Seed size,number and strategies in annual plants: a comparative functional analysis and synthesis

Background and AimsPlants depend fundamentally on establishment from seed. However, protocols in trait-based ecology currently estimate seed size but not seed number. This can be rectified. For annuals, seed number should simply be a positive function of vegetative biomass and a negative function of seed size.MethodsUsing published values of comparative seed number as the ‘gold standard’ and a large functional database, comparative seed yield and number per plant and per m² were predicted by multiple regression. Subsequently, ecological variation in each was explored for English and Spanish habitats, newly calculated C-S-R strategies and changed abundance in the British flora.Key ResultsAs predicted, comparative seed mass yield per plant was consistently a positive function of plant size and competitive ability, and largely independent of seed size. Regressions estimating comparative seed number included, additionally, seed size as a negative function. Relationships differed numerically between regions, habitats and C-S-R strategies. Moreover, some species differed in life history over their geographical range. Comparative seed yield per m² was positively correlated with FAO crop yield, and increasing British annuals produced numerous seeds. Nevertheless, predicted values must be viewed as comparative rather than absolute: they varied according to the ‘gold standard’ predictor used. Moreover, regressions estimating comparative seed yield per m² achieved low precision.ConclusionsFor the first time, estimates of comparative seed yield and number for >800 annuals and their predictor equations have been produced and the ecological importance of these regenerative traits has been illustrated. ‘Regenerative trait-based ecology’ remains in its infancy, with work needed on determinate vs. indeterminate flowering (‘bet-hedging’), C-S-R methodologies, phylogeny, comparative seed yield per m² and changing life history. Nevertheless, this has been a positive start and readers are invited to use estimates for >800 annuals, in the Supplementary data, to help advance ‘regenerative trait-based ecology’ to the next level.     

Prostaglandin E2 regulates melanocyte dendrite formation through activation of PKCzeta

Prostaglandins are lipid signaling intermediates released by keratinocytes in response to ultraviolet irradiation (UVR) in the skin. The main prostaglandin released following UVR is PGE(2), a ligand for 4 related G-protein-coupled receptors (EP(1), EP(2), EP(3) and EP(4)). Our previous work established that PGE(2) stimulates melanocyte dendrite formation through activation of the EP(1) and EP(3) receptors. The purpose of the present report is to define the signaling intermediates involved in EP(1)- and EP(3)-dependent dendrite formation in human melanocytes. We recently showed that activation of the atypical PKCzeta isoform stimulates melanocyte dendricity in response to treatment with lysophosphatidylcholine. We therefore examined the potential contribution of PKCzeta activation on EP(1)- and EP(3)-dependent dendrite formation in melanocytes. Stimulation of the EP(1) and EP(3) receptors by selective agonists activated PKCzeta, and inhibition of PKCzeta activation abrogated EP(1)- and EP(3)-receptor-mediated melanocyte dendricity. Because of the importance of Rho-GTP binding proteins in the regulation of melanocyte dendricity, we also examined the effect of EP(1) and EP(3) receptor activation on Rac and Rho activity. Neither Rac nor Rho was activated upon treatment with EP(1,3)-receptor agonists. We show that melanocytes express only the EP(3A1) isoform, but not the EP(3B) receptor isoform, previously associated with Rho activation, consistent with a lack of Rho stimulation by EP(3) agonists. Our data suggest that PKCzeta activation plays a predominant role in regulation of PGE(2)-dependent melanocyte dendricity.     

The cAMP signaling pathway has opposing effects on Rac and Rho in B16F10 cells: implications for dendrite formation in melanocytic cells

