Annals of Botany 2009 104(2):i; doi:10.1093/aob/mcp180
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ContentSnapshots
Mannanases as transglycosylases in the plant cell wall (Botanical Briefing)
Transglycosylases
remodel the plant cell wall during periods of growth or senescence
by cutting a polysaccharide and attaching the newly created
end to another polysaccharide.
Schröder et al. (pp. 197–204) re-interpret the role of the hydrolytic enzyme endo-β-mannanase
as a transglycosylase by analogy to the role of xyloglucan endotransglucosylase/hydrolase,
the only other known transglycosylase in the cell wall.
Nectar and pollination drops (Invited Review)
Pollination drops
of gymnosperms and nectar (mainly of angiosperms) are secretions
related to plant reproduction. Although having very different
functions they share strong similarities, although with significant
differences.
Nepi et al. (pp. 205–219) review these similarities
and differences in the light of recent advances in the molecular
biology and proteomics of these two secretions, emphasizing
their biochemical and physiological complexity.
Floral elaiophores in the orchids
Floral elaiophores,
secreting oil as a food-reward to pollinators, are widespread
amongst orchids. In the
Bifrenaria clade (Maxillariinae
sensu lato),
Davies and Stpiczy
ska (pp. 221–234) show that elaiophores
of
Rudolfiella and Oncidiinae have similar anatomical organization,
but the plastids that they contain are very different:
Rudolfiella plastids resemble those in resin-secreting cells of
Rhetinantha (Maxillariinae
sensu stricto). Along with presence of palisade
secretory cells, the observations have phylogenetic implications
and support convergent evolution in response to pollinator pressures.
Disorganized distribution of homogalacturonan after Al stress
The inhibition of
root elongation is the primary symptom of Al toxicity; however,
the underlying basis of the process is unclear. Considering
the multiple physiological and biochemical functions of pectin
in plants,
Li et al. (pp. 235–241) demonstrate that Al
stress results in the disorganized distribution of homogalacturonan
epitopes, which correlates well with Al-induced root growth
inhibition in
Zea mays.
Heterochrony of the floret meristem in wheat
In wheat, the number
of fertile florets per spikelet is associated with ploidy level:
1–2 florets in diploids, 2–3 in tetraploids, and
>3 in hexaploids.
Shitsukawa et al. (pp. 243–251) demonstrate
that the difference in the number of floret primordia in diploid,
tetraploid and hexaploid wheats is caused by the heterochronic
initiation of floret meristem development from the spikelet
meristem.
Fruit and seed evolution in Diervilla and Lonicera clades
Jacobs et al. (pp. 253–276) examine fruit and seed anatomy and morphology in 52 Dipsacalean
taxa in combination with molecular data. Their phylogenetic
analysis supports a close affinity between
Lonicera plus
Leycesteria and
Symphoricarpos plus
Triosteum. The results further provide
support for a sister relationship of
Heptacodium and the Linnina
clade as opposed to
Heptacodium and the
Lonicera clade.
Ethylene-insensitive Lotus japonicus transgenics
Transgenic
Lotus japonicus, expressing the dominant insensitivity allele of the
Arabidopsis ethylene receptor gene
ETR1, are characterized by
Lohar et al. (pp. 277–285). They find that nodule number
is significantly increased due to higher infection success and
an expanded radial zone of successful nodule initiation. Nodulation
sensitivity to nitrate remains unaltered but lateral root numbers
decrease, while bacteroid numbers/symbiosomes increase, suggesting
early and late symbiosis effects of ethylene. (
Featured article in ContentSelect on p. iii.)
Climate change and germination in the sub-arctic
Milbau et al. (pp. 287–296) show that seed germination in sub-arctic species will not only
be affected by increasing summer temperatures, but also by colder
soil temperatures during winter, which are the result of a reduced
snow cover. The effects are mainly seen as changes in the timing
of germination, whereas final germination percentages are less
influenced. (
Featured article in ContentSelect on p. iii.)
Wood density and shade-tolerance in tropical trees
Nock et al. (pp. 297–306) show that wood density reflects differences in shade-tolerance
in six tropical tree species, and that radial gradients are
common. The findings suggest that a ‘whole-tree’
view of life history and biomechanics is important for understanding
patterns and consequences of radial variation in wood density.
Furthermore, the accuracy of estimates of stem biomass and carbon
is improved by taking density variations into account.
Photosynthetic response to feeding in Nepenthes
Carnivorous plants
of the genus
Nepenthes grow in nutrient-poor, wet and sunny
habitats and have evolved specialized traps – the pitchers.
Pavlovi
et al. (pp. 307–314) report that
Nepenthes enhances
its rate of photosynthesis as a result of increased nutrient
acquisition from prey. So carnivory can provide a competitive
advantage over non-carnivorous plants in nutrient-poor habitats.
Enhancing artemisinin in Artemisia annua through N supply
Growth and maximization
of artemisinin concentration in
A. annua are manipulated by
Davies et al. (pp. 315–323) by changing nutrient application.
They find that nitrogen application rate has an optimum for
maximal growth, while higher rates have no further effect but
reduce artemisinin concentration. Maximization of artemisinin
yield (amount per plant) requires optimization of leaf biomass
through nitrogen supply. (
Featured article in ContentSelect on p. iv.)
Pollen source, kernel structures and embryo compounds in maize
Pollen source affects
the kernel oil concentration in maize through modifications
of both the embryo/kernel ratio and the embryo oil concentration.
Tanaka et al. (pp. 325–334) analyse the effects of pollen
source on growth of kernel structures, embryo chemical allocation,
and on histology of the embryos. The effects on both the embryo/kernel
ratio and embryo chemical allocation seem to be related to the
early-established sink strengths of the embryo, i.e. sink size
and sink activity.
AMF affects clonal integration in white clover
Du et al. (pp. 335–343) provide the first experimental evidence that arbuscular mycorrhizal
fungi (AMF) can modify the effects of clonal integration on
the plasticity and performance of the clonal species
Trifolium repens (white clover) in heterogeneous environments. In particular,
AMF may partly replace the effects and benefits of clonal integration
in low-nutrient habitats, possibly more so where fungal species-richness
is high.
Application of Mo enhances cold resistance in wheat
Sun et al. (pp. 345–356) demonstrate that molybdenum regulates the expression of
COR genes in ABA-dependent and ABA-independent pathways in winter
wheat under low temperatures. Comparison of Mo-efficient and
Mo-inefficient winter wheat cultivars suggests that Mo might
regulate the ABA-dependent pathway of
COR gene expression under
low-temperature stress. Notably, the response of the ABA-dependent
pathway to Mo is prior to that of the ABA-independent pathway.
(
Featured article in ContentSelect on p. iv.)
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