nonheterocystous diazotrophic cyanobacterium Trichodesmium IMS101. * Biophysical methods such as fluorescence kinetic microscopy, fast repetition rate (FRR) fluorimetry, and in vivo and in vitro spectroscopy of pigment composition were used, and nitrogenase activity and the abundance of key proteins were measured. * Fe limitation caused a fast down-regulation of nitrogenase activity and protein levels. By contrast, the abundance of Fe-requiring photosystem I (PSI) components remained constant. Total levels of phycobiliproteins remained unchanged according to single-cell in vivo spectra. However, the regular 16-kDa phycoerythrin band decreased and finally disappeared 16-20 d after initiation of Fe limitation, concomitant with the accumulation of a 20-kDa protein cross-reacting with the phycoerythrin antibody. Concurrently, nitrogenase expression and activity increased. Fe limitation dampened the daily cycle of photosystem II (PSII) activity characteristic of diazotrophic Trichodesmium cells. Further, it increased the number and prolonged the time period of occurrence of cells with elevated basic fluorescence (F(0)). Additionally, it increased the effective cross-section of PSII, probably as a result of enhanced coupling of phycobilisomes to PSII, and led to up-regulation of the Fe stress protein IsiA. * Trichodesmium survives short-term Fe limitation by selectively down-regulating nitrogen fixation while maintaining but re-arranging the photosynthetic apparatus.     

Phosphorus limitation of the freshwater benthic diatom Didymosphenia geminata determined by the frequency of dividing cells

1. Unlike other nuisance algal species, the freshwater benthic diatom Didymosphenia geminata typically forms blooms in low‐nutrient rivers. The negative association between D. geminata blooming behaviour and nutrient levels appears at both catchment and smaller scales. We conducted a series of trials in streamside experimental channels colonised with D. geminata using water from the D. geminata‐affected, oligotrophic Waitaki River, South Island, New Zealand to determine how elevated nitrate and phosphate concentrations affected D. geminata cell division. Because D. geminata blooms are typically most pronounced in unshaded waters, we also investigated the growth response to shading. In all experiments, we used the frequency of dividing cells (FDC) as a metric of cell division. 2. Concentrations of nitrate and dissolved reactive phosphorus (DRP) in the Waitaki River were very low (4 mg m^?3‐N and <1 mg m^?3 DRP). In pilot trials, substrata colonised by D. geminata were subjected to enrichment by either switching the water source toN‐ and P‐rich spring water or by adding a stock solution. Both trials resulted in periods of rapid cell division lasting at least 8 days. 3. Experimental addition of alone triggered an initial cell division which was not sustained. However, addition of alone or together with resulted in prolonged elevation in cell division indicating that the cell division rate was P‐limited. 4. Reduced light levels resulted in decreased FDC in D. geminata in both ambient and N, N + P and P‐enriched river water. 5. Stimulation of D. geminata division rate by addition of above ambient levels confirms that, while blooming behaviour is often associated with oligotrophic rivers, the cells divide faster with greater levels of phosphorus enrichment.     

Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability

Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P_max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes Scenedesmus quadricauda, Chlamydomonas globosa, cryptophyte Cryptomonas ovata and ochrophyte Cyclotella meneghiniana. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in S. quadricauda and Cry. ovata. Cry. ovata can be characterized as a low light-acclimated species, whereas S. quadricauda and Cyc. meneghiniana can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P_max with PUFAs and light. In S. quadricauda and Cyc. meneghiniana, PUFAs negatively affected the relationship between P_max and light. In Chl. globosa, lower light coincided with higher PUFAs and lower P_max, but PCA also indicated that PUFAs had no direct influence on P_max. PUFAs and P_max were unaffected by light in Cry. ovata. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation.     

Response of the cyanobacterium Gloeotrichia echinulata to iron and boron additions – an experiment from Lake Erken

1. This study considers whether the availability of iron and boron are important influences on the development of the cyanobacterium Gloeotrichia echinulata in Lake Erken, Sweden.
2. In an in situ experiment, phosphate and nitrate were added to all enclosures, but pelagic colonies of G. echinulata only increased in abundance in enclosures to which iron had also been added.
3. An even greater increase in the abundance of G. echinulata occured in enclosures in which the additions of phosphate, nitrate and iron were complemented by additions of boron.
4. Boron additions, together with phosphate and nitrate but without iron, did not stimulate the growth of G. echinulata .     