A hallmark of melanocytic cells is their ability to form dendrites in response to growth factors and to ultraviolet irradiation. It is known that the cyclic adenosine monophosphate (cAMP) second messenger pathway stimulates melanocyte dendrite formation because agents that increase cAMP such as forskolin and dibutyrl cAMP induce dendrite formation in normal human and murine melanocytes and melanoma cell lines. The Rho family of guanosine triphosphate (GTP)-binding proteins regulates cytoskeletal reorganization in all cells tested and Rac and Rho have both been shown to regulate melanocyte dendrite formation. In this report, we analyzed the effect of cAMP on the activation of Rac and Rho and show that elevation of cAMP stimulates Rac and inhibits Rho in B16F10 cells. The Rho GTP-binding proteins have also been shown to either cross-activate or inhibit each other and in this report we show that Rac activates Rho in B16F10 cells. Microinjection of C3 botulinum exoenzyme toxin, an agent that specifically inactivates Rho or microinjection of constitutively active mutant Rac protein-induced dendricity in human melanocytes and in B16F10 and B16F1 murine melanoma cell lines. We conclude that cAMP-mediated dendrite formation in melanocytic cells is mediated through upregulation of Rac activity and downregulation of Rho activity.     

A re-analysis of agricultural production and consumption: implications for understanding the British Iron Age

Patterning in the carbonized seed assemblages from Iron Age sites in Britain has led to the development of several explanatory models. The most influential of these, by Martin Jones, proposed that grain-rich assemblages represent producer sites and weed-/chaff-rich assemblages consumer sites. The assumptions underlying this model and the method of constructing the diagrams are discussed and a new approach is put forward, stressing the need for appropriate levels of analysis and interpretation. It is concluded that a predominance of grain-rich samples is far more likely to be an indicator of the scale of production and consumption, than a means of distinguishing between the two. A review of the evidence from Iron Age Britain indicates that grain-rich site assemblages primarily occur in the south of the country, and frequently co-occur with pits, used for the storage of surplus grain. Moreover, such pits are concentrated in hillforts. It is proposed that the grain stored in such pits may have been used in large communal feasts and that the hillforts functioned as locations for feasting.

The genetic ghost of an invasion past: colonization and extinction revealed by historical hybridization in Senecio

Hybridization is an important evolutionary factor in the diversification of many plant and animal species. Of particular interest is that historical hybridization resulting in the origin of new species or introgressants has occurred between species now geographically separated by great distances. Here, we report that Senecio massaicus, a tetraploid species native to Morocco and the Canary Islands, contains genetic material of two distinct, geographically separated lineages: a Mediterranean lineage and a mainly southern African lineage. A time-calibrated internal transcribed spacer phylogeny indicates that the hybridization event took place up to 6.18 Ma. Because the southern African lineage has never been recorded from Morocco or the Canary Islands, we hypothesize that it reached this area in the distant past, but never became permanently established. Interestingly, the southern African lineage includes S. inaequidens, a highly invasive species that has recently become widespread throughout Europe and was introduced at the end of the 19th century as a 'wool alien'. Our results suggest that this more recent invasion of Europe by S. inaequidens represents the second arrival of this lineage into the region.     

Non-enzymatic developmental functions of acetylcholinesterase--the question of redundancy

Despite in vitro demonstrations of non-enzymatic morphogenetic functions in acetylcholinesterase (AChE), the AChE knockout phenotype is milder than might be expected, casting doubt upon the relevance of such functions in vivo. Functional redundancy is a possible explanation. Using in vitro findings that AChE is able to bind to laminin-111, together with detailed information about the interaction sites, as well as an epitope analysis of adhesion-inhibiting anti-AChE mAbs, we have used molecular docking and bioinformatics techniques to explore this idea, investigating structurally similar molecules that have a comparable spatiotemporal expression pattern in the embryonic nervous system. On this basis, molecules with which AChE could be redundant are the syndecans, glypicans, perlecan, the receptor tyrosine kinase Mer, and the low-density lipoprotein receptor. It is also highly likely that AChE may be redundant with the homologous neuroligins, although there is no evidence that the latter are expressed before synaptogenesis. AChE was observed to dock with Gas6, the ligand for Mer, as well as with apolipoprotein E3 (but not apolipoprotein E4), both at the same site as the laminin interaction. These findings suggest that AChE may show direct functional redundancy with one or more of these molecules; it is also possible that it may itself have a unique function in the stabilization of the basement membrane. As basement membrane molecules are characterized by multiple molecular interactions, each contributing cumulatively to the construction and stability of the network, this may account for AChE's apparently promiscuous interactions, and also for the survival of the knockout.