Water-Stress-Induced Changes in the Pattern of Protein Synthesis in Maize Seedling Mesocotyls: A Comparison with the Effects of Heat Shock

Abstract

Cut segments from the growing and non-growing regions of 4-d-old maize seedling mesocotyls exhibit reduced protein synthesis when subjected to water-stress imposed directly by incubation in solutions of polyethylene glycol. Growing mesocotyl tissue can recover full protein synthesis upon return to a fully-hydrated condition following stress to -0-5 MPa, while non-growing tissue recovers well from greater stresses (-0-75 to -1-0 MPa), and in lesser time. Using two-dimensional electrophoresis and fluorography of de novo synthesized proteins in vivo it was possible to follow changes in protein synthesis in the non-growing tissue under water-stress and upon subsequent recovery. The synthesis of several proteins was reduced by stress, although that of others intensified. Those proteins exhibiting reduced synthesis under stress were synthesized at control levels (i.e. the same levels as in unstressed tissue) when the stress was relieved. Some proteins whose synthesis was intensified under stress retained this intensification upon return to full hydration. No unique proteins were synthesized in response to water-stress, in contrast to the 'heat-shock' proteins induced when the mesocotyls were subjected to high temperature. Hence water-stress induces quantitative rather than qualitative changes in the pattern of protein synthesis.