Cultivation and characterization of the MaMV-DC cyanophage that infects bloom-forming cyanobacterium Microcystis aeruginosa

The MaMV-DC cyanophage, which infects the bloom-forming cyanobacterium Microcystis aeruginosa, was isolated from Lake Dianchi, Kunming, China. Twenty-one cyanobacterial strains were used to detect the host range of MaMV-DC. Microcystic aeruginosa FACHB-524 and plaque purification were used to isolate individual cyanophages, and culturing MaMV-DC with cyanobacteria allowed us to prepare purified cyanophages for further analysis. Electron microscopy demonstrated that the negatively stained viral particles are tadpole-shaped with an icosahedral head approximately 70 nm in diameter and a contractile tail approximately 160 nm in length. Using one-step growth experiments, the latent period and burst size of MaMV-DC were estimated to be 24–48 hours and approximately 80 infectious units per cell, respectively. Restriction endonuclease digestion and agarose gel electrophoresis were performed using purified MaMV-DC genomic DNA, and the genome size was estimated to be approximately 160 kb. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed four major structural proteins. These results support the growing interest in using freshwater cyanophages to control bloom-forming cyanobacterium.     

Molecular cloning and physical mapping of the nitrogenase structural genes from the filamentous, non-heterocystous cyanobacterium Pseudanabaena sp. PCC7409

Abstract Sequences homologous to the structural genes for dinitrogenase ( nifD and nifK ) and nitrogenase reductase ( nifH ) have been cloned from the filamentous, non-heterocystous cyanobacterium Pseudanabaena PCC7409. The nifHDK ⁻ homologous sequences were shown to reside on a 6.5-kb Eco RI restriction fragment by using a restriction fragment encoding the Klebsiella pneumoniae nifHDK genes as a heterologous hybridization probe. This 6.5-kb restriction fragment was cloned from a λ gt.wes Eco RI library of the Paseudanabaena sp. PCC7409 genome. This fragment was subcloned into the plasmid vector pUC9 to generate plasmid pPSU20. A detailed physical map of the insert in plasmid pPSU20 was determined, and relative positions of the nifH, nifD , and nifK homologous sequences on this fragment were determined by hybridization analysis with gene-specific fragments derived from the corresponding Anabaena sp. PCC7120 genes. The results indicate that these genes are contiguous in Pseudanabaena sp. PCC 7409 and are arranged in the order nifH, nifD , and nifK . This arrangement resembles that observed for other non-heterocystous cyanobacteria but differs from that observed for Anabaena, Calothrix , and Nostoc species.     

Transient state characteristics of adaptation to changes in light conditions for the cyanobacterium Oscillatoria agardhii

Transitions in growth irradiance level from 92 to 7 Em^-2 s^-1 and vice versa caused changes in the pigment contents and photosynthesis of Oscillatoria agardhii. The changes in chlorophyll a and C-phycocyanin contents during the transition from high to low irradiance (HL) were reflected in photosynthetic parameters. In the LH transition light utilization efficiencies of the cells changed faster than pigment contents. This appeared to be related to the lowering of light utilization efficiencies of photosynthesis. As a possible explanation it was hypothesized that excess photosynthate production led to feed back inhibition of photosynthesis. Time-scales of changes in the maximal rate of O₂ evolution were discussed as changes in the number of reaction centers of photosystem II in relation to photosynthetic electron transport. Parameters that were subject to change during irradiance transitions obeyed first order kinetics, but hysteresis occurred when comparing HL with LH transients. Interpretation of first order kinetic analysis was discussed in terms of adaptive response vs changes in growth rate.Non-standard abbreviations Chla chlorophyll a - CPC C-phycocyanin - PS II photosystem II - PS I photosystem I - RC II reaction center of photosystem II - P photosynthetic O₂-evolution - I irradiance, Em^-2 s^-1 - light utilization efficiency of cells, mmol O₂·mg dry wt^-1·h^-1/Em^-2 s^-1 - light utilization efficiency of photosynthetic apparatus, mol O₂·mol Chla ^-1·h^-1/Em^-2 s^-1 - P_max maximal rate of O₂ evolution by cells, mol O₂·mg dry wt^-1·h^-1 - P_max maximal rate of O₂ evolution by photosynthetic apparatus, mol O₂·mol·Chla ^-1·h^-1 - LL low light, E m^-2 s^-1 - HL high light, E m^-2 s^-1 - LH low to high light transition - HL high to low light transition - k specific rate of adaptation, h^-1 - specific growth rate, h^-1 - Q pool size of cell constituent, mol·mg dry wt^-1 - q net synthesis rate of cell constituent, mol·mg dry wt^-1·h^-1     

