Sorus Formation Research Articles

Identification of differential gene expression related to reproduction in the sporophytes of Saccharina japonica.

Saccharina japonica, a significant brown macroalga in the Pacific Ocean, serves as a food source and industrial material. In aquaculture, collecting mature sporophytes for seedling production is essential but challenging due to environmental changes. In this study, transcriptomic analysis of vegetative and sorus tissues was done to identify differentially expressed genes (DEGs) and enhance our understanding of sorus formation regulation in S. japonica. KEGG pathway and Gene Otology (GO) analysis revealed that upregulated DEGs were involved in folate biosynthesis, riboflavin metabolism, and amino acid biosynthesis. In addition, the upregulation of genes associated with cell wall remodeling, such as mannuronan C-5-epimerases, vanadium-dependent haloperoxidases, and NADPH oxidase, was observed in sorus parts. Meanwhile, downregulated DEGs in sorus portions included genes related to chloroplast function. These findings will help us understand the regulatory mechanisms behind sorus formation in S. japonica and extracellular matrix remodeling in brown algae.

Relationship between environmental conditions and biennial growth of kelp Saccharina japonica var. ochotensis, northern Hokkaido, Japan

The kelp Saccharina japonica var. ochotensis occurs in the northern Sea of Japan. A monthly diving survey was conducted at two sampling stations, Tsugaru in Rebun Island and Hourai in Wakkanai district in northern Hokkaido, Japan, from March 2013 to November 2014. Oceanographic conditions, water temperature, nitrate, and irradiance were recorded, and several differences were observed between Tsugaru and Hourai. Higher irradiance at Tsugaru during July and August led to enhanced photosynthesis by sporophytes, and the lower temperature in this area led to increased storage of mannitol from April to September, with more sulfated polysaccharide in sporophytes and greater blade thickness compared to kelp specimens at Hourai. Higher water temperatures in Tsugaru during September and February led to larger sporophytes, whereas lower winter water temperatures in Hourai led to smaller sporophytes. Higher water temperatures from September to February and lower nitrate concentrations throughout the year except in April 2013 and March 2014 in Tsugaru were associated with higher sorus formation rates and lower regeneration (transition from annual to biennial sporophytes) rates than at Hourai. Irradiance at Tsugaru was higher than at Hourai from July to August. Lower temperatures and lower radiation result in a lower rate of sorus formation; whereas higher nitrate concentrations give rise to higher rates of regeneration.

Successful initiation of sorus formation and viable zoospores in Ecklonia radiata on isolated lateral fronds under hatchery conditions

Successful initiation of sorus formation and viable zoospores in Ecklonia radiata on isolated lateral fronds under hatchery conditions

Sorus developmental biology of hybrid cultivar in Saccharina japonica: Environmental and endogenous regulation

The induction and regulation of sporogenesis in the kelp Saccharina japonica is particularly important due to the necessity of obtaining spores to produce “summer seedlings” in the kelp hatchery. However, some hybrid cultivars of S. japonica with excellent agronomic traits are late-maturing, which means the hybrid cultivars cannot produce spore at the time of “summer seedling” production and limits their application in practice. The effects of temperature, irradiance, nutrition level, and exogenous hormones on the sorus formation were investigated in this study, aiming to clarify the optimum inducible conditions for sorus formation of S. japonica. Based on the number of individuals forming sorus and the percentages of the sorus area on the sporophyte tissue discs, it was proposed that the optimal conditions for sorus formation were at 17 °C, 5 mg L−1 nitrate nitrogen, 0.5 mg L−1 phosphorus, 10−6 mol L−1 abscisic acid (ABA), and irradiance of 60-100 μmol photons m−2 s−1. Then, the vegetative tissue discs of S. japonica sporophyte were cultured under the above optimal conditions to induce the sorus formation, and the duration from vegetative tissue to sours formation and zoospores release was divided into five stages. The anatomical structure changes, antioxidant activity, reactive oxygen species (ROS) level, MDA content, and endogenous hormone levels were determined at the five stages during sorus formation. Significant accumulation of ROS was observed but the content of malondialdehyde stayed at a stable level indicating that ROS may have an important role in the regulation of sorus formation rather than their potential cytotoxic effects. For the endogenous hormone analysis, indole-3-acetic acid (IAA) was lowered and ABA was elevated in the early stages during sorus formation. The GA3 trend was consistent with IAA. The contents of dihydrozeatin, isopentenyladenine, and isopentenyladenosine were significantly lower in vegetative tissue than that in sorus tissue. These results indicated ROS and hormones may play an important role in the endogenous regulation of sorus formation in S. japonica. The relevant results herein can lay a foundation for studying the external conditions and endogenous regulation of sorus formation for the kelp hybrids of late-maturing.

