Background and aims: Control of diseases in the key tropical staple,
cassava, is dependent on resistant genotypes, but the innate mechanisms
are unknown. The aim was to study phenylpropanoids and associated
enzymes as possible defence components.
Methods: Phenylalanine ammonia‐lyase (PAL), phenylpropanoids and
peroxidases (POD) were investigated in elicited cassava suspension cells
and leaves. Yeast elicitor was the most effective of several microbial
and endogenous elicitors. Fungitoxicity was determined against the
cassava pathogens Fusarium solani, F. oxysporum and the saprotroph
Key results: A single and rapid (≥2–3 min) oxidative burst, measured as
hydrogen peroxide, occurred in elicited cells. PAL activity was induced
maximally at 15 h and was preceded by PAL mRNA accumulation, which
peaked at 9 h. Symplasmic POD activity increased four-fold in cells, 48
h post-elicitation. POD isoforms (2-7 isoforms, pI 3·1-8·8) were
detected in elicited and unelicited cells, extracellular medium and
leaves but two extracellular isoforms were enhanced post-elicitation.
Also expression of a cassava peroxidase gene MecPOD1 increased in
elicited cells. Only anionic forms oxidized scopoletin, with highest
activity by isoform pI 3·6, present in all samples. Unidentified
phenolics and possibly scopolin increased post‐elicitation, but there
was no enhancement of scopoletin, rutin or kaempferol-3-O-rutinoside
concentration. Fungal germ tube elongation was inhibited more than
germination by esculetin, ferulic acid, quercetin and scopoletin. T.
harzianum was generally more sensitive than the pathogens and was
inhibited by ≥50 µg mL–1 of ferulic acid and quercetin and ≥0 µg mL–1 of
Conclusions: Phenolic levels in cells were not enhanced and were,
theoretically, too low to be inhibitory. However, in combination and
when oxidized they may contribute to defence, because oxidation of
esculetin and scopoletin by peroxidase and of esculetin by tyrosinase
enhanced their fungitoxicity up to 20-fold.
Gomez-Vasquez, R., Day, R., Buschmann, H., Randles, S., Beeching, J.R. and Cooper, R.M. Phenylpropanoids, Phenylalanine Ammonia Lyase and Peroxidases in Elicitor-challenged Cassava (Manihot esculenta) Suspension Cells and Leaves. Annals of Botany (2004) 94 (1) 87-97. [DOI: 10.1093/aob/mch107]
Phenylpropanoids, Phenylalanine Ammonia Lyase and Peroxidases in Elicitor-challenged Cassava (Manihot esculenta) Suspension Cells and Leaves