Organic acids enhance the uptake of lead by wheat roots

The uptake and bioavailability of lead (Pb) in soil–plant systems remain poorly understood. This study indicates that acetic and malic acids enhance the uptake of Pb by wheat (Triticum aestivum L.) roots under hydroponic conditions. The net concentration-dependent uptake influx of Pb in the presence and absence of organic acids was characterized by Michaelis–Menten type nonsaturating kinetic curves that could be resolved into linear and saturable components. Fitted maximum uptake rates (V _max) of the Michaelis–Menton saturable component in the presence of acetic and malic acids were, respectively, 2.45 and 1.63 times those of the control, while the Michaelis–Menten K _m values of 5.5, 3.7 and 2.2 μM, respectively, remained unchanged. Enhanced Pb uptake by organic acids was partially mediated by Ca²⁺ and K⁺ channels, and also depended upon the physiological function of the plasma membrane P-type ATPase. Uptake may have been further enhanced by an effectively thinner unstirred layer of Pb adjacent to the roots, leading to more rapid diffusion towards roots. X-ray absorption spectroscopic studies provided evidence that the coordination environment of Pb in wheat roots was similar to that of Pb(CH₃COO)₂·3H₂O in that one Pb atom was coordinated to four oxygen atoms via the carboxylate group.     

Histidine Absorption across Apical Surfaces of Freshwater Rainbow Trout Intestine: Mechanistic Characterization and the Influence of Copper

The essential amino acid histidine performs critical roles in health and disease. These functions are generally attributed to the amino acid itself, but could also be mediated by a positive effect on trace element bioavailability. Mechanistic information regarding the absorption of histidine across the gastrointestinal tract is essential for understanding the interplay between amino acid and mineral nutrients and the implications of these interactions for nutrition and toxicology. Using intestinal brush-border membrane vesicles obtained from freshwater rainbow trout, absorption of histidine over the range 0.78–780 μm was found to be saturable, with a maximal transport rate (J _max) of 9.1 ± 0.8 nmol mg protein⁻¹ min⁻¹ and a K _m (histidine concentration required to reach 50% of this level) of 339 ± 68 μm. Histidine uptake was highly specific as 10-fold elevated levels of a variety of amino acids with putative shared transporters failed to significantly inhibit uptake. Elevated levels of d-histidine, however, impaired uptake of the natural l-isomer. The presence of “luminal” copper (8.3 μm) significantly increased both the J _max and K _m of histidine transport. This suggests that chelated copper–histidine species cross the brush-border epithelium through transport pathways distinct from those used by histidine alone.     

Silicon accumulation and water uptake by wheat

Silicon (Si) content in cereal plants and soil-Si solubility may be used to estimate transpiration, assuming passive Si uptake. The hypothesis for passive-Si uptake by the transpiration stream was tested in wheat (Triticum aestivum cv. Stephens) grown on the irrigated Portneuf silt loam soil (Durixerollic calciorthid) near Twin Falls, Idaho. Treatments consisted of 5 levels of plant-available soil water ranging from 244 to 776 mm provided primarily by a line-source sprinkler irrigation system. Evapotranspiration was determined by the water-balance method and water uptake was calculated from evapotranspiration, shading, and duration of wet-surface soil. Water extraction occurred from the 0 to 150-cm zone in which equilibrium Si solubility (20°C) was 15 mg Si L^–1 in the A_p and B_k (0–58 cm depth) and 23 mg Si L^–1 in the B_kq (58–165 cm depth).At plant maturity, total Si uptake ranged from 10 to 32 g m^–2, above-ground dry matter from 1200 to 2100 g m^–2 and transpiration from 227 to 546 kg m^–2. Silicon uptake was correlated with transpiration (Si_up=–07+06T, r²=0.85) and dry matter yield with evapotranspiration (Y=119+303ET, r²=0.96). Actual Si uptake was 2.4 to 4.7 times that accounted for by passive uptake, supporting designation of wheat as a Si accumulator. The ratio of Si uptake to water uptake increased with soil moisture. The confirmation of active Si uptake precludes using Si uptake to estimate water use by wheat.     

