Seasonal acclimatization of thallus proline contents of Mastocarpus stellatus and Chondrus crispus: intertidal rhodophytes that differ in freezing tolerance

Mastocarpus stellatus and Chondrus crispus often co‐occur in the lower intertidal of Northern Atlantic rocky shorelines. At our field site along the Maine coast (USA), Mastocarpus stellatus thalli possessed greater contents of proline when compared with thalli of Chondrus crispus. In addition, M. stellatus thalli acclimated to colder growth conditions in winter/early spring by increasing proline content several fold; no seasonal acclimation in proline content was observed in C. crispus. Proline accumulates in the tissues of a broad diversity of freezing‐tolerant organisms and is among the most common cryoprotectant molecules. Thus, our observations provide a basis for the previously well‐documented greater freezing tolerance of Mastocarpus stellatus when compared with Chondrus crispus.     

Stress tolerance and reactive oxygen metabolism in the intertidal red seaweeds Mastocarpus stellatus and Chondrus crispus

Mastocarpus stellatus and Chondrus crispus are morphologically similar red seaweeds that co-occur on rocky intertidal seashores in the Northern Atlantic. Mastocarpus stellatus grows higher on the shore and is more tolerant of environmental stress, caused by factors such as freezing and desiccation, than C. crispus. Here we report a correlation between reactive oxygen metabolism and stress tolerance, which suggests that reactive oxygen metabolism may play a role in stress tolerance of intertidal red seaweeds. Mastocarpus stellatus scavenged added H₂O₂ slightly faster, and was more resistant to oxidative stress induced by addition of H₂O₂ and Rose Bengal, than C. crispus. These data were consistent with higher levels of ascorbate and β-carotene and higher activities of catalase and glutathione reductase, in M. stellatus. Tocopherol content and activities of superoxide dismutase and ascorbate peroxidase were similar in both species. Activities of reactive oxygen scavenging enzymes generally increased with tidal height in M. stellatus; this was, however, not a consistent trend in C. crispus.     

Comparative genomic analyses of transport proteins encoded within the red algae Chondrus crispus,Galdieria sulphuraria,and Cyanidioschyzon merolae11

Galdieria sulphuraria and Cyanidioschyzon merolae are thermo‐acidophilic unicellular red algal cousins capable of living in volcanic environments, although the former can additionally thrive in the presence of toxic heavy metals. Bioinformatic analyses of transport systems were carried out on their genomes, as well as that of the mesophilic multicellular red alga Chondrus crispus (Irish moss). We identified transport proteins related to the metabolic capabilities, physiological properties, and environmental adaptations of these organisms. Of note is the vast array of transporters encoded in G. sulphuraria capable of importing a variety of carbon sources, particularly sugars and amino acids, while C. merolae and C. crispus have relatively few such proteins. Chondrus crispus may prefer short chain acids to sugars and amino acids. In addition, the number of encoded proteins pertaining to heavy metal ion transport is highest in G. sulphuraria and lowest in C. crispus. All three organisms preferentially utilize secondary carriers over primary active transporters, suggesting that their primary source of energy derives from electron flow rather than substrate‐level phosphorylation. Surprisingly, the percentage of inorganic ion transporters encoded in C. merolae more closely resembles that of C. crispus than G. sulphuraria, but only C. crispus appears to signal via voltage‐gated cation channels and possess a Na⁺/K⁺‐ATPase and a Na⁺ exporting pyrophosphatase. The results presented in this report further our understanding of the metabolic potential and toxic compound resistances of these three organisms.     

Drag, drafting, and mechanical interactions in canopies of the red alga Chondrus crispus.

Dense algal canopies, which are common in the lower intertidal and shallow subtidal along rocky coastlines, can alter flow-induced forces in their vicinity. Alteration of flow-induced forces on algal thalli may ameliorate risk of dislodgement and will affect important physiological processes, such as rates of photosynthesis. This study found that the force experienced by a thallus of the red alga Chondrus crispus (Stackhouse) at a given flow speed within a flow tank depended upon (1) the density of the canopy surrounding the thallus, (2) the position of the thallus within the canopy, and (3) the length of the stipe of the thallus relative to the height of the canopy. At all flow speeds, a solitary thallus experienced higher forces than a thallus with neighbors. A greater than 65% reduction in force occurred when the thallus drafted in the region of slower velocities that occurs in the wake region of even a single upstream neighbor, similar to the way racing bicyclists draft one behind the other. Mechanical interactions between thalli were important to forces experienced within canopies. A thallus on the upstream edge of a canopy experienced 6% less force than it did when solitary, because the canopy physically supported it. A thallus in the middle of a canopy experienced up to 83% less force than a solitary thallus, and forces decreased with increasing canopy density. Thus, a bushy morphology that increases drag on a solitary thallus may function to decrease forces experienced by that thallus when it is surrounded by a canopy, because that morphology increases physical support provided by neighbors.     

