<Emphasis Type="Italic">Cedrela</Emphasis> and <Emphasis Type="Italic">Toona</Emphasis> genera: a rich source of bioactive limonoids and triterpenoids

Cedrela P. Browne is a genus of trees, strictly related to Toona, in the Meliaceae, a family of flowering plants in the order Sapindales, which is among the most diverse sources of secondary metabolites in the Angiospermae. The most abundant metabolites in these genera are limonoids, tetranortriterpenes possessing diverse structural features, apotirucallanes, tirucallanes, and other triterpenes. The chemical constituents isolated from the genera Cedrela and Toona over the past decades, together with their biological activities, have been compiled in this article. The allelochemical and the phytotoxic activity of limonoids and triterpenoids seem to play a crucial role in the ecological function of these metabolites. While, the most promising use in human field seems related to their antimalarial and anti-inflammatory effects, even that further investigation are still needed.     

The meaning of Darwin's 'abominable mystery'

Charles Darwin's "abominable mystery" has come to symbolize just about all aspects of the origin and early evolution of flowering plants. Yet, there has never been an analysis of precisely what Darwin thought was so abominably mysterious. Here I explicate Darwin's thoughts and frustrations with the fossil record of flowering plants as revealed in correspondence with Joseph Hooker, Gaston de Saporta, and Oswald Heer between 1875 and 1881. I also examine the essay by John Ball that prompted Darwin to write his "abominable mystery" letter to Hooker in July of 1879. Contrary to what is generally believed, Darwin's abominable mystery has little if anything to do with the fossil prehistory of angiosperms, identification of the closest relatives of flowering plants, questions of the homologies (and character transformations) of defining features of flowering plants, or the phylogeny of flowering plants themselves. Darwin's abominable mystery and his abiding interest in the radiation of angiosperms were never driven primarily by a need to understand the literal text of the evolutionary history of flowering plants. Rather, Darwin was deeply bothered by what he perceived to be an abrupt origin and highly accelerated rate of diversification of flowering plants in the mid-Cretaceous. This led Darwin to create speculative arguments for a long, gradual, and undiscovered pre-Cretaceous history of flowering plants on a lost island or continent. Darwin also took refuge in the possibility that a rapid diversification of flowering plants in the mid-Cretaceous might, if real, have a biological explanation involving coevolutionary interactions between pollinating insects and angiosperms. Nevertheless, although generations of plant biologists have seized upon Darwin's abominable mystery as a metaphor for their struggle to understand angiosperm history, the evidence strongly suggests that the abominable mystery is not about angiosperms per se. On the contrary, Darwin's abominable mystery is about his abhorrence that evolution could be both rapid and potentially even saltational. Throughout the last years of his life, it just so happens that flowering plants, among all groups of organisms, presented Darwin with the most extreme exception to his strongly held notion natura non facit saltum, nature does not make a leap.     

Flowering in the uniflora mutant of tomato (Lycopersicon esculentum Mill.): description of the reproductive structure and manipulation of flowering time

The uniflora (uf) mutant of tomato (Lycopersicon esculentum Mill.) is known to produce solitary, normal, fertile flowers instead of inflorescences. Histological and SEM studies revealed that this unusual reproductive structure resulted from the inability of the plant to produce an inflorescence and not from post-initiation abortion processes affecting young flower buds. Development prior to floral transition was apparently not affected by the mutation since rates of germination and leaf initiation were identical in both uf and the Ailsa Craig (AC) initial cultivar. However, the time of flowering of the mutant was always delayed as compared to AC. In uf, environmental conditions markedly influenced flowering time which occurred early in all individuals in summer, but was strongly delayed during winter, with less than 20% plants reaching flowering before having initiated 40 leaves. Defoliation treatments stimulated floral transition in uf plants since 100% flowering occurred whatever the season and since the time of floral transition was usually advanced in comparison to the non-defoliated control plants. Similarly, compared to intact uf plants, flowering of terminal meristem of cuttings and upper axillary bud of decapitated plants was promoted. The involvement of correlative influences and assimilate availability in the control of flowering in tomato is suggested by these findings.     

Comparative study on the evolution of chloroplast ribosomal 5S RNA of a living fossil plant, Cycas revoluta Thumb

The complete nucleotide sequence of Cycas revoluta Thunb chloroplast 5 S rRNA was determined. It consists of 122 nucleotides. This is the only known 5 S rRNA sequence in Gymnospermae. It is highly homologous with chloroplast 5 S rRNA of higher plants (92-97%), but less homologous (about 54%) with those of lower plants. There is however 67% homology between Cycas and a procaryote a. nidulans. The chloroplast 5 S rRNAs of Angiospermae are nearly identical with each other (95-97%). S. oligorhize and L. minor have 100% homology among themselves. We have constructed a phylogenic tree of 5 S rRNA sequences from fifteen plant chloroplasts. The result suggests that the emergence of algae occurred at an early stage of plant chloroplast evolution and that green plants originated from green algae. This is in agreement with the classical view and other theories of molecular evolution. However there is no common ancestor in the case of Bryophyta and ferns. Among the Angiospermae, a precise evolutionary process cannot be deduced because the Knuc values among the species are very close to each other.     