Characterisation of <Emphasis Type="SmallCaps">l</Emphasis>-alanine and glycine absorption across the gut of an ancient vertebrate

This study utilised an in vitro technique to characterise absorption of two amino acids across the intestinal epithelium of Pacific hagfish, Eptatretus stoutii. Uptake of l-alanine and glycine conformed to Michaelis–Menten kinetics. An uptake affinity (K _m; substrate concentration required to attain a 50% uptake saturation) of 7.0 mM and an uptake capacity (J _max) of 83 nmol cm⁻² h⁻¹ were described for l-alanine. The K _m and J _max for glycine were 2.2 mM and 11.9 nmol cm⁻² h⁻¹, respectively. Evidence suggested that the pathways of l-alanine and glycine absorption were shared, and sodium dependent. Further analysis indicated that glycine uptake was independent of luminal pH and proline, but a component of uptake was significantly impaired by 100-fold excesses of threonine or asparagine. The presence of a short-term (24 h) exposure to waterborne glycine, similar in nature to that which may be expected to occur when feeding inside an animal carcass, had no significant impact on gastrointestinal glycine uptake. This may indicate a lack of cross talk between absorptive epithelia. These results are the first published data to describe gastrointestinal uptake of an organic nutrient in the oldest extant vertebrate and may provide potential insight into the evolution of nutrient transport systems.     

Urea uptake and urease activity in Corynebacterium glutamicum

When Corynebacterium glutamicum is grown with a sufficient nitrogen supply, urea crosses the cytoplasmic membrane by passive diffusion. A permeability coefficient for urea diffusion of 9 × 10^–7 cm s^–1 was determined. Under conditions of nitrogen starvation, an energy-dependent urea uptake system was synthesized. Carrier-mediated urea transport was catalyzed by a secondary transport system linked with proton motive force. With a K _m for urea of 9 μM, the affinity of this uptake system was much higher than the affinity of urease towards its substrate (K _m approximately 55 mM urea). The maximum uptake velocity depended on the expression level and was relatively low [2–3.5 nmol min^–1 (mg dry wt.)^–1]. Received: 11 August 1997 / Accepted: 2 December 1997     

Root respiratory quotient and nitrate uptake in hydroponically grown non-mycorrhizal and mycorrhizal wheat

 Oxygen and CO₂ fluxes were measured in hydroponically grown mycorrhizal and non-mycorrhizal Triticum aestivum L. cv. Hano roots. The NO₃ ^– uptake of the plants was used to estimate the amount of root respiration attributable to ion uptake. Plants were grown at 4 mM N and 10 μM P, where a total and viable mycorrhizal root colonisation of 48% and 18%, respectively, by Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) was observed. The O₂ consumption and NO₃ ^– uptake rates were similar and the CO₂ release was higher in mycorrhizal than in non-mycorrhizal wheat. This resulted in a significantly higher respiratory quotient (RQ, mol CO₂ mol^–1 O₂) in mycorrhizal (1.27±0.13) than in non-mycorrhizal (0.79±0.05) wheat. As the biomass and N and P concentrations in mycorrhizal and non-mycorrhizal wheat were the same, the higher RQ resulted from the mycorrhizal colonisation and not differences in nutrition per se. Accepted: 26 March 1999     

Sodium-dependent and -independent Choline Uptake by Type II Epithelial Cells from Rat Lung

The uptake of ³H-labeled choline by a suspension of isolated type II epithelial cells from rat lung has been studied in a Ringer medium. Uptake was linear for 4 min at both 0.1 μm and 5.0 μm medium choline; at 5 μm, only 10% of the label was recovered in a lipid fraction. Further experiments were conducted at the low concentration (0.1 μm), permitting characterization of the properties of high-affinity systems. Three fractions of choline uptake were detected: (i) a sodium-dependent system that was totally inhibited by hemicholinium-3 (HC-3); (ii) a sodium-independent uptake, when Na⁺ was replaced by Li⁺, K⁺ or Mg²⁺, inhibited by HC-3; (iii) a residual portion persisting in the absence of Na⁺ and unaffected by HC-3. Choline uptake was sigmoidally related to the medium Na⁺ concentration. Kinetic properties of the uptake of 0.1 μm ³H-choline in the presence and absence of medium Na⁺ were examined in two ways. (a) Inhibition by increasing concentrations of unlabeled choline (0.5–100 μm) was consistent with the presence of two Michaelis-Menten-type systems in the presence of Na⁺; a Na⁺-dependent portion (a mean of 0.52 of the total) had a K _m for choline of 1.5 μm while K _m in the absence of Na⁺ (Li⁺ substituting) was 18.6 μm. (b) Inhibition by HC-3 (0.3–300 μm) gave K_i values of 1.7 μm and 5.0 μm HC-3 for the Na⁺-dependent and -independent fractions. The apparent K _m of the Na⁺-dependent uptake is lower than that reported previously for lung-derived cells and is in the range of the K _m values reported for high-affinity, Na⁺-dependent choline uptake by neuronal cells. Received: 18 February 1997/Revised: 7 December 1997     

