Tissue steep gradients

Microscale measurements of lAA levels in tissue sections through the vascular cambium of both Pinus and Populus [199,200] have revealed the existence of a steep gradient of lAA levels across the cambium. The existence of these gradients supports the idea that auxin functions in the plant as a positional signal which can specify developmental... 

Checks develop at points of weakness, e.g. along rays. Hence flat-sawn boards face-check and quarter-sawn boards edge-check. Probably the rays dry faster than the surrounding tissue but are restrained from shrinking, and are stretched tangentially, in the sense that they are unable to shrink as much as they would like. A steep moisture gradient favours eheeking. 

Regulation of Calcium Homeostasis Calcium homeostasis necessitates the maintenance of a dynamic equilibrium of calcium fluxes between three different compartments which harbor the mineral ion in vastly different concentrations. Thus, homeostatic control mechanisms ought to modulate calcium fluxes between different body compartments in a way which allows the generation and maintenance of steep concentration gradients between the skeletal tissue, the extracellular fluid and the intracellular - that is, the cytoplasmic compartment. Of particular importance thereby is the rigid control of plasma free Ca " ", because even small deviations from the normal level induce profound changes in both intracellular free Ca, as well as in the amount of calcium deposited at skeletal sites, inevitably causing adverse effects on bone health (cf. Whedon 1980). 

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