摘要:

ABSTRACTThe nitrate uptake capacity of mature blade tissue of the giant kelp,Macrocystis pyrifera(L.) C. Ag., was examined as a function of the availability of light and nitrate. Time course measurements indicated that nitrate uptake rate, as measured by the incorporation of15N, was significantly increased by N starvation. The response was linear over the first hour of exposure regardless of the N status of the tissue indicating that surge uptake was not responsible for the increase. The Michaelis‐Menten parameters Vmaxand Ks, however, were not significantly changed by either growth nitrate concentration or growth irradiance as a result of high variability among blades. Similarly, the initial slope (α) of the nitrate uptake kinetics curves was unaffected. Concentration of photosynthetic pigments increased in response to increased nitrate availability but not to increased growth irradiance. Time course and pigment data demonstrated that mature blade tissue responds to increased N availability by decreasing its capacity to take up nitrate and by increasing its investment in photosynthetic pigments, perhaps for N storage or enhanced light‐harvesting capabilities and the increase in reducing power available for N assimilation. This study provides evidence for a dynamic regulatory system that responds to changes in nitrate availability in an integrated ma

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00573.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTSeveral studies have suggested that phytoplankton play a role in the iodine cycle. Using a short‐term incubation technique for determining the uptake of iodate by phytoplankton, cultures ofThalassiosira oceanicaHasle,Skeletonema costatum(Greville) Cleve,Emiliania huxleyi(Lohmann) Hay and Mohler, andDunaliella tertiolectaButcher were found to be capable of assimilating iodate at rates ranging from 0.003 to 0.24 nmol IO3−·μg chlorophyll a−1·h−1. The kinetics for the uptake of iodate can be modeled, and the similarity between the model and experimental results suggests that there is a steady state between iodate uptake and release of dissolved iodine from the cells, presumably in the form of iodide. Two experiments were conducted in the Sand Shoal Inlet of the Cobb Bay estuary (37°15′N, 75°50′W). The uptake of iodate was 0.26 and 0.08 nmol IO3−·μg chlorophyll a−1·h−1during high and low tide, respectively. Using field estimates based on measured levels of iodate in the estuary, we estimate that phytoplankton can take up as much as 3% of the ambient pool of iodate on a daily basis and the entire pool in about 1 month. Thus, phytoplankton can be a significant component of the global iodine cycle by mediating changes in the speciation of iodine

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00580.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTClones of the filamentous green algaCtenocladus circinnatusBorzi were isolated from algae collected at Abert Lake (Oregon) and Mono Lake (California). Stock cultures were exposed to varied salinities of natural lake water to examine the effects on growth rate, cell form, chlorophylla, and water content. Growth rates were reduced in both clones with increased salinity over the range 25–100 g·L−1and were almost completely inhibited at 150 g·L−1. Chlorophyllaincreased between salinities of 25 and 100 g·L−1, reflecting slower growth, higher proportions of akinetes, and smaller cell sizes as salinity increased. Tissue water content remained essentially constant from 25 to 100 g·L−1salinity. Shorter cell dimensions with increased salinity suggest that a lower surface‐to‐volume ratio may reduce the potential for passive loss of cell water. Prior acclimation of stock cultures to elevated salinity provided no enhancement of growth response at any salinity. The results indicate that environmental salinity can limit the productivity and distribution ofCte

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00588.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe synthesis of fatty acids and lipids inNannochloropsissp. was investigated by labeling cellsin vivowith [14C]‐bicarbonate or [14C]‐acetate. [14C]‐bicarbonate was incorporated to the greatest extent into 16:0, 16:1, and 14:0 fatty acids, which are the predominant fatty acids of triacylglycerols. However, more than half of the [14C]‐acetate was incorporated into longer and more desaturated fatty acids, which are constituents of membrane lipids. [14C]‐acetate was incorporated most strongly into phosphatidylcholine, which rapidly lost label during a 5‐h chase period. The label associated with phosphatidylethanolamine also decreased during the chase period, whereas label in other membrane lipids and triacylglycerol increased. The dynamics of labeling, along with information regarding the acyl compositions of various lipids, suggests that 1) the primary products of chloroplast fatty acid synthesis are 14:0, 16:0, and 16:1; 2) C20fatty acids are formed by an elongation reaction that can utilize externally supplied acetate; 3) phosphatidylcholine is a site for desaturation of C18fatty acids; and 4) phosphatidylethanolamine may be a site for desaturation of C20

