Seed dispersal of wild radishes and its association with within-population spatial distribution.

BACKGROUND: The wild radishes, Raphanus raphanistrum and R. pugioniformis (Brassicaceae) are native to the East Mediterranean region. However, whereas R. raphanistrum is widely distributed worldwide, the endemic R. pugioniformis is limited to specific habitats. In R. raphanistrum the diaspores of the indehiscent fruits comprise glabrous, light, single-seeded segments, whereas the intact fruits of R. pugioniformis are heavy and covered with spiny backward-pointing trichomes. We aimed to investigate whether the structure of the diaspores was directly associated with long- and short-range dispersal in R. raphanistrum and R. pugioniformis, respectively. We further surveyed within-population spatial distributions, to test the hypothesis that short- and long-range dispersal contribute to a patchy vs. uniform distribution patterns of R. pugioniformis and R. raphanistrum, respectively. RESULTS: The results indicated that dispersal by wind and run-off water was substantially lower for diaspores of R. pugioniformis than for those of R. raphanistrum diaspores. Supporting the hypothesis that backward-pointing trichomes promote adherence to soil particles, the displacement on soil surface of R. pugioniformis fruits depended on their orientation relative to wind direction. Furthermore, trichome removal from fruits of R. pugioniformis significantly reduced wind velocity needed to remove fruits that were placed on soils typical of the species' natural habitats. The spatial-distribution survey results indicated a patchy distribution of R. pugioniformis populations as compared with the more uniform arrangement in the studied populations of R. raphanistrum; consistent with the unidirectional vs. homogeneous wind dispersal of the respective diaspores, with respect to wind direction. In addition, R. pugioniformis population sizes changed less between years than those of R. raphanistrum. CONCLUSIONS: Overall, our results indicate that fruit structure is strongly linked to dispersal ability and spatial distribution of the two closely related wild radish species. Whereas R. raphanistrum inhabits homogenous sandy soil habitats, the distribution range of R. pugioniformis includes heterogeneous environments in which growth niches are scarcer. We suggest that the different modes of dispersal have evolved as adaptive traits appropriate to the species' specific habitats.

In vivo analysis of the size- and time-dependent uptake of NaYF4:Yb,Er upconversion nanocrystals by pumpkin seedlings.

We have investigated the kinetics of the uptake and the translocation of nanoparticles in plants. Nearly monodisperse NaYF4:Yb,Er nanocrystals were used, either spherical particles with a diameter of 14 nm or nanorods with a length of 41 nm and a diameter of 22 nm. After watering pumpkin seedlings (Cucurbita maxima) with aqueous colloidal solutions of the particles, intact nanocrystals in the plants were detected in vivo by exciting their upconversion luminescence with a near infrared laser diode (978 nm). The particle concentration in different plant parts was determined by X-ray fluorescence spectroscopy (XRF), making use of the high sensitivity of Yttrium in XRF measurements and its low natural abundance in plants. The results show a fast uptake and translocation of the nanoparticles in all plant organs within three hours. The smaller particles move in the plants faster than the larger ones.

Molecular signals for late Tertiary/early Quaternary range splits of an Eurasian steppe plant: Clausia aprica (Brassicaceae).

Several vegetation belts stretch continuously from Europe to Asia, taiga and steppe being most prominent. Numerous plant species within these belts share a conspicuous distribution area, which is longitudinally contracted or disrupted approximately along longitude 70 degrees E. To date no hypothesis for this intriguing distribution pattern has been put forward. We detected molecular footprints in the contemporary genetic composition in nuclear DNA (ITS1, ITS2) and chloroplast DNA (trnL-trnF spacer region) of the steppe element Clausia aprica (Brassicaceae) providing evidence for a severe longitudinal range split and genetic differentiation east of the Ural Mountains about 1 million years ago caused by Quaternary climatic oscillations. Clausia aprica provides the first phylogeographical analysis on the intraspecific evolution of an Eurasian steppe plant.

Chloroplast DNA phylogeny and biogeography of Lepidium (Brassicaceae).

