Growth Inhibition & Bleaching in Higher Plants & Euglena by O-Methylthreonine; Reversal by Isoleucine

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Abstract
Albinism or bleaching of the new leaves of various plants was induced by treating the roots or leaves with a few milligrams of an amino acid analog, DL-O-methylthreonine. Old leaves that were present at the time of treatment were not affected. Higher rates stopped the growth of certain crops and weeds completely and the plants succumbed in most cases. Other amino acid analogs including O-methylallothreonine O-methylserine, [beta]-methoxyvaline and a-methylthreonine did not cause bleaching of the green chlorophyll color. The inhibiting effect of O-methylthreonine on growth and chlorophyll formation of wheat and bean plants was reversed by adding 4 to 9 times as much DL-isoleucine as O-methylthreonine. Threonine and other amino acids such as serine, valine, leucine and norleucine had no reversing effect. Chlorophyll formation was also inhibited in Euglena gracilis by 100 ppm O-methylthreonine in the growth medium, and this bleaching was reversed by adding 10 times as much DL-isoleucine. In Euglena, DL-leucine and to a lesser extent DL-norleucine also exerted reversing effects on the inhibition of growth and chlorophyll formation cause by O-methylthreonine, but DL-serine, DL-threonine and DL-valine had very little if any reversing effect. The results indicated that O-methylthreonine may be a competitive antagonist of isoleucine utilization in higher plants because of their close structural relationship.