尖叶拟船叶藓种群能量生殖配置的研究

首次报道了苔藓类植物的能量生殖配置情况.在尖叶拟船藓(Dolichomitriopsis diversiformis)种群整个生长周期中,各器官热值由大到小顺序为:雌器苞(9305.1 J/g)＞成熟孢子体(9196.1 J/g)＞配子体(4075.6 ～ 6558.6 J/g).能量配置比例的顺序为:配子体>孢子体>雌器苞.配子体生长所分配的能量占绝对优势,成熟孢子体的能量配置仅为3.2 %.实验结果表明:尖叶拟船叶藓生殖器官(雌器苞和孢子体)的能量配置较低,但具有较高的热值,生殖期需要消耗较多的能量.     

分子标记在鉴别拟船叶藓属和猫尾藓属中的应用

船叶藓科的拟船叶藓属(Dolichom itriopsis)和猫尾藓属植物(Isothecium)非常相似,不易从外部表型上进行属间物种的区分.以尖叶拟船叶藓6个居群、猫尾藓1个居群及疑似尖叶拟船叶藓种1个居群为材料,进行了随机扩增多态性(RAPD)标记分析,结果表明:50个随机引物中有15个引物扩增的产物具有多态性,15个引物共扩增出77条带,其中多态性条带为71条,多态带比率高达92.21%.聚类分析结果表明,疑似种与猫尾藓有较近的亲缘关系,与尖叶拟船叶藓亲缘关系较远.同时测定了疑似尖叶拟船叶藓种的rDNA的ITS全序列,与Genbank已知序列比对结果表明,疑似种与猫尾藓的同源性高达94.74%,而与尖叶拟船叶藓的同源性只有80.64%.进一步支持了RAPD的聚类结果,说明疑似种是猫尾藓而非尖叶拟船叶藓.     

濒危植物尖叶拟船叶藓的过氧化物同工酶分析

采用聚丙烯酰胺凝胶电泳技术分析了濒危植物尖叶拟船叶藓7个自然居群的过氧化物同工酶．结果表明：尖叶拟船叶藓在13个位点表现酶带．其中 Pod-4、Pod-6、Pod-7为7个居群共有,是尖叶拟船叶藓的特征带;1号居群酶带最多,为12条,除与其他居群共有的3条主带外,还出现了其特有的3务酶带;尖叶拟船叶藓存在哑等位基因现象,有两个稀有基因 Pod-5和 Pod-11．3号和5号、4号和6号有较强的同源性．据此认为尖叶拟船叶藓具有较丰富的遗传多样性．     

梵净山尖叶拟船叶藓的遗传多样性分析

采用RAPD技术,选取10个引物对梵净山的尖叶拟船叶藓(Dolichomitriopsis diversiformis)自然分布区的南、北坡14个居群153个个体的总DNA进行了扩增,共得到196个位点.统计分析表明:(1)梵净山尖叶拟船叶藓在物种水平有较高的遗传多样性,居群水平的遗传多样性相对较低.(2)该藓种遗传多样性高低与海拔高度无关,但南坡的多样性水平略高于北坡.(3)遗传多样性的63.29%发生在居群间,只有36.71%发生在居群内.研究结果提示尖叶拟船叶藓的遗传多样性受小生境的影响较大,遗传漂变和环境适应可能是影响居群分化的主要原因.     

尖叶拟船叶藓光系统Ⅱ光合荧光特性、活性氧代谢与耐脱水生理生态适应的关系

以广布湿生藓类——湿地匐灯藓(Plagiomnium acutum)为比较材料,研究东亚特有濒危植物尖叶拟船叶藓(Dolichomitriopsis diversiformis)在不同快速脱水和复水胁迫下PSⅡ的叶绿素光合荧光变化和活性氧代谢及抗氧化系统变化,探讨两种藓类生理生态适应性差异的成因,以初步确定尖叶拟船叶藓受水分条件限制分布狭窄趋于濒危的原因。结果显示:(1)尖叶拟船叶藓的光合电子传递在脱水后可被极微弱光完全抑制,其抑制光强的恢复明显慢于湿地匐灯藓;其PSⅡ最大光化学效率(Fv/Fm)和实际光化学量子效率(YⅡ)先降而后升,恢复较慢;光化学淬灭(q P)复水后恢复较快,非光化学淬灭(NPQ)的绝对值和变化速率则始终低于湿地匐灯藓。(2)尖叶拟船叶藓活性氧水平明显高于湿地匐灯藓;其SOD、CAT、APX等抗氧化系统酶活性整体变化幅度较大,抗氧化保护物质(As A)含量则明显低于湿地匐灯藓。以上结果表明尖叶拟船叶藓受到环境水分因子限制的原因主要有:(1)PSⅡ的反应中心色素(P680)对脱水伤害较为敏感;(2)复水修复过程中抗氧化保护系统的保护能力偏低。     