Two intergenic spacers, trnT-trnL and trnL-trnF, and the trnL intron of cpDNA were sequenced to study phylogenetic relationships and biogeography of 73 Lepidium taxa. Insertions/deletions of ≥3 bp (base pairs) provided reliable phylogenetic information whereas indels ≤2 bp, probably originating from slipped-strand mispairing, are prone to parallelism in the context of our phylogenetic framework. For the first time, an hypothesis of the genus Lepidium is proposed based on molecular phylogeny, in contrast to previous classification schemes into sections and greges (the latter category represents groups of related species within a given geographic region), which are based mainly on fruit characters. Only a few of the taxa as delimited in the traditional systems represent monophyletic lineages. The proposed phylogeny would suggest three main lineages, corresponding to (1) sections Lepia and Cardaria, (2) grex Monoplocoidea from Australia, and (3) remaining taxa, representing the bulk of Lepidium species with more or less resolved sublineages that sometimes represent geographical correspondence. The fossil data, easily dispersible mucilaginous seeds, widespread autogamous breeding systems, and low levels of sequence divergence between species from different continents or islands suggest a rapid radiation of Lepidium by long-distance dispersal in the Pliocene/Pleistocene. As a consequence of climatic changes in this geological epoch, arid/semiarid areas were established, providing favorable conditions for the radiation of Lepidium by which the genus attained its worldwide distribution.

Evolutionary Changes in Floral Structure within Lepidium L. (Brassicaceae).

The basic floral ground plan is remarkably constant across Brassicaceae. However, within Lepidium (ca. 175 species), deviations from this ground plan are common, with over half of Lepidium species having only two stamens rather than the usual six and a further eighth of the species having only four stamens. Furthermore, petals are reduced in size in a majority of Lepidium species. In order to determine the frequency and direction of changes in floral structure within Lepidium, we have inferred the phylogeny within the genus from sequences of the internal transcribed spacers of the nuclear ribosomal DNA. On the basis of this inferred phylogeny, we conclude that floral structure within Lepidium is relatively fluid. In order to account for the phylogenetic distributions of the different floral ground plans, at least two independent reductions to the two-stamen condition and at least one reversal to flowers with increased organ numbers are likely to have occurred. To account for the frequency of morphological evolution observed within the genus, we propose that some clades within Lepidium may be predisposed to changes in floral structure. In addition, several transoceanic dispersals are needed to explain the geographic distributions of the clades inferred from the phylogeny.

Phylogenetic relationships of Thlaspi s.l. (subtribe Thlaspidinae, Lepidieae) and allied genera based on chloroplast DNA restriction-site variation.

Chloroplast DNA restriction-site variation was analyzed in 30 accessions representing 20 species from the major lineages in Thlaspi s.l. (previously described as genera by Meyer 1973, 1979) and allied genera from the subtribe Thlaspidinae (Peltaria, Teesdalia, Cochlearia, Ionopsidium, Aethionema). A total of 161 variable restriction sites were detected. Phylogenetic analyses indicated a division of Thlaspi s.l. into three groups consistent with Meyer's genera Thlaspi s. str., Microthlaspi and Noccaea/Raparia. The genus Thlaspi s.l. as currently described proved to be paraphyletic because one of its major lineages, i.e. Thlaspi s. str., appeared to be more closely related to other genera (Peltaria, Teesdalia) than to the remaining lineages of Thlaspi s.l., i.e. Noccaea/Raparia and Microthlaspi. Sequence divergence values (100 x p) between the Thlaspi s.l. lineages were similar to values between these groups and related genera (Teesdalia, Peltaria), respectively. Chloroplast DNA variation was also used to assess subtribal classification of the genera studied. The cpDNA data were inconsistent with the controversial taxonomic classifications based on morphology. The molecular data would suggest that (1) the subtribe Thlaspidinae, as traditionally described, is not monophyletic; (2) the Thlaspidinae should be reduced to a group consisting of Thlaspi s. str., Peltaria, Teesdalia, Microthlaspi, Noccaea/Raparia, and that Aethionema should be excluded from the Thlaspidinae; and (3) Cochlearia and Ionopsidium represent the subtribe Cochleariinae.