中国新记录属——绿叠球藻属及其系统位置

在对上海市树附生藻类的调查中,发现了1个中国新记录属——绿叠球藻属(Chlorokybus)。对该属1个新记录种绿叠球藻(Chlorokybus atmophyticus)的主要形态学特征进行了详细描述,对其系统位置讨论结果认为,绿叠球藻是一个比较特殊的藻类,在陆生植物演化上具有特殊的地位,支持将其作为一个独立的目——绿叠球藻目(Chlorokybales)处理。     

A clade uniting the green algae Mesostigma viride and Chlorokybus atmophyticus represents the deepest branch of the Streptophyta in chloroplast genome-based phylogenies

Background  

The Viridiplantae comprise two major phyla: the Streptophyta, containing the charophycean green algae and all land plants, and the Chlorophyta, containing the remaining green algae. Despite recent progress in unravelling phylogenetic relationships among major green plant lineages, problematic nodes still remain in the green tree of life. One of the major issues concerns the scaly biflagellate Mesostigma viride, which is either regarded as representing the earliest divergence of the Streptophyta or a separate lineage that diverged before the Chlorophyta and Streptophyta. Phylogenies based on chloroplast and mitochondrial genomes support the latter view. Because some green plant lineages are not represented in these phylogenies, sparse taxon sampling has been suspected to yield misleading topologies. Here, we describe the complete chloroplast DNA (cpDNA) sequence of the early-diverging charophycean alga Chlorokybus atmophyticus and present chloroplast genome-based phylogenies with an expanded taxon sampling.     

Accumulation of glycinebetaine during cold acclimation and freezing tolerance in leaves of winter and spring barley plants

A study was performed to examine whether or not betaine (glycinebetaine), a compatible solute, is accumulated in response to cold stress and is involved in mechanisms that protect plants from freezing injury. For this purpose, we used near-isogenic lines of barley, with each line differing only in a single gene for the spring type of growth habit; the various lines were produced by back-crosses to a recurrent cultivar of the winter type. The winter type of growth habit requires a low temperature for triggering of flower development (vernalization), whereas the spring type does not. Betaine was accumulated to five times the basal level over the course of 3 weeks at low temperature (5 °C) in the winter-type cultivar and in a spring-sh line having the sh gene for the spring-type growth habit, but the level was only doubled in the spring-Sh3 line, which carried the Sh₃ gene for the spring-type growth habit. Among near-isogenic lines of the same cultivar, the levels of betaine accumulated in leaves at low temperature were well correlated with the percentages (on a dry weight basis) of green leaves that survived freezing injury (-5 °C). This observation indicates the possibility, separate from the recognized role of betaine in the response to salinity and/or drought, that betaine accumulates in response to cold stress and that the accumulation of betaine during cold acclimation is associated to some extent with freezing tolerance in leaves of barley plants.     

Phylogenetic analysis of Dunaliella (Chlorophyta) emphasizing new benthic and supralittoral isolates from Great Salt Lake

Dunaliella, a commercially important chlorophyte, is globally distributed in saline habitats. Morphological species have not been definitively reconciled with phylogenetic analyses. Considerable genetic diversity continues to be discovered in new isolates, especially from soil and benthic habitats. Twenty‐nine new isolates from Great Salt Lake, Utah, many from benthic or supralittoral habitats, were phylogenetically analyzed using ITS1+5.8S+ITS2 in comparison to a broad sampling of available sequences. A few new isolates align in one branch of a bifurcated monophyletic Dunaliella salina clade and several cluster within monophyletic D. viridis. Several others align with relatively few unnamed strains from other locations, comprising a diverse clade that may represent two or more new species. The overall Dunaliella clade is relatively robust, but the nearest outgroups are ambiguously placed with extremely long branches. About half of the isolates, all from benthic or supralittoral habitats, have been persistently sarcinoid in liquid media since isolation. This trait is spread across the Dunaliella phylogeny. The morphology of two sarcinoid strains was documented with light microscopy, revealing an extensive glycocalyx. Clumping behavior of unicellular and sarcinoid strains was unaffected by presence or absence of Mg²⁺ or Ca²⁺, addition of lectin‐inhibiting monosaccharides, or water‐soluble factors from morphologically opposite strains. Results from this investigation have significantly expanded our current understanding of Dunaliella diversity, but it seems likely that much remains to be discovered with additional sampling.     