Planned seedling production in the distribution area of Saccharina japonica : Sorus formation through the induction of sporophyte maturation and the culture of the seedlings produced

Inconsistency in maturation of saccharinan kelp due to changes in the marine environment is a problem in terms of securing seedlings for aquaculture. In Hokkaido, the main producing area of Saccharina japonica, it has become a challenge to stably secure the parental algae of the species for aquaculture. When maturation was induced by short-day conditions in naturally collected S. japonica sporophytes as well as in the sporophytes collected from them and cultivated, sorus formation began in approximately 3 weeks and spread to 0.4%–16.8% on the upper side area and 23.2%–41.1% on the underside area after about 5 weeks, with the highest rates, 23.2%–59.5%, observed around the base part of the underside. Sorus formation began from the base and middle parts in the top-intact thalli and from the marginal part in the top-cut thalli. The released zoospore germlings grew steadily as aquaculture seedlings, and the blade width and wet weight of the seedlings collected in August and subjected to mariculture in November were significantly larger after approximately five and a half months compared to those of thalli cultivated using a conventional method (i.e. thalli collected just prior to the mariculture). Seedling production through maturation induction in sporophytes would be a feasible option for seedling production facilities and would be helpful for stably producing seedlings without the effect of the natural environment.

Phenology of annual kelp Eckloniopsis (Phaeophyceae, Laminariales) forest on a Diadema barren in Uchiura Bay, Central Pacific Coast of Honshu, Japan

On the southern coast of Uchiura Bay, central Pacific, Japan, Diadema barrens have expanded since the 1980s but Eckloniopsis radicosa (annual kelp endemic to Japan) has remained in deeper waters (>10 m in depth). Phenology of the kelp was studied on isolated boulders from December 2011 for a year. Young sporophytes appeared in December and rapid growth from April brought the maximum blade length (83.3 ± 13.9 cm) and width (56.8 ± 12.7 cm) and standing crop (7.4 kg m−2) in May and June, respectively. Sorus formation began in June and spore release occurred from July to September. Blade length decreased from August and disappeared in November though holdfast remained. The unique holdfast-like spiny ball was found to provide habitats for mobile animals; its forests have an important role to maintain the biodiversity on barrens. During the period, water temperature was between 14.6 and 27.8 °C, salinity was stable around 34–35 ‰, and nutrients were never depleted. Tolerance to large and frequent fluctuation of water temperature (7 °C in a day), rapid growth in winter to spring, and occurrence on limited boulders in soft substrata may be the reasons for the success in the maintenance of its forest in Diadema barrens.

Effects of ocean acidification on different life-cycle stages of the kelp Laminaria hyperborea (Phaeophyceae)

Abstract Our objective for this study was to evaluate the influence of preindustrial and expected future atmospheric CO2 concentrations (280 μatm and 700 μatm pCO2, respectively) on different life-cycle stages of the kelp Laminaria hyperborea from Helgoland (Germany, North Sea). Zoospore germination, gametogenesis, vegetative growth, sorus formation and photosynthetic performance of vegetative and fertile tissue were examined. The contribution of external carbonic anhydrase (exCA) to C-supply for net-photosynthesis (net-PS) and the Chla- and phlorotannin content were investigated. Female gametogenesis and vegetative growth of sporophytes were significantly enhanced under the expected future pCO2. rETR(max) and net-PS of young vegetative sporophytes tended to increase performance at higher pCO2. The trend towards elevated net-PS vanished after inhibition of exCA. In vegetative sporophytes, phlorotannin content and Chla content were not significantly affected by pCO2.

