INTERVARIETAL DIFFERENCES IN THE AMINO-ACID COMPOSITION OF PEA ROOTS AS RELATED TO THEIR RESPONSE TO SALINITY

The salt tolerance of three cultivars of Pisum sativum L. as defined by root growth on saline substrate was in the order Dan > Alaska > Laxton Progress. The total content of free amino acids decreased in Alaska, but not in Laxton Progress, with increasing salinity, while the content of the free basic amino acids increased with salinity. In both cultivars salinity induced accumulation of free proline, but not enough to maintain the osmotic adaptation of the cytoplasm. Proline accumulation could not account for the greater tolerance of the Alaska cultivar. Both cultivars contain large amounts of glutamic acid and homoserine. The amino acid composition of protein of the Alaska cultivar is affected much more by salinity than is that of Laxton Progress. In Alaska salinity induces an increase in aspartic and glutamic acids, threonine, serine, leucine and isoleucine. The total content of basic amino acids decreases with salinity. The protein of Laxton Progress is very rich in leucine and its amount slightly decreases with salinity. In the most tolerant cultivar, Dan, there is more proline in the protein than in the other two cultivars and its content of leucine increases with salinity. The only features which show some correlation with salinity tolerance are proline content (Dan > Alaska > Laxton Progress) and an increase in leucine content in the protein, with increasing salinity. © 1979, Annals of Botany Company.