Determinate growth is predominant and likely ancestral in squamate reptiles

Body growth is typically thought to be indeterminate in ectothermic vertebrates. Indeed, until recently, this growth pattern was considered to be ubiquitous in ectotherms. Our recent observations of a complete growth plate cartilage (GPC) resorption, a reliable indicator of arrested skeletal growth, in many species of lizards clearly reject the ubiquity of indeterminate growth in reptiles and raise the question about the ancestral state of the growth pattern. Using X-ray micro-computed tomography (µCT), here we examined GPCs of long bones in three basally branching clades of squamate reptiles, namely in Gekkota, Scincoidea and Lacertoidea. A complete loss of GPC, indicating skeletal growth arrest, was the predominant finding. Using a dataset of 164 species representing all major clades of lizards and the tuataras, we traced the evolution of determinate growth on the phylogenetic tree of Lepidosauria. The reconstruction of character states suggests that determinate growth is ancestral for the squamate reptiles (Squamata) and remains common in the majority of lizard lineages, while extended (potentially indeterminate) adult growth evolved several times within squamates. Although traditionally associated with endotherms, determinate growth is coupled with ectothermy in this lineage. These findings combined with existing literature suggest that determinate growth predominates in both extant and extinct amniotes.     

Andromonoecy and developmental plasticity in Chaerophyllum bulbosum (Apiaceae–Apioideae)

Background and Aims

Andromonoecy, the presence of hermaphrodite and male flowers in the same individual, is genetically fixed or induced, e.g. by fruit set. Little is known about the forces triggering andromonoecy in the Apiaceae. In the present study, a natural population of the protandrous Chaerophyllum bulbosum was investigated to elucidate architectural constraints and effects of resource reallocation.

Methods

Three sets of plants (each n = 15) were treated by hand pollination, pollinator exclusion and removal of low-order inflorescences. Fifteen untreated plants were left as controls.

Key Results

Untreated plants produce umbels up to the third branch order, with increasing proportions of male flowers from 15 % (terminal umbel) to 100 % (third-order umbels). Fruit set correspondingly decreases from 70% (terminal umbel) to <10 % (second-order umbels). Insignificant differences from hand-pollinated plants do not reveal any sign of pollinator limitation at the study site. Bagged individuals show the same increase in male flowers with age as untreated plants, indicating that the presence of andromonoecy is not induced by fruit set. After umbel removal, individuals tend to present a higher number of hermaphrodite flowers and fruits in the umbels of second and third order. Three plants (25 %) produced an additional branch order composed of 100 % male umbels.

Conclusions

Inherited andromonoecy and the plastic response to environmental conditions are interpreted as a self-regulating system saving investment costs and optimizing fruit set at the same time.     

Lotus japonicus NOOT‐BOP‐COCH‐LIKE1 is essential for nodule,nectary, leaf and flower development

The NOOT‐BOP‐COCH‐LIKE (NBCL) genes are orthologs of Arabidopsis thaliana BLADE‐ON‐PETIOLE1/2. The NBCLs are developmental regulators essential for plant shaping, mainly through the regulation of organ boundaries, the promotion of lateral organ differentiation and the acquisition of organ identity. In addition to their roles in leaf, stipule and flower development, NBCLs are required for maintaining the identity of indeterminate nitrogen‐fixing nodules with persistent meristems in legumes. In legumes forming determinate nodules, without persistent meristem, the roles of NBCL genes are not known. We thus investigated the role of Lotus japonicus NOOT‐BOP‐COCH‐LIKE1 (LjNBCL1) in determinate nodule identity and studied its functions in aerial organ development using LORE1 insertional mutants and RNA interference‐mediated silencing approaches. In Lotus, LjNBCL1 is involved in leaf patterning and participates in the regulation of axillary outgrowth. Wild‐type Lotus leaves are composed of five leaflets and possess a pair of nectaries at the leaf axil. Legumes such as pea and Medicago have a pair of stipules, rather than nectaries, at the base of their leaves. In Ljnbcl1, nectary development is abolished, demonstrating that nectaries and stipules share a common evolutionary origin. In addition, ectopic roots arising from nodule vascular meristems and reorganization of the nodule vascular bundle vessels were observed on Ljnbcl1 nodules. This demonstrates that NBCL functions are conserved in both indeterminate and determinate nodules through the maintenance of nodule vascular bundle identity. In contrast to its role in floral patterning described in other plants, LjNBCL1 appears essential for the development of both secondary inflorescence meristem and floral meristem.     

Fecundity regulation by atresia in turbot Scophthalmus maximus in the Baltic Sea

Down‐regulation of fecundity through oocyte resorption was assessed in Baltic Sea turbot Scophthalmus maximus at three locations in the period from late vitellogenesis in April to spawning during June to July. The mean ± s.d . total length of the sampled fish was 32·7 ± 3·1 cm and mean ± s.d . age was 6·2 ± 1·5 years. Measurements of atresia were performed using the ‘profile method’ with the intensity of atresia adjusted according to the ‘dissector method’ (10·6% adjustment; coefficient of determination was 0·675 between methods). Both prevalence (portion of fish with atresia) and intensity (calculated as the average proportion of atretic cells in fish displaying atresia) of atresia were low in prespawning fish, but high from onset of spawning throughout the spawning period. Atretic oocytes categorized as in early alpha and in late alpha state occurred irrespective of maturity stage from late prespawning individuals up to late spawning fish, showing that oocytes may become atretic throughout the spawning period. Observed prevalence of atresia throughout the spawning period was almost 40% with an intensity of c. 20%. This indicates extensive down‐regulation, i.e. considerably lower realized (number of eggs spawned) v. potential fecundity (number of developing oocytes), suggesting significant variability in reproductive potential. The extent of fecundity regulation in relation to fish condition (Fulton's condition factor) is discussed, suggesting an association between levels of atresia and fish condition.     

