Sampling for 3-hydroxytyramine and polyphenoloxidase in sugar beets

Abstract

3-Hydroxytyramine is associated with resistance to Cercospora leaf spot. Polyphenoloxidase is capable of oxidizing 3-hydroxytyramine. The sequence of steps followed in determining a reliable sampling procedure for 3-hydroxytyramine and polyphenoloxidase analysis of sugar beet leaves and various problems encountered are presented. The content of 3-hydroxytyramine in beet leaves reached a peak when the leaves were 1/2 to fully expanded and then decreased. Time of maximum content apparently depended on the genotype. The content of polyphenoloxidase reached a maximum when the leaves were fully expanded and did not decrease significantly in mature leaves from older plants. The optimum time for sampling leaves to determine both 3-hydroxytyramine and polyphenoloxidase activity was when the leaves were fully expanded. The most reliable portion of the leaf for sampling was a transverse section from the center of the leaf. Leaves from seedlings contained less 3-hydroxytyramine than leaves from older plants; and the younger leaves on a given plant contained more 3-hydroxytyramine than did senile leaves from the same plant. On a given plant younger leaves contained less polyphenoloxidase activity than did older leaves. Injury, by scratching the leaf surface, caused an increase in 3-hydroxytyramine content.