Effects of growth temperature and chilling duration on leaf phenology of <Emphasis Type="Italic">Fauria crista</Emphasis>-<Emphasis Type="Italic">galli</Emphasis> subsp. <Emphasis Type="Italic">japonica</Emphasis>, an alpine snowbed geophyte

I examined the effects of growth temperature and winter duration on the leaf phenology of Fauria crista-galli plants, which have an indeterminate growth habit. After a 220-day chilling treatment, the leaf expansion and green periods of plants maintained at 25/20°C were much longer than those of plants maintained at 15/10°C and of plants at the natural habitat obtained in a previous study. The results indicate that early growth cessation and early leaf senescence in the natural habitat are not only due to endogenous rhythm but determined to some extent by cool summer temperatures. When grown at 15/10°C, the green period of individual leaves and plants was much shorter after a long chilling treatment (220 days) than after a short chilling treatment (110 days). The plants sprouted during or immediately after the termination of chilling treatment, suggesting that the decrease in the green period results partly from an advance of endogenous developmental stages during the chilling treatment and that the timing of snowmelt potentially affects the time of leaf senescence in the natural habitat.     

Low-temperature tolerance and genetic potential in wheat (Triticum aestivum L.): response to photoperiod, vernalization, and plant development

It is frequently observed that winter habit types are more low-temperature (LT) tolerant than spring habit types. This raises the question of whether this is due to pleiotropic effects of the vernalization loci or to the linkage of LT-tolerance genes to these vernalization loci. Reciprocal near-isogenic lines (NILs) for alleles at the Vrn-A1 locus, Vrn-A1 and vrn-A1, determining spring and winter habit respectively, in two diverse genetic backgrounds of wheat (Triticum aestivum L.) were used to separate the effects of vernalization, photoperiod, and development on identical, or near identical, genetic backgrounds. The vrn-A1 allele in the winter lines allowed full expression of genotype dependent LT tolerance potential. The winter allele (vrn-A1) in a very cold tolerant genetic background resulted in 11°C, or a 2.4-fold, greater LT tolerance compared to the spring allele. Similarly, the delay in development caused by short-day (SD) versus long-day (LD) photoperiod in the identical spring habit NIL resulted in an 8.5°C or 2.1-fold, increase in LT tolerance. The duration of time in early developmental stages was shown to underlie full expression of genetic LT-tolerance potential. Therefore, pleiotropic effects of the vernalization loci can explain the association of LT tolerance and winter habit irrespective of either the proposed closely linked Fr-A1 or the more distant Fr-A2 LT-tolerance QTLs. Plant development progressively reduced LT-acclimation ability, particularly after the main shoot meristem had advanced to the double ridge reproductive growth stage. The Vrn-1 genes, or other members of the flowering induction pathway, are discussed as possible candidates for involvement in LT-tolerance repression.     

Phylogenetic relationships of four charophycean green algae inferred from complete nuclear-encoded small subunit RRNA gene sequences

Complete nuclear-encoded (18S) small subunit rRNA gene sequences were determined for four charophycean green algae, Chlorokybus atmophyticus, Coleochaete orbicularis, Klebsormidium flaccidum, and Nitella sp. Chlorokybus atmophyticus and Coleochaete orbicularis have been previously suggested to represent the most basal and most derived taxa within the charophytes, respectively. However, parsimony analysis of our 18S rDNA sequences along with a selection of other complete green algal and land plant 18S rDNA sequences yields a gene tree topology in which Chlorokybus is the most basal taxon, followed by the branching of Coleochaete and Klebsormidium. Two “sister” clades then diverge, one including Nitella and the land plants, and the second, members of the Chlorophyceae and Pleurastrophyceae. Despite producing slightly diiferent gene tree topologies than those inferred from parsimony, distance analyses of the 18S rDNA sequences also do not indicate a strong affinity between the land plants and Coleochaete. Rather, Klebsormidium and Coleochaete are virtually equidistant from the land plant taxa. Other data are needed in order to assess the unexpected findings reported here, particularly the position of Coleochaete.     

