Gelidium amansii is an ecologically and economically important red alga, but its commercial cultivation faces challenges due to inefficient artificial seedling production. Reliance on wild harvesting fails to meet industrial demand and exacerbates pressure on natural resources. To address this, we systematically investigated the effects of culture methods, plant growth regulators (PGRs), and light quality on adventitious bud development in G. amansii segments. Aerated culture significantly enhanced bud induction, yielding 15.29 ± 0.80 buds per segment, with a bud length of 1617.84 ± 466.99 μm and a relative growth rate of 80.89 ± 23.33 μm d−1. Application timing was critical: 0.01 mg L−1 2,4-D promoted bud initiation during days 0–30, while subsequent application of 0.01 mg L−1 IBA accelerated elongation. Both blue and white light significantly promoted bud number compared to red light. Furthermore, blue light resulted in significantly greater bud elongation than both white and red light at later stages. To address attachment challenges, we used coir or cotton ropes as substrates and a bioadhesive consisting of 2% (w/v) sodium alginate (dissolved at 60 °C for 10 min) cross-linked by spraying with 3% (w/v) CaCl₂ solution (approximately 10 mL, set for 15 min). Endpoint measurements at Day 20 showed that this bioadhesive ensured high segment adhesion and did not significantly reduce bud formation or final bud elongation under the conditions tested. Collectively, this study establishes optimized protocols for G. amansii segment culture, thereby advancing scalable seedling production for sustainable mariculture.

Germplasm of kelp (e. g. Saccharina japonica) is preserved as gametophyte clones under low light and low temperature. However, long-term storage causes a gradual decline in gametophyte vigor, specifically, the loss of reproductive capacity, threatening effective germplasm utilization. Using gametophytes preserved from 1981 to 2020, we systematically evaluated vigor changes and characterized the decline from morphological, physiological, biochemical, and epigenetic perspectives. Gametogenesis and development rates decreased significantly with storage duration. Long-preserved gametophytes exhibited elongated rod-shaped cells, thickened cell walls, and increased plastids. Soluble protein content, catalase activity (CAT), and total antioxidant capacity (T-AOC) were negatively correlated with storage duration (P < 0.01), whereas H₂O₂ and malondialdehyde (MAD) levels were positively correlated (P < 0.01), indicating intensifying oxidative stress. Global 5-mC methylation declined sharply with storage time (r = −0.952, P < 0.01), and multiple methylation-related genes showed dynamic expression during gametophyte development: the methyltransferase gene SJ02917 was upregulated on day 6 (the transition period from vegetative growth to gametogenesis), SJ00150 peaked on day 9 (the oogonia formation stage), whereas the demethylase gene SJ04314 showed the highest expression level on day 0 (the initial developmental stage). Based on these findings, we propose an integrated hypothesis: long-term storage disrupts ROS homeostasis, which is associated with global DNA hypomethylation. We speculate that this epigenetic alteration may affect the expression of cell cycle regulators, thereby modulating the transition from mitosis to cell differentiation. However, this hypothesis currently lacks direct causal evidence and requires future validation. Soluble protein, CAT, T-AOC, H₂O₂, MDA, and 5-mC% emerged as key vigor indicators. This study provides both a mechanistic framework for understanding vigor decline and a practical basis for monitoring germplasm health during long-term preservation.

