| Effect of germination, seed abrasion and seed size on polyphenol oxidase assay
activity in wheat. Plant Breeding 120:369-373 |
| Demeke,T., Chang,H.G. and Morris, C.F. |
| Polyphenol oxidase (PPO) is one of the major enzymes responsible
for browning of wheat food products. Wheat cultivars differ in PPO
activity and plant breeders wish to select germplasm and cultivars
with low PPO activities. Prior to harvest, seeds may be exposed to
conditions conducive to preharvest sprouting and mechanical dam-
age may occur during harvesting and subsequent handling. Sprout-
ing, mechanical damage and seed size may affect PPO assay activity
and therefore impinge upon the breeder's ability to accurately select
low PPO genotypes. The effects of incipient germination, mechanical
abrasion and seed size on PPO assay activity were investigated using
the cultivars `Klasic' (hard white spring, high PPO), `Penawawa'
(soft white spring, high PPO) and `ID377s' (hard white spring, low
PPO). The influence of embryo vs. distal portions of the seed on
PPO assay activity was also examined. PPO activity was assayed
with constant mixing using L-3,4-dihydroxyphenyl alanine (L-DOPA)
substrate at pH 6.5 at room temperature; absorbance of the reaction
solution was measured at 475 nm. There was no change in PPO
assay activity for seeds imbibed in water for up to 8 h. PPO assay
activity increased in seeds imbibed from 8 to 16 h, and then
gradually declined with increasing imbibing time. PPO assay activity
initially increased as a result of mechanical abrasion but then
gradually declined with increasing abrasion time. Large seeds had a
higher total PPO assay activity than small seeds, but the difference
in activity was not proportional to seed weight. There was only a
slight difference in PPO assay activity between half-seeds with or
without the embryo. Overall, PPO assay activity in dry seeds was
stable and exposure of seeds to injury and moisture did not make
any signifcant change in PPO assay activity among the cultivars or
their relative rankings.
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