Hydration dependent polysome-monosome interconversion in the germinating castor bean endosperm

Castor bean seeds germinated for 40 br under a condition ofunlimited water availability were placed for 1 to 5 days ina condition such as to interrupt any further water uptake. Thefollowing phenomena were observed: a) the rate of synthesisof glucose-6-phosphate, phosphogluconate and NADP isocitratedehydrogenases progressively decreased, then completely stopped;b) polysomes disappeared while monosomes correspondingly increased;c) the endogenous capacity of isolated ribosomes to incorporateamino acid into proteins fell to zero, while in the presenceof poly-U phenylalanine incorporation remained practically constant.When the seeds were placed again in contact with water, theenzyme activities began to increase again; polyribosomes werereformed both from old ribosomes preexisting in the treatedendosperms and from new synthesized ribosomes; the endogenouscapacity of the ribosomes to perform protein synthesis (on anRNA basis) regained their original levels. These data suggest that some factor affecting mRNA or its interactionwith ribosomes, rather than a modification of ribosomal structureis responsible for the stoppage of protein synthesis causedby interrupting water uptake. (Received July 15, 1968; )