INTRODUCTION:Saccharina japonica, the first domesticated marine plant in global aquaculture, has been cultivated for nearly a century, adapting to diverse marine environments in China. This domestication has led to significant genetic changes, but the genomic mechanisms driving these adaptations remain unclear. Unraveling these mechanisms is critical for genetic improvement and conservation, especially in the face of environmental challenges. OBJECTIVES:This study investigates the genomic changes and genetic variations underlying the domestication of S. japonica, focusing on its transition from wild populations in Japan to northern China and subsequent adaptation to southern China. METHODS:Using the newly assembled nuclear genome of S. japonica (WSJ-1) as a reference, we analyzed genetic variations and selective sweeps across wild, northern, and southern populations. Key genes associated with environmental adaptation were identified, and genomic forces driving these adaptations were explored. Furthermore, transcriptome analyses and chemical content were performed to characterize the expression patterns of key economic traits linked to domestication. RESULTS:Our findings firstly examined genetic introgression from cultivars into wild populations. Stronger selection pressures were observed during the transition from wild to northern populations compared to northern-to-southern adaptations. Selective sweeps revealed genes like heat shock protein 70 and long-chain acyl-CoA synthetase involved in temperature and oxygen adaptation in northern populations. In southern populations, nutrient and abscisic acid-related genes were selected. Blade morphology genes exhibited distinct transcriptional patterns and positive selection, while alginate-related genes showed differential expression without strong selection signals. Additionally, GST gene clusters, potentially influenced by retro transposition events, were positively selected, contributing to stress responses and growth in S. japonica. CONCLUSION:Our findings unveil key genetic adaptations in the domestication of S. japonica, providing novel insights for its genetic improvement and conservation. These results are also crucial for sustaining seaweed cultivation under changing environments.

Saccharina japonica is an economically important alga in China, which was originally derived from wild populations in Japan. Owing to the environmental temperatures in the Chinese cultivation sites being higher than those in its native habitat, heat tolerance is recognized as an important breeding objective for the development of superior kelp varieties. However, a precise evaluation system for high-temperature tolerance traits in kelp is lacking, along with systematic and comparisons across varieties and strains. This study evaluated 100 kelp gametophyte samples from different years and regions, using growth and photosynthetic indicators to establish a high-temperature tolerance evaluation index and identify high-temperature-tolerant gametophytes. By integrating relative growth rate and chlorophyll fluorescence parameters, the heat tolerance of kelp gametophytes spanning more than 40 years was evaluated and compared across multiple dimensions. After high-temperature stress, kelp gametophytes from the most recent 20s exhibited the highest relative growth rate, and minimal decline, likely due to the long-term exposure to warmer cultivation environments. In contrast, 1980s gametophytes exhibited the greatest reduction in photosynthetic possibly due to prolonged storage under low-temperature, low-light conditions,, making them more sensitive to heat stress. In recent years, the rapid increase in temperature and the pursuit of higher production yields may have contributed to the enhanced heat tolerance observed in kelp gametophyte growth during the 2020s. However, changes in photosynthetic capacity may require longer periods of acclimation and accumulation. Overall, from the 1980s to the 2020s, the heat tolerance of kelp gametophytes gradually increased. In summary, this study developed an evaluation model for high-temperature tolerance in kelp gametophytes To the best of our knowledge, this is the first systematic evaluation and comparison of heat tolerance among kelp varieties and strains in China over the past 40 years. This collection of superior high-temperature-tolerant germplasm materials that was obtained is of great significance for kelp germplasm innovation and the breeding of superior varieties.

Efficient and synchronous seedling production remains a bottleneck in commercial cultivation of Saccharina japonica, a key species in global seaweed aquaculture. The transition from vegetative growth to reproductive development in gametophytes directly influences reproductive output and the efficiency of seedling cultivation techniques. This study evaluated the effects of indole-3-acetic acid (IAA), N6-(Delta 2-isopentenyl) adenosine (iPR), and uniconazole (UCZ) on the growth-reproduction transition of female gametophytes aiming to improve the seedling technology based on gametophyte clone. iPR consistently enhanced developmental rates by 8.8-13.6% across all tested concentrations (0.1-1 mg/L), with higher concentrations accelerating the response. In contrast, IAA promoted development only at low concentration (0.1 mg/L) but inhibited it at high concentration (1 mg/L), while UCZ showed transient promotion at high concentrations and inhibition at low concentrations. Transcriptome analysis revealed that iPR promotes early reproductive entry by mobilizing protein turnover, energy metabolism, and DNA replication pathways. Enrichment analysis of differentially expressed genes (DEGs) synchronized with key developmental events indicated significant enrichment of oxidative stress-related pathways, highlighting the role of reactive oxygen species (ROS) in gametophyte development. Moreover, cell cycle regulators (E2F, CYCD, CDK) and endogenous hormone biosynthesis genes (ABA, IAA, CKs, JA) were dynamically regulated under iPR treatment. This study provides important insights into the regulatory role and molecular mechanisms of cytokinins in the reproductive development of S. japonica and supports the application of iPR as a practical tool to improve seedling synchronization and yield in commercial kelp aquaculture.