Crystallization and preliminary X-ray diffraction studies of oxidized flavodoxin from Chondrus crispus, a red alga

Crystals of the oxidized form of flavodoxin from a red alga, Chondrus crispus, have been grown in ammonium sulfate solution by the dialysis method. The crystals belong to the orthorhombic system, space group P2(1)2(1)2(1), with unit cell dimensions of a = 63.6, b = 48.8, and c = 56.8 A. The asymmetric unit contains one molecule of flavodoxin. The crystals diffract X-rays to about 2.0 A resolution and are stable to X-ray beams. The diffraction patterns changed significantly upon soaking the crystal in a solution of a platinum complex. The major heavy-atom sites in the platinum derivative crystal have been identified from the difference Patterson function calculated at 4 A resolution.     

The evolutionary origin of red algae as deduced from the nuclear genes encoding cytosolic and chloroplast glyceraldehyde-3-phosphate dehydrogenases from Chondrus crispus

Algae are a heterogeneous group of photosynthetic eukaryotes traditionally separated into three major subdivisions: rhodophytes, chlorophytes, and chromophytes. The evolutionary origin of rhodophytes or red algae and their links to other photosynthetic and nonphotosynthetic eukaryotes have been a matter of much controversy and speculation. Here we present the first cDNAs of nuclear protein genes from red algae: Those encoding cytosolic and chloroplast glyceraldehyde-3-phosphate dehydrogenases (GAPDH) from Chondrus crispus. A phylogenetic analysis including GAPDH gene sequences from a number of eukaryotic taxa, cyanobacteria, and purple bacteria suggests that chloroplasts and rhodoplasts together form a monophyletic group of cyanobacterial descent and that rhodophytes separated from chlorophytes at about the same time as animals and fungi. The composite GAPDH tree further demonstrates that chloroplast and cytosolic GAPDH genes are closely related to their homologs in cyanobacteria and purple bacteria, respectively, the presumptive ancestors of chloroplasts and mitochondria, thereby firmly establishing the endosymbiotic origin of these nuclear genes and their fixation in eukaryotic cells before the rhodophyte/chlorophyte separation. The present data are in conflict with phylogenetic inferences based on plastid-encoded rbcL sequences supporting a polyphyletic origin of rhodoplasts and chloroplasts. Comparison of rbcL to GAPDH phylogenies suggests that rbcL trees may be misleading because they are composed of branches representing ancient duplicated (paralogous) genes. Correspondence to: R. Cerff     

DNA sequence,structure, and phylogenetic relationship of the mitochondrial small-subunit rRNA from the red alga Chondrus crispus (Gigartinales,Rhodophytes)

The entire nucleotide sequence containing the small-subunit ribosomal RNA gene (SSU rRNA) from the mitochondrial genome of Chondrus crispus was determined. To our knowledge, this is the first sequence of a mitochondrial 16S-like rRNA from a red alga. The length of this gene is 1,376 nucleotides. Its secondary structure was constructed and compared with other known secondary structures from eubacteria and from mitochondria of land plants, green and brown algae, and fungi. Phylogenetic trees were built upon SSU rRNA sequence alignment from mitochondria and eubacteria. The results show that rhodophytes and chromophytes provide additional links in the evolution of mitochondria between the green plant lineage and the nonplant lineages.Correspondence to: C. Boyen     

An assessment of the AFLP method for investigating population structure in the red alga Chondrus crispus Stackhouse (Gigartinales, Florideophyceae)

