TITLE:
Phenolic Profiles and Polyphenol Oxidase (PPO) Gene Expression of Red Clover (Trifolium pratense) Selected for Decreased Postharvest Browning
AUTHORS:
Isabelle A. Kagan, Randy D. Dinkins, Norman L. Taylor
KEYWORDS:
Trifolium pratense L., Browning, PPO, Clovamide, Isoflavone, HPLC
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.7 No.10,
July
27,
2016
ABSTRACT: Red clover (Trifolium pratense L.) is a legume
forage abundant in phenolic compounds. It tends to brown when cut for hay, due
to oxidation of phenolic compounds catalyzed by polyphenol oxidase (PPO), and
subsequent binding to proteins. Selecting for a greener hay may provide
information about the relationship of browning, PPO, and phenolics to each
other. The red clover Kenland cultivar was selected over eight breeding cycles
for decreased browning after being cut and dried 48 h in the field. Expression
of PPO1 and PPO3, in Kenland and three of the eight cycles, was compared by
real-time quantitative PCR. Phenolic compounds in Kenland and Cycle 8,
collected 0, 24, and 48 h after cutting, were quantified by high-performance
liquid chromatography (HPLC). Visual browning scores decreased 12% between
Kenland and Cycle 8 (P = 0.02). PPO1 and PPO3 gene expression were not affected
by selection. Clovamide decreased 26% in Cycle 8 relative to Kenland (P =
0.016). Sissotrin decreased 10% in Cycle 8 (P = 0.043). Neither total
formononetin nor total biochanin A was affected by selection (P = 0.63 and
0.45, respectively). These results suggest that when selecting clover for
decreased postharvest browning, a decrease occurs in a phenolic compound that
can bind protein independently of PPO. However, PPO1 and PPO3 gene expression, and
the major red clover isoflavones, are minimally affected.