Calcium influx at the tip of growing root-hair cells of Arabidopsis thaliana

The role of extracellular Ca 2+ in root-hair tip growth has been investigated in Arabidopsis thaliana (L.) Heynh. Root-hair length was found to be dependent on the concentration of Ca 2+ in the growth medium, with maximum length achieved at [Ca 2+ ] of 0.3–3.0 mM. Using a non-intrusive calcium-specific vibrating microelectrode, an extracellular Ca 2+ gradient was detected at the tips of individual growing root-hair cells. The direction of the gradient indicated a net influx of Ca 2+ into root-hair cells. No gradient was detected near the sides of the root hairs or at the tips of non-growing root hairs. When root hairs were exposed to the Ca 2+ -channel blocker nifedipine, tip growth stopped and the extracellular Ca 2+ gradient was abolished. These results indicate that Ca 2+ influx through plasma-membrane Ca 2+ channels is required for normal root-hair tip growth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47478/1/425_2004_Article_BF00199963.pd

Mathematical and computational modelling of vegetated soil incorporating hydraulically-driven finite strain deformation

In this paper a new model for the hydro-mechanical behaviour of rooted soils is developed. It is a physically-based model that couples finite strain soil deformation with unsaturated water and air flow, while improving on existing cohesion-based approaches to mechanical root reinforcement and empirical soil water-uptake approaches typically used to deal with rooted slopes. The model is used to show that the dynamics of soil-water pressure and soil deformation depend strongly on the physics of the root-water uptake and the elasto-plastic soil mechanics. Root water uptake can cause suctions and corresponding soil shrinkage sufficiently large to necessitate a finite-strain approach. Although this deformation can change the intrinsic permeability, hydraulic conductivity remains dominated by the water content. The model incorporates simultaneous air-flow, but this is shown to be unimportant for soil-water dynamics under the conditions assumed in example simulations. The mechanical action of roots is incorporated via a root stress tensor and a simulation is used to show how root tension is mobilised within a swelling soil. The developed model may be used to simulate both laboratory experiments and full-scale vegetated slopes

Relationships between paranoid thinking, self-esteem and the menstrual cycle.

This study aimed to investigate whether paranoid experiences and levels of self-esteem fluctuate over the menstrual cycle and whether levels of self-esteem are lower when perceived persecution is felt to be deserved. Measures of anxiety, depression, persecution, deservedness and self-esteem were completed on-line by 278 women over their menstrual cycle. Responses were compared at the paramenstrual (3 days before and after menses onset) and mid-cycle phase. At the paramenstrual phase persecution, negative self-esteem, anxiety and depression were higher and positive self-esteem was lower than at mid-cycle. A greater proportion of women experienced persecution as deserved at the paramenstrual phase. This was associated with higher depression and negative self-esteem scores. Increased levels of deservedness significantly strengthened the relationship between persecution and negative, but not positive, self-esteem. These findings suggest that the paramenstrual phase is a time of vulnerability to increased paranoid experiences, an increased likelihood that feelings of persecution will feel deserved and lowered self-esteem. The findings support the view that interpersonal sensitivities may be key to menstrual cycle symptoms and have an impact on relationships. Further, the study illustrated that ideas developed for psychosis could make a valuable contribution to understanding and managing this aspect of menstruation-related distress