Comparing Variational Properties of Homologous Floral and Vegetative Characters in Dalechampia scandens: Testing the Berg Hypothesis

The Berg hypothesis posits that, in plants with specialized pollination systems, floral characters should evolve to become integrated with each other and decoupled from vegetative characters. We test this hypothesis by comparing serially homologous and morphologically similar characters in leaves and involucral bracts in the Neotropical vine Dalechampia scandens, which has a specialized pollination system based on resin-collecting bees. The involucral bracts serve a number of specialized floral functions, including signaling and protection, that may put them under stronger selection for precision than the less specialized leaves. The homology and morphological similarity of the leaves and bracts allow us to make a sharper test of Berg’s hypothesis than is possible in most other systems. We found support for the hypothesis in that the bracts had lower coefficients of variation than the leaves for comparable traits. Also in support of the hypothesis, we found essentially zero phenotypic correlations between bracts and leaves at the same time that we found moderate correlations between different leaves and between different bracts. In contradiction to the hypothesis, however, we did not find higher correlations among traits within bracts than within leaves, and we found no evidence of bracts being more developmentally stable than the leaves.     

高领藓属(高领藓科)一新种——卷尖高领藓

描述了高领藓属Glyphomitrium(高领藓科Glyphomitriaceae)一新种——卷尖高领藓G. tortifolium Y. Jia, M. Z. Wang &; Y. Liu。它因体形大,叶片卷曲和雌苞叶具长尾尖而与G. elatum Takaki相似,但是又因它植物体更大,叶片狭披针形,雌苞叶在骤尖基部两侧略凹陷而区别于后者。     

Secretory structures at syconia and flowers of Ficus enormis (Moraceae): A specialization at ostiolar bracts and the first report of inflorescence colleters

The fig (Ficus L.) infructescence, called syconium, is a receptacle with an apical opening, the ostiole, closed by bracts. The ostiolar bracts produce an exudate, which is rather conspicuous in some species. It has not been histochemically analyzed yet, and the structures responsible for its production are still unknown. Some wild growing species of Ficus from Brazil produce high amounts of this ostiolar exudate. Ficus enormis (Mart. ex Miq.) Miq. grows as trees or shrubs in the Atlantic rainforest. Our goal was to identify the secretory structures present in the inflorescence and, to characterize histochemically the ostiolar tissues and exudates. Syconia samples of F. enormis were processed and stained according to the usual techniques in plant anatomy. The morphological analysis revealed different types of bracts, one type specialized in secretion, another showing transitional characteristics between secretory and non-secreting bracts, and a third one being non-secreting. They are designated as secretory ostiolar bracts, transitional bracts and wall bracts. The floral bracteoles, digital-shaped colleters present in the ostiole, at the syconium axis and at the flower receptacle, were also analyzed. All have similar structure, like finger-shaped secretory trichomes. The colleters present among ostiolar bracts may contribute to production and composition of the ostiole exudate.     

Parallelism in hill activity and anthocyanidin content in Euphorbia pulcherrima

Pigment compositions and Hill activities of red-leafy bracts, red-green leaves and green leaves of E. pulcherrima were studied. Interestingly enough, the chloroplasts from anthocyanidin-containing leaves are intrinsically more active than those from green leaves.     