Saccharina japonica is among the most economically significant seaweeds globally. Seedling cultivation based on gametophyte clones is pivotal for efficient propagation and hybrid breeding of this species. Critically, inducing the transition from vegetative growth to reproductive development in gametophytes represents a fundamental challenge for this technology. While environmental regulators of this transition have been extensively studied, the role of endogenous phytohormones in this process remains largely unknown. This study quantitatively analyzed endogenous phytohormones in female gametophytes across four stages (vegetative growth, as Control; early, middle, and late stage of reproductive development, ESRD, MSRD, LSRD). A total of 35 phytohormones were identified. Among them, the types and contents of phytohormones exhibited significant differences between the Control and LSRD stages, while the ESRD and MSRD stages were relatively similar. Furthermore, the characteristic hormone profiles distinctively varied across the different stages. With respect to specific phytohormone categories, Auxins were predominant throughout all stages and increased significantly with development, while the content of multiple CKs increased markedly during the LSRD. Jasmonic acid and salicylic acid exhibited opposing trends in their concentration changes across the four stages. Furthermore, a decrease in the levels of growth-inhibitory phytohormones during the LSRD implies the transition from reproductive development to the sporophyte stage in female gametophytes. This study establishes a new theoretical foundation for enhancing the efficiency of gametophyte clone-based seedling production and elite cultivar breeding.

Pyropia haitanensis, relies heavily on conchocelis maturation for its production. However, the prolonged conchocelis development time limits the factory breeding of P. haitanensis. The development of algae is closely concerned in phycospheric microbial communities, yet little is known about the variations in these microbial communities across different conchocelis life stages. This study employed 16S rRNA, ITS gene sequencing and untargeted metabolomics to compare and analyze the phycospheric microbial communities and metabolites between filamentous conchocelis and sporangia branchlet stages. We identified 19 microorganisms with significantly different abundances and established a significant positive correlation with 10 key metabolites. These findings suggested that phycospheric microorganisms actively participated in metabolite synthesis during conchocelis maturation, influencing development, defense response, hormone levels, sulfur metabolism, protein and photosynthetic pigment synthesis. The differential microorganisms between filamentous conchocelis and sporangia branchlet stages were a vital factor in metabolite accumulation, highlighting the interconnectedness between phycospheric microorganisms and metabolites. Our research provided theoretical guidance for utilizing beneficial microorganisms to facilitate conchocelis maturation.

BACKGROUND:Chemical-induced acute lung injury is characterized by impaired epithelial regenerative capacity, leading to acute pulmonary edema. Numerous studies have investigated the therapeutic potential of endogenous stem cells with particular emphasis on alveolar type 2 epithelial (AEC2) cells owing to their involvement in lung cell renewal. Sox9, a transcription factor known for its role in maintaining stem cell properties and guiding cell differentiation, marks a subset of AEC2 cells believed to contribute to epithelial repair. However, the role of Sox9+AEC2 cells in the distal lung alveolar cells and the potential roles in chemically induced acute lung injury have never been explored. METHODS:In this study, we generated Sox9flox/flox;SftpcCre-ERT2 mice and examined the effects of Sox9+AEC2 cells on the pathophysiology of epithelial damage during chemical-induced acute lung injury. Subsequently, Sox9-CreERT2 Ai9 mice were used for lineage tracing to elucidate the repair mechanisms. RESULTS:Our findings revealed that Sox9+AEC2 cells endowed with stem cell properties induced cell proliferation during lung injury, predominantly in the damaged alveolar region. This process is accompanied by the regulation of inflammatory responses and orderly differentiation, thereby promoting epithelial regeneration. CONCLUSION:These results provide compelling in vivo genetic evidence supporting the characterization of Sox9+AEC2 cells as bona fide lung epithelial stem cells, demonstrating their multipotency and self-renewal capabilities during lung repair and regeneration. The identification of Sox9+AEC2 cells as crucial contributors to the promotion of epithelial repair underscores their potential as therapeutic targets in chemical-induced acute lung injury.

