Growth Rate Of Thalli Research Articles

Physiological and transcriptome analysis of acclimatory response to cold stress in marine red alga Pyropia yezoensis

Red macroalga Pyropia yezoensis is a high valuable cultivated marine crop. Its acclimation to cold stress is especially important for long cultivation period across winter in coasts of warm temperate zone in East Asia. In this study, the response of P. yezoensis thalli to low temperature was analyzed on physiology and transcriptome level, to explore its acclimation mechanism to cold stress. The results showed that the practical photosynthesis activity (indicated by ΦPSII and qP) was depressed and pigment allophycocyanin content was decreased during the cold stress of 48 h. However, the Fv/Fm and non-photochemical quenching increased significantly after 24 h, and the average growth rate of thalli also rebounded from 24 to 48 h, indicating a certain extent of acclimation to cold stress. On transcriptionally, the low temperature promoted the expression of differentially expressed genes (DEGs) related to carbohydrate metabolism and energy metabolism, while genes related to photosynthetic system were depressed. The increased expression of DEGs involved in ribosomal biogenesis and lipid metabolism which could accelerate protein synthesis and enhance the degree of fatty acid unsaturation, might help P. yezoensis thallus cells to cope with cold stress. Further co-expression network analysis revealed differential expression trends along with stress time, and corresponding hub genes play important roles in the systemic acquired acclimation to cold stress. This study provides basic mechanisms of P. yezoensis acclimation to cold temperature and may aid in exploration of functional genes for genetic breeding of economic macroalgae.

Combined Influences of Light and Nitrogen Enrichment on the Physiological Performance of a Golden Tide Alga (Sargassum horneri)

Sargassum golden tides (GT) are common in numerous coastal areas all over the world, and it adversely affects local marine life. Eutrophication is critical for Sargassum GT development. However, its physiological and ecological mechanism remains unclear. To investigate the responses of drifting Sargassum horneri, the species causing GT in the western Pacific, to light and enriched nitrogen, we set three light conditions (Low-light (LL), 10 μmol photons m−2 s−1; Middle-light (ML), 60 μmol photons m−2 s−1; and High-light (HL), 300 μmol photons m−2 s−1) and three nitrogen conditions (Natural seawater, the final concentration of N was 31.8 μmol L−1, including 30.5 μmol L−1 of NO3− and 1.3 μmol L−1 of NH4+; Enrichment of NO3−, final concentration of N was 200 μmol L−1; and Enrichment of NH4+, the final concentration of N was 200 μmol L−1), and grew the thalli under varying conditions for 10 days before determining the growth and utilization of carbon and nitrogen. Based on the accumulated data, the elevated light level led to a higher growth rate of alga. In the LL culture, the higher capacity for carbon utilization, which was reflected by the higher maximum photosynthetic carbon fixation rate (Vmax), resulted in the elevated growth rates of thalli in the nitrogen-enriched media as compared with the natural seawater. Furthermore, a higher growth rate was found in the enrichment of NH4+ despite a low affinity for inorganic carbon indicated by a higher value of the half-saturation constant (K0.5). In the ML treatment, an insignificant difference in growth rate was found in three nitrogen cultures, except for a slight increase in the enrichment of NH4+ than the enrichment of NO3−. In the HL treatment, compared with natural seawater culture, enrichment of NO3− or NH4+ accelerated the growth of alga, with no significant difference between the two nitrogen sources. Such enhancement in growth was related to the more photosynthetic carbon fixation, indicated by the higher value of Vmax and soluble carbohydrates content of alga cultured with NO3− and NH4+ enrichments. Additionally, the uptake and assimilation products of nitrogen, such as pigments and soluble proteins, remained unaffected by nitrogen source enrichment of NO3− or NH4+ at all three light levels. In conclusion, enrichment of NO3− and NH4+ exhibited different influences on the growth of S. horneri at different light levels, which was mainly associated with the capacity and efficiency of photosynthetic carbon utilization. At the HL level, both the enrichment of NO3− and NH4+ dramatically accelerate the growth of alga by stimulating the photosynthetic carbon fixation. Accordingly, we speculated that drifting S. horneri, exposed to HL level on the surface of the sea, were likely to develop rapidly to form GT in eutrophic oceanic areas with upwelled and river plume NO3− or NH4+ nutrients.

