雌雄异熟植物露蕊乌头开花时间对雌雄功能期及表型性别的影响

开花时间决定了植物雌雄功能的交配机会, 最终影响繁殖成功。交配环境假说认为雌雄异熟植物开花时间的差异能引起植物表型性别的变异, 改变种群内的交配环境, 影响植物对雌雄功能的最佳性分配。为了研究开花时间对雌雄异熟植物的雌雄性别时期及表型性别的影响, 本文以毛茛科雄性先熟植物露蕊乌头(Aconitum gymnandrum)为实验材料, 记录了雄性和雌性功能期, 分析了植株开花时间、花的雌雄功能期和表型性别的关系。结果表明: 在植物同一花序内, 较晚开放的花有更长的雄性期和更短的雌性期, 性分配在时间上偏雄。雌雄功能期在时间上的相对分配随植物开花时间的变化表现出相似的趋势： 较晚开的花或较晚开花的个体, 花的雄性功能期相对于雌性功能期更长, 在时间上更偏向雄性功能。而且, 开花时间的差异影响种群内花的性比和植物个体的表型性别动态。随着开花时间由早到晚的变化, 种群内早期以雄花为主,末期以雌花为主, 种群内性别环境由偏雄向偏雌变化, 因此植株个体的平均表型性别则从偏雌转向偏雄。本文结果支持交配环境假说, 雄性先熟的露蕊乌头开花早期, 种群内花的性别比偏雄, 种群表型性别环境偏雄, 因而植物个体平均表型性别偏雌, 性别分配(即时间分配)偏向雌性功能, 而晚开花个体的平均性别偏雄, 更偏向雄性功能的分配。     

Floral nectar production: what cost to a plant?

Floral nectar production is central to plant pollination, and hence to human wellbeing. As floral nectar is essentially a solution in water of various sugars, it is likely a valuable plant resource, especially in terms of energy, with plants experiencing costs/trade-offs associated with its production or absorption and adopting mechanisms to regulate nectar in flowers. Possible costs of nectar production may also influence the evolution of nectar volume, concentration and composition, of pollination syndromes involving floral nectar, and the production of some crops. There has been frequent agreement that costs of floral nectar production are significant, but relevant evidence is scant and difficult to interpret. Convincing direct evidence comes from experimental studies that relate either enhanced nectar sugar production (through repeated nectar removal) to reduced ability to produce seeds, or increased sugar availability (through absorption of additional artificial nectar) to increased seed production. Proportions of available photosynthate allocated by plants to nectar production may also indicate nectar cost. However, such studies are rare, some do not include treatments of all (or almost all) flowers per plant, and all lack quantitative cost–benefit comparisons for nectar production. Additional circumstantial evidence of nectar cost is difficult to interpret and largely equivocal. Future research should repeat direct experimental approaches that relate reduced or enhanced nectar sugar availability for a plant with consequent ability to produce seeds. To avoid confounding effects of inter-flower resource transfer, each plant should experience a single treatment, with treatment of all or almost all flowers per plant. Resource allocation by plants, pathways used for resource transfer, and the locations of resource sources and sinks should also be investigated. Future research should also consider extension of nectar cost into other areas of biology. For example, evolutionary models of nectar production are rare but should be possible if plant fitness gains and costs associated with nectar production are expressed in the same currency, such as energy. It should then be possible to understand observed nectar production for different plant species and pollination syndromes involving floral nectar. In addition, potential economic benefits should be possible to assess if relationships between nectar production and crop value are evaluated.     

Insect and wind pollination of an alpine biennial Aconitum gymnandrum (Ranunculaceae)

Wind pollination can provide reproductive insurance for animal‐pollinated dioecious plants in the absence of available pollinators, but combinations of insect and wind pollination (ambophily) have rarely been studied in hermaphrodite herbs. We examined the stable occurrence of insect pollination and wind pollination over 4 years in a population of a biennial Aconitum species (A. gymnandrum) with actinomorphic and degenerate sepals. The total frequency of visits of two bumblebee species showed no distinct fluctuations in the studied population among the 4 years. However, seed production of netted flowers after emasculation indicated wind pollination had occurred. The seed number of bagged flowers with one visit by bumblebees was significantly less than that of netted flowers after one visit, or in control flowers. Both seed number and fruit set of netted flowers were significantly lower than in control flowers. These results suggest that wind pollination provides supplementary pollen to unvisited and/or once‐visited flowers, but accounts for only a small amount of seed production compared to bumblebee pollination in natural conditions. Such a combination of insect and wind pollination might play an important role in maintaining sexual reproduction of this biennial herb, allowing it to persist in arid habitats on the Qinghai‐Tibetan Plateau, especially during Quaternary glacial periods when pollinator populations oscillated extensively.     