Kinetic and thermodynamic behaviour of wall-bound peroxidase from wheat leaves infected with stripe rust

We have identified two types of peroxidases (POX), one ionically and one covalently bound to the particulate fraction, in stripe rust-infected and -uninfected wheat (Triticum aestivum L.) leaves. The cell walls contained a high level of POX, of which 73–76% was extractable by 1% NaCl and 24–26% by 5 mM EDTA in infected and non-infected leaves of HD 2329. The NaCl-released POX constituted the predominant fraction. Both NaCl- and EDTA-extracted POX exhibited maximum activity at pH 5.0 and had a K _m (enzyme–substrate affinity measure) value of 1.61–1.70 and 1.64–1.67 mM, respectively, with o-dianisidine as the substrate. The V _max (maximum catalytic rate) in the two extractions ranged between 7.06–7.45 and 6.65–7.82 μmol min⁻¹ g⁻¹ fresh weight. A temperature optimum of 50°C was observed for both the NaCl- and EDTA-released fractions. The two POX fractions showed a differential response to metal ions, suggesting their distinctive nature. Sodium azide inhibited POX activity markedly, which suggested the presence of heme as a prosthetic group. Inhibition of wall-bound POX by iodine and the regeneration of activity by mercaptoethanol suggested the involvement of cysteine in the active site of the enzyme. These two forms showed greater differences in terms of thermodynamic properties, such as the energy of activation (E _a) and enthalpy change (ΔH), while entropy (ΔS) and free energy changes were similar. The results further show that pathogen infection of the leaves of this susceptible wheat cultivar induces an increase in the activity and kinetics of POX, which may be critical in the response of the plant cell to infection.     

Characteristics of amino acid uptake in barley

Plants have the ability to take up organic nitrogen (N) but this has not been thoroughly studied in agricultural plants. A critical question is whether agricultural plants can acquire amino acids in a soil ecosystem. The aim of this study was to characterize amino acid uptake capacity in barley (Hordeum vulgare L.) from a mixture of amino acids at concentrations relevant to field conditions. Amino acids in soil solution under barley were collected in microlysimeters. The recorded amino acid composition, 0–8.2 μM of l-Serine, l-Glutamic acid, Glycine, l-Arginine and l-Alanine, was then used as a template for uptake studies in hydroponically grown barley plants. Amino acid uptake during 2 h was studied at initial concentrations of 2–25 μM amino acids and recorded as amino acid disappearance from the incubation solution, analysed with HPLC. The uptake was verified in control experiments using several other techniques. Uptake of all five amino acids occurred at 2 μM and below. The concentration dependency of the uptake rate could be described by Michaelis–Menten kinetics. The affinity constant (K _m) was in the range 19.6–33.2 μM. These K _m values are comparable to reported values for soil micro-organisms.     

Enhanced cadmium accumulation in maize roots—the impact of organic acids

Low molecular weight organic acids are important components of root exudates and therefore, knowledge regarding the mechanisms of cadmium (Cd) uptake and distribution within plants under the influence of organic acids, is necessary for a better understanding of Cd behavior in the plant–soil system. In this study, acetic and malic acids increased the uptake of Cd by maize (Zea mays L. cv. TY2) roots and enhanced Cd accumulation in shoots under hydroponic conditions. Concentration-dependent net Cd influx in the presence and absence of organic acids could be resolved into linear and saturable components. The saturable component followed Michaelis–Menten kinetics, which indicated that Cd uptake across the plasma membrane was transporter-mediated. While the K _m values were similar, the V _max values in the presence of acetic and malic acids were respectively 6.0 and 3.0 times that of the control. Zinc transporters were the most probable pathways for Cd accumulation. It was hypothesized that Cd(II)–organic acid complexes associated with the root zone, could decompose and liberate Cd²⁺ for subsequent absorption by maize roots; and that in the layer of the roots or within the root free space, depletion of Cd²⁺ was buffered by the presence of Cd(II)–organic acid complexes. Plant response to elevated Cd levels involved overproduction of organic acids in maize roots as a resistance mechanism to alleviate Cd toxicity.     