As an economically and ecologically important seaweed inhabiting the subtidal zone, the growth and development of kelp Saccharina japonica are regulated by various environmental factors including blue light. However, studies on the mechanisms underlying the regulation of blue light on kelp gametophyte are still very poor. This study compared the reproductive development rate of S. japonica gametophytes under different blue light exposure durations and found blue light can promote the transition of S. japonica gametophytes from vegetative growth (cell mitosis) to gametogenesis (gamete cell differentiation), with a 12-h blue light exposure being the most efficient. To investigate the role of cell cycle-related genes during gametogenesis of S. japonica gametophytes, Cyclin, CDK, E2F/DP and RBR were first identified in S. japonica. By analyzing cis-acting elements, conserved domains, and phylogenetic relationships of the E2F/DP family, we found that the E2F/DP family had the highest number of light-responsive cis-acting elements and was well conserved in brown algae. RNA-seq data were used to reveal the expression changes of cell cycle-related genes during the gametogenesis. RT-qPCR further corroborated the expression patterns revealed by RNA-seq data, and especially the expression of gene SjRBR fluctuated significantly during the process of blue light-induced gametogenesis. Based on the expression patterns of the aforementioned cell division-related genes at different developmental stages of the gametophyte, we hypothesize that these genes may play a crucial role in regulating the vegetative growth and gametogenesis of the gametophyte. These findings will further enhance our understanding of cell fate determination in multicellular organisms and will also contribute to improving the efficiency of kelp seedling culture techniques based on gametophyte clone.

Symbiotic bacteria are highly associated with the growth and development of seaweeds, primarily due to their ability to secrete bioactive metabolites. Reactive oxygen species (ROS) play a critical role in regulating growth and development in S. japonica, but the interactions between symbiotic bacterial communities and ROS on the vegetative and sorus areas of S. japonica remain unclear. In this study, the content of ROS (hydrogen peroxide), malondialdehyde (MDA) and NADPH in the vegetative and sorus areas of S. japonica were determined. Results revealed significantly higher concentration of ROS, MDA, and NADPH in the sorus area, indicating an elevated oxidative environment in reproductive areas. Using 16S rRNA gene amplicon sequencing, both epiphytic and endophytic bacterial communities were analyzed. Comparative analysis revealed pronounced divergence in endophytic bacterial diversity and composition between vegetative and sorus areas. Notably, the core genera norank_f_Rhizobiaceae exhibited strong positive correlations with NADPH accumulation, suggesting their potential role in both oxidative process modulation and holobiont functional stability of S. japonica. These findings suggest potential interactions between symbiotic bacteria and ROS metabolism during S. japonica sorus development, offering new perspectives for understanding and potentially improving seaweeds cultivation strategies to enhance stress resilience.