树干附生尖叶拟船叶藓性比和有性生殖的比例

通过对贵州梵净山树干附生尖叶拟船叶藓的野外调查和室内研究,结果表明,在44个被调查样方共计1320株植株中,尖叶拟船叶藓单株的性比为8♀∶1♂(N=1320),其中25.0%的单株没有进行性表达;其种群的性比为5♀∶1♀♂(雌性种群:混合种群,N=44),没有发现雄性种群;其单株的有性生殖的比例为10.5%,种群的有性生殖比例为9.3%。结果表明尖叶拟船叶藓种群具有明显的雌性偏向,其种群的自然更新更多的是依赖各种营养繁殖。     

尖叶拟船叶藓的77K荧光光谱及对强光照的短期适应

报道了东亚特有濒危植物尖叶拟船叶藓(Dolichomitriopsis diversiformis)在不同光质的光照诱导下的低温77K荧光光谱及状态转移的初步研究结果,实验中,尖叶拟船叶藓在77K下出现了3条发射带,分别是F680、F685、F720nm,并没有出现存在于大部分高等植物中的F695nm和F740nm两个峰．经过PSⅡ光诱导后、在77K下出现了F680nm,这个峰在77K下出现是首次报道,而以前的研究认为只在4K下才出现这一条光谱带,这一结果表明尖叶拟船叶藓叶绿体的两个光系统结构与其他高等植物存在着差异。在自然光下,PSⅡ与PSⅠ的总能量比是2.04,经过15min的PSⅡ光(670nm)诱导后,PSⅡ与PSⅠ的总能量比变成了1．28(状态2),当用15min的PSⅠ光(716nm)照射后,PSⅡ与PSⅠ的总能量比从2．04变成了3．4l(状态1)。在自然光下,由尖叶拟船叶藓的光系统的外部LHCⅡ所吸收的激发能是整个光系统激发能的21．19％．这说明尖叶拟船叶藓对光的短期调节能力是21．19％．尖叶拟船叶藓的光系统的外部LHCⅡ有51．7％位于PSⅡ中,48．3％在PSⅠ中.     

贵州梵净山森林树干附生尖叶拟船叶藓分布格局研究*

通过使用双向指示种分析( TWINSPAN) 和无偏对应分析( DCA) 两种方法进行研究的结果表明, 梵净山
树干附生尖叶拟船叶藓在群落水平上的分布与森林群落类型相对应, 其所在群落可以分成贵州青冈- 箭竹群落、
贵州青冈+ 巴东栎+ 雷公鹅耳枥- 箭竹群落、贵州青冈- 短柱柃群落、大钟杜鹃+ 多脉青冈- 野八角群落、亮
叶水青冈+ 多脉青冈+ 贵州青冈- 箭竹群落和贵州青冈- 尖叶山茶- 野八角群落6 类树附生苔藓植物群落类型。
尖叶拟船叶藓在梵净山的垂直分布范围为海拔1 650~ 2 080 m; 在树干垂直分布表现为下部显著多于中部, 中部
显著多于上部; 在不同树种间的分布存在显著差异。分析了影响树附生尖叶拟船叶藓生态分布的相关因素。     

贵州梵净山森林树干附生尖叶拟船叶藓分布格局研究

通过使用双向指示种分析（TWINSPAN）和无偏对应分析（DCA）两种方法进行研究的结果表明,梵净山树干附生尖叶拟船叶藓在群落水平上的分布与森林群落类型相对应,其所在群落可以分成贵州青冈-箭竹群落、贵州青冈＋巴东栎＋雷公鹅耳枥-箭竹群落、贵州青冈-短柱柃群落、大钟杜鹃＋多脉青冈-野八角群落、亮叶水青冈＋多脉青冈＋贵州青冈-箭竹群落和贵州青冈-尖叶山茶-野八角群落6类树附生苔藓植物群落类型。尖叶拟船叶藓在梵净山的垂直分布范围为海拔1650～2080m;在树干垂直分布表现为下部显著多于中部,中部显著多于上部;在不同树种间的分布存在显著差异。分析了影响树附生尖叶拟船叶藓生态分布的相关因素。     