MOLECULAR AND MORPHOLOGICAL DATA IDENTIFY A CRYPTIC SPECIES COMPLEX IN ENDOPHYTIC MEMBERS OF THE GENUS COLEOCHAETE BRÉB. (CHAROPHYTA: COLEOCHAETACEAE)1

The genus Coleochaete Bréb. is a relatively small group of freshwater microscopic green algae with about 15 recognized species. Although Coleochaete has long been considered to be a close relative of embryophytes, a comprehensive study of the genus has not been published since Pringsheim's 1860 monograph. As part of a systematic study of Coleochaete, we investigated four accessions of the genus that are morphologically similar to the endophytic species C. nitellarum Jost. Each of the four cultures was determined to be capable of endophytic growth in Nitella C. A. Agardh, a member of the closely related order Charales. Maximum likelihood and maximum parsimony analyses were performed on nucleotide data from the chloroplast genes atpB and rbcL that were sequenced from 16 members of the Coleochaetales and from other members of the Charophyceae, embryophytes, and outgroup taxa. These analyses indicate that the Coleochaetales are monophyletic and that the endophytic accessions are members of the scutata group of species. In addition, cell size and nucleotide data suggest that at least three different endophytic species may be represented. Herbivory, nutritional benefits, and substrate competition are three hypotheses that could explain the evolution and maintenance of the endophytic habit in Coleochaete. These data also imply that diversity in the genus may be markedly underestimated.     

Development of a new diagnostic marker for growth habit selection in faba bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.) breeding

Faba bean varieties with determinacy of the apical meristem are relevant to green production. A diagnostic CAPS (cleavage amplification polymorphic sequence) marker for determinate growth habit (ti) in faba bean was previously developed by Avila et al. (Mol Breed 17:185–190, 2006) but was effective only on a limited range of cultivars or genotypes. In this study, we studied the reasons for this limited application and developed a new marker useful for most faba bean-breeding programs. By designing a new set of primers, the complete genomic Vf_TFL1 sequences from different genotypes contrasting for the character were obtained and additional base changes associated with the ti phenotype were identified. The comparison among faba bean sequences showed that the previous CAPS marker was based on a SNP (single nucleotide polymorphism) at position 469 in the intron 2–3, a silent mutation. On the contrary, a SNP at position 26 that distinguishes determinate and indeterminate growth habit genotypes lead to an amino acid change (Leu-9 to Arg) in the determinate growth habit genotypes that could account for the ti phenotype. A dCAPS marker based on this SNP that creates a TaqI site in the ti allele was developed. The marker was 100% successful in predicting ti phenotypes in a broad range of faba bean germplasm representing all major cultivars historically grown in Europe. The outcome confirms the utility of the new dCAPS in worldwide marker-assisted selection programs.     

MiniMax,a new diminutive <Emphasis Type="Italic">Glycine max</Emphasis> genotype with a rapid life cycle,embryogenic potential and transformation capabilities

We developed Glycine max cv MiniMax (PI643148) that has a rapid life cycle, short stature and characteristic simple sequence repeat (SSR) markers that could make it useful for mutant screening, functional genomics, genetic mapping and other studies involving soybeans. We demonstrate that MiniMax is able to make somatic embryos (SEs) that rapidly develop into plantlets. Thus, the rapid cycling habit carries over into aspects of plant regeneration. Chimaeras (having transformed roots with untransformed aerial stocks) have been produced rapidly under non-axenic conditions using Agrobacterium rhizogenes-mediated transformation. Part of these experiments involved the engineering an enhanced green fluorescent protein (eGFP) reporter cassette outside the multi-cloning site of a plant expression vector, permitting non-invasive visual screening of the transformed roots. The rapid cycling growth habit of MiniMax, its ability to efficiently generate SEs and ability to be transformed should prove useful for basic aspects of G. max molecular and genetic research.     