Effect of nitrate-nitrogen limitation on photosynthesis of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)

Abstract Nitrate limited growth of the diatom Phaeodactylum tricornutum in chemostat cultures produced marked changes in biochemical composition and a six-fold reduction in the specific growth rate. This was associated with a reduction in the carbon and chlorophyll a specific light saturated rates, with little effect on light limited photosynthesis. Variations in specific growth rate were quantitatively related to carbon specific net photosynthesis and maximum chlorophyll a specific light saturated rates were positively correlated with cell nitrogen contents. The correlation between nitrogen content and photosynthesis for P. tricornutum and the differential effect of nitrogen supply on the light response curve of photosynthesis is qualitatively and quantitatively similar to published results for terrestrial vascular plants. There was little change in the photon (quantum) yield of photosynthesis which was not significantly different from 0.125mol O₂ mol photon^-1 the theoretical upper limit based on the Z scheme, even under severe nitrate deficiency. The capacity to maintain a high photon yield under nitrate limitation is discussed in relation to the nitrogen requirements of the stromal and membrane components of the photosynthetic apparatus.     

Marine heatwaves and decreased light availability interact to erode the ecophysiological performance of habitat-forming kelp species

Coastal marine ecosystems are threatened by a range of anthropogenic stressors, operating at global, local, and temporal scales. We investigated the impact of marine heatwaves (MHWs) combined with decreased light availability over two seasons on the ecophysiological responses of three kelp species (Laminaria digitata, L. hyperborea, and L. ochroleuca). These species function as important habitat-forming foundation organisms in the northeast Atlantic and have distinct but overlapping latitudinal distributions and thermal niches. Under low-light conditions, summertime MHWs induced significant declines in biomass, blade surface area, and Fv/Fm values (a measure of photosynthetic efficiency) in the cool-water kelps L. digitata and L. hyperborea, albeit to varying degrees. Under high-light conditions, all species were largely resistant to simulated MHW activity. In springtime, MHWs had minimal impacts and in some cases promoted kelp performance, while reduced light availability resulted in lower growth rates. While some species were negatively affected by summer MHWs under low-light conditions (particularly L. digitata), they were generally resilient to MHWs under high-light conditions. As such, maintaining good environmental quality and water clarity may increase resilience of populations to summertime MHWs. Our study informs predictions of how habitat-forming foundation kelp species will be affected by interacting, concurrent stressors, typical of compound events that are intensifying under anthropogenic climate change.     

不同光照强度下三角叶滨藜光合作用对盐激胁迫的响应

以溶液培养的三角叶滨藜植株为材料研究了不同光照条件下其叶片光合作用对盐(NaCl)激胁迫的即刻反应及变化规律.结果表明,三角叶滨藜光合作用对盐激胁迫的响应有8 min左右的滞后期.在光照强度为100umol·m-2·-1和100 mmol·L-1浓度NaCl共同作用下,三角叶滨藜叶片净光合速率略有上升;但随NaCl浓度和光照强度进一步增加,其净光合速率呈下降趋势,且光照越强,盐胁迫导致的净光合速率下降幅度越大.同时,弱光下或强光低浓度NaCl胁迫下,盐激胁迫导致的净光合速率下降主要是气孔限制引起的;而强光下,高浓度的NaCl胁迫导致的净光合速率下降在盐激胁迫处理的前30-40 min主要由气孔限制引起.40 min后则主要由非气孔限制引起.可见,不同光照强度和NaCl浓度胁迫下三角叶滨藜叶片光合作用响应规律不同,引起净光合速率下降机制各异.     