棉花苞叶光呼吸和PSII热耗散对土壤水分的响应

在新疆气候生态条件下, 采用膜下滴灌植棉技术, 设置不同滴灌水分处理, 研究了不同滴灌量条件下棉花(Gossypium hirsutum)苞叶和叶片碳同化、光呼吸作用、光系统II (PSII)热耗散作用及其光破坏防御机制的差异, 以揭示滴灌节水条件下棉花苞叶缓解光抑制的机理及与棉花抗旱特性的关系。结果表明: 棉花开花后苞叶及叶片在高温强光下实际光化学效率(Φ_PSII)显著降低, 发生明显的光抑制现象, 但苞叶的光抑制程度较叶片轻; 与正常滴灌量处理相比, 节水滴灌条件下棉花水分亏缺, 叶片净光合速率(P_n)、Φ_PSII、光呼吸(P_r)、光化学猝灭系数(q_P)降低, 非光化学猝灭系数(NPQ)升高, 叶片光抑制程度加重, 而苞叶P_n、Φ_PSII、P_r、q_P、NPQ变化不大, 与正常滴灌量处理相比, 光抑制程度无显著差异。苞叶光呼吸速率与光合速率的比值(P_r/P_n)显著高于叶片; 滴灌节水条件下棉花适度水分亏缺对苞叶光呼吸及P_r/P_n无显著影响。高温强光下, 棉花节水滴灌对叶片PSII量子产量的转化与分配影响显著, 但对苞叶的影响不显著; 苞叶非调节性能量耗散的量子产量(Y(NPQ))高于叶片, 因此能有效地将PSII的过剩光能以热的形式耗散。综上所述, 与叶片相比, 苞叶对轻度水分亏缺不敏感, 是棉花适应干旱逆境较强的器官, 苞叶光呼吸和热耗散作用对光破坏防御具有重要意义。     

A structure–activity relationship study on antiosteoclastogenesis effect of triterpenoids from the leaves of loquat (Eriobotrya japonica)

Our previous results elucidated that the leaves of Eriobotrya japonica possessed the potential to suppress ovariectomy-induced bone mineral density deterioration, and ursolic acid, the major bioactive component in these leaves, suppressed the osteoclast differentiation. The aim of this study was to discover more candidates for development of novel antiosteoclastogenesis agents from the leaves of E. japonica. Phytochemical analysis following a cell-based osteoclastic tartrate-resistant acid phosphatase (TRAP) activity assay revealed 11 more compounds with a potent antiosteoclastogenesis effect. The potency of ursane-type triterpenoids from the leaves of E. japonica prompted us to investigate the structure–activity relationships underlying their antiosteoclastogenesis. The results revealed that both the hydroxyl group at C-3 and the carboxylic group at C-17 played indispensable roles in the antiosteoclastogenesis activity of ursane-type triterpenoids. The configuration at C-3 (a beta-form of the hydroxyl group) was found to be important for this activity. While introducing a hydroxyl group at C-19 increased the inhibitory activity of ursane-type triterpenoids carrying an alpha-form hydroxyl group at C-3. The bioactivity analyses of ursolic acid and oleanolic acid demonstrated that the antiosteoclastogenesis effect of ursolic acid may be related to different positions of the C-29 and C-30 methyl groups on the E-ring, since oleanolic acid showed limited activity. The addition of a hydroxyl group at C-2 would dramatically improve the inhibition of oleanane-type triterpenoids. Collectively, these findings could provide important clues for the improvement of multi-targeted antiosteoclastogenesis agents from the leaves of E. japonica.     

Goodmania (Polygonaceae), a new genus from California

A new genus,Goodmania, is described for the species currently known asOxytheca luteola Parry of central and southern California. A member of Polygonaceae, subfamily Eriogonoideae,Goodmania is an isolated genus, distinct fromEriogonum by the awned bracts, and fromOxytheca by its involucral bracts not forming a distinct tube, yellow flowers, non-glandular pubescence, and small, paired cauline leaves.Goodmania is seemingly related to the Death Valley endemic,Gilmania, but differs in having a whorl of five involucral bracts subtending the cluster of short-pedicellate flowers.     

Photorespiration and photoinhibition in the bracts of cotton under water stress

Gas exchange and chlorophyll fluorescence parameters of PSII were analyzed in the bracts and leaves of cotton plants after anthesis. Photosynthetic activity and photorespiration were measured in the leaves and bracts of cotton grown under either normal or reduced water-saving drip irrigation. The photosynthetic performance, amount of chlorophyll and Rubisco, and net photosynthesis were greater in the bracts than that in the leaves under water stress. The actual photochemical efficiency of PSII decreased in both the bracts and leaves after anthesis under reduced irrigation. However, the decrease was smaller in the bracts than in the leaves, indicating that the bracts experienced less severe photoinhibition compared to the leaves. The greater drought tolerance of bracts could be related to differences in relative water content, instantaneous water-use efficiency, and photorespiration rate. The ratio of photorespiration to net photosynthesis was much higher in the bracts than in leaves. Furthermore, water deficiency (due to the water-saving drip irrigation) had no significant effect on that ratio in the bracts. We hypothesized that photorespiration in the bracts alleviated photoinhibition and maintained photosynthetic activity.     