Plasticity of Lythrum salicaria and Phragmites australis growth characteristics across a European geographical gradient

Plants of Lythrum salicaria and Phragmites australis originating from localities across the European north–south geographical gradient were cultivated in parallel in an outdoor tub experiment. A strong correlation was found between growth and morphometric characteristics related to plant size (plant height, basal diameter, aboveground- and belowground plant biomass, etc.) and the position of the respective populations along the north–south gradient. Plants of both L. salicaria and P. australis from the southern localities grew taller and more vigorously and flowered later than plants from relatively more northern localities. From this point of view, the plants originating from south European populations were comparable to invasive North American plants. Our study indicates that explanation of the competitive success of populations invading new geographical areas may involve the role of geographic gradients within the species native range.     

露蕊乌头(毛茛科)不同海拔居群的传粉生态学

对青藏高原东北部两个不同海拔地点（互助,2460m和海北,3200m）的露蕊乌头Aconitum gymnandrum的传粉生态学进行了比较研究。研究结果表明高海拔居群的单花花期、雄性期持续时间、雌性期持续时间比低海拔长。露蕊乌头不存在无融合生殖现象,尽管高度自交亲和,但产生种子必须依赖传粉媒介。熊蜂是露蕊乌头的主要传粉昆虫,两个居群均存在传粉限制。熊蜂取食花蜜为主,在同一个花序上的访问顺序以由下向上为主,但在互助居群和海北居群有3．9％和2．7％的访花是由上向下进行的。统计发现有37．7％和29．3％的访问行为发生在同一植株内;因此,同株异花传粉造成的自交在露蕊乌头中仍然不能避免。低海拔居群的熊蜂种类和访花频率均高于高海拔居群,但自然状态下两个居群的结实率并没有显著差异。高海拔露蕊乌头居群可能具有较长的柱头持续时间,从而补偿了由于访花频率低带来的结实率降低。     

Size-dependent sex allocation in Aconitum gymnandrum (Ranunculaceae): physiological basis and effects of maternal family and environment

Theory predicts size-dependent sex allocation (SDS): flowers on plants with a high-resource status should have larger investment in females than plants with a low-resource status. Through a pot experiment with Aconitum gymnandrum (Ranunculaceae) in the field, we examined the relationship between sex allocation of individual flowers and plant size for different maternal families under different environmental conditions. We also determined the physiological base of variations in plant size. Our results support the prediction of SDS, and show that female-biased allocation with plant size is consistent under different environmental conditions. Negative correlations within families showed a plastic response of sex allocation to plant size. Negative genetic correlations between sex allocation and plant size at the family level indicate a genetic cause of the SDS pattern, although genetic correlation was influenced by environmental factors. Hence, the size-dependency of sex allocation in this species had both plastic and genetic causes. Furthermore, genotypes that grew large also had higher assimilation ability, thus showing a physiological basis for SDS.     

露蕊乌头（Aconitum gymnandrum Maxim）花序内位置依赖的性分配

植物会采取什么样的繁殖对策来保障它的雌性和雄性繁殖成功,特别是那些生活在高寒地区的植物,已经引起了很多学者的关注.通过野外盆栽试验对青藏高原东部高寒草甸上的常见物种露蕊乌头(Aconitum gymnandrum Maxim)花序内的性分配模式进行了研究,发现同其它顶向式(从花序基部到顶部)开花的植物一样,随着花从基部到顶部的次序,露蕊乌头的心皮数、雌蕊重、种子数和种子重/果实减少;而花药数,花粉数/胚珠数以及雄蕊重/雌蕊重增大,顶部花表现出偏雄的性分配.结籽率在不同的位置间没有显著差异,不受花粉数量的限制;去花实验没有增加剩余部位花的种子数,只是增加了种子大小,这是花序内不可避免的位置效应导致了花序内位置依赖的性分配模式.     

Integrating hormones into the floral-transition pathway of Arabidopsis thaliana

The transition from vegetative to reproductive growth is a major phase change in angiosperms. In annual plants such as Arabidopsis thaliana (Arabidopsis), this change is irreversible, and as such, the regulation of its timing must be tightly controlled. Plant hormone (phytohormone) signalling is known to regulate suites of morphogenic processes in Arabidopsis a role in flowering-time control is starting to emerge as one key-controlling step. This review focuses on experimental evidence in the Arabidopsis that both classical and newly described phytohormones serve within the signal network leading to a reproductive phase transition, as both positive and repressive elements, depending on the phytohormone and growth conditions. Examples of genetic and pharmacological experiments that implicate phytohormones as components of the floral-timing syndrome will be described. I hope that this review will serve as a primer for future research on the mechanisms of action for each respective phytohormone on the floral transition in Arabidopsis, and lead to further experimentation on the crosstalk that likely bridges between them.     