The angiosperm radiation revisited, an ecological explanation for Darwin's 'abominable mystery'

One of the greatest terrestrial radiations is the diversification of the flowering plants (Angiospermae) in the Cretaceous period. Early angiosperms appear to have been limited to disturbed, aquatic or extremely dry sites, suggesting that they were suppressed in most other places by the gymnosperms that still dominated the plant world. However, fossil evidence suggests that by the end of the Cretaceous the angiosperms had spectacularly taken over the dominant position from the gymnosperms around the globe. Here, we suggest an ecological explanation for their escape from their subordinate position relative to gymnosperms and ferns. We propose that angiosperms due to their higher growth rates profit more rapidly from increased nutrient supply than gymnosperms, whereas at the same time angiosperms promote soil nutrient release by producing litter that is more easily decomposed. This positive feedback may have resulted in a runaway process once angiosperms had reached a certain abundance. Evidence for the possibility of such a critical transition to angiosperm dominance comes from recent work on large scale vegetation shifts, linking long-term field observations, large scale experiments and the use of simulation models.     

The Effects of Growth Regulators on Flowering of Chenopodium murale Plants in vitro

In vitro culture of Chenopodium murale L. (ecotype 197) green and herbicide SAN 9789 - treated "white" plants was established and the effects of benzylaminopurine (BAP), indole-3-acetic acid (IAA) and gibberellic acid (GA₃) on growth and flowering were tested. Green plants did not flower on glucose free media, while 17 % of plants flowered on 5 % glucose-containing medium. SAN 9789 (10^–5 M) inhibited growth and flowering. BAP and IAA (0.1 – 5 mg dm^–3) also inhibited growth and flowering of green and "white" plants. GA₃ (10 mg dm^–3) stimulated leaf development in green plants, but had no significant effect on "white" plants, and stimulated flowering of green (41 %) and "white" (33 %) plants.     

稀有植物小丛红景天花部综合特征与繁育系统

对稀有物种生物学特征及繁育系统的研究将有利于我们对稀有物种的保育。该文通过野外定位观测稀有植物小丛红景天(Rhodiola dumulosa)的花部综合特征,并运用杂交指数、花粉-胚珠比的方法首次对其繁育系统进行初步测定。结果表明:该物种单花花期一般为5~6 d,开花过程中花柱逐渐伸长并向外弯曲,子房开裂并逐渐伸长,花药散粉具有先后顺序,一般外轮对萼花药先散粉,其后1 d左右对瓣花药开始散粉。单花花期依照其形态和散粉时间可分为6个阶段:花蕾期、内轮散粉期、内轮散粉末期、外轮散粉期、外轮散粉末期和凋谢期。而种群花期一般可持续30 d以上,不同海拔观测地点有所不同,海拔2 202 m处的观测地点B开花物候最为滞后。由于其杂交指数不小于4,花粉-胚珠比在700~1 000之间, 根据Dafni(1992)和Cruden(1977)的标准,初步判定该物种的繁育系统属于异交为主,部分自交亲和,传粉过程需要传粉者。     

Pollen Ingestion by <Emphasis Type="Italic">Chrysoperla externa</Emphasis> (Hagen) Adults in a Diversified Organic Agroecosystem

Chrysoperla externa (Hagen) larvae prey on pest insects and mites in agroecosystems, and adults mainly feed on pollen, nectar, and honeydew. Therefore, preserving this lacewing in crop systems depends on having plants that provide these resources. The objectives of this research were to identify pollen grains ingested by Ch. externa adults collected in a diversified organic agroecosystem and to evaluate whether there is a difference in the amount of ingested pollen grains between males and females. The adults of Ch. externa were collected in four different crops during 13 months in Seropédica, state of Rio de Janeiro, Brazil, using a collecting net. The adults were killed and underwent acetolysis, in order to recover the pollen in the gut. A total of 37,441 pollen grains from 19 Angiospermae families were found, besides 16 Pteridophyte spores. Among the recognized pollen grains, those of Poaceae were the majority, both in frequency of occurrence (87.5%) and in quantity (33496), and were found and recovered in every month of collection. Females and males ingested, respectively, 71.9 and 28.1% of the total number of Angiospermae pollen grains consumed by both sexes. The highest number of Poaceae pollens was obtained from the females (72.1% of the total number of Poaceae pollen, recovered from females + males). Taken as a whole, this study showed that adults of Ch. externa find possibilities to maintain throughout the year, in different crops, but the main source of pollen to males and females was Poaceae plants.     