Principles of the light-limited chemostat: theory and ecological applications

Light is the energy source that drives nearly all ecosystems on planet Earth. Yet, light limitation is still poorly understood. In this paper, we present an overview of the principles of the light-limited chemostat. The theory for light-limited chemostats differs considerably from the standard theory for substrate-limited chemostats. In particular, photons cannot be mixed by vigorous stirring, so that phototrophic organisms experience the light-limited chemostat as a heterogeneous environment. Similar to substrate-limited chemostats, however, light-limited chemostats do reach a steady state. This allows the study of phototrophic microorganisms under well-controlled light conditions, at a constant specific growth rate, for a prolonged time. The theory of the light-limited chemostat is illustrated with several examples from laboratory experiments, and a variety of ecological applications are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photosynthetic responses of Coffea arabica leaves to a short-term high light exposure in relation to N availability

It is known that the coffee (Coffea arabica L.) plant which is originally from shade habitats would have a limited ability to grow under full sun. Previous work has shown that nitrogen fertilisation can reduce the leaf damage when the plants are exposed to high light intensities during several days. In the present work we aimed to study the effects of the high irradiance during the first hours and evaluate the positive contribution of nitrogen fertilisation in the case of short-term exposure to strong light. Young plants (1.5–2 years old) grown in 1.5 kg of a mixed soil were supplemented with a nutrient solution containing 15 mM nitrogen in the form of NH₄NO₃, every 7 days (2N treatment), 15 days (1N treatment) and 45 days (0N treatment). Top mature leaves were exposed to a photosynthetic photon flux density of 1 500 μmol m^?2 s^?1 for a maximal period of 8 h, and changes in photosynthesis and pigment composition were monitored along the period of high light exposure. Photosynthetic capacity, leaf conductance to water vapour, electron transport capacity and maximum carboxylation activity, as well as some leaf fluorescence parameters (minimal fluorescence, photochemical efficiency of PSII and quantum yield of photosynthetic electron transport) were reduced by the stress, with a generally stronger impact observed in the 0N plants. The photochemical quenching was affected only in the 0N plants, while the non-photochemical quenching increased in 2N plants but decreased in the 0N ones. The results showed that 2N plants presented a better initial status of the photosynthetic parameters and of the content of photoprotective pigments. Those plants showed ability to trigger some protective mechanisms, as observed by the tendency to increase the xanthophyll pool content, specially in zeaxanthin and in non-photochemical quenching. Also, protein content presented a tendency to increase after 1.5 h, which was maintained until the end of the high light period. We conclude that nitrogen availability is a key factor in the acclimation process to high light.     

七子花苗期光合日进程及光响应

对七子花苗期光合日进程及光响应进行了研究,结果表明:(1)净光合速率的日进程曲线呈双峰型,胞间CO2浓度的日进程基本与净光合速率相反,中午胞间CO2浓度增高表明净光合速率午间降低主要受非气孔限制因素的影响。暗呼吸速率日进程呈单峰曲线,中午最高。光能利用效率以上午7∶00为最高,中午最低,以后又逐渐上升。(2)净光合速率最适温度为25～30℃,高光合有效辐射和高温下光抑制加剧。(3)29℃下饱和光强为890μmolm 2s 1,表观量子效率为0.0325,光补偿点为44μmolm 2s 1;随着光合有效辐射的增强,气孔阻力减小,但光合有效辐射过高,气孔阻力却有所上升。(4)在29℃的饱和光强下,羧化效率为0.0351,CO2补偿点为173μmolmol 1,低于或高于饱和光强,羧化效率下降,CO2补偿点升高。     

Photosynthetic response of Nereocystis luetkeana (Phaeophyta) to high light

Photosynthetic response to high light was determined for Bull kelp, Nereocystis luetkeana (K. Mertens) Postels and Ruprecht in order to understand how this species is affected by short‐term fluctuations in irradiance. Exposure of N. luetkeana blades to high intensity photosynthetically active radiation (1000 µmol photons m^?2 s^–1) caused increased non‐photochemical quenching of fluorescence and higher de‐epoxidation ratios for xanthophyll pigments indicating that energy‐quenching xanthophylls were used to protect blades against photoinhibition. Despite initiation of these photoprotective mechanisms, maximum photochemical efficiency of photosystem II (F_v/F_m) decreased 40% in response to a 60 min exposure to 1000 µmol photons m^?2 s^–1 photosynthetically active radiation indicating that photoinhibition had occurred. Light‐saturated rates of oxygen evolution were not changed significantly by the high light treatment. Recovery of maximum photochemical efficiency of photosystem II to within 8% of initial values occurred after a 300‐min dim light period. Younger sections of the blades were slightly more susceptible to high light damage than older sections. Middle sections of the blades were more prone to light‐induced damage at water temperatures of 7°C or 18°C, as compared to 13°C. Exposure to biologically effective ultraviolet‐B radiation (UV‐B_be) (up to 4.5 kJ m^–2 day^–1) in photoinhibitory light conditions did not significantly affect light‐induced damage to photosystem II.     