Nectar production and carbohydrate composition across floral sexual phases: contrasting patterns in two protandrous Aconitum species (Delphinieae,Ranunculaceae)

In dichogamous species, it is necessary that pollinators are attracted both to male- and female-phase flowers in order to achieve effective cross-pollination. We investigated, over a two-year period, how nectar production and composition differs in protandrous flowers of Aconitum lycoctonum L. and Aconitum carmichaelii Debeaux, two species originating from different geographical regions. Flowers of A. carmichaelii secreted approx. 2.5-fold more nectar than flowers of A. lycoctonum. The nectar of A. carmichaelii was sucrose-dominant (87.6:9.5:2.9, sucrose:fructose:glucose), whereas sucrose-rich nectar, lacking glucose, occurred in A. lycoctonum (39.9:60.1, sucrose:fructose). Total sugar concentration was similar (53%, on average) in both species. These species also showed contrasting patterns in nectar production and composition between the floral sexual phases. On average, in A. carmichaelii, male-phase flowers produced 2.4-fold more nectar than female-phase flowers in the two years of study, and nectar was sucrose-dominant, irrespective of sexual phase. By contrast, nectar production in A. lycoctonum was biased towards the male phase in one year of study and towards the female phase in the other, and whereas nectar was sucrose-dominant during the male-phase, it was fructose-rich during the female phase, indicating sucrose re-absorption. Although the characteristics of nectar in these Aconitum species indicate pollination by bumblebees, it is possible that their biogeographical history, and not pollinator selection alone, is important in understanding the lack of glucose in A. lycoctonum nectar. Variability in nectar production and/or carbohydrate composition between sexual phases suggests indirectly that nectar traits complement each of the latter. Nevertheless, further research is required if we are to understand the significance of these disparities in pollination ecology, i.e. for promoting pollinator movements between flowers and plants in order to achieve cross-pollination and avoid inbreeding.     

广州地区3种睡莲花开放的日变化规律分析

为了解睡莲属(Nymphaea)植物开花的日变化规律,以广州华南农业大学湿地公园的睡莲属植物为对象进行观察和分析。结果显示,晚上开花类的热带睡莲,其日变化是花朵于晚上开放并持续至第二天上午,白天开花类的热带睡莲和耐寒睡莲,其开放时间为白昼,开放时间因种类不同而有所差异。白天开花的热带睡莲‘独立’(Nymphaea‘Independence’)和耐寒睡莲‘科罗拉多’(Nymphaea‘Colorado’)单朵花期3~4 d,耐寒睡莲墨西哥黄睡莲(N.mexicana)单朵花期2 d,雌雄蕊先后成熟以达到异花授粉的目的,单朵睡莲开放期间雄蕊群呈现不同形态。‘独立’睡莲呈现日出而开,日落则合的开花生物钟,10月至12月,光照时间缩短导致‘独立’睡莲开闭节律缩短。观察结果可为园林水景中睡莲属植物配置提供准确的数据支持。     

植物CO基因研究进展

CO(constans)是植物开花时间光周期调控途径中的一个重要基因.目前从拟南芥、水稻、油菜、马铃薯等多个物种中都已经克隆到CO同源基因.CO基因在不同物种中具有保守的锌指结构和核定位区域,但是不同植物中的作用机理并不完全相同.序列分析表明该基因在被子植物与裸子植物之间、双子叶植物与单子叶植物之间以及不同科、属的植物之间均有明显分化,说明CO基因可能在植物进化中起到了重要作用.本文综述了近年来有关植物CO基因的研究进展,并对其在物种中的进化进行分析,为CO基因进一步研究提供参考.     

Geographical and Seasonal Variation in the Richness of Ant-Plant Interactions in México1

The richness and seasonal variation of ant-plant interactions were compared in four habitats in México: lowland tropical dry forest (La Mancha, Veracruz), coastal sand dune matorral (San Benito, Yucatán), semiarid highland vegetation (Zapotitlán, Puebla), and lower montane humid forest (Xalapa, Veracruz). The effects of temperature and precipitation on the seasonal distribution of the number of ant-plant interactions differed among habitats. The general linear models fitted to the ant-plant interaction curves explained 78.8 percent of the variation for La Mancha, 80.1 percent for Zapotitlán, 18 percent for San Benito, and 29.5 percent for Xalapa. Even though rainfall is low in Zapotitlán and San Benito, minimum temperature was the most important factor accounting for the seasonal distribution and low number of interactions. At La Mancha, with milder minimum temperatures and higher water availability, temperature alone did not account for the seasonal distribution and number of interactions, whereas the effect of the precipitation × temperature interaction was highly significant. Xalapa exhibits the lowest temperatures and the highest precipitation, but the role of these factors was only marginal. We suggest that the vegetation at Xalapa, a mixture of tropical and temperate floristic elements, constrains ant-plant interactions due to a limited presence of nectaries. Also, ants are less abundant in cool and relatively aseasonal habitats. The other habitats have tropical floristic elements that are abundant and frequently have nectar-producing structures. We report considerable variation among habitats in the number and seasonal distribution of ant-plant interactions, and suggest that it is due to the effect of variation in environmental parameters, the richness of plants with nectaries in the vegetation, and habitat heterogeneity.