Discovery of new natural products with both anti-inflammatory effects on activated microglia and protective activity on dopaminergic neurons is a new strategy to find new drug leads against neuroinflammation in Parkinson's disease. In this work, nine new limonoids, named thaigranatumins A-I (1-9), and two new protolimonoids, named thaigranatumins J (10) and K (11), were obtained from seeds of the Thai mangrove, Xylocarpus granatum. The structures of these compounds were established by analysis of spectroscopic data, single-crystal X-ray diffraction (Cu Kα), and comparison of experimental and calculated ECD spectra. Thaigranatumin A (1), containing a C-16/C-30 δ-lactone ring-D and a tetra-substituted C8-O-C17-bridged tetrahydrofuran ring-F, is the first limonoid featuring a unique 6/6/6/6/6/5/5-fused heptacyclic framework. Thaigranatumin G (7) exhibited both inhibitory effects on the protein expression of iNOS, COX2, and IL-1β in lipopolysaccharide-stimulated mouse microglia BV2 cells and neuroprotective activity against rotenone-induced injury in mouse midbrain dopaminergic neuron MN9D cells in a dose-dependent manner. Preliminary bioassays indicated that thaigranatumin G might be a valuable lead against neuroinflammation, thus warranting further studies.

The gametophyte clonal lines of Saccharina japonica have extremely important application values in aspects such as seedling cultivation and genetic resource conservation. Under unfavorable conditions, S. japonica gametophytes cease reproductive development and instead form multicellular clones through mitosis. However, under suitable conditions, these gametophytes can transition from vegetative growth to reproductive development. While extensive research has elucidated the environmental conditions that induce this transition, studies investigating the intrinsic regulatory mechanisms underlying this process remain exceedingly rare. Our findings indicate that treatment with H2O2 accelerated the transition from vegetative growth to reproductive development in gametophytes. During this critical phase, genes related to reactive oxygen species (ROS) scavenging enzymes, cell signaling, cell division and cell wall polysaccharide metabolism exhibited differential expression patterns. Notably, the differential expression of ROS scavenging enzymes led to H2O2 accumulation, which in turn induced changes in the expression of cell signaling-related genes. This process inhibited the MitogenActivated Protein Kinase (MAPK) signaling pathway, suppressing cell division. Concurrently, ROS differentially regulated genes associated with cell wall polysaccharide metabolism, inhibiting cell wall synthesis while enhancing its elasticity. This study will further deepen our understanding of the intrinsic regulatory mechanisms underlying kelp gametophyte reproductive development, and will contribute to the efficiency enhancement of the cultivation methods for kelp seedlings based on delayed gametophyte clone.

Saccharina japonica has been cultivated in China for almost a century. From Dalian to Fujian, the lowest and the highest seawater temperatures in the period of cultivation increased by 14℃ and 8℃, respectively. Its adaptation to elevated seawater temperature is an example of securing the natural habitats of a species. To decipher the mechanisms underlining S. japonica adaptation to relative high seawater temperature, we assembled 516.3 Mb female gametophyte genome and 540.3 Mb of the male, respectively. The gametophytes isolated from southern China kelp cultivars acclimated to the relative high seawater temperature by transforming amino acids, glycosylating protein, maintaining osmotic pressure, intensifying the innate immune system, and exhausting energy and reduction power through the PEP-pyruvate-oxaloacetate node and the iodine cycle. They adapted to the relative high seawater temperature by transforming amino acids, changing sugar metabolism and intensifying innate immune system. The sex of S. japonica was determined by HMG-sex, and around this male gametophyte determiner the stress tolerant genes become linked to or associated with.