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00594.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe excessive growthof Ulva rigidaC. Agardh, a green seaweed present in the Northern Adriatic Sea, is a problem for the inhabitants and the economy of the region. As information about hormonal control of growth in seaweeds is scarce, our aim was to investigate the presence of endogenous polyamines and their absorption by algal cells and to correlate the findings with terrestrial plants. Free polyamines (putrescine, spermidine, and spermine) were present endogenously in the algal thallus at concentrations ranging from 4 to 134 μM. Putrescine and spermidine were also present in the seawater in which the alga usually grows at concentrations between 0 and 0.9 μM. Uptake of labeled polyamines occurred, but it was inhibited by cations present in the seawater. Uptake was investigated also by incubation in distilled water. In this case, uptake displayed characteristics similar to those observed in higher plant systems. Uptake studies in seawater showed that polyamine accumulation in algal cells occurred and that it followed a concentration gradient and displayed linear kinetics. The mechanism proposed that of a passive uptake, as indicated also by the inability of metabolic inhibitors to block transport. There was evidence for polyamine binding to external cell sites, but polyamine uptake by protoplasts as well as polyamine translocation and secretion by the whole thallus was also demonstrated. Since cultured and actively growing thallus discs displayed a higher uptake ability than freshly collected ones, a role for polyamines in sustaining growth is discusse

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00599.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe relationship between the diadinoxanthin cycle and changes in fluorescence yield in the diatomChaetoceros muelleriLemm. (clone CH10, Amorient Aquafarm, Inc., Hawaii) was investigated. High‐light‐induced changes in fluorescence yield and xanthophyll de‐epoxidation occurred very rapidly (first order rate constant 1.60 min−1). The observed light‐induced changes in diatoxanthin and diadinoxanthin concentration were consistent with a two‐pool scheme for diadinoxanthin, one of which does not undergo de‐epoxidation. Changes in xanthophyll concentration correlated with changes inin vivoabsorbance indicating that diadinoxanthin cycle activityin vivocan be monitored spectrophotometrically. However, changes in cell absorbance were small relative to total optical absorption cross section. Increases in the concentration of diatoxanthin were linearly correlated with increases in the rate constant for thermal de‐excitation in the antenna of photosystem II (PSII). Antenna quenching produced or mediated by diatoxanthin may, thus, protect the PSII reaction center in diatoms. Changes in the maximum fluorescence yield suggested that changes in the reaction center also contributed to nonphotochemical quenching of fluorescence. Thus, reaction center quenching affected the relationship between antenna quenching and changes in photochemical efficiency producing the effect of a decrease in fluorescence yield without a decrease in photochem

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00606.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThe time courses of photosynthetic rates in red light, with and without additional blue light, were investigated and compared in 20 species of brown algae. Species could be separated into two groups on the basis of the rhythmicity of their photosynthesis in red light and the kinetics of their responses to blue‐light pulses. One group, which consisted of members of the Ectocarpales, Chordariales, and Dictyosiphonales, was characterized by strong and persistent circadian rhythmicity in red light. The photosynthetic responses of these species to blue‐light pulses started within 10–30 s of the beginning of blue‐light treatment and mostly contained at least two distinct kinetic components. An early component, which reached a maximum about 5–10 min after the blue‐light pulse, was always detectable. Later components were seen as separate peaks or shoulders after an additional 10–20 min. The decay of the response in this group of species was mostly slow, with half‐lives of between 0.5 and 1.5 h. In the second group of species, consisting of members of the Dictyotales, Laminariales, and Fucales, photosynthesis in red light was usually non‐rhythmic, although circadian rhythms with a weak amplitude or of transient occurrence were observed in some plants of some species. The increase in photosynthesis in response to a blue‐light pulse was not detectable until 70–330 s after the start of blue‐light treatment, and the response itself had only a single component, with a maximum after about 10 min and half‐life of 10–20 min. The lengths of the lag‐phases were positively correlated with the times taken to reach the peak in this group, although the lag‐phases and the half lives sometimes varied with time in individual plants. Two members of the Sphacelariales(Sphacelaria, Cladostephus)did not fit into either of the two groups because their photosynthesis was rhythmic, but their responses had long lag‐phases, a single component, and moderately long half‐lives. The differences in the kinetics of the photosynthetic response to blue‐light pulses, which have been described for the two main groups of species, are thought to indicate that there are two distinct mechanisms by which light‐saturated photosynthesis responds to blue light in brown algae. Since in some species the maximal photosynthesis after a blue‐light pulse and the rate of photosynthesis in continuous blue light also varied in a circadian pattern, the response to blue li

