All posts by Alex

About Alex

Alex is the editorial assistant at Annals of Botany

Pollination by sexual deception in Pterostylis

Pollination by sexual deception in Pterostylis

Pollination by sexual deception in Pterostylis

Pterostylis is an Australasian terrestrial orchid genus of more than 400 species, most of which use a motile, touch-sensitive labellum to trap dipteran pollinators. The mode of attraction, however, is uncertain. Phillips et al. find that a single species of male gnat (Mycetophilidae) visits and pollinates the rewardless flowers of P. sanguinea, and that the gnats often show probing copulatory behaviour on the labellum, leading to its triggering and the temporary entrapment of the gnat in the flower. Pollen deposition and removal occurs as the gnat escapes from the flower via the reproductive structures. The labellum is the sole source of the chemical attractant involved. It is predicted that sexual deception will be widespread in the genus, although the diversity of floral forms suggests that other mechanisms may also operate.

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Hydraulic integration in tree root vessels

Hydraulic integration in tree root vessels

Hydraulic integration in tree root vessels

Plants can adapt to their environment by varying the hydraulic integration of their xylem network. While much is known about xylem organization in aerial parts, roots have been less well studied. Johnson et al. measure xylem embolism resistance and connectivity in roots of two co-occurring tree species in a semi-arid habitat, Quercus fusiformis and Sideroxylon lanuginosum.They find that Quercus vessels are primarily solitary, while Sideroxylon xylem is highly connected, leading to resistant and vulnerable xylem networks, respectively. Pit membrane thickness plays less of a role in embolism resistance than expected, suggesting that xylem organization is an important trait that has yet to be fully explored.

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Biomechanical responses of hemlock to herbivory

Biomechanical responses of hemlock to herbivory

Biomechanical responses of hemlock to herbivory

Exotic invasive herbivores can overwhelm poorly defended native hosts, and result in reduced growth and survival. Severe damage may also alter the biomechanics of the attacked plant. Soltis et al. study the impact of feeding by hemlock woolly adelgid, Adelges tsugae, on the biomechanics of eastern hemlock trees, Tsuga canadensis, and find evidence of weakness and brittleness in attacked twigs and needles. Changes in resource allocation may contribute to these mechanical effects, and can increase plant susceptibility to subsequent mechanical stresses, such as wind or snow load. The interaction between herbivory and physical environmental stresses is probably accelerating the decline of eastern hemlock in North America.

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Density × species evenness effects on coexistence and growth

Density × species evenness effects on coexistence and growth

Density × species evenness effects on coexistence and growth

There is considerable evidence for the presence of positive species diversity–productivity relationships in plant populations, but the parameters determining the type and strength of the relationship are poorly defined. Collet et al. study a tree plantation that mixes beech (Fagus sylvatica) and sycamore (Acer pseudoplatanus) according to a double gradient of density and species’ proportion, and find that density and tree size are the primary factors determining individual growth and stand productivity. Mixtures of these two functionally similar species have highest production at maximum evenness, indicating a complementary effect between them. The presence of a mixture combines both stabilizing mechanisms (individuals from both species show higher growth when surrounded by individuals from the other species) and equalizing mechanisms (the two species have very similar growth curves) that, in turn, determine the species’ relative dominance.

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Intracellular ice and cell survival in seeds of Acer

Intracellular ice and cell survival in seeds of Acer

Intracellular ice and cell survival in seeds of Acer

Efforts to cryopreserve germplasm of recalcitrant-seeded species are hampered by potentially lethal intracellular freezing events. Wesley-Smith et al. study embryonic axes of silver maple, Acer saccharinum, subjected to various drying, cooling and warming treatments and find that intracellular ice formation is not necessarily lethal. In fully hydrated axes cooled at an intermediate rate, the interiors of many organelles are apparently ice-free and this may prevent the disruption of vital intracellular machinery. The findings challenge the accepted paradigm that intracellular ice formation is always lethal, as the results show that cells can survive intracellular ice if crystals are small and localized in the cytoplasm.

