Action of gibberellic acid in a dwarf maize mutant: an X-ray microanalysis study

Quantitative X-ray microanalysis of calcium in sea urchin eggs after quick-freezing and freeze-substitution. Validity of the method

Freeze-substitution was used to study the distribution of calcium in sea urchin eggs, and the validity of the technique was assessed. We followed the fate of both total and exchangeable calcium of sea urchin eggs in two species (Paracentrotus lividus and Arbacia lixula) after the various treatments needed for freeze-substitution and embedding. We compared the calcium content either by X-ray microanalysis of Epon-embedded sections of freeze-substituted eggs (6.2 +/- 0.71 mmoles/kg of Epon-embedded tissue) or by flame spectrometry analysis of living eggs (32.3 +/- 1.30 nmoles/mg protein). After standardization of units, both values lead to similar total calcium content. We also measured the movements of 45Ca from prelabelled eggs. Exchangeable 45Ca as well as total calcium appeared unaffected by the preparative treatment for X-ray microanalysis. In conclusion, our preparative technique for X-ray microanalysis can be considered appropriate for our material and allows us to undertake a subcellular quantification of calcium in various organelles.

The effects of salinity on ion concentrations within the root cells of Zea mays L

Zea mays is a salt-sensitive crop species which in saline (≦100 mol m(-3) NaCl) conditions suffers considerable growth reduction correlated with elevated Na(+) and Cl(-) concentration within the leaves. To increase understanding of the regulation of ion uptake and transport by the roots in saline conditions, ion concentrations within individual root cortical cells were determined by X-ray microanalysis. There was variation in Na(+), K(+) and Cl(-) distributions among individual cells, which could not be correlated with their spatial position in the roots. Generally, however, in response to saline growth conditions (100 mol m(3) NaCl) Na(+) and Cl(-) were mostly localized in the vacuoles, although their concentrations were also sometimes increased in the cytoplasm and cell walls. The concentration of K(+) in the cytoplasm was usually maintained at a level (mean 79 mol m(-3)) compatible with the biochemical functions ascribed to this ion.

Freeze-substitution

Freeze-substitution is a technique suitable for the preparation of unicellular and multi-cellular plant and animal specimens for conventional light microscopy, TEM and SEM. It is also widely used as a means of preparing animal and plant tissues for the localization of water soluble substances by analytical electron microscopy, autoradiography or visual detection of precipitates. The technical requirements of preparation, together with an evaluation of the procedures, are presented for various applications. Careful selection and evaluation of freezing technique, substitution solvent and regime are required for meaningful results.