Annals of Botany 2008 102(5):NP; doi:10.1093/aob/mcn196
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How do poplar trees reorientate their stems? (Botanical Briefing)
Tension wood can
be formed in a poplar tree in order to bend its stem or branches
so that an optimal habit of the tree is maintained.
Mellerowicz et al. (pp. 659–665) present a model based on cell wall analysis data that explains
how tension in the cell walls might be generated.
Cambial activity and intra-annual xylem formation in conifers
Most recent studies
of cambial activity and xylem cell differentiation essentially
focus on the stem, with little knowledge about root growth over
a short time scale.
Thibeault-Martel et al. (pp. 667–674) compare cambial activity and intra-annual tree-ring formation
in stems and roots by analysing developing xylem tissues sampled
weekly from
Abies balsamea and
Picea mariana in a Canadian boreal
forest.
Nectar producton in the distylous species Fagopyrum esculentum
Cawoy et al. (pp. 675–684) describe the structures that secrete nectar and investigate
internal and external parameters influencing nectar volumes
and sugar concentrations in
Fagopyrum esculentum. They show
that nectar is secreted by trichomes and probably proceeds,
at least in part, from phloem sap. Nectar secretion is strongly
influenced by floral morph type, plant age, inflorescence position
and light.
Morphological and AFLP-based diversity within dog-roses
De Cock et al. (pp. 685–697) describe the morphological and AFLP-based diversity within Belgian
dog-roses (
Rosa section
Caninae). Although the hybridogenic
character of the section
Caninae is emphasized, three taxonomical
groups are distinguished:
Rubigineae,
Vestitae and
Caninae.
In addition, indications were found that current or historical
interspecific hybridization influences the genetic constitution
of a population.
Pollination biology and staminode function of Jacaranda
The pollination
biology of
Jacaranda oxyphylla is studied by
Guimarães et al. (pp. 699–711) with an emphasis on staminode function. The chemical composition
of the secretion of the glandular trichomes of the staminode,
and the physical arrangement of the staminode inside the floral
tube and its influence on reproductive success suggest that
this structure is multifunctional and is involved in morphological
and chemical interactions with pollinating bees.
Parthenocarpic fruits in Bursera morelensis
Ramos-Ordoñez et al. (pp. 713–722) describe formation of fruits and seeds of
Bursera morelensis in relation to seed predation by insects and show evidence of
the production of parthenocarpic fruit. Insects were only collected
in parthenocarpic fruit, suggesting this could be a strategy
for deceiving the parasites and reducing the probability of
seeded fruit being parasitized.
Variation of pollinators and pollen limitation in Nierembergia
Oil-secreting flowers
and oil-collecting bees are highly specialized systems.
Cosacov et al. (pp. 723–734) explore temporal and spatial variations in pollinator activity,
assemblage composition and pollen limitation in the oil-producing
Nierembergia linariifolia (Solanaceae). The great interpopulation
variations in plant–pollinator interaction and fitness
consequences suggest that this system should be viewed as a
mosaic of locally selective processes and locally specialized
interactions.
Effects of salinity and form of nitrogen supply in Nerium
Abdolzadeh et al. (pp. 735–746) grow rosebay plants under different salt treatments with ammonium
or nitrate as the nitrogen form. Changes in ion concentration
in plants, xylem sap exuded from roots and stems, and phloem
sap were determined. Nitrate-fed plants showed more salt tolerance
than ammonium-fed plants. The slower growth of ammonium-fed
plants under salinity was associated with a higher accumulation
and cycling of Na
+ and Cl
– in shoots, probably causing
harmful effects.
Rodent pollination in Colchicum in southern Africa
Kleizen et al. (pp. 747–755) investigate the reproductive biology of the genus
Colchicum in the Succulent Karoo, South Africa, recording rodent pollination
in Colchicaceae for the first time.
Colchicum scabromarginatum depends exclusively on rodents while
C. coloratum subsp.
coloratum relies on rodents, birds and autonomous selfing for seed production.
Both species display geoflorous inflorescences and have nocturnal
anthesis and nectar production.
Germination of dimorphic seeds of an inland desert halophyte
Germination of
Suaeda aralocaspica dimorphic seeds is studied by
Wang et al. (pp. 757–769).
