Does breeding system affect pollen morphology? A case study in Zygophylloideae (Zygophyllaceae).

KEY MESSAGE: We found a correlation between large pollens and selfing and between psilate pollen walls and cleistogamy. Flowering plants display extraordinary diversity in pollen morphology, yet the functional significance of this variation is not well understood. Zygophylloideae is a lineage characterized by high diversity of breeding systems, ranging from obligate selfing to facultative selfing and further to facultative outcrossing. This group is particularly suitable for testing hypotheses about the influence of breeding system on pollen morphology. We studied pollen morphology in 20 species of Zygophylloideae and one species of Tribuloideae as an outgroup. A phylogeny of Zygophylloideae was created based on available DNA sequences and used to trace the evolution of pollen characters. We performed a phylogenetic analysis of correlated evolution between breeding system and several pollen characters. Three types of pollen morphology were found in the studied species. Tricolporate pollen with a small apocolpium, microreticulate ornamentation and medium size was determined as the ancestral state in Zygophylloideae. The correlation analysis indicated an association between large pollens and selfing and between psilate pollen wall and cleistogamy. We hypothesize that large size of pollen in selfing species is mainly associated with the low number of produced pollen indicating a trade-off between pollen size and number. The independence from pollen vector in cleistogamous flowers accounts for the evolution of smooth pollen walls in these species.

Developmental Changes in Time and Space Promote Evolutionary Diversification of Flowers: A Case Study in Dipsacoideae.

Diversification in flower shape and function is triggered by the high plasticity of flower meristems. Minute changes in space and time can profoundly affect the formation of adult structures. Dipsacoideae provides an excellent model system to investigate the evolutionary aspects of temporal and spatial changes in flower development due to its small size, the resolved phylogenetic framework, and significant diversity of perianth form and merosity. In the present study, we investigated the sequence of floral organ initiation and quantified the interactions between flower meristem expansion and petal primordium size in eight species representing two major clades of Dipsacoideae. Our quantitative study indicates the plasticity of the flower meristem for the regulation of pentamery either due to a decrease in petal primordium size (Scabiosa) or an increase in flower meristem size (Pterocephalus and Lomelosia) compared to tetramerous flowers. According to our results, temporal shifts of organ initiation during flower evolution contribute to the morphological diversity of perianth. Sepal reduction in members of the Dipknautids is paralleled by a delay in sepal initiation. The multiplication of sepals in Lomelosia and Pterocephalus is correlated with an extension of initiation time. Some heterochronies in early development do not affect adult morphology. The effects of a temporal change in early development can be enhanced, reduced, or eliminated by later changes of the growth rate during development. Our results confirm the hypothesis that the interaction between timing and space plays an important role for evolutionary diversification of flowers.

Correction: Understanding the unique flowering sequence in Dipsacus fullonum: Evidence from geometrical changes during head development.

[This corrects the article DOI: 10.1371/journal.pone.0174091.].

Understanding the unique flowering sequence in Dipsacus fullonum: Evidence from geometrical changes during head development.

The genus Dipsacus is characterized by a remarkable bidirectional flowering sequence and a rare phyllotactic pattern. Considering that flower initiation and flowering sequence may be interconnected, we document the development of the head meristem in Dipsacus fullonum. Our results indicate a gradual change in the geometry of the head meristem beginning with a dome shaped stage, continuing with a remarkable widening in the middle part of the head meristem and ending in a spindle-like form. Quantitative data confirm that meristem expansion is higher in the middle part than at the base of the meristem. Likewise, the size of the flower primordia in the middle part of the young head is significantly larger than at the base soon after initiation. We conclude that the change in the geometry of the meristem and the availability of newly generated space result in the promotion of the middle flowers and the bidirectional flowering sequence at anthesis. Our investigation on phyllotactic patterns reveals a high tendency (30%) of the head meristem to insert or lose parastichies. This finding can also be attributed to changes in the expansion rate of the meristem. Dependent on the spatio-temporal relation between meristem expansion and primordia initiation, either flower primordia are promoted or additional parastichies appear. Our results emphasize the important role of geometry in flower development and phyllotactic pattern formation.

Comparative study of inflorescence development in Oleaceae.

PREMISE OF THE STUDY: Investigations of inflorescence architecture offer insight into the evolution of an astounding array of reproductive shoot systems in the angiosperms, as well as the potential to genetically manipulate these branching patterns to improve crop yield and enhance the aesthetics of horticultural species. The diversity of inflorescences in the economically important family Oleaceae was studied from a comparative developmental point of view for the first time, based on species of seven genera (Chionanthus, Fontanesia, Fraxinus, Jasminum, Ligustrum, Olea, Syringa). METHODS: Series of developmental stages of chemically fixed inflorescences were studied with epi-illumination light microscopy. KEY RESULTS: All taxa studied have inflorescences with terminal flowers. The inflorescences are mostly panicles, but in some cases thyrsoids or compound botryoids. Phyllotaxis of the flower-subtending bracts is mostly decussate, rarely tricussate (Fraxinus) or spiral (Jasminum). Accessory flowers or accessory inflorescences, almost unknown in Oleaceae as yet, were found in two genera. In Syringa, common bract-flower primordia are formed by a delay in early bract development compared to flower development. Such a delay is also expressed by the loss of bracts in the distal part of inflorescence branches in Syringa and Chionanthus. CONCLUSIONS: Significant variation in branching pattern and phyllotaxy was observed among the studied species of Oleaceae. The suppression of bracts and formation of accessory flowers were found as special features of inflorescence ontogeny. The occurrence of accessory flowers and accessory partial inflorescences is interesting from the point of view of dense and flower-rich inflorescences in ornamental species.