不同色彩珙桐叶片和苞片解剖结构及色素含量比较研究

以生长于同一生境下的粉红珙桐(粉红色叶片、苞片)与普通珙桐(绿色叶片、白色苞片)为试材,对比两种色彩珙桐叶片/苞片解剖结构和色素含量的差异,以揭示珙桐色彩转变的规律。结果显示：(1)两种珙桐叶片均属于异面叶类型,栅栏组织由一层长柱形细胞整齐排列而成,海绵组织排列疏松,部分粉红叶片的上表皮细胞向外凸起,绿叶无此现象;粉红叶片的总厚度及其表皮角质层、栅栏组织和海绵组织厚度都高于绿叶,而表皮较薄。(2)两种珙桐苞片均无栅栏组织和海绵组织的分化,粉红苞片上表皮细胞明显隆起,上表皮角质层增厚,而下表皮变薄。(3)粉红叶片的类黄酮、花色苷含量分别是绿色叶片的1.52倍、3.67倍,两者的光合色素含量无显著差异,但粉红叶片的叶绿素a/b值比绿色叶低很多;粉红苞片花色苷含量显著高于白色苞片,而两者类黄酮含量差异不大。研究表明,花色苷是珙桐叶片和苞片色彩转红的直接因素,类黄酮有助于叶片呈红色;粉红珙桐叶片/苞片的解剖结构发生了一定变化,对光能的利用效率更高,对阴湿环境的适应性增强。     

Cotton bracts are adapted to a microenvironment of concentrated CO2 produced by rapid fruit respiration

Background and Aims

Elucidation of the mechanisms by which plants adapt to elevated CO₂ is needed; however, most studies of the mechanisms investigated the response of plants adapted to current atmospheric CO₂. The rapid respiration rate of cotton (Gossypium hirsutum) fruits (bolls) produces a concentrated CO₂ microenvironment around the bolls and bracts. It has been observed that the intercellular CO₂ concentration of a whole fruit (bract and boll) ranges from 500 to 1300 µmol mol⁻¹ depending on the irradiance, even in ambient air. Arguably, this CO₂ microenvironment has existed for at least 1·1 million years since the appearance of tetraploid cotton. Therefore, it was hypothesized that the mechanisms by which cotton bracts have adapted to elevated CO₂ will indicate how plants will adapt to future increased atmospheric CO₂ concentration. Specifically, it is hypothesized that with elevated CO₂ the capacity to regenerate ribulose-1,5-bisphosphate (RuBP) will increase relative to RuBP carboxylation.

Methods

To test this hypothesis, the morphological and physiological traits of bracts and leaves of cotton were measured, including stomatal density, gas exchange and protein contents.

Key results

Compared with leaves, bracts showed significantly lower stomatal conductance which resulted in a significantly higher water use efficiency. Both gas exchange and protein content showed a significantly greater RuBP regeneration/RuBP carboxylation capacity ratio (J_max/V_cmax) in bracts than in leaves.

Conclusions

These results agree with the theoretical prediction that adaptation of photosynthesis to elevated CO₂ requires increased RuBP regeneration. Cotton bracts are readily available material for studying adaption to elevated CO₂.     