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Cold hardiness of Brachypodium distachyon accessions

Cold hardiness of Brachypodium distachyon accessions

Cold hardiness of Brachypodium distachyon accessions

Brachypodium distachyon is considered a powerful model system to study the response of temperate cereals to adverse environmental conditions. Colton-Gagnon et al.  examine cold acclimation and freezing tolerance in seven diploid accessions, and find that cold treatment accelerates the transition from the vegetative to the reproductive phase in all of them. This is associated with the gradual accumulation of BradiVRN1 transcripts, and the accessions exhibit a clear cold acclimation response by progressively accumulating proline, sugars and COR gene transcripts. However, whole-plant freezing tests show that the accessions only have a limited capacity to develop freezing tolerance when compared to winter varieties of temperate cereals such as wheat and barley. Furthermore, little difference in terms of survival is observed among the accessions tested despite their previous classification as either spring or winter genotypes.

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Growth and cellular patterns in petal epidermis of Antirrhinum

Growth and cellular patterns in petal epidermis of Antirrhinum

Growth and cellular patterns in petal epidermis of Antirrhinum

Analysis of cellular patterns in plant organs provides information about the orientation of cell divisions and predominant growth directions. Raczyńska-Szajgin and Nakielski study patterns in the epidermis of asymmetrical wild-type dorsal petals and symmetrical dorsalized petals of the backpetals mutant of Antirrhinum majus (snapdragon) to determine how growth in initially symmetrical petal primordia leads to the development of mature petals differing in their symmetry. They find that during primordia development a characteristic fountain-like cellular pattern is maintained with only slight modifications, and petal cells divide in non-random directions. These features of the cellular pattern are presumably related to principal directions of growth. Two scenarios are considered to explain how gradual modifications in these directions may contribute to the transition from a symmetric to an asymmetric cellular pattern in the wild type petal.

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Water deficit effects on structure of proleptic and epicormic shoots

Water deficit effects on structure of proleptic and epicormic shoots

Water deficit effects on structure of proleptic and epicormic shoots

Shoot characteristics differ depending on the meristem tissue that they originate from and the environmental conditions during their development. Negrón et al. observe and model the effects of plant water status on axillary meristem fate and flowering patterns along proleptic and epicormic shoots of almond trees, Prunus dulcis. They find that the two shoot types differ in their patterns of axillary meristem fates along the shoot, and in their axillary meristem fate responses to water stress. The structure of proleptic shoots is more sensitive to water stress than epicormic shoots and reflects differences in their ontogenetic status as well as growth rate patterns during the season.

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Outcrossing rate of clonal Comarum palustre

Clonal spread influences genetic structure and diversity in plant populations as well as their realized outcrossing rate. Using microsatellite markers, Somme et al. investigate genetic diversity and the effect of clone distribution, structure and size on the mating of bee-pollinated marsh cinquefoil, Comarum palustre (Rosaceae), which is a rare, self-compatible species that grows in endangered European wetlands.

Comarum palustre

Boloria aquilonaris on Comarum palustre. Photo: Frank Vassen / Flickr.

They find that clones are spatially clumped, with intermediate to no intermingling of the ramets, and large clones show lower outcrossing rates than small clones. Pollen dispersal mainly occurs within patches with very few pollination events occurring between patches of more than 25 m separation.These factors need to be taken into account in management strategies for ensuring population persistence.

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Heterodichogamy and thrips-pollination in Platycarya strobilacea

Heterodichogamy and thrips-pollination in Platycarya strobilacea

Heterodichogamy and thrips-pollination in Platycarya strobilacea

Heterodichogamy, a dimorphism in which two morphs coexist in a population and undergo synchronous reciprocal sex changes, is an extremely rare and poorly understood sexual system. Fukuhara and Tokumaru study Platycarya strobilacea (Juglandaceae) and demonstrate that it is heterodichogamous based on observations of inflorescence architecture, sexual expression and pollination biology. Pollination by thrips is suggested by their frequent presence with attached pollen grains, the scarcity of other insect visitors, the synchronicity of thrips number in male spikes with the maturation of female flowers, and the morphological characters shared with previously reported thrips-pollinated plants.

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