The appropriateness of the Amplified Fragment Length Polymorphism (AFLP) technique for investigating Chondrus crispus Stackhouse populations in the Maritime Provinces of Canada was assessed. The AFLP procedure was first subjected to reproducibility testing and three shortcomings were noted: 1) failure to reproduce band intensity between replicate runs for the same individual and primer pair; 2) failure of some bands to replicate; 3) lack of reproducibility for complete replicate runs for some individuals and primer pairs. In the last-mentioned case, the lack of reproducibility resulted in characteristic electropherograms indicative of weak reactions. These weak runs can be attributed to poor restriction digest/ligation reactions and/or substandard PCR, these failures ultimately resulting from low and inconsistent DNA quality. We recommend that reproducibility testing should be completed routinely in studies using the AFLP technique. In the current work, only fragments and individuals that gave reproducible results were used in subsequent analyses. The AFLP method resulted in highly variable markers within and between the populations of C. crispus included in this investigation, which prevented successful resolution of population structure. This situation could result from a lack of suitability for AFLP markers in population genetic studies, and/or too extensive genetic variation for C. crispus populations to be discerned by the AFLP technique. These two possible explanations are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Growth,lipid peroxidation and photosynthesis in two tall fescue cultivars differing in heat tolerance

Seedlings (70-d-old) of two tall fescue (Festuca arundinacea Schreb.) genotypes, heat-tolerant Jaguar 3 and heat-sensitive TF 66, were exposed to a high temperature stress of 35/30 °C (day/night) for 20 d and both light-saturated and CO₂-saturated leaf stomatal conductance decreased, especially in TF 66. Higher reductions of quantum efficiency, carboxylation efficiency and maximum photochemical efficiency of photosystem 2 in dark adapted leaves (measured as F_v/F_m) occurred in TF 66 than in Jaguar 3. High temperature stress increased photorespiration in the two plants, but more in TF 66. Moreover, high temperature stress also reduced the growth, chlorophyll content and caused cell membrane injuries in the two cultivars, the changes were again more pronounced in TF 66 than in Jaguar 3.     

Energy- and electron-transfer systems in algal photosynthesis. II. Oxidation-reduction reactions of two cytochromes and interactions of two photochemical systems in red algae

The functioning of cytochromes f and b in the electron-transfer chain of red algae, Porphyridium and Porphyra, was studied. Effects of inhibitors, temperature, etc. on the oxidation-reduction reactions of these cytochromes are shown. The interaction of two photochemical systems through dark electron-transfer in the 10-msec range was demonstrated. The reaction time of electron-transfer reactions was measured with pulsed excitation. Two electron-transfer paths, a non-cyclic path connecting two photochemical systems and a cyclic electron-transfer path around photochemical system I are postulated and a scheme for photosynthetic electron transfer in Porphyridium and Porphyra is presented.     

Silicon nutrition mitigates salinity stress in maize by modulating ion accumulation,photosynthesis, and antioxidants

Silicon is known to improve resistance against salinity stress in maize crop. This study was conducted to evaluate the influence of silicon application on growth and salt resistance in maize. Seeds of two maize genotypes (salt-sensitive ‘EV 1089’ and salt-tolerant ‘Syngenta 8441’) were grown in pots containing 0 and 2 mM Si with and without 50 mM NaCl. After detailed investigation of ion concentrations in different maize organs, both genotypes were further selected in hydroponic experiment on basis of their contrasting response to salinity stress. In the second experiment, pre-germinated seedlings were transplanted into nutrient solution with 0 and 60 mM NaCl with and without 2 mM Si. Both genotypes differed significantly in their response to salinity. Silicon addition alleviated both osmotic and oxidative stress in maize crop by improving the performance of defensive machinery under salinity stress. Silicon application also improved the water-use efficiency in both tested genotypes under both normal and salinity stress conditions. In conclusion, this study implies that the silicon-treated maize plants had better chance to survive under salinity conditions and their photosynthetic and biochemical apparatus was working far better than that of silicon-non-treated plants.     

Conformational changes in Chondrus crispus flavodoxin on dissociation of FMN and reconstitution with flavin analogues.