TRICHOMES AND CANNABINOID CONTENT OF DEVELOPING LEAVES AND BRACTS OF CANNABIS SATIVA L. (CANNABACEAE)

Trichome density and type and cannabinoid content of leaves and bracts were quantitated during organ ontogeny for three clones of Cannabis sativa L. Trichome initiation and development were found to occur throughout leaf and bract ontogeny. On leaves, bulbous glands were more abundant than capitate-sessile glands for all clones, although differences in density for each gland type were evident between clones. On pistillate bracts, capitate-sessile glands were more abundant than the bulbous form on all clones, and both types decreased in relative density during bract ontogeny for each clone. The capitate-stalked gland, present on bracts but absent from vegetative leaves, increased in density during bract ontogeny. The capitate-stalked gland appeared to be initiated later than bulbous or capitate-sessile glands during bract development and on one clone it was first found midway in bract ontogeny. Nonglandular trichomes decreased in density during organ ontogeny, but the densities differed between leaves and bracts and also between clones. Specific regulatory mechanisms appear to exist to control the development of each trichome type independently. In addition, control of trichome density seems to be related to the plant organ and clone on which the gland type is located. Cannabinoid synthesis occurs throughout organ development and is selectively regulated in each organ. Typically, cannabinoid synthesis occurred at an increasing rate during bract development, whereas in developing leaves synthesis occurred at a decreasing rate. Cannabinoid content on a dry weight basis was generally greater for bracts than leaves. Analyses of leaves indicate that other tissues in addition to glands may contain cannabinoids, while for bracts the gland population can accommodate the cannabinoid content for this organ. The functional significance of trichomes and cannabinoids in relation to evolution is discussed.     

Multifunctional bracts enhance plant fitness during flowering and seed development in Rheum nobile (Polygonaceae), a giant herb endemic to the high Himalayas

Specialized bracts are thought to be important for the successful reproduction of some plants and are regarded as adaptations to diverse driving forces. However, few empirical studies have quantified the adaptive significance of bracts within a cost–benefit framework. We explored the adaptive significance of large and showy bracts for reproduction in Rheum nobile, a giant herb endemic to the high Himalayas. We examined whether the bracts enhance reproductive success during flowering and seed development. Bracts increased flower and fruit temperature on sunny days, greatly decreased the intensity of ultraviolet-B (UV-B) radiation reaching flowers and fruits, and prevented pollen grains being washed away by rain. Experiments indicated that high temperature could promote pollen germination, while pollen grains exposed to rain and UV-B radiation at ambient levels were seriously damaged. Furthermore, bract removal decreased the number of pollinators visiting flowers. When bracts were removed before or after flowering, fecundity and progeny quality were adversely affected, but seed predation by larvae of pollinators decreased. A cost–benefit analysis demonstrated that the cost of bracts, i.e., increased seed predation, is modest. Our results suggest that the bracts of R. nobile promote pollen germination, protect pollen grains from rain and intense UV-B radiation, enhance pollinator visitation during flowering, and facilitate the development of fertilized ovules during seed development. We conclude that multifunctional bracts of R. nobile are an effective adaptive strategy in alpine environments and might have been selected for because of abiotic environmental conditions as well as for enhancing pollination success.     

Optical and anatomical characteristics of bracts from the Chinese "glasshouse" plant, Rheum alexandrae Batalin (Polygonaceae), in Yunnan, China

Bracts that lacked chlorophyll were compared with rosette leaves on the Chinese glasshouse plant Rheum alexandrae Batalin. The structures were analyzed anatomically and with photospectrometry. Histological features were significantly different between the bracts and the rosette leaves. Epidermal pavement cells and palisade cells were larger in the bracts than in the rosette leaves, but the ratio of the intercellular spaces to the cells in the palisade layer was the same in the two structures. Absorption spectrum analyses of the half-translucent bracts showed that, despite their thinner structure, they absorbed ultraviolet (UV) radiation more efficiently than did the green rosette leaves. The characteristics of the R. alexandrae bracts were different from those of the Himalayan glasshouse plant Rheum nobile. These results suggest that R. alexandrae evolved bracts as an adaptive strategy to protect the inflorescence from UV radiation. Received: August 22, 2001 / Accepted: October 15, 2001     

Photosynthesis of bract and its contribution to seed maturity inCarpinus laxiflora

