Abstract
Homogenates were prepared from the leaves of hydroponically cultivated sunflower (Helianthus annuus, L.) under deficient, normal and toxic B conditions and the phenylalanine ammonia‐lyase activity together with the ortho‐diphenolic and micronutrient content were measured every week from one month to flowering
The restoration of enzymatic activity on the exogenous addition of borate “in vivo”; was also studied.
Both B toxicity and deficiency resulted in increased phenylalanine ammonia‐lyase activity in the homogenates
The toxicity effect was early and sustained and the deficiency effect late and transitory. “In vitro”; borate addition to the reaction mixture did not significantly change the phenylalanine‐ammonia‐lyase activity in the homogenates.
There was no statistical correlation between the phenylalanine‐ammonia‐lyase activity and any micronutrient content in leaves.
A high accumulation of ortho‐diphenolics appeared in B‐deficient leaves only after 28 days of differential culture and may be responsible for the drop in phenylalanine‐ammonia‐lyase activity noted at this time.