Regulation of polyamine metabolism in Pyropia cinnamomea (W.A. Nelson), an important mechanism for reducing UV‐B‐induced oxidative damage

It is generally accepted that ultraviolet (UV) radiation can have adverse affects on phototrophic organisms, independent of ozone depletion. The red intertidal seaweed Pyropia cinnamomea W.A. Nelson (previously Porphyra cinnamomea Sutherland et al. 2011), similar to many other intertidal macrophytes, is exposed to high levels of UV radiation on a daily basis due to emersion in the upper littoral zone. It has been shown that seaweeds, like higher plants, respond to an increased activity of antioxidative enzymes when exposed to stress. However, earlier investigations have shown that P. cinnamomea also compensates for stress due to UV radiation by increasing polyamine (PA) levels, especially bound‐soluble and bound‐insoluble PAs. The PA precursor putrescine (PUT) can be synthesized via two enzymatic pathways: arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). Both of these enzymes showed increased activity in P. cinnamomea under UV stress. In higher plants, ADC is the enzyme responsible for increased PA levels during stress exposure, while ODC is correlated with cell division and reproduction. However, there are contrary findings in the literature. Using two irreversible inhibitors, we identified the enzyme most likely responsible for increased PUT synthesis and therefore increased stress tolerance in P. cinnamomea. Our results show that changes in the PA synthesis pathway in P. cinnamomea under UV stress are based on an increased activity of ADC. When either inhibitor was added, lipid hydroperoxide levels increased even under photosynthetically active radiation, suggesting that PAs are involved in protection mechanisms under normal light conditions as well. We also show that under optimum or low‐stress conditions, ODC activity is correlated with PUT synthesis.     

A NEW LOOK AT AN ANCIENT ORDER: GENERIC REVISION OF THE BANGIALES (RHODOPHYTA)1

The red algal order Bangiales has been revised as a result of detailed regional studies and the development of expert local knowledge of Bangiales floras, followed by collaborative global analyses based on wide taxon sampling and molecular analyses. Combined analyses of the nuclear SSU rRNA gene and the plastid RUBISCO LSU (rbcL) gene for 157 Bangiales taxa have been conducted. Fifteen genera of Bangiales, seven filamentous and eight foliose, are recognized. This classification includes five newly described and two resurrected genera. This revision constitutes a major change in understanding relationships and evolution in this order. The genus Porphyra is now restricted to five described species and a number of undescribed species. Other foliose taxa previously placed in Porphyra are now recognized to belong to the genera Boreophyllum gen. nov., Clymene gen. nov., Fuscifolium gen. nov., Lysithea gen. nov., Miuraea gen. nov., Pyropia, and Wildemania. Four of the seven filamentous genera recognized in our analyses already have generic names (Bangia, Dione, Minerva, and Pseudobangia), and are all currently monotypic. The unnamed filamentous genera are clearly composed of multiple species, and few of these species have names. Further research is required: the genus to which the marine taxon Bangia fuscopurpurea belongs is not known, and there are also a large number of species previously described as Porphyra for which nuclear SSU ribosomal RNA (nrSSU) or rbcL sequence data should be obtained so that they can be assigned to the appropriate genus.     

CHIMERAS WITH MOSAIC PATTERN IN ARCHEOSPORE GERMLINGS OF PYROPIA YEZOENSIS UEDA (BANGIALES,RHODOPHYTA)1

In the marine crop Pyropia yezoensis (Ueda) M. S. Hwang et H. G. Choi, it is known that conchospores from heterozygous conchocelis develop into sectored gametophytic blades (chimeras), but archeospores asexually released from haploid blades do not usually grow into chimeric blades. In this study, chimeras with mosaic pattern consisting of the green and wildtype colors were developed from archeospores that were released from a blade piece containing a cell cluster of green color induced by heavy‐ion beam irradiation. To make clear whether these archeospores were produced from the green‐colored cells or the wildtype‐colored cells, cell clusters of the green mutant, wildtype, and mosaic pattern were cut out from the grown chimera, and archeospores were released from each of the three blade pieces. Archeospores from the green‐mutant blade piece and from the wildtype blade piece developed into only green‐mutant blades and wildtype blades, respectively. In contrast, archeospores from the blade piece with mosaic pattern developed into green‐mutant blades, wildtype blades, and chimeric blades with mosaic pattern of the two colors, although the frequency of the chimeras was low. Because each gametophytic cell possesses a single plastid, it is difficult to explain the occurrence of the new chimeras as a mutation of the plastid DNA. Thus, the new chimeras are considered to be due to transposable elements in Pyropia.     