溪流岩生明叶藓的孢子体分布格局及其生殖特性研究

通过实地踏查,对湖南省德夯地质公园九龙溪景区35个样地315个样方的溪流岩生明叶藓进行调查研究,以揭示其生殖生物学特性.结果表明:(1)共分离出明叶藓单株4 427株,其中有孢子着生的单株1 439株,单株着生孢子体数量从1个到12个.(2)明叶藓种着生1个孢子体的植株数占有孢子体着生植株总数的53.79%,且分别显著多于着生孢子体2~12个的植株数(P<0.01);着生1～3个孢子体的植株数占孢子体植株总数的比例达88.74%,说明明叶藓中单株着生1～3个孢子体的植株占绝对多数.(3)明叶藓的孢子体主要着生在主茎上(94.85%),各级分枝上较少产生孢子体.(4)明叶藓在单株水平上有性生殖的比例为32.5%,在种群水平上有性生殖的比例为97.1%,说明有性生殖在雌雄同株的明叶藓种群中普遍存在.     

The cost of realized sexual reproduction: assessing patterns of reproductive allocation and sporophyte abortion in a desert moss

The desert moss Syntrichia caninervis exhibits one of the most skewed sex ratios in the plant kingdom, with female individuals far outnumbering male individuals (exceeding 14♀:1♂). The "cost of sex hypothesis" derives from allocational theory and predicts that the sex which is most expensive should be the rarer sex. This hypothesis, which, as considered here represents the realized cost of sexual reproduction, is contingent upon two assumptions that are explored: (1) that male sex expression is more expensive than female sex expression, and (2) that sexual reproduction is resource limited. Using inflorescence biomass and discounting sperm, male sex expression was found to be in the neighborhood of one order of magnitude more expensive than female sex expression, and this difference is reflected in higher numbers of gametangia per male inflorescence, presence of paraphyses in male inflorescences, and a much longer developmental time for male inflorescences. The realized cost of female reproduction from two communities dominated by S. caninervis was found to be lower than the realized cost of male sexual reproduction. Resource-limited reproduction was assessed by determining the frequency of sporophyte abortion, the age distribution of sporophyte abortions, and patterns of sporophyte abortion that may be density dependent. Among ten sexually reproducing populations, abortive sporophytes occurred at a frequency of 0.64. Abortive sporophytes averaged 8% the mass of mature sporophytes, and cohort sporophytes from the same individual female were found to abort in a density-dependent pattern. We conclude that the two assumptions, upon which the cost of sex hypothesis depends, are supported.     

Costs of sporophyte production in the moss,Dicranum polysetum

We investigated the cost of sporophyte production in the moss Dicranum polysetum both by examining patterns of growth and reproduction in unmanipulated shoots and by experimentally manipulating sexual reproduction.The estimated proportion of total carbon investment allocated to sexual reproduction in sporophyte-producing shoots over the study period was 74.8%. Unmanipulated shoots that aborted all sporophytes had a significantly higher growth in the top shoots than shoots that produced sporophytes. In sporophyte-producing shoots, total apical growth decreased proportionately with the number of sporophytes.Experimental prevention of sporophyte development resulted in significantly higher total apical growth of the gametophytes. Shoots where current perichaetia were lacking when marked had a mass increase in the top shoots similar to manipulated sporophytic shoots whereas sporophytic control shoots grew significantly less than these two categories.The difference between control shoots and manipulated shoots in the mass of vegetative apical growth was mainly because of different length increments whereas mass per unit length was similar between groups. The probability to reproduce sexually in the year after the manipulation, and the biomass allocated to this reproduction, were not affected by the experimental treatment.     

An experimental demonstration of the cost of sex and a potential resource limitation on reproduction in the moss Pterygoneurum (Pottiaceae)

The cost of sexual reproduction is incurred when the current reproductive episode contributes to a a decline in future plant performance. To test the hypotheses that a trade-off exists between current sexual reproduction and subsequent clonal regeneration and that resources limit reproduction and regeneration, plants of the widespread moss Pterygoneurum ovatum were subjected to induced sporophytic abortion, upper leaf removal, and nutrient amendment treatments. Sexually reproducing plants were slower or less likely to produce regenerative structures (protonemata or shoots) and produced fewer regenerative tissue areas or structures. The ability and the timeline to reproduce sexually and regenerate clonally were unaffected by an inorganic nutrient amendment. However, when leaves subtending the sporophyte were removed, the sporophytes were less likely to mature, tended to take a longer time to mature, and were smaller compared to sporophytes from shoots with a full complement of upper leaves. Our findings indicate that plants investing in sexual reproduction suffer a cost of decreased clonal regeneration and indicate that sporophyte maturation is resource-limited, with upper leaves contributing to the nutrition of the sporophyte. This study represents only the second explicit experimental demonstration of a trade-off between sexual and asexual reproduction in bryophytes.     