A Preliminary Study on the Mechanisms of Growth and Physiological Changes in Response to Different Temperatures in Neopyropia yezoensis (Rhodophyta)

As an economically valuable red seaweed, Neopyropia yezoensis (Rhodophyta) is cultivated in intertidal areas, and its growth and development are greatly influenced by environmental factors such as temperature. Although much effort has been devoted to delineating the influence, the underlying cellular and molecular mechanisms remain elusive. In this study, the gametophyte blades and protoplasts were cultured at different temperatures (13 °C, 17 °C, 21 °C, 25 °C). Only blades cultured at 13 °C maintained a normal growth state (the relative growth rate of thalli was positive, and the content of phycobiliprotein and pigments changed little); the survival and division rates of protoplasts were high at 13 °C, but greatly decreased with the increase in temperature, suggesting that 13 °C is suitable for the growth of N. yezoensis. In our efforts to delineate the underlying mechanism, a partial coding sequence (CDS) of Cyclin B and the complete CDS of cyclin-dependent-kinase B (CDKB) in N. yezoensis were cloned. Since Cyclin B controls G2/M phase transition by activating CDK and regulates the progression of cell division, we then analyzed how Cyclin B expression in the gametophyte blades might change with temperatures by qPCR and Western blotting. The results showed that the expression of Cyclin B first increased and then decreased after transfer from 13 °C to higher temperatures, and the downregulation of Cyclin B was more obvious with the increase in temperature. The phosphorylation of extracellular signal-regulated kinase (ERK) decreased with the increase in temperature, suggesting inactivation of ERK at higher temperatures; inhibition of ERK by FR180204 significantly decreased the survival and division rates of protoplasts cultured at 13 °C. These results suggest that downregulation of Cyclin B and inactivation of ERK might be involved in negatively regulating the survival and division of protoplasts and the growth of gametophyte blades of N. yezoensis at high temperatures.

Zinc toxicity alters the photosynthetic response of red alga Pyropia yezoensis to ocean acidification.

The globally changing environmental climate, ocean acidification, and heavy metal pollution are of increasing concern. However, studies investigating the combined effects of ocean acidification and zinc (Zn) exposure on macroalgae are very scarce. In this study, the photosynthetic performance of the red alga Pyropia yezoensis was examined under three different concentrations of Zn (control, 25 (medium), and 100 (high) μg L-1) and pCO2 (400 (ambient) and 1000 (high) μatm). The results showed that higher Zn concentrations resulted in increased toxicity for P. yezoensis, while ocean acidification alleviated this negative effect. Ocean acidification increased the relative growth rate of thalli under both medium and high Zn concentrations. The net photosynthetic rate and respiratory rate of thalli also significantly increased in response under ocean acidification, when thalli were cultured under both medium and high Zn concentrations. Malondialdehyde levels decreased under ocean acidification, compared to ambient CO2 conditions and either medium or high Zn concentrations. The activity of superoxide dismutase increased in response to high Zn concentrations, which was particularly apparent at high Zn concentration and ocean acidification. Immunoblotting tests showed that ocean acidification increased D1 removal, with increasing expression levels of the PSII reaction center proteins D2, CP47, and RbcL. These results suggested that ocean acidification could alleviate the damage caused by Zn exposure, thus providing a theoretical basis for a better prediction of the impact of global climate change and heavy metal contamination on marine primary productivity in the form of seaweeds.

