Response of seedlings of radish (Raphanus sativus) to osmotic shock and external hydrostatic pressure.

The effects of an osmotic shock (300 mM mannitol, -0.67 MPa) or/and increased external hydrostatic pressure on seedlings (42-h-germinated seeds) of radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) were investigated. The osmotic shock did not inhibit H+ extrusion and net K+ uptake, and did not affect the levels of make acid. reducing sugars, sucrose or amino acids or of the energy charge (i.e. the synthesis of energy-rich phosphate bonds). but inhibited the synthesis of proteins. RNA and DNA. measured as incorporation of labelled precursors. When the osmotic shock was applied together with an increased external hydrostatic pressure of the same magnitude (+0.67 MPa). the same metabolic parameters and the inhibition of synthesis of RNA and DNA were not substantially affected. while the inhibition of protein synthesis was practically reversed and the energy charge decreased; the recovery of protein synthesis was not due to a change in labelled leucine uptake capability. Increased external hydrostatic pressure alone decreased the energy charge without affecting the other parameters considered. The possibility that protein synthesis activity is directly controlled by cell turgor pressure (internal hydrostatic pressure) is discussed. [ABSTRACT FROM AUTHOR]