제주도에 서식하는 보호대상 해조류 넓미역의 생태학적 특성: 생장 및 성숙

Ecological characteristics of Undariopsis peterseniana, an endangered brown alga, were investigated from January to December 2007 at Jeju Island, Korea. The U. peterseniana population formed dense patches at depths of 12~17 m depth. Growth in length of the alga reached a maximum of at June. Sorus were observed from May to August, and a maturation peak was detected in June, when bottom seawater temperatures were around . After zoospore release, the alga bleached and disappeared after August. Developmental initiation of sporophytes occurred at temperature above , and sorus formation required approximately 236 degree-days. This is the first study to examine a U. peterseniana population throughout the entire year in a natural habitat.

Significance of radical oxygen production in sorus development and zoospore germination in Saccharina japonica (Phaeophyceae)

We investigated production of radical oxygen species (ROS) in sorus development of sporophyte discs and during zoospore germination of Saccharina japonica (Phaeophyceae) using the fluorescent dye 2′,7′-dichlorofluorescein diacetate (DCFH-DA). Quantitative analysis of ROS showed high intracellular production during the stages of zoosporangium formation when paraphyses elongated. In this stage, remarkable ROS release was observed. ROS production was also observed histologically (under a fluorescence microscope) in the elongating paraphyses and the sorus zoosporangia. The sorus had significantly higher phenol content, antioxidant capacity and ROS scavenging enzyme activities (ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase) than adjacent non-sorus blade sectors. Thus, intracellular ROS scavenging mechanisms are active during ROS production in sorus formation. In contrast, iodine content was lower in the sorus than in the adjacent non-sorus tissues, suggesting the existence of an antioxidant defense mechanism based on iodine efflux. We demonstrated that ROS production is an important phenomenon in the reproduction of the S. japonica sporophyte. Furthermore, ROS were also observed in the zoospore germination processes. We discuss the physiological and ecological roles of ROS production in sorus formation and zoospore germination.

Regulation of Sorus Formation by Auxin in Laminariales Sporophyte

Young sporophytes of Laminaria japonica Areshoug were cultured in six indole-acetic acid (IAA) concentrations (0, 10−8, 10−7, 10−6, 10−5, 10−4 M) to examine the effect of auxin on growth. The effects of auxin on sorus formation were also examined by using discs taken from the adult sporophyte. The auxin contents and IAA oxidase activities in the thallus and sorus parts of the sporophyte were determined with the blade and sporophyll of other Laminariales plants, Undaria pinnatifida (Harvey) Suringar and Alaria crassifolia Kjellman. The young sporophytes of L. japonica showed highest elongation rate in 10−5 M IAA. In contrast, the sorus formation on the discs cultured in 10−5 M IAA was markedly delayed in comparison with other concentrations, indicating that sorus formation was suppressed by IAA. Free and conjugated auxin contents were lower in the reproductive parts than in the vegetative parts. In three Laminariales sporophytes, IAA oxidase activity was about 3–9 times higher in the reproductive parts than in the vegetative parts. Taken together these results suggest that the growth and reproduction of Laminariales sporophytes are regulated by internal auxin levels. Elucidating the regulation mechanism is likely to provide information that is important for the management of plant production and the assessment of the physiological status of plants in the field.

Breaking seasonal limitation: year-round sporogenesis in the brown alga Laminaria saccharina by blocking the transport of putative sporulation inhibitors

Year-round induction of sporogenesis of Laminaria saccharina was performed by mechanically blocking the transport of the putative sporulation inhibitors produced by the blade meristem and culturing the plants in constant short days. Sporogenesis was successfully induced by removal of the blade meristem, either by cultivating distal blade fragments or by performing a transverse cut in the frond. The earliest sorus formation after artificial induction was 10 days. The age of the sporophytes used for induction was 6–11 months or 2 years in tank-grown or field-collected sporophytes, respectively. Zoospores were successfully released in all cases. Thus, by year-round artificial induction of sporogenesis, (1) sporeling production of L. saccharina and thereafter sporophyte cultivation could be achieved without seasonal limitation, and (2) the life cycle of L. saccharina (from spore to spore) could be completed within 8 months under controlled conditions.