The apoflavodoxin produced by precipitation of Chondrus crispus flavodoxin with trichloroacetic acid migrates as a single molecular species on non-denaturing PAGE, but at a much lower Rm than the flavoprotein. Values of s and D were significantly lower than for the flavodoxin, but their substitution in the Svedberg equation indicated the molecular mass was closely similar to that of the flavodoxin. This was confirmed by meniscus-depletion sedimentation-equilibrium studies. The Stokes radius of the apoflavodoxin was 3.65 nm, compared with 2.33 nm for the flavodoxin, and estimates of frictional coefficient ratio suggested the apoprotein was in extended conformation compared with the roughly globular shape of the flavodoxin. The Ka for FMN binding was 2.8 x 10(8)M, and the electrophoretic and physicochemical properties of the reconstituted flavoprotein were closely similar to those of the native flavodoxin. FAD, iso-FMN and thio-FMN were also bound effectively, but methyl-FMN and riboflavin were bound only weakly, if at all. The reconstituted flavoproteins were active to various extents in mediating electron transfer from NADPH to cytochrome c catalysed by flavodoxin-NADP+ oxidoreductase, the highest activity being with the thio-FMN flavodoxin.     

Seasonal variation in plant hydraulic traits of two co-occurring desert shrubs, Tamarix ramosissima and Haloxylon ammodendron, with different rooting patterns

Effective hydraulic responses to varying soil moisture and evaporative demand are crucial to plant survival in arid ecosystems. This study was carried out during two growing seasons (2004?C2005) on two typical desert shrub species, Tamarix ramosissima and Haloxylon ammodendron, co-occurring in the Gurbantonggut Desert (Central Asia), to investigate their hydraulic responses to seasonal variations in water availability. The root distribution was studied by excavating the intact root systems. Leaf-specific apparent hydraulic conductance (K _l) for the two species was calculated based on leaf water potential (?? _l) and transpiration rate (T _r), which were monitored during the growing seasons. T. ramosissima had a deeper taproot (3.1 vs. 2.6 m) and a larger root surface area (3.02 vs. 1.28 m²) than H. ammodendron. Combined with a higher ?? _l, this meant that it maintained a better water status in general. For the deep-rooting T. ramosissima, the seasonal pattern of its predawn leaf water potential (?? _pd) was in high accordance with the seasonal changes in soil moisture at a depth of 2.6?C2.8 m, which was largely influenced by the upflow of groundwater through capillary ascent, and barely responded to rain events. For the shallow-rooting H. ammodendron, the seasonal pattern of ?? _pd was closely related to soil moisture in the upper layer at a depth of 0?C0.2 and 0.6?C0.8 m, which was recharged periodically by rain events and responded acutely to rainfall above 5 mm. The two species differed in their maximum transpiration rates (T _rmax) and ?? _pd: in T. ramosissima, T _rmax gradually dropped with decreasing ?? _pd; in H. ammodendron, T _rmax showed no significant response to ?? _pd. For T. ramosissima, the major water resource was groundwater and vadose zone water, and ?? _l contributed significantly to transpiration regulation. For H. ammodendron, the primary water resource was precipitation input, which was not sufficient to keep the ?? _l for this species outside the critical range of leaf shedding in summer. Thus, for these two representative species that share the same habitat, contrasting response strategies to water limitation were observed in relation to water acquisition and root distribution characteristics.     

Oxygen Uptake and Photosynthesis of the Red Macroalga, Chondrus crispus, in Seawater: Effects of Oxygen Concentration

With an experimental system developed for aquatic plants using the mass spectrometry technique and infrared gas analysis of CO₂, we studied the responses to various O₂ concentrations of gas exchanges with the red macroalga Chondrus crispus S. The results were as follows. (a) Irrespective of the CO₂ concentration, net photosynthesis was O₂ sensitive with a 45 to 70% stimulation at 2% O₂. Even with high CO₂, a significant Warburg effect was detected. (b) Although photosynthesis was CO₂ sensitive, O₂ photoconsumption was only weakly affected by CO₂ even at high CO₂ where it was still photodependent. (c) O₂ photoconsumption was always sensitive to O₂ concentration whatever the CO₂ concentration, but with O₂ exceeding 20% the kinetics disagreed with the Michaelis-Menten model, with saturation being reached more rapidly. With various CO₂ concentrations, the apparent K_m (O₂) ranged from 4 to 16% O₂ with a relatively constant V_max (O₂) of about one-third the V_max (CO₂). (d) Dark respiration seemed to be O₂ insensitive. These results are discussed in relation to the nature of the processes able to consume O₂ in the light, and seem to be consistent with a significant involvement of a Mehlertype reaction.