Leaf and stem growth in the Lepidodendrales

Measurement of leaf length and stem diameter in three Upper Carboniferous l.epidodendron species shows an exponential relationship between these parameters. Larger axes bear longer leaves even in material which had apparently completed its primary' growth. It is suggested that this is a direct product of the determinate growth pattern of the ontogeny of arborescent lycopods. Measurements of Cyclostigma from the Irish Devonian are not explicable in these terms, and it is suggested that some specimens were immature at fossilization. It is recommended that the term leaf cushion be applied to the expanded leaf base in the Lepidodendrales at all growth stages, and not only after leaf abscission. Problems in the terminology of 'young' and 'old' growth stages in these determinate plants are discussed.     

Mapping and QTL analysis of horticultural traits in a narrow cross in cucumber (Cucumis sativus L.) using random-amplified polymorphic DNA markers

An 80-point genetic map [77 random-amplified polymorphic DNAs (RAPD), F (female sex expression), de (determinate), and ll (little leaf)] was constructed from a narrow cross in cucumber using the determinate, gynoecious, standard-sized leaf line G421 and the indeterminate, monoecious, little leaf line H-19. The map defined nine linkage groups and spanned ca. 600 cM with an average distance between markers of 8.4 ± 9.4 cM. The RAPD loci BC-551 and BC-592 were found to flank ll at 3.4 and 12.2 cM, respectively. The locus OP-L18-2 was linked (16 cM) to de, and the F locus was flanked by markers at 44 and 31 cM. One-hundred F3 families were used to identify quantitative trait loci (QTL) for sex expression, main stem length, number of lateral branches, days to anthesis, fruit number and weight, fruit length and diameter, and fruit length: diameter ratio in two replicated test locations (Wisconsin and Georgia). QTL on linkage group B explained major portions (R2 = ca. 2 to 74%) of the variation observed for sex expression, main stem length, lateral branch number, and fruit diameter (LOD = 2.1 to 29.8). Although ca. 62 to 74% of the variation for sex expression was associated with a putative QTL spanning the F locus (OP-AJ-2 to F and F to de), other regions (three) of the genome were important for the determination of sex in the F3 families examined depending upon environment. The number of genomic regions affecting main stem length (five) and number of lateral branches (three) coincided with expectations as determined by calculations of minimum number of genes in previous studies. Evaluation of QTL associated with several fruit number determinants of early, first-harvest yield demonstrating additive genetic variance (i.e., sex expression, main stem length, and number of laterals) suggests that marker-assisted selection may have utility for the development of determinate, multiple lateral branching germplasm suited for once-over mechanical harvesting in this population.     

Determinate root growth and meristem maintenance in angiosperms

BACKGROUND: The difference between indeterminate and determinate growth in plants consists of the presence or absence of an active meristem in the fully developed organ. Determinate root growth implies that the root apical meristem (RAM) becomes exhausted. As a consequence, all cells in the root tip differentiate. This type of growth is widely found in roots of many angiosperm taxa and might have evolved as a developmental adaptation to water deficit (in desert Cactaceae), or low mineral content in the soil (proteoid roots in various taxa). SCOPE AND CONCLUSIONS: This review considers the mechanisms of determinate root growth to better understand how the RAM is maintained, how it functions, and the cellular and genetic bases of these processes. The role of the quiescent centre in RAM maintenance and exhaustion will be analysed. During root ageing, the RAM becomes smaller and its organization changes; however, it remains unknown whether every root is truly determinate in the sense that its RAM becomes exhausted before senescence. We define two types of determinate growth: constitutive where determinacy is a natural part of root development; and non-constitutive where determinacy is induced usually by an environmental factor. Determinate root growth is proposed to include two phases: the indeterminate growth phase, when the RAM continuously produces new cells; and the termination growth phase, when cell production gradually decreases and eventually ceases. Finally, new concepts regarding stem cells and a stem cell niche are discussed to help comprehend how the meristem is maintained in a broad taxonomic context.     

关于一些植物学术语的中译等问题(三)

(1)确定rhizome的中文译名"根状茎"符合此术语的定义,同时认为另一中文译名"根茎"不符合有关定义,且易引起误解,应予废弃。(2)介绍了在中国植物学文献中稀见的2种属于有限花序类的花序类型,有限伞形花序和有限头状花序。根据有关欧美专家的花序研究,介绍了在中国植物学文献中放在无限花序类的隐头花序和柔荑花序系由聚伞花序演化而出,而应属于有限花序类的论断;同时,作者提出楼梯草属梨序楼梯草组的雄隐头花序系由同属的骤尖楼梯草组的有限头状花序演化而出的论点。