Synchytrium endobioticum

<i>Synchytrium endobioticum</i>

Critical Contents of Nitrogen and Phosphorus for Sorus Formation in Four Laminaria Species

The critical contents of nitrogen and phosphorus for sorus formation in Laminaria angustata, L. japonica, L. ochotensis and L. religiosa were measured using cultured discs cut from the sporophytes. In L. japonica, fertile sporophytes were also used. Discs were cultured in Provasoli's enriched seawater or nutrient-poor seawater at 10 °C under 100 μmol photons m−2 s−1 of irradiance (12L:1̅2̅D̅). Regardless of the nutrient conditions in the culturemedia, the contents of nitrogen and phosphorus in the sorus part of discs and sporophytes of L. japonica were above 1.78 mgN cm−3 and 0.19 mgP cm−3 respectively, showing these values are critical for sorus formation in this species. Discs of L. angustata, L. ochotensis and L. religiosa in PES had higher contents of nitrogen and phosphorus in sorus parts than in L. japonica. The sorus area increased with accumulation of nitrogen or phosphorus in all species, but in L. angustata it was small despite the high contents of nitrogen and phosphorus, showing that this alga has a high nutritional cost in reproduction that might be a physiological adaptation to cold and nutrient-rich habitats.

Inducible effects of abscisic acid on sporophyte discs from Laminaria japonica Areschoug (Laminariales, Phaeophyceae)

The effects of exogenous abscisic acid (ABA;10−7–10−5 M), a knownplantgrowth regulator, on reproduction and growth were investigated by culturingdiscs from sporophytes of Laminaria japonica Areschoug.ABAplays a role in triggering sorus formation, and it was found that sorusformation of discs was fastest in 10−5 M ABA. Theapplication of 10−5 M ABA to culturing discs alsosuppressed the expansion of surface area. ABA contents in sorus and vegetativeparts of the sporophyte were determined by bioassay. The mean ABA content insorus parts obtained from sporophytes was 0.222 ± 0.053μg equivalent-ABA g wet weight−1, which wasabout five times higher than the content found in vegetative parts (0.048± 0.009 μg equivalent-ABA g wetweight−1). Taken together these results suggest that sorusdevelopment requires an elevated level of ABA and is associated with decreasingvegetative growth and that the ABA level of the sporophyte may play a crucialrole in reproduction.

Isolated, distal blade discs of the brown alga Laminaria digitata form sorus, but not discs, near to the meristematic transition zone

Blade discs of vegetative thalli of Laminaria digitata (Huds.) Lamour. from Helgoland (North Sea) cut at 5–15 cm distance from the blade/stipe transition, formed sorus in the laboratory after 7–12weeks, 5 months earlier than whole fronds in the field. Sorus formation occurred in a broad range of daylength regimes or temperatures, at 8–16 h light pe rday and 6–12 °C. No sorus was developed during three months by meristematic blade discs cut from the lowermost 3 cm portion of the blade, nor from whole thalli cultured in parallel to isolated blade discs. These findings point to the possible existence of sporulation inhibitors produced by the laminarian meristem.

Sorus development on median and marginal parts of the sporophyte of Laminaria japonica Areschoug (Phaeophyceae)

Sorus formation on median and marginal parts of Laminaria japoncia Areschoug was investigated by cultivating sporophytes from December 1996 to September 1997 in Southern Hokkaido, Japan. Simultaneously, discs (ca. 3 cm in diameter) that were cut off monthly from median and marginal parts of the cultivated sporophytes were incubated in our laboratory. All the cultivated sporophytes formed sori on the median parts from January to August, while all the median and marginal discs formed sori at 10 under 46 μmol photon m-2s-1 (12L:12D) in enriched medium. There was no difference in sorus area between median and marginal discs. These results indicated that the marginal parts are able to produce sori, although the greater part of them are actually washed away before forming sori in the sea. The marginal part is probably in a state of `resource limitation' on the reproduction because the resource outflowed from this part to the basal part for the growth of sporophytes.