IDENTIFICATION AND CHARACTERIZATION OF THE CATALASE GENE PyCAT FROM THE RED ALGA PYROPIA YEZOENSIS (BANGIALES,RHODOPHYTA)1

Catalase is an antioxidant enzyme that plays a significant role in protection against oxidative stress by reducing hydrogen peroxide. The full‐length catalase cDNA sequence as isolated from expressed sequence tags (ESTs) of Pyropia yezoensis (Ueda) M. S. Hwang et H. G. Choi (PyCAT) through rapid amplification of cDNA ends (RACE) was identified and characterized. It encoded a polypeptide of 529 amino acids, which shared 36%–44% similarity with other known catalase proteins. Phylogenetic analysis revealed that PyCAT was closer to the catalases from plants than from other organisms. The PyCAT mRNA expression was investigated using real‐time PCR to determine life‐cycle‐specific expression and the expression pattern during desiccation. The mRNA expression level in gametophytes was significantly higher than in sporophytes, and the mRNA expression level of PyCAT was significantly up‐regulated during the desiccation process. The recombinant PyCAT protein was purified and analyzed biochemically. The recombinant PyCAT protein exhibited high enzymatic activity (28,000 U·mg^?1) with high thermal stability and a broad pH range. All these results indicate that the PyCAT is a typical member of the plant and algal catalase family and may play a significant role in minimizing the effect of oxidative damage in P. yezoensis during desiccation.     

SELECTION OF INTERNAL CONTROL GENE FOR EXPRESSION STUDIES IN PORPHYRA HAITANENSIS (RHODOPHYTA) AT DIFFERENT LIFE‐HISTORY STAGES1

Accurate gene quantification depends on the use of an appropriate internal control gene, which should be verified before its use for normalizing data. Housekeeping genes, which are expressed at relatively constant levels, are generally regarded as candidate internal control genes. To determine the ideal internal control for gene expression profiles for Porphyra haitanensis T. J. Chang et B. F. Zheng (Bangiales, Rhodophyta) at different life‐history stages, we used absolute quantification to assess the expression levels of six housekeeping genes (18S ribosomal RNA, 30S ribosomal protein, glyceraldehyde‐3‐phosphate dehydrogenase, elongation factor 3, alpha‐tubulin, and beta‐tubulin) at the sporophyte and gametophyte stages. Housekeeping genes were selected by comparing the differences of observed copy numbers in sporophytes and in gametophytes. TubB (beta‐tubulin) was found to be the optimal internal control gene, because it showed the smallest difference of gene expression. Compared with TubB, other housekeeping genes had greater variation of expression to different degrees.     

Isolation and characterization of microsatellite loci from a commercial cultivar of Porphyra haitanensis

Here we report 11 polymorphic microsatellite loci obtained from Porphyra haitanensis through an enriched genomic library. The analysis of 22 individuals from conchocelis phase of P. haitanensis, which possess a diploid nuclear phase, showed that allelic diversity range from three to six alleles. The polymorphism revealed by these loci will be extremely useful for genetic mapping, marker‐assistant selection, germplasm characterization and evolutionary studies in Porphyra.     

无机碳供应与光照条件对坛紫菜光合功能的影响

海藻群体密度过大常引起海水中CO_2供应和光照强度降低,为探讨这两种环境条件对坛紫菜光合作用的影响,在4种条件下培养坛紫菜,即390μL·L^-1(正常空气)+全日光、20μL·L^-1(低CO_2供应)+全日光、390μL·L^-1+低日光(光照强度为全日光的20%)、20μL·L^-1+低日光,测定藻体的碳酸酐酶活性、光合速率,以及不同温度下开放状态光系统Ⅱ最大量子产量(F_ v'/F _m').结果表明:低CO_2供应和低日光下生长的坛紫菜具有较高的碳酸酐酶活性,并且低日光能够提高海藻最大碳饱和光合放氧速率(V _max).在低日光下,生长在低CO_2海水中的坛紫菜V _max显著低于正常CO_2海水中生长的海藻V _max;在全日光下,低CO_2下生长的海藻V _max却高于正常CO_2下生长的海藻V _max.生长在低CO_2和低日光条件下的海藻在低温(10℃)和高温(30℃)下,藻体的F_ v'/F _m'变化不明显;而生长在390μL·L^-1+全日光环境中的海藻在高温环境下200 min后,藻体的F_ v'/F _m'相比40 min时的F_ v'/F _m'降低76.4%.低CO_2和低日光提高坛紫菜光合无机碳利用能力以及适应短期温度变化的能力,而低CO_2对海藻光合速率的影响与海藻所处光照环境有关.     

Speciation in the marine crop Pyropia yezoensis (Bangiales,Rhodophyta)

In the marine red alga Pyropia yezoensis, commonly known in Japan as nori, sympatric occurrence of two cryptic species Pyropia sp. 2 and Pyropia sp. 3 on the same rock in a natural habitat has been confirmed by molecular analysis and detailed morphological observations. To confirm whether Pyropia sp. 2 and Pyropia sp. 3 were reproductively isolated in the sympatric population, 170 blades that had previously been studied using a maternally inherited plastid marker were examined with a nuclear gene marker. The results suggested that Pyropia sp. 2 and Pyropia sp. 3 with identical morphological features were reproductively isolated in the sympatric population and that they were different species based on the biological species concept. Although gametophytic blades of Pyropia were usually assumed to be haploid, 18 of 170 blades possessed both of the two genotypes derived from Pyropia sp. 2 and from Pyropia sp. 3. These results inferred that allodiploid blades were generated from the interspecific hybridization between these two cryptic species. The present findings provide insights for future studies on the speciation mechanism in seaweeds, particularly for genera that contain numerous species.