Fungitoxic properties of selected South African plant species against plant pathogens of economic importance in agriculture

Thirty‐nine plant species, representing 20 families from the subclasses Rosidae, Asteridae, Commelinidae and Liliidae, were collected from the Blyde River Canyon Nature Reserve, Mpumalanga, South Africa. Crude extracts were prepared and bioassayed, at equal concentrations, for their antifungal potential by determining the inhibitory effects on the mycelial growth of seven economically important plant pathogenic fungi. Statistically significant differences between plants and plant parts were observed as well as the resistance of different fungi to treatment with different plant extracts. The most significant mycelial growth inhibition was obtained with extracts from two species of the subclass Liliidae, namely Aristea ecklonii and Agapanthus inapertus. The crude extract of A. ecklonii performed best of all extracts as it totally inhibited the mycelial growth of all seven of the plant pathogenic test organisms and outperformed the inhibition by a broad spectrum synthetic fungicide (carbendazim/difenoconazole). Crude extracts of A. inapertus showed complete inhibition of four and strong inhibition of the remaining three plant pathogenic fungi. Although not as efficient as the previous two species, the extract of Anisopappus junodii, from the subclass Asteridae, also showed promising antifungal activity by completely inhibiting mycelial radial growth of two and strongly inhibiting that of the remaining five fungi.     

Magnitude and timing of leaf damage affect seed production in a natural population of Arabidopsis thaliana (Brassicaceae)

Background

The effect of herbivory on plant fitness varies widely. Understanding the causes of this variation is of considerable interest because of its implications for plant population dynamics and trait evolution. We experimentally defoliated the annual herb Arabidopsis thaliana in a natural population in Sweden to test the hypotheses that (a) plant fitness decreases with increasing damage, (b) tolerance to defoliation is lower before flowering than during flowering, and (c) defoliation before flowering reduces number of seeds more strongly than defoliation during flowering, but the opposite is true for effects on seed size.

Methodology/Principal Findings

In a first experiment, between 0 and 75% of the leaf area was removed in May from plants that flowered or were about to start flowering. In a second experiment, 0, 25%, or 50% of the leaf area was removed from plants on one of two occasions, in mid April when plants were either in the vegetative rosette or bolting stage, or in mid May when plants were flowering. In the first experiment, seed production was negatively related to leaf area removed, and at the highest damage level, also mean seed size was reduced. In the second experiment, removal of 50% of the leaf area reduced seed production by 60% among plants defoliated early in the season at the vegetative rosettes, and by 22% among plants defoliated early in the season at the bolting stage, but did not reduce seed output of plants defoliated one month later. No seasonal shift in the effect of defoliation on seed size was detected.

Conclusions/Significance

The results show that leaf damage may reduce the fitness of A. thaliana, and suggest that in this population leaf herbivores feeding on plants before flowering should exert stronger selection on defence traits than those feeding on plants during flowering, given similar damage levels.     

"Florigen ": an intriguing concept of plant biology.

"Florigen" is the name that Mikhail Chailakhyan coined in 1937 for the putative hormone regulating flowering. At this concept, plant physiologists arrived following early research concerning the effects of temperature and day length on the transition from vegetative to reproductive stages of plants. The existence of florigen was postulated on the experimental backgrounds involving i) the response of plants to inductive conditions; ii) transmission of a flowering stimulus by grafting; iii) extraction of this stimulus from induced plants. This experimental results showed the existence of florigen at least as concept because they always failed to offer the experimental evidence of its chemical existence. The myth of florigen persisted as long as the end of the Seventies, when physiologists began to consider flowering as a complex process in which various classes of hormones might variously interplay.     

Occurrence of the plant growth regulator jasmonic acid in plants

The natural occurrence of jasmonic acid and its methyl ester in plants has been studied using different methods such as GC, GC-MS, HPLC, radioimmunoassay, and bioassay. Jasmonic acid was detected in several Leguminosae plants and a number of species belonging to nine other Angiospermae families. Highest amounts occurred in fruit parts, especially the immature pericarp, but it was found also in flowers and vegetative plant parts, e.g. leaves, stems, and germs. Young apple fruits contain both jasmonic acid and methyl jasmonate, and in Douglas fir, the only Gymnospermae species studied, only the methyl ester could be detected. Jasmonic acid is discussed as an endogenous plant growth regulator widely distributed in higher plants.     

