Interrelationships between cytoplasmic Ca2+ peaks, pollen hydration and plasma membrane conductances during compatible and incompatible pollinations of Brassica napus papillae.

We have investigated Ca(2+)-involving cell signaling, plasma membrane potentials and conductances and callose formation during early stages of pollination of papillae of Brassica napus. Using fluorescence imaging of calcium green-1, we found that application of a range of pollen types and controls all rapidly produced small localized peaks in papillar cytoplasmic [Ca2+]. This response was more frequent in compatible than incompatible interactions and was correlated with subsequent hydration of the applied pollen grains, indicating that it may be a differential prerequisite of the compatible signaling pathway leading to successful pollinations. In contrast, a slight trend to increased plasma membrane conductance (but with no indications of action potential-like responses) and also callose deposition in papillae adjacent to pollen grains followed pollination in both SC and SI interactions, indicating that alterations in plasma membrane permeability and callose deposition during early phases of pollination are not primary determinants of the fate of attempted pollinations.

An electron microscopic and spectroscopic study of murine epiphyseal cartilage: analysis of fine structure and matrix vesicles preserved by slam freezing and freeze substitution.

Newborn mice epiphyseal growth plates were preserved by slam freezing/freeze substitution and examined by conventional electron microscopy, stereopsis, high voltage electron microscopy, and electron spectroscopic imaging (ESI). To illustrate the improved ultrastructure of this cryogenic procedure, conventional, aqueously fixed growth plates were included showing collapsed hypertrophic chondrocytes surrounded by a depleted and condensed extracellular matrix. In contrast, the cryogenically prepared epiphyses contain chondrocytes and extracellular matrix vesicles both in direct contact with proteoglycan filaments retained in an expanded state. ESI is an electron microscopic technique which enables the direct localization of atomic elements superimposed over fine structural details. This technique was used to examine the colocalization of calcium and phosphorus within matrix vesicles and within their associated extracellular environments. Matrix vesicles appeared in three distinct diameter ranges. The integrity of the matrix vesicles was examined at various stages of mineralization and also within the mineralized zone of provisional calcification.