The two seed morphs exhibited distinct differences in dormancy
and germination characteristics.
Suaeda aralocaspica is the
first cold desert halophyte for which non-deep Type 2 physiological
dormancy has been documented. A conceptual model is presented
that ties these results together and puts them into an ecological
context.
Impact of iron supply on recovery of Cd-stressed photosynthesis
In order to clarify
the importance of Cd-induced Fe deficiency in Cd effects on
photosynthesis,
Solti et al. (pp. 771–782) examine the
restoration kinetics of photosynthetic parameters of Cd-stressed
Populus glauca leaves following application of excess iron.
Correlations amongst leaf iron content and structural and functional
parameters of photosynthesis are discussed.
Ecotypic differentiation of Calopogon tuberosus
Calopogon tuberosus is a model orchid to study ecotypic differentiation.
Kauth et al. (pp. 783–793) find that seed germination among populations differs greatly
between germination media and photoperiod. Northern seedlings
allocated more biomass to corms, while corm formation was delayed
in southern populations. Selection pressures on nutrient requirements
for germination, corm formation and growing season may be causing
ecotypic differentiation within this species.
Effects of P on Al resistance in Lespedeza
Aluminium toxicity
and phosphorus deficiency often co-exist in acidic soils, and
phosphate fertilizers are often applied to acid soils to increase
crop production. However,
Sun et al. (pp. 795–804) find
that P enhances Al resistance in Al-resistant
Lespedeza bicolor but not in Al-sensitive
L. cuneata under relative higher Al
stress, although P in
L. cuneata might also possess an alleviative
potential.
Labellar micromorphology of two euglossine-pollinated orchids
Davies and Stpiczy
ska (pp. 805–824) show that comparison of labellar micromorphology, in particular
the presence of pseudopollen, supports the inclusion of
Scuticaria in Maxillariinae. Furthermore, pseudopollen indicates that
Scuticaria may not be exclusively pollinated by euglossine bees. However,
branched trichomes in
Scuticaria, a character hitherto unknown
for Maxillariinae, distinguish it from other members of this
subtribe. Conversely, a lack of distinctive labellar features
means micromorphology is of limited use in establishing the
phylogenetic relationships of
Dichaea.
White clover for northern environments
The exploitation
of white clover in northern areas is limited by a lack of cultivars
that combine persistence and high yield.
Helgadóttir et al. (pp. 825–834) cross populations of northern origin with high-yielding commercial
cultivars of more southerly origin. They demonstrate that it
is possible to simultaneously select for good winter survival
and larger leaves, and hence higher yielding ability.
No advantage of elevated CO2 for a spring ephemeral plant
The response of
Eythronium americanum, a common spring ephemeral, to CO
2 is
examined by
Gutjahr and Lapointe (pp. 835–843). No net
increase in biomass or growth rate was recorded under higher
CO
2 despite higher photosynthetic rates. Plant growth was sink-limited
and the excess carbon at higher CO
2 was lost through respiration.
Exploring linkages amongst functional traits in Nepenthes
Osunkoya et al. (pp. 845–853) show that longevity of assimilatory organs in the carnivorous
Nepenthes is significantly linked to the organ's construction
cost, lignin content and tissue density, but these effects are
non-additive. The leaf payback time, a measure of carbon economy,
is longer than that of non-carnivorous species.
Molecular-genetic classification of species
Oak species are
often difficult to delimit morphologically.
Gugerli et al. (pp. 855–863) introduce an approach to classify European white oaks (
Quercus petraea,
Q. pubescens,
Q. robur) based on nuclear microsatellites.
Multilocus genotypes revealed high group assignment probabilities
confirming morphological classification. This approach is thus
useful in resolving critical taxa, an issue relevant in forestry.
Seed germination and seedling emergence of three spring geophytes
Temperature requirements
for seed germination and seedling growth are investigated in
Hyacinthoides non-scripta,
Narcissus pseudonarcissus and
Scilla bifolia by
Vandelook and van Assche (pp. 865–875). The
under-developed embryos grow continuously from the moment of
dispersal in spring until germination in autumn or winter, whilst
the seedlings grow continuously but slowly until emergence in
spring. The different stages of development occur in response
to different temperatures.
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