Rapid Changes in Levels of Polyribosomes in Zea mays in Response to Water Stress

Sucrose gradient profiles of polyribosomes from the coleoptilar node region of seedlings of Zea mays L. were obtained without pelleting and redispersion of the particles. Water stress caused a shift of ribosomes from the polymeric to the monomeric form, starting about 30 minutes after stress initiation and when the water potential of the tissue began to decrease measurably. After about 4 hours of stress (a decrease in tissue water potential of about 5 bars), most of the higher polymers of ribosomes had shifted to monoribosomes. Release of stress caused the ribosomes to revert from monomeric to polymeric form after a lag period apparently determined by the extent of prior stress. Use of bentonite and isolation of polyribosomes from combined stressed and control tissue gave results indicating that the reduced polyribosomal level was not an artifact caused by ribonuclease during isolation.Incubating roots in cycloheximide (2 micrograms per milliliter) had no effect on the proportion of polyribosomes in control roots, but it prevented the loss of polyribosomes caused by stress. Since cycloheximide inhibits the release of nascent polypeptide from polyribosomes, it appears possible that stress-effected loss in polyribosomes occurs only if polypeptides can be terminated and released.