Iron-limited growth and kinetics of iron uptake in Magnetospirillum gryphiswaldense

Growth and magnetite formation in Magnetospirillum gryphiswaldense MSR-1 were found close to the maximum at an extracellular iron concentration of 15–20 μM. Ferrous iron was incorporated by a slow, diffusion-like process. Several iron chelators including various microbial siderophores were unable to promote transport of iron into the cells. In contrast, spent culture fluids stimulated the uptake of ferric iron in iron-depleted cells at a high rate, whereas fresh medium and transport buffer were unable to promote iron uptake. However, no siderophore-like compound could be detected in spent culture fluids by the Chrome Azurol S assay. Ferric iron uptake followed Michaelis-Menten kinetics with a K _m of 3 μM and a V _max of 0.86 nmol min^–1 (mg dry weight)^–1, suggesting a comparatively low-affinity, but high-velocity transport system. Iron incorporation was sensitive to 2,4-dinitrophenol and carbonylcyanide-m-chlorophenylhydrazone, indicating an energy-dependent transport process. Received: 21 May 1996 / Accepted: 7 August 1996     

Effects, distribution and uptake of silicon in banana (Musa spp.) under controlled conditions

Three contrasted genotypes of Musa spp. (M. acuminata cv Grande Naine, M. acuminata spp. Banksii and M. balbisiana spp. Tani) were grown for 6 weeks under optimal conditions in hydroponics and were submitted to a wide range of Si supply (0–1.66 mM Si) to quantify the Si uptake and distribution in banana, as well as the effect of Si on banana growth. The level of Si supply did not affect plant growth, nor the rate of water and nutrient uptake. The rate of Si uptake and the Si concentration in plant tissues increased markedly with the Si supply. At the highest Si concentrations (1.66 mM), silicon absorption was essentially driven by mass flow of water (passive transport). However, at lower Si concentrations (0.02–0.83 mM), it was higher than its uptake by mass flow and caused the depletion of silicon in the nutrient solution, suggesting the existence of active processes in silicon transport. The distribution of silicon among shoot organs (pseudostem < petiole and midrib < young lamina < old leaf) confirmed the major role of transpiration in silicon accumulation and was not dependent on silicon supply. However, other mechanisms of transport might be operating in the roots and in the petiole and midrib of young leaves, whose silicon concentration was unexpectedly high at low Si supply (0.02 mM) compared to higher levels of Si. The three genotypes did not exhibit consistent differences in their responses to silicon supply.     

Ectoenzymatic Activity and Uptake of Monomers in Marine Bacterioplankton Described by a Biphasic Kinetic Model

Abstract The kinetics of bacterial hydrolytic ectoenzymatic activity and the uptake of monomeric compounds were investigated in the Northwestern Mediterranean Sea. Aminopeptidase and α- and β-glucosidase activities were analyzed by using fluorogenic substrates at 15–22 concentrations ranging from 1 nM to 500 μM. Radiolabeled glucose and a mixture of amino acids were chosen as representatives of monomeric compounds, and the bacterial uptake rates (assimilation plus respiration) were determined over a wide range of substrate concentrations (from 0.2 nM to 3 μM). We found biphasic kinetics both for hydrolytic enzymes and uptake systems: high affinity enzymes at low concentrations of substrates (K _m values ranged from 48 nM to 2.7 μM for ectoenzymes and from 1.4 nM to 42 nM for uptake systems), and low affinity enzymes at high concentrations of substrates (K _m values ranged from 18 μM to 142 μM for ectoenzymes and from 0.1 μM to 1.3 μM for uptake systems). Transition between high and low affinity enzymes was observed at 10 μM for aminopeptidase and from 1 μM to 25 μM for glucosidases, and it was more variable and less pronounced for the uptake of glucose (40 nM–0.28 μM) and amino acids (10 nM–0.16 μM). Results showed that the potential rates of hydrolysis and uptake are tightly coupled only if the high affinity hydrolytic ectoenzymes and the low affinity uptake systems are operating simultaneously. Received: 5 March 1998; Accepted: 31 July 1998     

