Pr:flavonoid 3'-hydroxylase in maize seedlings, leaf sheaths and aleurone

A microsomal preparation has been obtained from seedlings and leaf sheaths that catalyzes the addition of a hydroxyl group at the 3'-position of flavonoid compounds. This activity has also been assayed in aleurone tissue that had been scraped from the seed and used as the source of the hydroxylase. Thus far it has not been possible to obtain the hydroxylating, microsomal particle free of the aleurone tissue. Utilization of genetic materials specifically defined as to the dosage of Pr or pr results in the confirmation of a gene:enzyme (Pr:hydroxylase) relationship that has long been thought to be true. The specific activity ratio for the hydroxylase in seedlings, considering Pr Pr, Pr pr and pr pr stocks is 3:1:0.15, respectively. The specific activity ratio for aleurone tissue of Pr Pr Pr, Pr Pr Pr, Pr pr pr, and pr pr pr is 3.4:1.4:1:0. Pr Pr and pr pr stocks were assayed for leaf sheath activity over a six week period during the growing season. Anthesis occurred during the fifth week at or near the peak of hydroxylase activity, at which time the pr pr tissue had 18% of the hydroxylase activity found in the Pr Pr tissue.

When the flavonoid compounds in aleurone tissue were extracted and identified, cyanidin and pelargonidin were both found in all the stocks. For Pr Pr Pr, Pr Pr pr, Pr pr pr and pr pr pr, quantitative data for cyanidin and pelargonidin and cyanidin/pelargonidin ratios were 9.0:5.6:2.7:0.1, respectively. Reducing this to its simplest form gives a ratio of 3.3:2.1:1:0.03, which is very close to the gene dosage ratio of 3:2:1:0. The data obtained for the individual pigments did not follow this fixed ratio in the same manner. Thus, it would seem that the pigment ratio is more closely controlled by the gene dosage than is the individual pigment concentration.

R. Larson
 
 


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