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00612.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTThree different chlorophyll (chl)c‐type pigments were isolated from two cryptophyte species by silica thin‐layer chromatography or polyethylene high‐performance liquid chromatography.Chroomonassp. Hansgirg contained chlc1and magnesium‐2,4‐divinylpheoporphyrin a, mono‐methylester; chlc2and magnesium‐2,4‐divinylpheoporphyrin a5monomethylester were found inCryptomonas maculata(syn.Rhodomonas maculataButcher). These identifications were based on spectral characteristics and on comparison with reference pigments isolated from the synurophyceanSynura peterseniiKorshikov and the prasinophyteMantoniella squamataManton&Park. Neither of the cryptophyte species contained chlc1and chlc2.The significance of chlc1as a major pigment and the occurrence of magnesium‐2,4‐divinylpheoporphyrin a5monomethylester in cryptop

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00621.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTCeratium fusus(Ehrenb.) Dujardin was exposed to light of different wavelengths and photon flux densities (PFDs) to examine their effects on mechanically stimulable bioluminescence (MSL). Photoinhibition of MSL was proportional to the logarithm of PFD. Exposure to I μmol photons·m−2s−1of broadband blue light (ca. 400–500 nm) produced near‐complete photoinhibition (≥90% reduction in MSL) with a threshold at ca. 0.01 μmol photons·m−2·s−1. The threshold of photoinhibition was ca. an order of magnitude greater for both broadband green (ca. 500–580 nm) and red light (ca. 660–700 nm). Exposure to narrow spectral bands (ca. 10 nm half bandwidth) from 400 and 700 nm at a PFD of 0.1 μmol photons·m−2·s−1produced a maximal response of photoinhibition in the blue wavelengths (peak ca. 490 nm). A photoinhibition response (≥ 10%) in the green (ca. 500–540 nm) and red wavelengths (ca. 680 nm) occurred only at higher PFDs (1 and 10 μmol photons·m−2·s−1). The spectral response is similar to that reported forGonyaulax polyedraStein andPyrocystis lunulaSchütt and unlike that ofAlexandrium tamarense(Lebour) Balech et Tangen. The dinoflagellate's own bioluminescence is two orders of magnitude too low to result in self‐photoinhibition. The quantitative relationships developed in the laboratory predict photoinhibition of bioluminescence in popula

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00627.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY

摘要:

ABSTRACTProtoplasts were prepared fromUlva fasciataDelile, and their photosynthetic performance was measured and compared with that of thalli discs. These protoplasts maintained maximal rates of photosynthesis as high as those of thalli (up to 300 μmol O2·mg chlorophyll−1·h−1) for several hours after preparation and were therefore considered suitable for kinetic studies of inorganic carbon utilization. The photosynthetic K1/2(inorganic carbon) at pH 6.1 was 3.8 μM and increased to 67, 158, and 1410 μM at the pH values 7.0, 7.9, and 8.9, respectively. Compared with these protoplasts, thalli had a much lower affinity for CO2but approximately the same affinity for HCO3−. Comparisons between rates of photosynthesis and the spontaneous dehydration of HCO3−(at 50 μM inorganic carbon) revealed that photosynthesis of both protoplasts (which lacked apparent activity of extracellular/surface‐bound carbonic anhydrase) and thalli (which were only 25% inhibited by the external carbonic anhydrase inhibitor acetazolamide) could not be supported by CO2formation in the medium at the higher pH values, indicating HCO3−uptake. Since both protoplasts and thalli were sensitive to 4,4′‐diisothiocyanostilbene‐2,2′‐disulfonate, we suggest that HCO3−transport was facilitated by the membrane‐located anion exchange protein recently reported to function in certainUlvathalli. These findings suggest that the presence of a cell wall may constitute a diffusion barrier for CO2, but not for HCO3−, utilization

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1994.00633.x

出版商:Blackwell Science Inc    

年代:1994

数据来源: WILEY