Protein carbonylation and arginine utilization in cold- and warm-stratified pistachio (Pistacia vera L.) kernels

Abstract

The role of protein modifications and amino acid metabolism in the dormancy breaking of pistachio (Pistacia vera L.) kernels during moist chilling (5 ºC) and warm stratification (25 ºC) were studied. Cold-stratified kernels showed germination up to 97%, while warm-stratified ones had low germination (40%). Increased protein solubility at neutral pH was accompanied by protein carbonylation in both cotyledons and embryonic axes during cold treatment, whereas these values decreased under warm incubation. Amino acid accumulation occurred in both tissues of cold- and warm-stratified kernels. Arginase activity increased in both tissues of cold-stratified kernels but significantly declined during warm treatment. While arginine decarboxylase activity of both organs increased under cold and warm stratification of pistachio kernels, ornithine aminotransferase activity declined during these periods. These results show that increased protein solubility and its carbonylation during cold stratification may induce the protein mobilization and accumulation of amino acids for their subsequent direction to the proper metabolic pathways. In this way, protein modification and arginine metabolism by arginase can be considered germination-specific events during cold stratification of kernels.