The role of calcium in the recall of stored morphogenetic information by plants

Flax seedlings grown in the absence of environmental stimuli, stresses and injuries do not form epidermal meristems in their hypocotyls. Such meristems do form when the stimuli are combined with a transient depletion of calcium. These stimuli include the "manipulation stimulus" resulting from transferring the seedlings from germination to growth conditions. If, after a stimulus, calcium depletion is delayed, meristem production is also delayed; in other words, the meristem-production instruction can be memorised. Memorisation includes both storage and recall of information. Here, we focus on information recall. We show that if the first transient calcium depletion is followed by a second transient depletion there is a new round of meristem production. We also show that if an excess of calcium follows calcium depletion, meristem production is blocked; but if the excess of calcium is in turn followed by another calcium depletion, again there is a new round of meristem production. The same stored information can thus be recalled repeatedly (at least twice). We describe a conceptual model that takes into account these findings.     

Associations between household and neighbourhood socioeconomic status and systolic blood pressure among urban South African adolescents

Factors resulting in high risk for cardiovascular disease have been well studied in high income countries, but have been less well researched in low/middle income countries. This is despite robust theoretical evidence of environmental transitions in such countries which could result in biological adaptations that lead to increased hypertension and cardiovascular disease risk. Data from the South African Birth to Twenty cohort, Bone Health sub-sample (n = 358, 47% female), were used to model associations between household socioeconomic status (SES) in infancy, household/neighbourhood SES at age 16 years, and systolic blood pressure (multivariate linear regression) and risk for systolic pre-hypertension (binary logistic regression). Bivariate analyses revealed household/neighbourhood SES measures that were significantly associated with increased systolic blood pressure. These significant associations included improved household sanitation in infancy/16 years, caregiver owning the house in infancy and being in a higher tertile (higher SES) of indices measuring school problems/environment or neighbourhood services/problems/crime at 16 years of age. Multivariate analyses adjusted for sex, maternal age, birth weight, parity, smoking, term birth, height/body mass index at 16 years. In adjusted analyses, only one SES variable remained significant for females: those in the middle tertile of the crime prevention index had higher systolic blood pressure (β = 3.52, SE = 1.61) compared with the highest tertile (i.e. those with the highest crime prevention). In adjusted analyses, no SES variables were significantly associated with the systolic blood pressure of boys, or with the risk of systolic pre-hypertension in either sex. The lack of association between SES and systolic blood pressure/systolic pre-hypertension at age 16 years is consistent with other studies showing an equalization of adolescent health inequalities. Further testing of the association between SES and systolic blood pressure would be recommended in adulthood to see whether the lack of association persists.     

Steady-state kinetic behaviour of functioning-dependent structures

A fundamental problem in biochemistry is that of the nature of the coordination between and within metabolic and signalling pathways. It is conceivable that this coordination might be assured by what we term functioning-dependent structures (FDSs), namely those assemblies of proteins that associate with one another when performing tasks and that disassociate when no longer performing them. To investigate a role in coordination for FDSs, we have studied numerically the steady-state kinetics of a model system of two sequential monomeric enzymes, E(1) and E(2). Our calculations show that such FDSs can display kinetic properties that the individual enzymes cannot. These include the full range of basic input/output characteristics found in electronic circuits such as linearity, invariance, pulsing and switching. Hence, FDSs can generate kinetics that might regulate and coordinate metabolism and signalling. Finally, we suggest that the occurrence of terms representative of the assembly and disassembly of FDSs in the classical expression of the density of entropy production are characteristic of living systems.     

The Arabidopsis vitamin E pathway gene5-1 mutant reveals a critical role for phytol kinase in seed tocopherol biosynthesis

We report the identification and characterization of a low tocopherol Arabidopsis thaliana mutant, vitamin E pathway gene5-1 (vte5-1), with seed tocopherol levels reduced to 20% of the wild type. Map-based identification of the responsible mutation identified a G-->A transition, resulting in the introduction of a stop codon in At5g04490, a previously unannotated gene, which we named VTE5. Complementation of the mutation with the wild-type transgene largely restored the wild-type tocopherol phenotype. A knockout mutation of the Synechocystis sp PCC 6803 VTE5 homolog slr1652 reduced Synechocystis tocopherol levels by 50% or more. Bioinformatic analysis of VTE5 and slr1652 indicated modest similarity to dolichol kinase. Analysis of extracts from Arabidopsis and Synechocystis mutants revealed increased accumulation of free phytol. Heterologous expression of these genes in Escherichia coli supplemented with free phytol and in vitro assays of recombinant protein produced phytylmonophosphate, suggesting that VTE5 and slr1652 encode phytol kinases. The phenotype of the vte5-1 mutant is consistent with the hypothesis that chlorophyll degradation-derived phytol serves as an important intermediate in seed tocopherol synthesis and forces reevaluation of the role of geranylgeranyl diphosphate reductase in tocopherol biosynthesis.     

Evolutionary conservation advice for despotic populations: habitat heterogeneity favours conflict and reduces productivity in Seychelles magpie robins

Individual preferences for good habitat are often thought to have a beneficial stabilizing effect for populations. However, if individuals preferentially compete for better-quality territories, these may become hotspots of conflict. We show that, in an endangered species, this process decreases the productivity of favoured territories to the extent that differences in productivity between territories disappear. Unlike predictions from current demographic theory on site-dependent population regulation (ideal despotic distribution), we show that population productivity is reduced if resources are distributed unevenly in space. Competition for high-quality habitat can thus have detrimental consequences for populations even though it benefits individuals. Manipulating conflict (e.g. by reducing variation in habitat quality) can therefore prove an effective conservation measure in species with strong social or territorial conflict.