Expected CO2-induced ocean acidification modulates copper toxicity in the green tide alga Ulva prolifera

Cu is considered to be toxic to macroalgae at higher levels. Ocean acidification can also alter the physiological performances of macroalgae. However, little is known regarding the interactive effects of Cu and ocean acidification on macroalgae. In this study, a green tide macroalga, Ulva prolifera, was cultured at the conditions of three levels of Cu (control, 0.5μM, and 2μM) and pCO2 (ambient, 1000μatm, and 1400μatm) to investigate the responses of U. prolifera to interaction of Cu exposure and ocean acidification. The relative growth rate of thalli decreased with the rise of Cu for all pCO2 conditions except the 1000μatm pCO2. Compared with the control, 2μM Cu reduced the net photosynthetic rate for all pCO2 conditions while 0.5μM Cu only reduced it at 1400μatm pCO2. The inhibition rate of Cu on the relative growth rate and net photosynthetic rate was reduced at 1000μatm pCO2 but was magnified at 1400μatm pCO2. Contrary to growth, the dark respiration rate was enhanced by 0.5μM Cu at ambient pCO2 and by 2μM Cu at ambient and 1000μatm pCO2, although it was reduced by 2μM Cu at 1400μatm pCO2 compared to the control. The 0.5μM Cu did not affect the relative electron transport rate (rETR) for any pCO2 condition but 2μM Cu decreased it for all pCO2 conditions except 1000μatm pCO2. The mute effect of 0.5μM Cu on the net photosynthetic rate and rETR at ambient pCO2 may be due to more Chl a and Chl b being synthesized. In addition, 2μM Cu and 1400μatm pCO2 led to branched thalli, which may be a defense mechanism against the stress of high Cu and pCO2. Our data, for the first time, demonstrate that a modest increase of pCO2 can alleviate the toxicity of Cu to U. prolifera whilst a further increase exacerbates it. U. prolifera can respond to the stress of Cu pollution and ocean acidification via physiological and morphological alterations.

Effects of deep seawater medium on growth and amino acid profile of a sterile Ulva pertusa Kjellman (Ulvaceae, Chlorophyta)

The potential use of deep seawater (DSW) for the cultivation of macroalgae was evaluated by analysis of the growth rate of thalli (by surface area), photosynthetic pigment content, and total free amino acid content of sterile Ulva pertusa cultured in the control medium (one-fifth strength Provasoli’s enriched seawater (PES) medium), surface seawater (SSW) medium and also seawater medium collected from 400 m depth (400-DSW) and 1,200 m depth (1,200-DSW). The growth rate of the sterile U. pertusa grown in 400-DSW and 1,200-DSW was similar to that of thalli cultured in the one-fifth strength PES medium that had previously been shown to be the optimum concentration for the cultivation of Ulva. Photosynthetic pigment content in the control medium, 400-DSW- and 1,200-DSW-cultured thalli was 1.7–2.0 times higher than that of the SSW-cultured thalli. The total free amino acids content of the control medium and SSW-cultivated thalli was 264 ± 64 and 120 ± 39 mg per 100 g dry weight, whereas the 400-DSW- and 1,200-DSW-cultivated thalli had significantly more amino acids (342 ± 69–327 ± 64 mg per 100 g dry weight). The results of this study indicate that DSW has a high potential for cultivation of edible macroalgae without any supply of extra nutrient until it grows to harvest size.

Extreme phenotypic variation in Cetraria aculeata (lichenized Ascomycota): adaptation or incidental modification?

Phenotypic variability is a successful strategy in lichens for colonizing different habitats. Vagrancy has been reported as a specific adaptation for lichens living in steppe habitats around the world. Among the facultatively vagrant species, the cosmopolitan Cetraria aculeata apparently forms extremely modified vagrant thalli in steppe habitats of Central Spain. The aim of this study was to investigate whether these changes are phenotypic plasticity (a single genotype producing different phenotypes), by characterizing the anatomical and ultrastructural changes observed in vagrant morphs, and measuring differences in ecophysiological performance. Specimens of vagrant and attached populations of C. aculeata were collected on the steppes of Central Spain. The fungal internal transcribed spacer (ITS), glyceraldehyde-3-phosphate dehydrogenase (GPD) and the large sub-unit of the mitochondrial ribosomal DNA (mtLSUm), and the algal ITS and actin were studied within a population genetics framework. Semi-thin and ultrathin sections were analysed by means of optical, scanning electron and transmission electron microscopy. Gas exchange and chlorophyll fluorescence were used to compare the physiological performance of both morphs. Vagrant and attached morphs share multilocus haplotypes which may indicate that they belong to the same species in spite of their completely different anatomy. However, differentiation tests suggested that vagrant specimens do not represent a random sub-set of the surrounding population. The morphological differences were related to anatomical and ultrastructural differences. Large intercalary growth rates of thalli after the loss of the basal-apical thallus polarity may be the cause of the increased growth shown by vagrant specimens. The anatomical and morphological changes lead to greater duration of ecophysiological activity in vagrant specimens. Although the anatomical and physiological changes could be chance effects, the genetic differentiation between vagrant and attached sub-populations and the higher biomass of the former show fitness effects and adaptation to dry environmental conditions in steppe habitats.