Kinetic and thermodynamic properties of wall bound invertase in heat tolerant and susceptible cultivars of wheat

We have identified two types of invertases, one bound ionically and the other covalently to the particulate fraction in grains of heat tolerant C 306 and heat susceptible WH 542 cultivars of wheat (Triticum aestivum L.). The cell walls contained a high level of invertase activity, of which 79.2–72.8% was extractable by 2 M NaCl and 14.9–21.1% by 0.5% EDTA in C 306 and WH 542, respectively. The NaCl-released invertase constituted the predominant fraction. Using 5–100 mM sucrose and pH range of 4.0–7.0, the apparent Michaelis constant (K _m, enzyme substrate affinity measure) of enzyme ranged from 5.73 to 16.06 mM for C 306 and from 6.08 to 19.86 mM for WH 542. The V _max (maximum catalytic rate) values at these pH were higher in C 306 (0.63–11.04 μg sucrose hydrolysed min⁻¹) than WH 542 (0.51–8.73 μg sucrose hydrolysed min⁻¹). By employing photo-oxidation and by studying the effect of pH on K _m and V _max, the involvement of histidine and α-carboxyl groups at the active site of the enzyme was indicated. The two cultivars also showed differential response in terms of thermodynamic properties of the enzyme i.e. energy of activation (E _a), enthalpy change (ΔH) and entropy change (ΔS). NaCl-released invertase showed differential response to metal ions in two cultivars suggesting their distinctive nature. Mn²⁺, Cu²⁺, Hg²⁺, Mg²⁺, Zn²⁺ and Cd²⁺ were strong inhibitors in WH 542 as compared to C 306 while K⁺, Ca²⁺ were stimulators in both the cultivars. Overall the results suggest that genetic differences exist in wall bound invertase properties of wheat grains as evident in its altered kinetic behaviour.     

Carrier-mediated acetate uptake in Corynebacterium glutamicum

Acetate is effectively taken up by whole cells of Corynebacterium glutamicum via a specific carrier with a pH optimum of 8. The K _m of acetate uptake was 50 μM and the V _max 25–35 nmol/mg dw min. The activation energy was determined to be 70 kJ/mol. Acetate uptake was competitively inhibited by propionate with a K _i of about 30 μM and blocked by addition of sulfhydryl reagents. The transport activity was clearly dependent on the membrane potential, but independent of the presence of Na⁺-ions. It is concluded that uptake of acetate proceeds by a secondary, proton coupled mechanism.     

The kinetics of NH4 + and NO3 − uptake by Douglas fir from single N-solutions and from solutions containing both NH4 + and NO3 −

The kinetics of NH₄ ⁺ and NO₃ ⁻ uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the V_max of NH₄ ⁺ uptake was higher than that of NO₃ ⁻ uptake. The K_m of NH₄ ⁺ uptake and K_m of NO₃ ⁻ uptake differed not significantly. When both NH₄ ⁺ and NO₃ ⁻ were present, the V_max for NH₄ ⁺ uptake became slightly higher, and the K_m for NH₄ ⁺ uptake remained in the same order. Under these conditions the NO₃ ⁻ uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH₄ ⁺ occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}     

Effect of root volume and nitrate solution concentration on growth,fruit yield,and temporal N and water uptake rates by apple trees

Meager information is available on the specific effects of root volume (V) and N concentration in the water (C_N) on uptake rates of water and N by apple trees, as related to fruit yield and tree growth. To investigate this relationship, Golden Delicious/Hashabi trees were grown for 5 years in containers of 200, 50 and 101. Trees in the 200–1 containers were irrigated with a nutrient solution containing 10.7±1.3, 7.1±1.5 or 2.5±1.0 mM NO₃. Trees in the remaining two container-volume treatments were uniformly supplied with a solution of 7.1±1.5 mM NO₃. Elevated C_N had no effect on the rate of water uptake, but increased the rate of N absorption by the trees from 2.4 to 4.8 g N tree⁻¹ day⁻¹ during July. The stimulated N uptake rate stemmed from enhanced fluxes of N uptake by the roots. C_N had a negligible effect on root weight and root permeability to NO₃ and water. The elevated N uptake rate did not result in greater fruit yield and growth, or greater N content in tree organs, indicating considerable release of N from living and decaying roots to the growth medium. Reducing the container volume decreased yield, total dry matter production and N and water uptake rates, but increased root permeability to NO₃ and water, and total soluble solids in fruits. The all-season average C_N in the irrigation solution above which N concentration in the transpiration stream was lower than the inflowing C_N was 4.2 mM NO₃.     

