Freezing Tolerance and Solute Changes in Contrasting Genotypes of Lolium perenne L. Acclimated to Cold and Drought

Abstract

Clonal ramets of 12 contrasting genotypes of Lolium perenne L. were grown in sand or soil-based compost and maintained under well-watered conditions at 20/15°C or acclimated to low temperature (2°C) or to a restricted water supply. Freezing tolerance was measured as LT50 following exposure to sub-zero temperatures in a freezing tank. Measurements were also made of osmotic potential, water-soluble carbohydrates, free proline, free amino acids, and minerals in entire tillers. Acclimation to both drought and cold lowered LT50, induced osmotic adjustment, and increased concentrations of proline and amino acids, Rooting medium had little effect on LT50, but caused large differences in osmotic potential and in proline and amino-acid concentrations. There was considerable genetic diversity for all characters measured, except for mineral contents. There was, however, no relationship between LT50 and osmotic potential or solute content that was consistent across the three sources of variation (growing medium, acclimation, genotype). Furthermore, the diverse genotypic values of cold-induced freezing tolerance were not correlated with those of drought-induced tolerance. It is concluded that more precise measurements are needed of the partitioning of solutes during acclimation and of the sensitivity of different organs and tissues to freezing.