Abstract:
Oxalate oxidase is a pathogenesis‐related enzyme that occurs naturally in plants and
whose activity is observed to increase when hosts are attacked by oxalic acidproducing
pathogens, countering the effects of the acid and thus conferring
resistance to infection. This study, through two assays, sought to investigate the
level of oxalate oxidase activity in six Kenyan sunflower (Helianthus annuus L.)
varieties namely: Kenya Fedha, Rekord, Issanka, H8998, H4038 and H4088. The
reaction of oxalate oxidase with its substrate, oxalic acid, yields hydrogen peroxide
which can be assayed calorimetrically as a measure of enzyme activity. In this study,
an assay which focused on release of hydrogen peroxide from sunflower leaf discs
incubated in a buffer containing oxalic acid was conducted. A detached leaflet assay
was also conducted to assess the ability of oxalate oxidase to prevent necrosis in
response to exogenous application of oxalic acid to plant tissue whereby lesion sizes
were measured. The oil content of the six sunflower varieties was also determined
to identify the ones with the highest oil‐yielding potential. The test sunflower
varieties differed significantly (p<0.05) in oxalic acid degradation and in their
hydrogen peroxide production, indicating varying degrees of oxalate oxidase
activity. H4088 and H8998 had the highest seed oil content and were identified as
superior sunflower varieties that could be recommended for edible oil production
in Kenya. However, H8998 may require genetic transformation to enhance its
disease resistance capacity.
