The cold dependent accumulation of COR TMC-AP3 in cereals with contrasting, frost tolerance is regulated by different mRNA expression and protein turnover

The accumulation of specific cold-regulated (COR) proteins is a component o f the hardening process and different amount of COR proteins has been relat ed to different degrees of cold tolerance. A number of different mechanisms controls the accumulation of the COR proteins in the plant cells. In this work we describe the mechanisms controlling the accumulation of the COR pro tein TMC-AP3, a putative chloroplastic amino acid selective channel protein [1] in barley, durum, wheat, emmer and bread wheat. Winter barley and, to less extent, winter bread wheal. showed a higher cor tmc-ap3 expression at low temperature than the spring one while no significant differences were d etected between the emmer and the durum. wheat genotypes. After 2 days of d e-hardening the transcript level dropped down in the same way in all tested genotypes, nevertheless the decrease in protein content was genotype depen dent. In all frost resistant genotypes the amount of COR TMC-AP3 after 9 da ys of de-hardening was higher compared with that of susceptible ones. These findings suggest that resistant and susceptible genotypes have different p rotein degradation rate and/or mRNA translational efficiency. Differences i n the protein degradation rate were not dependent from the amino acidic seq uence of the protein, being extremely similar in all tested genotypes. A ge netic study based on Chinese spring/Cheyenne chromosome substitution lines showed that the turnover of TMC-AP3 is a polygenic trait controlled by a nu mber of loci being the most important located on chromosomes 1B, 2B, 2D and 4D. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.