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.
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.
Wheat is the most important food crop in the temperate world, being used to produce bread, pasta, noodles and a range of other baked goods and foods. The ability to produce this wide range of products is largely determined by the grain storage proteins (prolamins), which form a viscoelastic network, called gluten, in dough formed from wheat flour. The classification into gliadins and glutenins has proved to be remarkably durable, but does not reflect the true molecular and evolutionary relationships of the proteins.
The ω-gliadin storage proteins of wheat are of interest in relation to their impact on grain processing properties and their role in food allergy, particularly the ω-5 sub-group and wheat-dependent exercise-induced anaphylaxis. The ω-gliadins are also known to be responsive to nitrogen application. A recent study published in Annals of Botany compares the effects of cultivar and nitrogen availability on the synthesis and deposition of ω-gliadins in wheat grown under field conditions in the UK, including temporal and spatial analyses at the protein and transcript levels.
The results show that wheat ω-gliadins vary in amount and composition between cultivars, and in their response to nitrogen supply. Their spatial distribution is also affected by nitrogen supply, being most highly concentrated in the sub-aleurone cells of the starchy endosperm under higher nitrogen availability.
Wan, Y., Gritsch, C.S., Hawkesford, M.J., & Shewry, P.R. (2014) Effects of nitrogen nutrition on the synthesis and deposition of the ω-gliadins of wheat. Annals of Botany, 113(4), 607-615. doi: 10.1093/aob/mct291
A vast quantity of empirical evidence suggests that insufficient quantity or quality of pollen may lead to a reduction in fruit set, in particular for self-incompatible species. A recent study in Annals of Botany uses an integrative approach that combines field research with marker gene analysis to understand the factors affecting reproductive success in a widely distributed self-incompatible species, Prunus virginiana (Rosaceae).
The results show that even though P. virginiana is a widespread species, fragmented populations can experience significant reductions in fruit set and pollen limitation in the field. Detailed examination of one fragmented population suggests that these linitations may be explained by an increase in biparental inbreeding, correlated paternity and fine-scale genetic structure. The consistency of the field and fine-scale genetic analyses, and the consistency of the results within patches and across years, suggest that these are important processes driving pollen limitation in the fragment.
Suarez-Gonzalez, A., & Good, S.V. (2014) Pollen limitation and reduced reproductive success are associated with local genetic effects in Prunus virginiana, a widely distributed self-incompatible shrub. Annals of Botany, 113 (4): 595-605. doi: 10.1093/aob/mct289.
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.
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.
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.
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.
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.
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.