Floral ontogeny in Astragalus compactus (Leguminosae: Papilionoideae: Galegeae): variable occurrence of bracteoles and variable patterns of sepal initiation.

Comparative studies of floral ontogeny represent a growing field that promise to provide new insights on floral evolution. Floral ontogenetic information has been used successfully in Leguminosae for re-examining phylogenetic relationships at different levels. Using epi-illumination light microscopy, we present original ontogenetic data in Astragalus compactus, which was chosen because of its unusual arrangement of inflorescence and variable occurrence of bracteoles on flowers. Based on our results, uncommon ontogeny of the inflorescence led to the arrangement of flowers in four different positions. Variation was observed not only in the presence of bracteoles, but also in the order of sepal initiation in flowers of the same inflorescence. Surprisingly, besides the widely stated unidirectional pattern, bidirectional, sequential and an atypical unreported order were observed. High degree of overlapping between whorls and formation of two types of common primordia also were found. The variable occurrence of bracteoles suggests that the species is in an intermediate state towards fully lacking of bracteoles. We propose that the variability of the sequence of sepal initiation is possibly a consequence of the function of mechanical forces generated by surrounding leaves. Relationships between mechanical force and auxin signalling are discussed.

Ontogenetic variation of volatiles and antioxidant activity in leaves of Astragalus compactus Lam. (Fabaceae).

The genus Astragalus is a rich source of a variety of biologically active compounds including phenols, saponins, polysaccharides and essential oils. The present study was conducted to determine ontogenetic variation of the volatile organic compounds as well as total phenolic contents and antioxidant activity in leaves of A. compactus. The leaves of plant were harvested at vegetative, flowering and fructification stages and were analyzed by gas chromatography coupled with mass spectrometry (GC-MS). Total phenolic content (TPC) was determined using the Folin-Ciocalteau reagent and the antioxidant capacity was evaluated with the 1,1-diphenyl-2-picrylhydrazyl (DPPH) test. Different classes of volatile compounds were identified including alcohols, esters, hydrocarbons, sterols and terpenoides. Significant variation of these compounds was found during phenological stages of development. Sterols and hydrocarbons were the main components of essential oils at the vegetative stage. The presence of terpenoides (phytol) and alcohols (docosanol) was significant at the flowering stage. Fructification phase was characterized by the high content of sterols and hydrocarbons and absence of phytol. The antioxidant activity and phenolic content were related to the physiological stage and the highest amount detected at fructification phase. The ontogenetic variations of phenolic contents and antioxidant properties are largely contributed by climatic factors such as temperature and solar radiation.

Ontogenetic Variation of Total Phenolics and Antioxidant Activity in Roots, Leaves and Flowers of Astragalus compactus Lam. (Fabaceae).

INTRODUCTION: The potential health risks and toxicity of synthetic antioxidants resulted in an upsurge of interest in phytochemicals as new sources of natural antioxidants. Phenolics of Astragalus L. (Fabaceae) possess antioxidant properties and have been shown to have a protective effect against several degenerative diseases. The objective of this study was to determine total phenolics and antioxidant activity of methanolic extracts from different parts of A. compactus Lam. at different phenological phases and to investigate the correlations between antioxidation and the contents of the total phenolics. METHODS: Total phenolic content (TPC) was determined using the Folin-Ciocalteau reagent and the antioxidant capacity was evaluated with the 1,1-diphenyl-2-picrylhydrazyl (DPPH) test. RESULTS: Generally, the TPC in leaves was higher than that of the roots and flowers. TPC in leaves, roots and flowers of the species varied from 5.01-8.25, 4.29-7.89 and 4.19 µg GAE/mg DW, respectively. In addition, roots and leaves at fructification stage possessed higher TPC than vegetative and flowering stages. Therefore, the leaf extracts at fructification phase showed the highest TPC that accompanied with best antioxidant activity. In the root extracts, fructification stage was also characterized by the highest antioxidant activity. CONCLUSION: A positive relationship between antioxidant activity and TPC showed that phenolics were the dominant antioxidant components in the species. The results obtained suggest that A. compactus methanolic extracts may serve as potential sources of natural phenolic antioxidants and that the fructification phase could be considered as the best stage for the harvesting of this plant.