Light saturated net photosynthesis was measured in bracts and leaves ofCarpinus laxiflora, the major species in secondary forests in cool and intermediate temperate zones in Japan. The maximum net photosynthesis of leaves and bracts was essentially constant from May to early August and decreased gradually thereafter. For bracts, it was 3.2 μmol m⁻²s⁻¹, approximately half that for the leaves. The photosynthesis of bracts would thus appear to contribute significantly to seed maturity. The estimated production of bract based on the photosynthesis would make seeds (3 mg dry weight) mature for 37 days, assuming all photosynthate of the bracts to have been distributed in the seeds only. This was quite consistent with the growth curve for the seeds. A mast year phenomenon is discussed in relation to bract photosynthesis and leaf number.     

叶子花花瓣状苞片和叶片的比较转录组学研究

叶子花(Bougainvillea spectabilis Willd.)的苞片色彩鲜艳,呈花瓣状,在景观园艺和环境美化有着广泛应用。为了进一步了解花瓣状苞片的演化机制,该研究采用RNA-seq技术分别对苞片和叶片进行测序,比较苞片和叶片在基因表达水平的差异。最终获得54.48 M对长度为150bp的双向clean reads,从头拼接出55 782条Unigenes,平均长度为1 003.79bp,N50为1 402bp。共有30 874条Unigenes能被注释到公共数据库,其中有12 631条Unigenes能被注释到基因本体。差异化表达分析确定苞片和叶片差异表达的基因共有456个。该研究分别对不同组织差异表达的基因进行GO富集分析和KEGG富集分析,结果表明,在苞片中高表达的差异化基因有黄酮类合成相关的基因,花色合成关键酶多巴双加氧酶(DODA)以及发现与花瓣发育相关的基因,在叶片中高表达的差异化基因主要是参与光合作用。     

Morphological studies on the genusClematis Linn

While the axes of branched axillary inflorescences seen in most species ofClematis show fundamentally the same features in nodal vasculature as the vegetative stems, those of simple axillary inflorescences, having only a pair of opposite sterile bracts at specific positions, exhibit an exclusive feature in nodal vasculature because they have entirely lost lateral branches or buds in the bract axils. Noticeably, at the nodal level of the axis of the simple inflorescence ofC. japonica andC. Williamsii, trace bundles to the missing lateral branches are formed and extend unaltered beyond the node. Thus, in these two species stelar bundles in the inflorescence axis generally increase in number upwardly from six to eight or more through the node with sterile bracts. On the basis of both anatomical and morphological data, a probable evolutionary trend in floral shoots with simple axillary inflorescences is proposed. The type of floral shoot ofC. tosaensis bearing simple, scale-subtended and basally fascicled inflorescences is the most primitive and constitutes an initial phase of evolution, and progressive changes in a kind of inflorescence-subtending leaves as well as in the shape and position of the sterile bracts resulting in the type of floral shoot ofC. japonica and further in that ofC. obvallata. A floral shoot ofC. Williamsii follows another line of evolution from an ancestral type similar to that ofC. tosaensis.     

Optical and anatomical characteristics of bracts from the Chinese "glasshouse" plant,Rheum alexandrae Batalin (Polygonaceae), in Yunnan,China

Bracts that lacked chlorophyll were compared with rosette leaves on the Chinese glasshouse plant Rheum alexandrae Batalin. The structures were analyzed anatomically and with photospectrometry. Histological features were significantly different between the bracts and the rosette leaves. Epidermal pavement cells and palisade cells were larger in the bracts than in the rosette leaves, but the ratio of the intercellular spaces to the cells in the palisade layer was the same in the two structures. Absorption spectrum analyses of the half-translucent bracts showed that, despite their thinner structure, they absorbed ultraviolet (UV) radiation more efficiently than did the green rosette leaves. The characteristics of the R. alexandrae bracts were different from those of the Himalayan glasshouse plant Rheum nobile. These results suggest that R. alexandrae evolved bracts as an adaptive strategy to protect the inflorescence from UV radiation.