Genetic Characterization of a New Growth Habit Mutant in Tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>)

A mutant tomato cultivar (HT10-3-2) with indeterminate growth habit was obtained from a cultivar (T10-3-2) with determinate growth habit. The character of indeterminate growth habit in HT10-3-2 could be inherited stably. Unlike other normal growth habit cultivars, which are controlled by the SELF PRUNING gene, it was shown here that HT10-3-2 has no mutation in the sp gene. Two hundred random amplified polymorphic DNA (RAPD) primers were used to screen for polymorphism between the two genotypes from genomic DNA, and a polymorphic fragment (S168₁₄₅₈) was obtained and subsequently sequenced. However, Basic Local Alignment Search Tool searches indicated that the sequence of this RAPD fragment shares no significant homology with known sequences in GenBank. The RAPD marker (S168₁₄₅₈) was converted to a sequence characterized amplified region (SCAR) marker, SCA168₁₄₅₃. The SCAR marker was tested using an F₂ population derived from the cross of T10-3-2 and HT10-3-2 and the results showed that this marker was closely linked with the unknown factor influencing the growth habit in HT10-3-2.     

Comparative effects of the quality and quantity of light and temperature on the growth of Planktothrix agardhii and P. rubescens1

The effects of temperature, light intensity, and quality on the growth of the cyanobacteria Planktothrix agardhii (Gomont) Anag. et Komárek and P. rubescens (Gomont) Anag. et Komárek were assessed in batch cultures. The relative competitiveness of the green‐pigmented P. agardhii and the red‐pigmented P. rubescens was evaluated in separate and mixed cultures, under different light intensities and qualities (green, red, and white), and at two different temperatures, chosen as representative of the natural conditions favoring the respective blooms of each species. In monocultures, the P. rubescens strain appeared to be particularly well adapted to low intensities of green light and displayed a strong photoinhibition under high irradiance levels. The P. agardhii strain appeared less specialized with regard to light quality and also less sensitive to photoinhibition at higher irradiances. In competition experiments, temperature (15°C vs. 25°C) was the most important parameter in determining relative fitness of the species and competitive success. At 15°C, P. rubescens appeared to be much more competitive than P. agardhii, while P. agardhii was more competitive at 25°C. Under low irradiance, however, the pigmentation of these strains was of primary importance in determining the outcomes of the competition experiments. On the basis of our experimental results and on field observations, we propose that the successful growth leading to the proliferation of these two differently pigmented strains may largely depend on the combined conditions of light and temperature. The two strains, being genetically close relatives, could therefore be considered as two ecotypes that are adapted to different light and temperature environments. Competition experiments showed that the combination of these parameters largely controls the success of one strain in comparison to the other.     

ALGAL BIOMASS AND PRIMARY PRODUCTION WITHIN A TEMPERATE ZONE SANDSTONE

The use of dimethyl sulfoxide (DMSO) to extract chlorophyll a and ^l4C-labelled photosynthate from endolithic algae of sparsely vegetated, cold temperate grasslands on the Colorado Plateau in Arizona has yielded the first estimates of biomass and photosynthesis for this unusual community. These subsurface microorganisms are found widespread in exposed Coconino Sandstone, a predominant formation in this cold temperate region. The endolithic community in Coconino Sandstone, composed primarily of coccoid blue-green and coccoid/sarcinoid green algae, yielded a biomass value (as chlorophyll a content) of 87 mg m^-2 rock surface area and a photosynthetic rate of 0.37 mg CO₂ dm ² hr^-1 or 0.48 mg CO₂ mg^-1 chl a hr^-1. The endolithic algal community contributes moderate biomass (5–10%) and substantial photosynthesis (20–80%) to the sparse grassland ecosystem.     

TAXONOMIC AND GEOGRAPHIC DISTRIBUTION OF INTERNAL GEITONOGAMY IN NEW WORLD CALLITRICHE (CALLITRICHACEAE)

Internal geitonogamy (IG) is a unique self-fertilization system that occurs in the genus Callitriche. In IG self-fertilization is effected by pollen tube growth through vegetative tissues from the staminate to pistillate flowers. IG occurs in seven of the 22 species of Callitriche in the New World (C. heterophylla, C. heteropoda, C. lechleri, C. nubigena, C. rimosa, C. trochlearis, C. verna). Callitriche verna occurs in both the New and Old Worlds and represents the only known instance of IG in the latter region. IG is correlated with the amphibious growth habit and polyploidy, although not all polyploid amphibious species of Callitriche have IG. Correlations between IG and geographic distribution are not apparent. There is a tendency for species that possess IG to occur at higher elevations than those that lack this system.     