Annual patterns of phytoplankton density and primary production in a large, shallow lake: the central role of light

1. We studied the seasonal dynamics of suspended particulate matter in a turbid, large shallow lake during an annual period (2005–06). We relate the patterns of seston concentration (total suspended solids), phytoplankton biomass and water transparency to the seasonal pattern of incident solar radiation (I₀). We also report the seasonal trends of phytoplankton primary production (PP) and photosynthesis photoinhibition due to photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) (I_β and UV₅₀). 2. We first collected empirical evidence that indicated the conditions of light limitation persisted during the study period. We found that the depth‐averaged irradiance estimated for the time of the day of maximum irradiance (I_mean–noon) was always lower than the measured onset of light saturation of photosynthesis (I_k). 3. We then contrasted the observations with theoretical expectations based on a light limitation scenario. The observed temporal patterns of seston concentration, both on a volume and area basis, were significantly explained by I₀ (R² = 0.39 and R² = 0.37 respectively). The vertical diffuse attenuation coefficient (kd_PAR) (R² = 0.55) and the depth‐averaged irradiance (I_mean) (R² = 0.66), significantly increased with the I₀; while the irradiance reaching the lake bottom (I_out) significantly decreased with the incident irradiance (R² = 0.49). However, phytoplankton biovolume maxima were not coincident with the time of the year of maximum irradiance. 4. A significant positive relationship was observed between PP estimated on an area basis and I₀ (R² = 0.51, P < 0.001). In addition, the parameters describing the photosynthetic responses to high irradiances displayed marked seasonal trends. The photosynthesis photoinhibition due to PAR as well as to UV were significantly related to incident solar radiation (PAR: R² = 0.73; UV: R² = 0.74). These results suggest adaptation of the phytoplankton community in response to changes in incident solar radiation.     

Ferritin is required for rapid remodeling of the photosynthetic apparatus and minimizes photo-oxidative stress in response to iron availability in Chlamydomonas reinhardtii

Ferritin is a key player in the iron homeostasis due to its ability to store large quantities of iron. Chlamydomonas reinhardtii contains two nuclear genes for ferritin ( ferr1 and ferr2 ) that are induced when Chlamydomonas cells are shifted to iron-deficient conditions. In response to the reduced iron availability, degradation of photosystem I (PSI) and remodeling of its light-harvesting complex occur. This active PSI degradation slows down under photo-autotrophic conditions where photosynthesis is indispensable. We observed a strong induction of ferritin correlated with the degree of PSI degradation during iron deficiency. The PSI level can be restored to normal within 24 h after iron repletion at the expense of the accumulated ferritin, indicating that the ferritin-stored iron allows fast adjustment of the photosynthetic apparatus with respect to iron availability. RNAi strains that are significantly reduced in the amount of ferritin show a striking delay in the degradation of PSI under iron deficiency. Furthermore, these strains are more susceptible to photo-oxidative stress under high-light conditions. We conclude that (i) ferritin is used to buffer the iron released by degradation of the photosynthetic complexes, (ii) the physiological status of the cell determines the strategy used to overcome the impact of iron deficiency, (iii) the availability of ferritin is important for rapid degradation of PSI under iron deficiency, and (iv) ferritin plays a protective role under photo-oxidative stress conditions.     

Photosynthetic development of Ocimum basilicum cells on transition from phosphate to fructose limitation

Continuous culture was used to establish a steady state in fructose excess. Phosphate in the Murashige and Skoog type medium was found to be limiting growth; when phosphate concentration in the medium feed was doubled, the concentration of dry biomass and of all biomass elements increased After doubling the phosphate concentration fructose became limiting. Ocimun basilicum cells responded to the transition from phosphate limitation to fructose limitation by becoming greener and more photosynthetic; consequently, the yield on fructose increased.