Amino-acid composition and protein and carbohydrate accumulation in the grain of triticale grown under terminal water stress simulated by a senescingagent

Two field experiments involving two triticale genotypes and the application of a senescing agent (KI) to stimulate the effect of a terminal drought st ress were conducted at two sites during 1996. Although protein did not diff er between genotypes, significant differences were found in methionine and lysine. The percentage of amino acids in the grain increased linearly with grain-protein content, this relationship being non-linear in the same degre e for all amino acids. An inverse relationship (r(2) = 0.803) was found bet ween the rates of carbohydrate and protein accumulation in absence of the s enescing agent, indicating competition in the transport of proteins and car bohydrates to the grain. Terminal drought stress induced by KI application increased the amino-acid concentration in the grain, mainly due to a higher protein content. Nevertheless, the amino-acid composition of the protein d id not change after this application. The senescing agent, significantly re duced dry weight as well as carbohydrate- and protein-accumulation rates in the grain, thus forcing the grain to be filled with carbohydrates assimila ted before anthesis. Therefore, the grain-carbohydrate accumulation rate ap peared highly dependent (r(2) = 0.884) of the quantity of nonstructural car bohydrates available for studying protein and carbohydrate accumulation in small-grain cereals. (C) 2000 Academic Press.