Sex distribution and sporophyte frequency in a population of the clonal moss Hylocomium splendens

Abstract

The sex ratio and factors that affect sporophyte production were studied by following one population of the clonal moss Hylocomium splendens growing on top of a boulder in a S.E. Norwegian boreal spruce forest valley for 5 years. Sex of ca 75% of all segments recorded during the study period could be determined from records of occurrence of sporophytes, gametangia and branching patterns. The population had a 4:1 female-biased sex ratio. Of 1005 female segments recorded during the 5-year study period, 29.8% carried sporophytes. The frequency of sporophyte production in female segments varied more than threefold among years, and was apparently related to climatic favourability for bryophyte growth and development. At the scale of H. splendens segments, sporophyte production was favoured by large size of segments and high relative growth rates. A distinct low-size threshold for sporophyte production occurred in all years. This threshold was higher in years of low sporophyte frequency, with an absolute low limit of ca 2 mg segment dry weight. The fraction of female segments with sporophytes, and the number of sporophytes per sporophyte-carrying segment, increased with segment size from the low threshold to an upper size threshold, beyond which further increase in segment size did not imply increased sporophyte frequency. This may be caused by the spatial distribution of sex organs. Sporophyte production increased strongly upwards in the bryophyte carpet, even after vertical variation in size had been taken into account. This indicates that radiation plays a key role in initiation of sexual branches, and that the processes previously demonstrated to regulate vegetative branching apply to branching in general.     

Mate limited reproductive success in two dioicous mosses

We tested whether mate availability in the pleurocarpous dioicous mosses Rhytidiadelphus triquetrus and Abietinella abietina affects fertilization success by transplanting individual male shoots into non-sporophytic female colonies. Fertilization success in both species was limited by the availability of mates and distance-dependent, and the number of sporophytes produced was higher in R. triquetrus than in A. abietina . Our estimate of a maximum fertilization distance of 34 cm in R. triquetrus is an order of magnitude larger than previous estimates that have been based on non-manipulative approaches. In R. triquetrus the number of female reproductive branches and plot inclination (horizontal vs sloping) had significant effects on the number of sporophytes produced. In A. abietina , the number of female reproductive branches per plot did not affect sporophyte production. Within sloping experimental plots, sporophyte number was significantly higher, and the distance of sporophytes from the spermatozoid source was larger below the male transplants than above. We conclude that mate availability may be important for reproductive success in sessile dioecious organisms, and that the spatial structure at various scales is essential to understand their dynamics.     

Day Length and Temperature Strongly Influence Sexual Reproduction and Expression of a Novel MADS-Box Gene in the Moss Physcomitrella patens

Abstract: The effect of temperature and light conditions on sexual reproduction (sporophyte formation) of in vitro cultures of the moss Physcomitrella patens was analysed. All parameters tested, i.e., temperature, light intensity and day length had a strong impact on the number of sporophytes formed. The highest number of sporophytes, 559 g fresh weight, developed at 15 °C, 8 h light/day with an intensity of 20 μmol/m²/s. In contrast, at 25 °C, as well as with a day length of 16 h per day, the number of sporophytes was drastically reduced. Vegetative growth, determined as fresh weight per petri dish, was impeded under conditions favouring sporophyte formation, probably due to nutrient transfer to the sporophytes. Microscopic documentation of the developing sporophytes revealed that, although archegonia were arranged in bundles at the gametophore apices, usually only one archegonium per gametophore apex developed into a mature sporophyte. From an EST database six novel MADS-box genes were identified which, in phylogenetic analyses, did not cluster with the known groups of higher plant MADS-box genes. One of these genes was represented only as a singleton in a cDNA library specifically derived from gametophore apices and developing sporophytes, and, therefore, designated PpMADS-S. RNA amounts of PpMADS-S were two to three times higher under conditions that stimulate sporophyte development (15 °C, 8 h light per day) when compared to conditions favouring vegetative growth (25 °C, 16 h light per day), indicating a possible function in sexual reproduction of this moss. Thus, an efficient experimental system was established to study sex organ formation, fertilization and embryo development in Physcomitrella.     

