Increased Lysine and Seed Storage Protein in Rice Plants Recovered from Calli Selected with Inhibitory Levels of Lysine plus Threonine and S -(2-Aminoethyl)cysteine

Abstract

Experiments were designed to test whether variation in percent lysine in seed proteins could be recovered in plants regenerated from callus subjected to inhibitory levels of lysine plus threonine. Anther-derived callus was subjected to I millimolar lysine plus threonine for three successive passages and then once to the same concentration of S42-aminoethyl)cysteine. Plants were regenerated from the resistant callus. Plants recovered directly from tissue culture were normal in color, size and were 50% or less fertile. Second and third generation plants produced a wide range of variants including albinos, deep green plants both short and tall, and totally fertile as well as partially fertile plants. All regen-erated plants produced chalky or opaque seed. One unique second gen-eration line had 14% more lysine in seed storage proteins than the controls. This characteristic was transmitted to the next generation. The high lysine plants had reduced seed size with significantly higher levels of seed storage protein than the controls. The phenotypes recovered provide experimental materials for basic studies in protein synthesis and lysine metabolism and may become a source of material for rice breeding. The nutritional quality ofthe major cereal grains is not optimal because lysine and threonine are limiting amino acids in seed storage proteins (16). The efficient recovery of plants with altered lysine levels requires mutants either in the metabolism or catab-olism of lysine or in the (de)regulation of pathways leading to lysine and protein synthesis. Strategies exist for the recovery of mutants for lysine synthesis in microbial systems but few clearly defined systems or mutants are available in green plants. Lack of basic metabolic information in crop plants precludes the efficient recovery of single gene lysine mutants. Nonetheless, some progress has been made using tissue/anther culture tech-niques coupled with the use ofamino acid analogs and inhibitory levels of metabolic products, particularly AEC' and L+T. Com-binations of these compounds provide biochemical selection pressure for altered feedback inhibition or insensitivity to precise control of one or more of the enzymatic reactions associated with the fl-aspartokinase pathway for lysine and threonine