Abnormal Leaf morphologies associated with primary and secondary vein patterning defects in Catharanthus roseus: mid-vein defect converts simple leaf into binate compound leaf

Abstract

Simple petiolated leaves are formed on the wild type plants of apocynaceous medicinal-cum-floricultural species Catharanthus roseus. A C. roseus variant line homozygous for two loss-of-function mutations, an induced leafless inflorescence (lli) mutations and a natural bisected leaf (bil) mutation, was isolated on account of its unique leaf bisection phenotype which was characterized. The lli bil phenotype was highly penetrant but poorly expressed. Only about one-fourth of leaves of lli bil plants were bisected. Leaf bisection was correlated with premature termination of midvein. Degree of bisection varied from a nick at the apex of lamina to formation of two complete leaflets. The notch in 43 % of the bisected leaves bore a pin-like apical adventitious growth. The features of bisected leaves showed that midvein was essential for symmetrical development of smooth lamina spans on its either side; although the development of spans was independent. Several lateral veins emerged from proximal midvein and grew acropetally. Lamina development in the proximal region failed in the absence of local lateral veins. Bisected leaves were also formed as bi-lobed simple leaves, each lobe having its own primary (mid) vein arising from proximally bifurcated midvein. Also formed were completely bisected leaves. In these binately compound leaves, each leaflet had its own petiolule attached to the leaf petiole. The lli bil genotype of C. roseus perhaps provides the only example of a compound leaved variant evolving from a simple leaved species. This phenotype of lli bil leaves supports the suggestion that simple leaf form was ancestral in angiosperms.