Breeding has played an important role in the mariculture and industrialization of kelp in China. However, the current kelp breeding systems in China have encountered some problems relating to germplasm diversity, management, technological innovations, and regional co‐operation. This review summarizes the main challenges, such as top‐down and fragmented management of germplasm libraries, as well as private industry breeding without government regulations, inter‐cultivar accidental admixing and genetic erosion, loss of heterozygosity due to repeated selection and self‐crossing. We outline multiple potential approaches to breed cultivars with improved qualitative/quantitative traits which can be subjected to changing environments, for example: (i) establishing a national germplasm repository to enhance integrative collection and preservation of kelp resources; (ii) planning and implementing kelp breeding programmes according to strategic priorities and goal‐orientations; (iii) optimizing a hybridization‐based breeding pipeline to produce robust cultivars through the introgression of novel alleles and thus the expression of hybrid vigour; (iv) enriching the high‐quality annotated reference genomes and functional analysis of trait‐associated markers/loci to develop DNA‐based breeding technologies; (v) developing new priming‐based (e.g., thermal and disease resistance) bio‐engineering breeding strategies to meet future unpredictable climate change; and (vi) breeding towards an ecological kelp‐microbiome interaction‐based technique to produce cultivars with enhanced performance and adaptability to environmental scenarios. Collectively, the lessons learned from kelp breeding in China and the solutions proposed here may not only potentially improve or re‐invigorate the Chinese kelp industry, but will also assist other developing countries in taking corrective actions to develop a sustainable future kelp farming industry.

Ten new limonoids, named xylomolones E-N (1-10), and two new protolimonoids, named xylomolones O (11) and P (12), were isolated from seeds of the Thai mangrove Xylocarpus moluccensis, together with the known compound, hispidone acetonide (13). The structures of these compounds were established by extensive NMR spectroscopic data, single-crystal X-ray diffraction analysis, and comparison of experimental ECD spectra. The absolute configurations of xylomolones E (1) and L (8) were unambiguously determined by single-crystal X-ray diffraction analyses, conducted with Cu Kα radiation. Xylomolones E-L (1-8) are mexicanolide-type limonoids, among which xylomolones J (6) and K (7) contain a C7/C28δ-lactone ring, whereas xylomolones M (9) and N (10) are phragmalin-type limonoids. Xylomolones O (11) and P (12) are two new protolimonoids. In addition, the 1H and 13C NMR spectroscopic data for hispidone acetonide (13) was first assigned completely. In bioassay, xylomolones F (2), M (9), and P (12) exhibited moderate inhibitory activity against the production of NO in LPS-induced RAW 264.7 cells with IC50 values of 31.54 ± 7.27, 62.84 ± 17.62, and 22.7 ± 6.56 μM, respectively.

As an economically and ecologically important seaweed, the genetic improvement of kelp Saccharina japonica has emerged as a significant research focus in the field of algal aquaculture. Crossbreeding, an essential method for kelp breeding, has yielded numerous elite varieties that have found practical applications. However, the mechanism underlying heterosis in kelp remains unclear, and the selection of parents for hybridization still lacks precision. In this study, we employed multiple kelp cultivars from both southern and northern kelp farms in China as parental cultivars for hybridization, and compared the gametophyte development and sexual reproduction during the hybridization process, as well as the growth rate and heat tolerance of the resulting hybrid progeny. Our findings revealed that the gametophyte development rate of all crosses is prone to exceed that of the parental selfing group, implying that the outbreeding is more successful than selfing in kelp wild population. Certain crossing combinations exhibited significant heterosis in terms of growth rate and high temperature tolerance in the hybrid progeny, while the hybrid weakness was also observed in other crosses. Through an analysis of the physiological (Fv/Fm) and biochemical (Total Antioxidant Capacity, H2O2, and malondialdehyde) responses of the hybrids to high-temperature treatment, we discovered that the initial antioxidant level and the subsequent increase in antioxidant capacity within 24 h are crucial for the ability to tolerate high temperature stress. This study systematically evaluated the heterosis of multiple hybrids and attempted to elucidate the mechanism of heat-tolerant heterosis in S. japonica from physiological and biochemical perspectives. The novel insights gained from this study could provide valuable ideas and a foundation for future researches of kelp crossbreeding efforts.