Relationship between Nitrogen Content and Sorus Formation in the Brown Alga &lt;i&gt;Laminaria japonica&lt;/i&gt; Cultivated in Southern Hokkaido, Japan

Relationship between Nitrogen Content and Sorus Formation in the Brown Alga &lt;i&gt;Laminaria japonica&lt;/i&gt; Cultivated in Southern Hokkaido, Japan

和歌山県田辺湾における養殖ヒロメ種苗の沖出し時期と養成水深の検討

For the early harvest of Undaria undarioides (Yendo) Okamura, research was carried out to know the most suitable time and suspending depth in outplanting of seedlings, at Tanabe Bay in Wakayama Prefecture, Japan. The seedlings were outplanted in the sea on November 15 and December 5 and 15 1991, and in suspending depth of 0.5m, 1.5m and 2.5m. The blade size (blade length and width) and maturation by formation of zoosporangial sori were observed every 10 days. The seedlings which were outplanted at a depth of 0.5m on November 15 grew to the minimum commercial size (above the average blade length of more than 35cm) by the middle of January. U. undarioides could be harvested one month earlier than the usual outplant seedlings, due to early outplanting in the sea water temperature of less than 20°C. In the early outplanted seedlings, the blade grew wider and maturation was earlier than the usual outplanted seedlings.

Seasonal growth and carbon and nitrogen content in canopy and first-year plants of Laminaria hyperborea (Laminariales, Phaeophyceae)

The seasonal growth pattern of canopy plants has been compared with that of first-year plants. Large, canopy-forming sporophytes grew between January and June. The seasonal variation in total carbon content of the lamina reflected the seasonal pattern of storage carbohydrates, with high content in the summer and autumn, and decreasing content after growth started in January. Vegetative and reproductive laminae contained similar percentages of carbon in dry weight in January, indicating that the process of sorus formation did not involve high consumption of stored carbohydrates in reproductive plants. The nitrogen content of the laminae of canopy plants was high during the growth period and low during the rest of the year. The high nitrogen content during spring may reflect storage in a period of excess ambient nitrate.The first-year plants grew until the end of September, with the highest relative growth rate during July. During the summer the nitrogen dry weight content of the first-year plants was high (2–4%) compared to the canopy plants (about 1 % in the lamina). Also, the C: N ratio of the first-year plants was low from May to October (< 15), indicating that growth of the first-year plants was not nitrogen-limited during the summer. However, the low carbon content during the summer also contributed to the low C : N ratios of the first-year plants.

CIRCANNUAL GROWTH RHYTHM AND PHOTOPERIODIC SORUS INDUCTION IN THE KELP LAMINARIA SETCHELLII (PHAEOPHYTA)1

ABSTRACTGrowth and reproduction of laboratory‐grown sporophytes of Laminaria setchellii Silva were investigated in a tank system with controlled conditions of daylength, temperature, and nutrients (N and P). A circannual growth rhythm of the frond was detected under constant laboratory conditions. In continuous long‐day and night‐break conditions the period τ of the free‐running rhythm varied between 11.3 and 17.3 months; in short‐day conditions the frond grew indefinitely. The growth rhythm of individual plants could be synchronized by a simulated annual cycle of day‐length with a period of T = 12 months. The four seasons of the year were simultaneously simulated by phase shifting the annual cycle of daylength by 3, 6, or 9 months in three out of four tanks. The annual growth cycle followed these phase shifts, and initiation of the new blade always started just after the winter daylength minimum. The formation of sori was induced by a genuine photoperiodic short‐day reaction in 1‐ to 2‐year‐old plants. Sori became, visible 9–14 weeks after transfer of individual plants from long‐day to short‐day conditions, whereas plants cultured in continuous long‐day or night‐break conditions remained sterile. Sporophytes with or without blades were able to continue growth or produce new blades in continuous darkness.