EFFECT OF COLD STRESS AND HARDENING ON POLYSOMES IN SEEDLINGS OF WINTER CEREALS

No changes of any kind occurred in the sedimentation profiles or trans lational activity of polysomes during the period of cold hardening in seedlings of winter wheat (Triticum aestivum L.) or rye (Secale cereal e L.). Nonetheless, hardening led a sharp change in behavior of polyso mes during subsequent freezing of seedlings at -5-degrees-C for a peri od of 24 h and thawing at +2-degrees-C. Polysomes from hardened seedli ngs dissociated during freezing to monosomes, which were rapidly reass embled into polysomes during thawing of the tissues. We observed no de cline in the translational activity of polysomes here. In unhardened s eedlings under analogous influences, no changes occurred in the sedime ntation profiles of ribosomes, but their activity in a cell-free syste m of translation declined appreciably. Freezing of seedlings apparentl y led to a certain destabilization of ribosomes manifested in easier e xtraction of ribosomal proteins by 0.5 M KCl, which was expressed in h ardened and unhardened seedlings in equal measure. We observed loss of the bulk of high-molecular-weight proteins associated with ribosomes during isolation of polysome preparations from unhardened seedlings su bjected to freezing and thawing, whereas high-molecular-weight protein s were preserved in polysomes from hardened seedlings. It is hypothesi zed that these proteins are needed for optimization of translation.