Macrocystis pyrifera is a large perennial brown alga used as a raw material in the chemical, energy, and medicine industries. It is also a high-quality material for the construction of seaweed beds with extremely high economic and ecological value. In the 1980s, M. pyrifera was introduced to China, and many experiments on its seedling and cultivation technologies were undertaken. However, research on its ecological adaptability is relatively challenging, and the aquaculture industry has not yet developed due to bottleneck problems. In the present study, the MaxEnt model was used to predict the suitability and potential invasion risk of M. pyrifera in China to lay a foundation for M. pyrifera culture industry development and marine ecological construction. Parameter optimization showed that the predictive performance of the model was the best when the feature combination was product, quadratic, and hinge features and the regularization multiplier was 0.8. Considering the correlation between environmental attributes and their contribution to the model, six environmental factors were selected to construct a prediction model for the suitability of M. pyrifera. Among these, light intensity and temperature produced the greatest impact on the natural distribution of M. pyrifera. For high suitable growth probability, the optimal light intensity was > 2 μmol/(m2·s) and the optimum temperature range was 10.5~17℃. Combined with ArcGIS, the modeling results showed that the suitable habitats for M. pyrifera in China are mainly distributed in the Yellow Sea and Bohai Sea, accounting for approximately 13.17% of the sea area, with a marginal suitability of 5.46%, low suitability of 2.85%, moderate suitability of 1.20%, and high suitability of 3.66%. Furthermore, Liaodong Bay and Bohai Bay are suitable sea areas for the introduction and cultivation of M. pyrifera as well as the construction of M. pyrifera farms. Some areas in Liaodong Bay are highly suitable, indicating a certain risk of invasion. Therefore, ecological safety evaluations should be strengthened if M. pyrifera cultivation is promoted near this area.

Saccharina japonica gametophytes can survive a long period under unfavorable environmental conditions, while they also delay in growth and/or reproduction. Although the reproduction in delayed gametophyte of S. japonica was known to be strongly influenced by light intensity, light quality, and photoperiod, no previous studies have evaluated their interactive effects on gametogenesis. To evaluate these effects, we used an orthogonal experiment to expose delayed gametophytes of S. japonica to different light intensities, light qualities, and photoperiods for 12 days. The results showed that changes in light intensity rather than light quality and photoperiod significantly affected the relative growth rates of the delayed gametophytes. Blue light had the greatest promotion on reproduction rate. The optimal light conditions in the early vegetative growth phase in gametogenesis induction for the delayed gametophytes were at 60–80 µmol photons m −2 s −1 with daylength of 12 or 16 hours under white or blue light. When the delayed gametophytes were maintained in a constant light condition from delayed state to gametogenesis, the beneficial photoperiods for vegetative growth and reproductive rate were both 16L (16 hours of light): 8D (8 hours of dark). However, when the delayed S. japonica gametophytes achieve the optimal growth state during the first 6 days and then they were cultured at different light conditions for the following 6 days, the reproduction rate increased as the daylength decreased and attained a peak value in group of 8L:16D photoperiod, indicating that photoperiod adjustment at the transition period is crucial in the gametogenesis induction process of delayed gametophyte of S. japonica .

为优化诱导海带(Saccharina japonica)孢子囊形成的培养条件,本研究以晚熟的海带杂交品种为材料,比较了不同温度、光照强度、营养盐浓度、脱落酸浓度、孢子体横切、海带培养方式等培养条件对海带孢子囊形成的影响,确定了影响海带孢子囊形成的主要环境因素,筛选了室内促进海带孢子囊形成的最适培养条件.研究表明:在光照强度20～100μmol·m-2·s-1充气培养时,孢子体两面均能形成孢子囊,在光照强度60～100μmol·m-2·s-1时孢子囊成熟较快;室内培养的受光面与海上养殖的受光面是否一致对最终形成的孢子囊面积无显著影响,但背光一侧的孢子囊面积显著高于向光一侧(P<0·05).横切能够促进孢子囊的形成,但最终的孢子囊面积无显著差异(P>0·05).在孢子囊发育过程中需要充足的营养盐,其中N 5 mg/L+P 0·5 mg/L能较快地促进孢子囊发育,添加1×10-6～1×10-5 mol/L的外源脱落酸也能促进孢子囊形成.温度是影响海带孢子囊成熟的最主要环境因素,培养温度为17℃时孢子囊形成最快.Fe3+通过增加氮磷营养盐的吸收促进孢子囊的发育增殖,在培养液中添加外源Fe3+能够明显延缓孢子囊的形成,但对最终形成的孢子囊面积无显著影响.综上所述,室内诱导海带孢子囊形成的最适培养条件为:温度17℃、光照周期8:16(L:D)、光照强度60～100μmol·m-2·s-1、营养盐浓度N 5 mg/L+P 0·5 mg/L、脱落酸浓度1×10-6～1×10-5 mol/L、不额外添加Fe3+.本研究结果可用于适时诱导晚熟杂交海带形成孢子囊和晚熟杂交海带的夏苗培育生产.