Cost of chemical defence in the red alga Delisea pulchra

The concept of a cost of defence is fundamental to theories for the evolution of defences against consumers. However, the evidence for a cost of plant chemical defences is mixed, and often indirect. This is particularly true for marine macroalgae (seaweeds), for which inferences of cost to date rely almost exclusively on phenotypic correlations between one class of secondary metabolites (brown algal phlorotannins) and growth (or, in one instance, fecundity). No studies of the cost of seaweed chemical defense have experimentally manipulated the presence of secondary metabolites in a controlled fashion and only one previous study has considered genetic background as a factor. Here we measured the cost of halogenated furanones to the red seaweed Delisea pulchra in three ways: a) phenotypic correlations between concentrations of furanones and fecundity in field collected thalli; b) genetic correlations between concentrations of furanones and growth for clones of thalli grown from tetraspores, and c) by comparing growth rates of thalli for which furanone production was experimentally inhibited (furanone ‐) vs thalli which produced furanones (furanone +). Two of our three tests‐correlations between furanones and fecundity, and the growth of furanone (+) vs furanone (−) thalli‐indicated a cost of furanones to D. pulchra but genetic correlations between furanones and growth did not. We suggest that these apparently conflicting results are consistent with the consequences of apical growth in this alga, and may further result from a cost of furanones only being manifested at critical developmental stages or times of tissue differentiation.

Effect of water motion on the cultivation of the economic seaweed Gracilaria parvispora (Rhodophyta) on Molokai, Hawaii

A cage culture system was previously developed for the red alga Gracilaria parvispora Abbott on Molokai, HI; however, yields have shown marked variation, even among cages with identical stocking rates and fertilization treatments. Water motion, which can be affected by location and arrangement of the cages in the grow-out area, was hypothesized to be a factor contributing to the variation in yield. To examine this, the growth rates of thalli and the development of sporelings in relation to water motion were determined in replicated trials both in tanks and in small-scale field experiments. Generally, water motion had a substantial effect on both thallus growth rate and spore development. In the tank cultures of thalli, water velocities ranged up to 13.7 cm s −1, and relative growth rates (RGRs) ranged from 2.8% to 8.9% day −1. In the lagoon, water velocities ranged between 3.6 and 11.6 cm s −1. Relative growth rates of the thalli in the lagoon trials were 0.02–10.3% day −1. Sporeling density, a measure of spore development, was also significantly affected by water motion. In the tank trials, water motion ranged from near 0 to 6.50 cm s −1, and sporeling densities ranged from 1.4 cm −2 at lower water motion levels to 11.6 sporelings cm −2 at higher levels. Similar results were obtained in lagoon trials, with sporeling densities ranging from 0.2 to 6.7 cm −2. However, sporeling length was not significantly correlated with water motion. In previous trials, we have been able to achieve high sporeling densities, but elongation of sporelings has been inhibited. In the present trials, we were able to break the apparent sporeling dormancy by incubating the sporelings in tanks enriched in nutrients supplied by fish cultures. Consideration of the effects of water motion is important in designing culture systems for species of Gracilaria and other marine algae. The results also suggest that nutrients play a key role in regulating the early development of G. parvispora sporelings.

