Newly-sprouted leaves at the stem base differ anatomically and histochemically from the ‎crown leaves in Ficus johannis

Ficus species evolved physical and chemical defense mechanisms to cope with variable environmental conditions. Field observation of Ficus johannis Boiss. (Mountain Fig) indicated that newly-sprouted leaves developed at the base of the plant are skin irritating, but the crown leaves, out of animal reach, do not. Here, we investigated the anatomical and phytochemical characteristics of both leaves of F. johannis growing in the arid mountains of the United Arab Emirates (UAE). The results showed the presence of numerous tapering non-glandular and a few glandular trichomes on the newly-sprouted leaves. Gas chromatography-mass spectrometry (GC-MS) analysis showed the presence of 107 metabolites; out of them, 16 compounds were identified in the newly-sprouted leaves but not in the crown ones. β-Amyrin, α- amyrin, and β-amyrin acetate, known as irritant chemicals, were~5, 3, and 200 times higher in the newly-sprouted leaves than in the crown leaves, respectively. Our study is the first to report the presence of stinging trichomes in Ficus species, a rare type that has been reported in a few angiosperm families. These results indicated that the variety of trichomes on the newly-sprouted leaves and the leaf’s unique metabolites provide sufficient protection mechanisms against grazing animals.