Sargassum thunbergii is distributed on reefs and rock marshes in mid- and low-tide zones, and some are periodically exposed to lengthy low tides. Dehydration is a key factor affecting the survival of S. thunbergii at low tides. In this study, using wild S. thunbergii as experimental material, the water loss rate, chlorophyll fluorescence parameters, and biochemical parameters under different stresses were determined by dehydrating the thalli in an incubator for 0, 1, 3, and 6 h. The results showed that: (1) algae of different sizes have significantly different water loss rates under different stresses. The shorter the stress time and the larger the algae, the lower the water loss rate, indicating that the water retention capacity of S. thunbergii with larger thalli is higher. Wild S. thunbergii grow in clusters on reefs. The leaves in the lower part of the branches and near the holdfast are wide. The middle and upper leaves are narrow and long, respectively. The lower broad leaves are easily blocked by the upper branches. Therefore, differences in the growth environment cause differences in the ecological structure and biochemical components of S. thunbergii. High temperature, strong light, and water loss at low tide are the main factors that cause severe environmental stress to sessile S. thunbergii in the intertidal zone. (2) Dehydration significantly reduced the chlorophyll fluorescence value of S. thunbergii, and different parts of the same individual of S. thunbergii had significantly different tolerance to dehydration, with the lowest tolerance at branch tips and the strongest tolerance at the base. The non-regulatory energy-dissipation mechanism plays a major role in the dehydration response of S. thunbergii. Under dry exposure, the light energy utilization efficiency of S. thunbergii was significantly reduced. This reduction in active light protection capacity indicates that dehydration reduces the adaptability of S. thunbergii to excessive light intensity. Dehydration can damage the tips of small individuals that cannot recover, while the base part of large individuals could return to a normal physiological state. (3) Antioxidant enzymes (ASAFR, SOD) and non-antioxidant substances (soluble sugar and proline) in the tip part responded to dehydration, and the base part mainly responded by upregulation of protein, soluble sugar, and proline content to resist stress. S. thunbergii, located in the high and middle tide zones, is more likely to be stressed by high temperatures, strong light, and dehydration, and the physiological and biochemical characteristics of different parts of the thallus are also variable due to differences in external morphology. Algae mainly reduce damage to the photosynthetic system caused by a lack of water through a non-regulatory energy dissipation mechanism. The water retention capacity of the base was better than branch tips during dry exposure, and the damage to algal cells was low. The main roles are as heat shock proteins, soluble sugars, proline, and other small molecules, which can pass stress response, osmotic regulation, and anti-oxidation resists damage to cells caused by stress. The water retention capacity of the top cells was weak, and the stress was relatively strong. Antioxidant enzymes such as ASAFR and SOD in algae and non-antioxidant enzymes such as soluble sugars and proline, work together to resist dry exposure stress, reduce cell damage and maintain cell viability. In summary, under the stress of dry exposure, the antioxidant enzymes, antioxidant substances, and non-regulatory energy dissipation mechanisms of S. thunbergii play a role in maintaining cell activity. This study provides important guidance for exploring the ecological adaptability of S. thunbergii in resisting environmental stress.