Isolation and characterization of a single-copy actin gene from a sterile mutant of Ulva pertusa (Ulvales, Chlorophyta)

We constructed a cDNA library from sterile Ulva pertusa (Ulvales, Chlorophyta), and isolated and characterized a full-length cDNA clone encoding actin. The actin ( ACT) cDNA consisted of 1487 nucleotides (nt) and had an open reading frame (ORF) encoding a polypeptide of 377 amino acid (AA) residues. The ACT gene had one intron in the 5′-untranslated region and three introns in the coding region. Transcription started 26 nt downstream of the putative TATA box. A potential polyadenylation signal, TGTAG, was located 100 nt downstream of the terminator codon, TAG. Amino acid alignment with actins from various algae and land plants showed that sterile U. pertusa actin was more similar to actins from Chlorophyta, Phaeophyta, Euglenophyta, and higher plants (over 76.9%) than to actins from Rhodophyta. Southern blot analysis indicated that the sterile U. pertusa genome has only a single actin-encoding gene. Thalli grown on a 12D/12L photoperiod increased in surface area some two-fold over 24 h regardless of the nutritional conditions. The growth rate of thalli during the light period was significantly higher than that during the dark period. Northern hybridization indicated that the expression of actin mRNA was induced and repressed by the light and dark treatments, respectively. These results suggest that the U. pertusa cell division cycle has a periodicity of 24 h and that the ACT gene is highly transcribed during cell growth and development in the light period.

Nitrogen- versus phosphorus-limited growth and sources of nutrients for coral reef macroalgae

Recent investigations of nutrient-limited productivity in coral reef macroalgae have led to the conclusion that phosphorus, rather than nitrogen, is the primary limiting nutrient. In this study, comparison of the dissolved inorganic nitrogen:phosphorus ratio in the water column of Kaneohe Bay, Hawaii, with tissue nitrogen:phosphorus ratios in macroalgae from Kaneohe Bay suggested that nitrogen, rather than phosphorus, generally limits productivity in this system. Results of nutrient-enrichment experiments in a flow-through culture system indicated that inorganic nitrogen limited the growth rates of 8 out of 9 macroalgae species tested. In 6 of the species tested, specific growth rates of thalli cultured in unenriched seawater from the Kaneohe Bay water column were zero or negative after 12 d. These results suggest that, in order to persist in low-nutrient coral reef systems, some macroalgae require high rates of nutrient advection or access to benthic nutrient sources in addition to nutrients in the overlying water column. Nutrient concentrations in water samples collected from the microenvironments inhabited or created by macroalgae were compared to nutrient concentrations in the overlying water column. On protected reef flats, inorganic nitrogen concentrations within dense mats of Gracilaria salicornia and Kappaphycus alvarezii, and inorganic nitrogen and phosphate concentrations in sediment porewater near the rhizophytic algae Caulerpa racemosa and C. sertularioides were significantly higher than in the water column. The sediments associated with these mat-forming and rhizophytic species appear to function as localized nutrient sources, making sustained growth possible despite the oligotrophic water column. In wave-exposed habitats such as the Kaneohe Bay Barrier Reef flat, water motion is higher than at protected sites, sediment nutrient concentrations are low, and zones of high nutrient concentrations do not develop near or beneath macroalgae, including dense Sargassum echinocarpum canopies. Under these conditions, macroalgae evidently depend on rapid advection of low-nutrient water from the water column, rather than benthic nutrient sources, to sustain growth.

Life Expectancy in a Tulsa Cemetery: Growth and Population Structure of the Lichen Xanthoparmelia cumberlandia

-The demographics of a population of the foliose lichen Xanthoparmelia cumberlandia growing on gravestones in a Tulsa cemetery are presented. Because of the regular layout of granitic gravestones, the cemetery acted as a mechanism for generating experimental replicates and as a control for habitat variability. The lichen population was multi-modal, based on age classes. Thalli within each age class approximated a normal distribution of size. Age classes were separated by several years. Growth rates of thalli within age classes were independent of size, but growth was dependent on age class. Thallus growth varied among the months, and was correlated with precipitation but uncorrelated with temperature. Mortality rate was greatest in age class III, and lowest in class I (I youngest-III oldest thalli). A population model of the species showed that recruitment has been sporadic, yet highly successful when it did occur. The model depicts growth rates as independent of size within, but not among, the three age classes.

