Annals of Botany 2009 103(7):i; doi:10.1093/aob/mcp085
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ContentSnapshots
Evolution of land plants (Botanical Briefing)
True land plants
(embryophytes) evolved only once.
Becker and Marin (pp. 999–1004) describe recent progress in our understanding of the early evolution
of embryophytes from streptophyte algae. They present a hypothetical
reconstruction of evolutionary events that led to the origin
of the first land plants, and shaped the current diversity and
ecology of streptophytes.
Host-specific races and speciation in Orobanche
Host specificity
in the parasitic plant
Orobanche minor is quantified by
Thorogood et al. (pp. 1005–1014) using cross-infection experiments. The data provide evidence
that genetic races of
O. minor are physiologically adapted to
particular hosts. Host specificity may isolate races of
Orobanche on different hosts, accelerating genetic divergence and ultimately
speciation in the genus, and it is proposed that this mode of
speciation may be a widespread phenomenon in parasitic plants.
(
Featured article in ContentSelect on p. iii.)
Use of sediment CO2 by submerged rooted plants
The small, submerged
rosette plants called isoetids take up CO
2 from sediment for
photosynthesis.
Winkel and Borum (pp. 1015–1023) show
that sediment CO
2 can support photosynthesis of other submerged
rooted plants if they have a high root-to-shoot area ratio and
high tissue porosity. (
Featured article in ContentSelect on p. iii.)
Diel changes in structural biomass and N and C reserves
Dry biomass includes
the weights of a plant's structural and non-structural compounds,
mostly carbohydrates, carboxylates, amino acids and minerals.
Huanosto Magaña et al. (pp. 1025–1037) describe
diel growth in tomato plantlets in terms of total and structural
dry weight changes, highlighting large discrepancies in response
to light and N nutrition. They emphasize the role played by
C and N reserves in the uncoupling of resource use for growth
from resource acquisition.
Introgressive hybridization between Brassica and Isatis
Interspecific hybridization
and introgression are of wide occurrence in plant speciation.
In intertribal crosses between
Brassica rapa and
Isatis indigotica made by
Tu et al. (pp. 1039–1048), the hybrids show variations
in morphology, chromosomal/genomic components and produce novel
B. rapa types with altered genomic constitution or alien additions,
suggesting that complete or partial chromosome elimination and
diploidization with genomic rearrangements occur.
Origin of woodiness within a basically herbaceous group
The sister tribes
of Spermacoceae and Knoxieae in the Rubiaceae are essentially
herbaceous. Using microscopic wood anatomical observations in
combination with an independent molecular phylogeny,
Lens et al. (pp. 1049–1064) find that all the woody Spermacoceae species observed are derived
from herbaceous ancestors, while in Knoxieae there is a general
trend from (primary) woodiness towards herbaceousness and back
to (secondary) woodiness.
Pollination in Mediterranean Cytinus
Cytinus hypocistis is a rootless, stemless and leafless holoparasitic plant whose
flowers are only visible during the reproductive period when
they arise from the host.
de Vega et al. (pp. 1065–1075) conduct the first study of the pollination biology of this holoparasite,
combining long-term field observations together with experimental
pollination treatments, which reveal that ant mutualistic services
are essential for the pollination of this Mediterranean biological
oddity. (
Featured article in ContentSelect on p. iv.)
Partial self-incompatibility in Flourensia cernua
The strength of
self-incompatibility varies in
F. cernua, a species showing
pollen limitation.
Ferrer et al. (pp. 1077–1089) find
that poor availability of compatible mates may limit seed set
in the species, and that self-fertility allows reproductive
compensation in plants exhibiting either a partial or complete
breakdown of self-incompatibility. Partial self-incompatibility
may be favourable in this colonizing species, even though it
maintains low levels of inbreeding. (
Featured article in ContentSelect on p. iv.)
Environmental regulation of dormancy loss in Lomatium
At dispersal,
Lomatium dissectum seeds have under-developed embryos.
Scholten et al. (pp. 1091–1101) find that these seeds have a deep, complex morphophysiological
dormancy. Dormancy break and germination occur at low temperatures,
but seeds from moist habitats have longer cold-stratification
requirements than those from semi-arid environments. Interruption
of cold stratification by dehydration results in loss of seed
viability, or induced secondary dormancy.
A crop emergence model for Medicago
Using the framework
of a crop-emergence model,
Brunel et al. (pp. 1103–1117) find genetic diversity during germination and pre-emergence
growth in the model legume
Medicago truncatula. A set of ecophysiological
references is provided for
M. truncatula users and the authors
suggest such integrative characterizations are made before genetic
or genomic analyses.
Visibility vs. biomass in flowers
In a taxonomically
diverse array of insect-pollinated Mediterranean plants,
Herrera (pp. 1119–1127) examines within- and among-species variations in floral quantitative
traits. Although isometric from the standpoint of corolla allocation,
species with large, conspicuous flowers pay higher biomass costs
per millimetre of display. Linear size is in general more steady
than biomass. Any of the studied characteristics can vary significantly
among populations.
Population dynamics along a primary succession gradient
The demography
of pioneer-, early- and late-successional species and one ubiquitous
species is studied by
Marcante et al. (pp. 1129–1143) along a central alpine glacier foreland. Matrix modelling is
used to classify species demography. All species over all successional
stages behave like climax species in secondary successions.
The overall dominance of survival indicates a major difference
between primary and secondary succession.
Xylem anatomy and radial transport in Cryptomeria
The rays are generally
considered as the main structure that serves radial transport
in xylem.
Kitin et al. (pp. 1145–1157) demonstrate that
radial apoplastic transport can occur via a tracheid network
(radial grain and tangential-wall pitting of tracheids) in a
distinct pathway from that of the rays. They also show that
intercellular spaces of rays form continuous canals across xylem
rings.
Thermoregulation in lotus flowers (Short Communication)
Thermoregulation
in the flower of the Asian sacred lotus,
Nelumbo nucifera, has
been hypothesized to offer a direct energy reward for pollinators.
Using an artificial refrigeration instrument,
Li and Huang (pp. 1159–1163) find that low floral temperature during the fertilization period
significantly decreases seed production. Field pollination treatments
confirm that a stable temperature is important in post-pollination
events in lotus.
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Ann Bot 2009 103: iii.
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