观赏植物花期调控途径及其分子机制

开花期控制对观赏植物的生产和应用具有重要意义。目前关于高等植物成花机理的研究已经取得了突破性进展,为观赏植物花期调控开辟了新途径。该文总结了观赏植物花期调控的途径和方法,并对改良观赏植物花期的技术思路做了初步分析。通过与高等植物成花机制研究的对比分析发现,观赏植物开花机理的研究已有了长足发展,一些观赏植物的转基因研究也取得了丰硕成果。利用分子设计育种途径改良观赏植物的开花期,突破了传统方法的局限性,其研究和应用前景非常广阔。     

Role of VIN3-LIKE 2 in facultative photoperiodic flowering response in Arabidopsis

In Arabidopsis, expression of FLC and FLC-related genes (collectively called FLC clade) contributes to flowering time in response to environmental changes, such as day length and temperature, by acting as floral repressors. VIN3 is required for vernalization-mediated FLC repression and a VIN3 related protein, VIN3-LIKE 1/VERNALIZATION 5 (VIL1/VRN5), acts to regulate FLC and FLM in response to vernalization.^1–3 VIN3 also exists as a small family of PHD finger proteins in Arabidopsis, including VIL1/VRN5, VIL2/VEL1, VIL3/VEL2 and VIL4/VEL3. We showed that the PHD finger protein, VIL2, is required for proper repression of MAF5, an FLC clade member, to accelerate flowering under non-inductive photoperiods. VIL2 acts together with POLYCOMB REPRESSIVE COMPLEX 2 (PRC2) to repress MAF5 in a photoperiod dependent manner.Key words: photoperiod, chromatin, floweringThe decision to flower is critical to the survival of flowering plants. Thus, plants sense environmental cues to initiate floral transition at a time that both ensures and optimizes their own reproductive fitness. Using a model plant, Arabidopsis thaliana, genetic studies have shown that the regulation of floral transition mainly consists of four genetic pathways: the inductive photoperiod pathway, the autonomous pathway, the vernalization pathway and the gibberellin pathway.⁴ In Arabidopsis, these four flowering pathways eventually merge into a group of genes called floral integrators, including FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and LEAFY (LFY). Based on the response to specific photoperiod conditions, the flowering behaviors of plants can be classified into three groups: long day (LD), short day (SD) and day neutral response.^5,6 Depending on the requirement of day length, plants show either obligate or facultative responses. For example, henbane, carnation and ryegrass are obligate long day (LD) flowering plants which flower under increasing inductive photoperiod but do not flower at all under non-inductive photoperiod.⁵ On the other hand, plants including Arabidopsis, wheat, lettuce and barley, are considered to be facultative flowering plants. Thus, these plants exhibit early flowering under LD and late-flowering under non-inductive short days (SD). Studies on photoperiodic flowering time mainly focus on the inductive LD-photoperiod pathway in Arabidopsis.     

Hormonal regulation of reproductive development in higher plants

The present paper deals with the hormonal regulation of reproductive development,i.e. flowering and sex manifestation. Representation of hormonal regulation of flowering is based on the concept of florigen as a two-component, complementary system of flowering hormones, which consists of gibberellins and anthesins. Data are presented on the effect of extracts of gibberellin- and anthesin-type substances from the leaves of flowering and vegetatively growing plants under non-inductive conditions of day length. Experiments with flowering of plants under the influence of graftings serve as a basis for considering the question about the common nature of one of the florigen components — anthesins, for various plant species. The mechanism controlling tuberization in both intact and grafted plants is based on the participation of all the components of the hormonal system and constitutes one of the most vivid manifestations of integration of all the organs in the whole organism.     

Inhibitory Effect of Brassinosteroids on the Flowering of the Short-Day Plant Pharbitis nil

The effect of exogenous brassinosteroids (BR) on the flowering induction of Pharbitis nil was examined. Generally plants treated with brassinolide and castasterone form less number of flowers than control plants, but degree of flowering inhibition was depended on the concentration and the method of BR application as well as the length of the inductive dark period. In plants regenerated from sub-induced apices treated with brassinolide at concentration of 1 and 10 M the flower formation was inhibited completely.     

Sixty-Five Years of Searching for the Signals That Trigger Flowering

This review summarizes the long-term research of photoperiodic flower induction in two Chenopodium species, one of which, C. rubrum, is a short-day plant, while the other, C. murale, is a long-day plant. In the course of purification of florigenic extracts inducing flowering in C. rubrum plants kept under noninductive photoperiodic conditions, we did not succeed in identifying its active component(s). During the inductive treatment, the phloem transport of cytokinins was enhanced and their content in the shoot apex greatly increased for some time. The review also summarizes the results of the application of direct electric current to the leaves of C. rubrum plants. This treatment interferes with the transport of some active signal(s) from leaves to the apex, resulting in the inhibition of flowering induction. The problem of the rhythmicity of flowering in C. rubrum plants was considered, particularly, the possibility of melatonin (N-acetyl-5-methoxytryptamin) participation in photoperiodic induction. Melatonin accumulation in darkness appears to determine the amplitude of the flowering rhythm but not its phase or period.