Lichens as Monitors of Pollutant Elements at Permanent Sites in Maryland and Virginia

Concentrations of sulfur, nitrogen, and seven metal elements are reported for the lichen Flavoparmelia baltimorensis from three monitoring stations in Maryland and Virginia. At Plummers Island, Maryland, 15 km from the center of Washington, D.C., lichens have been collected for nearly 100 years. The other two stations, Bear Island, Maryland (21 km) and Stony Man Mountain, Virginia (120 km), were established in the 1970's by Mason Hale to help document changes in ambient air quality in the Washington, D.C. area. Concentrations of cadmium, chromium, nickel, zinc, and lead were consistently highest at Plummers Island and lowest at Stony Man Mountain; concentrations of the other four elements (nitrogen, sulfur, aluminum, and copper) were also consistently higher at Plummers Island than at Stony Man Mountain. Recent collections, in 1988 and 1992, revealed marked reductions in the concentration of all nine elements except aluminum at all three stations, providing limited, but encouraging, signs of improved air quality in the region. Known primarily for his research on lichen systematics, Mason Hale has nevertheless made a number of important contributions to the study of lichens as environmental indicators. From 1977 until shortly before his death in 1990, Mason and I participated in a number of environmental studies in the Washington, D.C. area designed to monitor changes in regional air quality. One of our principal sites was Plummers Island, Maryland, a small Potomac River island located just 15 km from the heart of Washington, D.C. The studies we carried out there were an extension of Mason's work begun in the late 1950's, and all have been supported by the Washington Biologists' Field Club, a local scientific society that promotes research on Plummers Island and the Potomac River Basin. In initiating his work on Plummers Island, Mason believed it was important to establish permanent study sites for monitoring lichen growth, element accumulation, and floristic composition as the regional environment changed. Mason's early work on the island was involved mainly with the longterm assessment of lichen growth rates (Hale 1970, 1972, 1973; Lawrey & Hale 1977); after 1965, it was expanded to include elemental analysis for pollutant elements, especially lead (Pb). This shift in emphasis was intended to document changes on the island caused by the construction of a bridge (The American Legion Memorial Bridge) supporting a major interstate highway (Interstate 495) over the island. The initial analyses of lichens from Plummers Island during the 1970's (Lawrey & Hale 1979) revealed extraordinarily high Pb values, which were indicative of the high Pb concentrations in automobile exhaust fallout reaching the island. It was at this time that another study site was established on Bear Island, Maryland, 6 km upstream from Plumm rs Island. Bear Island lichens have consistently contained lower concentrations of Pb and other pollut nt elements than Plummers Island lichens (Lawrey 1980; Lawrey & Hale 1981). Floristic analysis of the two islands (much of it unpublished) has also shown that the lichen communities on Plummers Isla d are far less diverse than those found on Bear Island, and that the growth rate of thalli of the dominant lichen species on both islands, Flavoparmelia baltimorensis, is significantly lower in Plummers Island communities. In 1980, we established another long-term study TABLE 1. Lead concentrations in thalli of Flavoparmelia baltimorensis collected from Plummers Island and Bear Island, Maryland and Stony Man Mountain, Virginia at various times. All values are mean concentrations (.tg/g dry weight ? S.E. of the mean). Sample size is two for historical samples and 10 for recent samples. Year Plummers Island Bear Island Stony Man Mt. 1907 82.3 (8.2) 1938 127.8 (14.8) 1958 327.9 (12.6) 197

GROWTH PHASES IN THE LIFE OF A LICHEN THALLUS

SummaryThe growth rates of thalli of foliose saxicolous lichens before and after the linear phase of growth were measured in 1973. Changes in the radial growth rate (measured as mm/year) with thallus size in the prelinear phase (thalli less than approximately 1.5 cm in diameter) were consistent with the hypothesis that early growth of these lichens is logarithmic. When growth in the prelinear phase was measured as a relative growth rate (measured as cm2/cm2/year) there was a rapid rise in growth rate until about 3 mm thallus diameter and then a decline in growth rate. The radial growth rate of non‐fragmenting thalli when compared with fragmenting thalli at different stages of fragmentation suggested that the radial growth rate does not significantly decline after fragmentation of the thallus. This result is not consistent with a postlinear phase in the radial growth of a lichen thallus.