THE GENETIC STRUCTURE OF SPOROPHYTIC AND GAMETOPHYTIC POPULATIONS OF THE MOSS,FUNARIA HYGROMETRICA HEDW

Patterns of phenotypic and genotypic variability in two populations of the moss, Funaria hygrometrica, were investigated using measurements of gametophytic and sporophytic morphology, sporophytic reproductive output, spore germination, gametophytic growth rates and tolerances of copper, cadmium, and low nutrient conditions, and electrophoretically detectable enzyme variation. The two populations differed in all traits measured, but complete monomorphism within populations at 14 enzyme loci suggested that each represented a single clone. Variability in gametophytic growth rates and responses to different experimental media, however, occurred among haploid sib families (families of meiotic progeny derived from the same sporophyte) and among sibs within families within both populations, suggesting high levels of genetic variability. Low mean reproductive output and a high level of variability among sporophytes in a mine site population probably reflected heavy metal toxicity. Based on this study, in combination with previous work on F. hygrometrica (Shaw, 19906), somatic mutation and/or nongenetic effects appear to contribute significantly to phenotypic variability in natural populations.     

Generational differences in response to desiccation stress in the desert moss Tortula inermis

BACKGROUND AND AIMS: Active growth in post-embryonic sporophytes of desert mosses is restricted to the cooler, wetter months. However, most desert mosses have perennial gametophytes. It is hypothesized that these life history patterns are due, in part, to a reduced desiccation tolerance for sporophytes relative to gametophytes. METHODS: Gametophytes with attached post-embryonic sporophytes of Tortula inermis (early seta elongation phenophase) were exposed to two levels of desiccation stress, one rapid-dry cycle and two rapid-dry cycles, then moistened and allowed to recover, resume development, and/or regenerate for 35 d in a growth chamber. KEY RESULTS: Gametophytes tolerated the desiccation treatments well, with 93 % survival through regenerated shoot buds and/or protonemata. At the high stress treatment, a significantly higher frequency of burned leaves and browned shoots occurred. Sporophytes were far more sensitive to desiccation stress, with only 23 % surviving after the low desiccation stress treatment, and 3 % surviving after the high desiccation stress treatment. While the timing of protonemal production and sporophytic phenophases was relatively unaffected by desiccation stress, shoots exposed to one rapid-dry cycle produced shoots more rapidly than shoots exposed to two rapid-dry cycles. CONCLUSIONS: It is concluded that sporophytes of Tortula inermis are more sensitive to rapid drying than are maternal gametophytes, and that sporophyte abortion in response to desiccation results from either reduced desiccation tolerance of sporophytes relative to gametophytes, or from a termination of the sporophyte on the part of the gametophyte in response to stress.     

CONTROL OF SEX RATIOS IN HAPLOID POPULATIONS OF THE MOSS,CERATODON PURPUREUS

Female biased sex ratios occur in a number of unrelated mosses. Such ratios refer to the relative numbers of male and female gametophytes in moss populations and are therefore more comparable to the numbers of pollen grains and ovules in populations of seed plants than to the numbers of male (microsporangiate) and female (megasporangiate) sporophytes. A survey of 11 populations of the moss, Ceratodon purpureus, showed that sex ratios are heterogeneous, but that female biases occur in more than half the populations. One hundred and sixty single spore isolates representing 40 sporophytes from one population demonstrated that female gametophytes outnumbered males by a ratio of 3:2 at the time of germination. Female gametophytic clones formed significantly more biomass than male clones, and individual female shoots were more robust. Male clones, however, produced more numerous stems. These sexually dimorphic traits may be related to life history differences between male and female gametophytes since females must provide nutritional support to the “parasitic” sporophyte generation, a burden that males do not share.     

MUTATIONAL LOAD IN A FERN POPULATION GROWING IN A POLLUTED ENVIRONMENT

The Osmunda regalis sporophyte is well organized for the storage and perpetuation of post-zygotic mutations. Techniques have been developed to detect sporophytes in which such mutations have occurred. Two populations were screened for sporophytes which are chimeras for gametophytic or recessive sporophytic lethals. The populations had different ecologies; one was in a pristine lake side bog and the other was growing in the waters of a river heavily polluted with industrial wastes. Post-zygotic mutations were detected only in the polluted river population. The level of mutational damage approximated that previously documented from chromosome studies.