Structural and functional properties of trichomes of xeromorphic leaves

Trichomes of xeromorphic leaves of 12 different species (Banksia speciosa, Corokia buddleioides, Correa backhousiana, Lavandula officinalis, Leucospermum grandiflorum, Metrosideros excelsa, Olea europaea, Olearia rotundifolia, Pittosporum crassifolium, Pittosporum sp., Rosmarinus officinalis, Senecio cineraria) and trichomes of mesomorphic leaves of five species (Achimenes grandiflora, Geum urbanum, Gynura aurantiaca, Populus alba, and Styrax officinalis) were stained with Sudan IV and Sudan black. In the trichomes of all xeromorphic leaves the walls of the basal or stalk cells stained with these reagents. However, none of the cell walls of the trichomes of the mesomorphic leaves were stained by the Sudan reagents. Portions of leaves of three of the xeromorphic species (Corokia, Correa, Olea) and leaves of three of the mesomorphic species (Achimenes, Geum, Gynura) were floated on 0.1 per cent Calcofluor white solution. Examination of cross-sections of these leaf portions in the fluorescence microscope indicated that even after 4 days of floating the Calcofluor, which is an apoplastic tracer, did not enter the trichome walls of the xeromorphic leaves. However, the Calcofluor brightener could already be detected in the trichome walls of the mesomorphic leaves after one day. The adapted properties of the trichomes of the xeromorphic leaves are discussed.