High extracellular accumulation of p-hydroxybenzoic acid, p-hydroxycinnamic acid and p-hydroxybenzaldehyde in leaves of Phoenix dactylifera L. affected by the brittle leaf disease

The work reported here is the first attempt to analyze the soluble and extracellular phenolics in the date palm affected by the brittle leaf disease. It aims to understand the biochemical basis of the date palm resistance to this pathology whose the causal agent is still unknown. The GC/EI-MS study of phenolic compounds separated from cell wall of healthy and affected leaves, revealed several modifications. In leaves presenting moderate symptoms, an enhanced extracellular accumulation of p-hydroxybenzoic acid, p-hydroxycinnamic acid and p-hydroxybenzaldehyde, was highlighted. This accumulation was accompanied with a significant decrease in abundance of acetophenones, particularly 2′-Hydroxy-4′,5′-dimethoxyacetophenone and acetosyringone. It was assumed that p-hydroxybenzoic acid and p-hydroxybenzaldehyde were formed as the major degradation products of p-coumaric acid. Further investigations and analyses have also shown that guaiacyl units have significantly decreased in supporting tissues. Withal, a progressive decrease of protein contents and peroxidase activity was registered. Such modifications severely affect the cell wall integrity and lead to the leaves’ friability, what gives the “Brittle leaf disease” its name. So, further investigations must be carried out in the aim to acquire better understanding concerning with this pathology.

► In MFC-affected leaves, an enhanced extracellular accumulation of p-HBA, p-HCA and p-HBAld, was found.
► p-HBA and p-HBAld were formed as the major degradation products of p-HCA.
► A progressive decrease of lignin, POX activity and protein contents, was also highlighted.
► Such modifications severely affect the cell wall integrity and lead to the leaves’ friability.