DEVELOPMENTAL STUDIES IN SMILAX (LILIACEAE). I. ORGANOGRAPHY AND THE SHOOT APEX

The ontogeny of the shoot and the tendril-bearing leaf was studied in four species of Smilax which differ considerably in growth habit. Growth is indeterminate in S. bona-nox, S. rotundifolia, S. laurifolia and determinate in S. pumila. Shoot apical organization in all four species is consistent with the tunica-corpus concept. The number of tunica layers varies from 2 in S. bona-nox, S. pumila, and S. rotundifolia to 3 (2–4) in S. laurifolia. A primary thickening meristem was observed in 5. laurifolia. Shoot tip abortion involving a cessation of vegetative growth resembling that found in many woody plants occurs in S. pumila. Even though there are distinct differences in growth habit, vigor, and anatomy, the four species share many developmental similarities. Hence, subtle changes in apical ontogeny may be associated with marked differences in habit.     

18S RIBOSOMAL DNA SEQUENCES INDICATE A MONOPHYLETIC ORIGIN OF CHAROPHYCEAE1

Nuclear-encoded small-subunit (18S) ribosomal RNA genes of Chara australis R. Brown (C. corallina var. nobilis f. nobilis R.D.W.) and Nitella flexilis (L.) Ag. were amplified by polymerase chain reaction, cloned, and completely sequenced. Using structural criteria, the sequences were aligned with 18S ribosomal DNAs (rDNAs) from 11 other chlorophyll b-containing algae and six higher plants (embryophytes). Phylogenetic trees were inferred by distance, neighbor-joining, parsimony, and maximum-likelihood approaches; confidence intervals were estimated by bootstrapping, and nonrandomness of tree structure was confirmed by permutation tests. 18S rDNAs of C. australis and two Nitella species were found to be specifically related and, together with 18S rDNAs of Chlorokybus atmophyticus Geitler, Klebsormidium flaccidum (A. Br.) Silva, Mattox, et Blackwell, and two Coleochaete species, support a robust monophyletic group (Charophyceae). Although most trees favored a specific sister-group relationship between Charophyceae and embryophytes, statistical tests revealed that a sister-group relationship between Charophyceae and Chlorophyceae could not be ruled out. Additional complete sequences from 18S rDNAs of lower land plants may be required to resolve phylogenetic relationships among these organisms.     

Primary hemiepiphytism and gametophyte morphology in <Emphasis Type="Italic">Elaphoglossum amygdalifolium</Emphasis> (Dryopteridaceae)

Elaphoglossum amygdalifolium holds a critical phylogenetic position as sister to the remaining ca. 600 extant species of Elaphoglossum and may provide important insight into the evolution of epiphytism in this clade of ferns. Here, we present the first examination of growth habit and gametophyte morphology for this species. We show that the cordate to elongate-cordate gametophytes occur up to 0.5 m above the ground on the base of tree trunks. Unlike the gametophytes of all other studied species of Elaphoglossum, rhizoids are absent along the thallus margin and the hairs present on the margin lack whitish waxy caps; both differences are pleisiomorphic for the genus. Sporelings of E. amygdalifolium produce a single long root that grows straight into the soil where it branches profusely. Mature sporophytes have long-creeping rhizomes that climb to heights of at least 3 m and produce two types of roots: “feeding roots” that reach the ground and “clasping roots” that anchor the sporophyte to its host plant. Our observations reveal that E. amygdalifolium is a primary hemiepiphyte, the first example of this growth habit to be documented in Elaphoglossum. Results of an ancestral state reconstruction of growth habit in bolbitidoid ferns show that both primary hemiepiphytism and holoepiphytism are equally likely to be the ancestral character state for Elaphoglossum.     

Microcladia exserta sp. nov. (Ceramiaceae,Rhodophyta) from the East coast of South Africa

Microcladia exserta, a new species of the red algal genus Microcladia Greville (Ceramiaceae, Ceramiales), is described from the Natal coast of South Africa. This small, creeping alga, an epiphyte on the coralline alga Amphiroa anceps (Lamarck) Decaisne, is distinguished from other species in the genus by the following combination of characteristics: the prostrate habit, the exerted position of the tetrasporangia, and the presence in the cortex of numerous and conspicuous vesicle cells. Evidence is presented to demonstrate that the criterion of an erect habit in Microcladia vs. a prostrate habit in Herpochondria used to separate these genera is not sound.