Growth and development of aerial roots of a tropical ornamental, Philodendron lacerum

Abstract

Philodendron lacerum, an ornamental aroid, produces aerial roots and subterranean ones. The two root types differ in morphological, anatomical and growth characteristics. Aerial roots, unlike the subterranean roots, do not produce laterals. Anatomically, aerial roots are distinguishable from subterranean roots by chlorenchyma and sclerenchyma cells in the cortex. Marked structural and growth differences exist between young and mature aerial roots. Mature aerial roots contain more sclerenchyma cells and chloroplasts and larger resin ducts than young roots. The elongation rate of young hanging roots was much greater than that of mature ones. Aerial roots in contact with a substratum produce few sclerenchyma cells and chloroplasts on the contact side; their growth rate, nonetheless, was not affected by the contact. Biochemical analyses of the aerial roots revealed that the extractable protein content was highest at the growing root apex and chlorophyll concentration was highest in the mature portion of the aerial roots. The growing root tip portion exhibits a higher activity of alkaline phosphatase, acid phosphatase and napthol AS-Bi-phosphohydrolase compared with the mature region of the aerial root. The activity of esterase, esterase lipase, leucine arylamidase, β-galactosidase and N-acetyl-β-glucosaminidase were detectable in the actively growing root tip region of the aerial root but were very low or absent in the mature root tissues. These findings are discussed in the light of the existing knowledge of aerial root development and its role in ecological adaptation.