Partitioning particulate scattering and absorption into contributions of phytoplankton and non-algal particles in winter in Lake Taihu (China)

Light scattering, backscattering, and absorption coefficients of particles were observed at 62 locations in Lake Taihu (China) in November 2008. A method using a priori knowledge and the measured data was proposed to partition particulate scattering and absorption into contributions of phytoplankton and non-algal particles. The results showed that phytoplankton weakly contributed to the particulate scattering and backscattering with the mean b _ph/b _p values usually below 10% and b _bph/b _bt values of 0.3–3.9% in the whole visible light spectrum, and an approximate relationship of b _bt ≈ b _bp ≈ b _bnap was regarded as reasonable in Lake Taihu. In contrast with scattering and backscattering, phytoplankton made more contributions to the particulate absorption with the mean a _ph/a _p values varying in a wide range of about 20–70%. Both the scattering and absorption spectra of non-algal particles can be modeled well by corresponding methods. A power function model was used to simulate the scattering spectra, which presented high predictive accuracies with MAPE values usually below 5% and RMSE values below 1.5 m⁻¹, while the spectral absorption model also performed well with mean S _nap being 0.0052 nm⁻¹ (standard deviation, SD = 0.0010 nm⁻¹). As to the phytoplankton absorption, a quadratic function model used was considered to have a good performance with corresponding parameters being supported at each wavelength in the spectral range of 400–700 nm. Additionally, two basic bio-optical parameters were determined, that is, b _nap^*(550) = 0.604 m² g⁻¹ and a _ph^*(675) = 0.0288 m² mg⁻¹. Overall, these results obtained in the present study supply us with new knowledge about optical properties of suspended particulates in an inland and highly turbid lake (Lake Taihu), which are beneficial to the development of analytical models of water color remote sensing.     

Chlorophyll fluorescence parameters and drought tolerance in a mapping population of winter bread wheat in the highlands of Iran

The usefulness of fluorescence parameters as drought tolerance selection criteria for winter bread wheat in the highlands of Iran was studied. A population of 142 recombinant inbred lines, derived from a cross between two common wheat varieties, Azar2 (winter type) and 87Zhong291 (facultative type), was used to analyze the correlation between grain yield and chlorophyll fluorescence parameters at the grain-filling stage under drought stress and supplementary irrigation conditions during 2006–2007 and 2007–2008 seasons at Maragheh experiment station of the Dryland Agricultural Research Institute (DARI) using a RCBD with three replications. The results showed significant differences among the lines in the grain yield and all fluorescence parameters under rainfed and irrigation conditions. The values of chlorophyll content, F ₀, F _m, F _v, F _v/F _m, LWP, YPEC, NPQ, and PI in the drought-tolerant genotypes were significantly higher than those in drought-sensitive genotypes under drought stress. Significant differences were observed between slope coefficients under drought, but not under supplementary irrigation conditions except NPQ (P = 5%). It was concluded that chlorophyll content, F ₀, F _m, F _v, F _v/F _m, LWP, YPEC, NPQ, and PI could be used as additional indicators in screening wheat germplasm for drought tolerance.     

Small scale vertical gradients of Arctic ice algal photophysiological properties

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (F _v/F _m), maximum relative electron transport rate (rETR_max), photosynthetic efficiency (α), and the photoadaptive index (E _k). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0–5 cm from ice–water interface) expressed low F _v/F _m (0.331–0.426) and low α (0.098–0.130 (μmol photons m⁻²s⁻¹)⁻¹) in December. F _v/F _m and α increased in March and May (0.468–0.588 and 0.141–0.438 (μmol photons m⁻²s⁻¹)⁻¹, respectively) indicating increased photosynthetic activity. In addition, increases in rETR_max (3.3–16.4 a.u.) and E _k (20–88 μmol photons m⁻² s⁻¹) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).