ROLES OF THE AF AND TL GENES IN PEA LEAF MORPHOGENESIS - CHARACTERIZATION OF THE DOUBLE MUTANT (AFAFTLTL)

The pleiofila phenotype (afaftltl double mutant) of Pisum sativum aris es from two single-gene, recessive mutations known to affect the ident ity of leaf pinnae, afila (af), and acacia (tl). The wild-type leaf co nsists of proximal leaflets and distal tendrils, whereas the pleiofila leaf consists of branched pinnae terminating in small leaflets. Using morphological measurements, histology, and SEM, we characterized the variation leaf form along the plant axis, in leaflet anatomy, and in l eaf development in embryonic, early postembryonic, and late postembryo nic leaves of aftl and wild-type plants. Leaves on aftl plants increas e in complexity more rapidly during shoot ontogeny than those on wild- type plants. Leaflets of aftl plants have identical histology to wild- type leaflets although they have smaller and fewer cells. Pinna initia tion is acropetal in early postembryonic leaves of aftl plants and in all leaves of wild-type plants, whereas in late postembryonic leaves o f aftl plants pinna initiation is bidirectional. Mast phenotypic diffe rences between these genotypes can be attributed to differential timin g (heterochrony) of major developmental events.