Annals of Botany 2008 102(2):iii; doi:10.1093/aob/mcn122
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Tranglutaminases are widespread cross-linking enzymes (Botanical Briefing)
Transglutaminases
post-translationally cross-link with polyamines or lysine.
Serafini-Fracassini and Del Duca (pp. 145–152) describe transglutaminase activity in algae and in organs and
sub-cellular compartments of angiosperms. Transglutaminases
are considered as modifiers of protein substrates in the cytoskeleton
and photosystems, and to be involved in cell wall organization,
fertilization, stress responses, senescence and programmed cell
death.
Architectural contexts for the emergence of zygomorphy in Asteridae
Correlations between
symmetry and other floral traits were examined in 163 taxa using
a phylogenetic comparative method (
Jabbour et al., pp. 153–165). They reveal the morphological contexts in which zygomorphy can
or cannot evolve. Polyandry in an actinomorphic background appears
as an alternative evolutionary pathway to zygomorphy in the
Asteridae.
Tofieldia glutinosa and the reproductive features of early monocots
The defining vegetative
features of monocots are well documented, but less is known
about the reproductive characteristics of the first monocotyledonous
plants.
Holloway and Friedman (pp. 167–182) examine the
embryology of
Tofieldia glutinosa, an early divergent monocot,
and reconstruct critical aspects of early monocot evolution.
Structuring of genetic diversity in Narcissus longispathus
Despite a restricted
range and fragmented distribution due to extreme specialization,
Medrano and Herrera (pp. 183–194) find that this endemic
Mediterranean daffodil retains high genetic diversity and extensive
diversification. The authors propose that dense population sampling
and consideration of different geographical scales are needed
to understand the genetic structure of habitat specialists restricted
to ecological islands.
Historical episodes, mountain ridges and genetic structure of Faxinus mandshurica
Using microsatellites,
Hu et al. (pp. 195–205) investigate genetic diversity
and spatial structure in endangered
F. mandshurica across north-east
China. They report a significant negative correlation between
intra-population genetic diversity and latitude, but also a
lack of modern genetic structure. Two recently challenged paradigms
of population genetics are discussed.
Coffee galactomannans
Coffee grains accumulate
large quantities of cell wall galactomannans, which influence
the production and quality of the coffee beverage. Following
identification of several genes for galactomannan biosynthesis,
Pré et al. (pp. 207–220) reveal the temporal control
of two genes that are probably responsible for most of the galactomannan
produced during coffee grain maturation.
β-Glucan synthase activity under water
Plants exhibit a
variety of physiological reactions in response to submergence.
Kimpara et al. (pp. 221–226) assessed the impact of the
synthesis of β-1,3: 1,4-glucan on the accelerated elongation
response of rice coleoptiles to submergence. Their results indicate
that together with degradation, the synthesis of cell wall polysaccharides
is regulated by submergence.
Cellular differentiation in moss protonemata
Pressel et al. (pp. 227–245) provide the first comprehensive account of the ultrastructural
changes that accompany the differentiation of moss protonemal
cells. Key developmental events include rupture of the tonopast
and the generation of longitudinal arrays of endoplasmic microtubules.
Fully differentiated caulonemal cells closely resemble moss
food-conducting cells whilst their ontogeny recalls that of
sieve elements.
Recovery from defoliation by flooded plants
The interactive
effects of flooding and defoliation on two forage species (
Paspalum dilatatum and
Lotus tenuis) with contrasting growth habits are
addressed by
Striker et al. (pp. 247–254). The results
provide basic information about plant responses to a major environmental
stress and help to understand the ecology of grassland and its
management.
Role of hard-seeded dormancy in a tropical shrub
Many species show
hard-seeded (physical) dormancy. In a continental-scale seed
burial trial with the legume
Parkinsonia aculeata,
van Klinken et al. (pp. 255–264) show that physical dormancy is a mechanism for maximizing seedling
establishment rather than a bet-hedging strategy. Seed persistence
can occur in refuges where dormancy-release cues are weak and
conditions for germination/establishment are poor.
Gene expression in bitter acid biosynthesis in Humulus lupulus
Valerophenone synthase
(VPS) in lupulin glands of female inflorescence bracts is a
key enzyme for producing bitter acids – crucial flavour
components in brewing.
Castro et al. (pp. 265–273) describe
polymorphisms between genotypes in the coding sequence of
VPS and demonstrate greater gene expression in varieties with higher
bitter acid.
Environmental stress and flowering in Mediterranean coastal shrubs
Prieto et al. (pp. 275–285) describe effects of temperature and rain on autumn flowering
of
Globularia alypum and
Erica multiflora over 4 years using
experimentally generated drought and warming.
Globularia alypum is shown as more sensitive to spring and summer rains and, overall,
flowering is more affected by water availability than by temperature.
Grain quality and grain morphology
The need to produce
consistently high-quality grain has driven much of wheat breeding
in recent years.
Farrell and Kettlewell (pp. 287–293) investigate the link between grain quality and grain morphology
following temperature-shock treatments. Although temperature
influences both quality and morphology, in this case the two
are not mechanistically linked.
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