Secretory vesicles are preferentially targeted to areas of low molecular SNARE density

Intercellular communication is commonly mediated by the regulated fusion, or exocytosis, of vesicles with the cell surface. SNARE (soluble N-ethymaleimide sensitive factor attachment protein receptor) proteins are the catalytic core of the secretory machinery, driving vesicle and plasma membrane merger. Plasma membrane SNAREs (tSNAREs) are proposed to reside in dense clusters containing many molecules, thus providing a concentrated reservoir to promote membrane fusion. However, biophysical experiments suggest that a small number of SNAREs are sufficient to drive a single fusion event. Here we show, using molecular imaging, that the majority of tSNARE molecules are spatially separated from secretory vesicles. Furthermore, the motilities of the individual tSNAREs are constrained in membrane micro-domains, maintaining a non-random molecular distribution and limiting the maximum number of molecules encountered by secretory vesicles. Together our results provide a new model for the molecular mechanism of regulated exocytosis and demonstrate the exquisite organization of the plasma membrane at the level of individual molecular machines

Shoot yield drives phosphorus use efficiency in Brassica oleracea and correlates with root architecture traits

The environmental and financial costs of using inorganic phosphate fertilizers to maintain crop yield and quality are high. Breeding crops that acquire and use phosphorus (P) more efficiently could reduce these costs. The variation in shoot P concentration (shoot-P) and various measures of P use efficiency (PUE) were quantified among 355 Brassica oleracea L. accessions, 74 current commercial cultivars, and 90 doubled haploid (DH) mapping lines from a reference genetic mapping population. Accessions were grown at two or more external P concentrations in glasshouse experiments; commercial and DH accessions were also grown in replicated field experiments. Within the substantial species-wide diversity observed for shoot-P and various measures of PUE in B. oleracea, current commercial cultivars have greater PUE than would be expected by chance. This may be a consequence of breeding for increased yield, which is a significant component of most measures of PUE, or early establishment. Root development and architecture correlate with PUE; in particular, lateral root number, length, and growth rate. Significant quantitative trait loci associated with shoot-P and PUE occur on chromosomes C3 and C7. These data provide information to initiate breeding programmes to improve PUE in B. oleracea

A Longitudinal Analysis of Moving Desires, Expectations and Actual Moving Behaviour

Residential mobility theory proposes that moves are often preceded by the expression of moving desires and expectations. Much research has investigated how individuals form these premove thoughts, with a largely separate literature examining actual mobility. Although a growing number of studies link premove thoughts to subsequent moving behaviour, these often do not distinguish explicitly between different types and combinations of premove thoughts. Using 1998–2006 British Household Panel Survey data, this study investigates whether moving desires and expectations are empirically distinct premove thoughts. Using multinomial regression models we demonstrate that moving desires and expectations have different meanings, and are often held in combination: the factors associated with expecting to move differ depending upon whether the move is also desired (and vice versa). Next, using panel logistic regression models, we show that different desire–expectation combinations have different effects on the probability of subsequent moving behaviour. The study identified two important groups generally overlooked in the literature: those who expect undesired moves and those who desire to move without expecting this to happen.The definitive, peer reviewed and edited version of this article is published in Environment and Planning A, 2011, 43(11), pp. 2742-2760, doi:10.1068/a44105