Roles of auxin and Uni in leaf morphogenesis of the afila genotype of pea (Pisum sativum)

Pea (Pisum sativum L.) plantlets with the afila (af) allele, alone or in combination with other leaf form mutations, were grown on media containing the auxin transport inhibitors 2,3,5,-triiodobenzoic acid (TIBA), N-1-naphthylphthalamic acid (NPA), or the weak auxin p-chlorophenoxyisobutyric acid (PCIB). The morphology of the resulting plantlets was analyzed, and shoot tips were fixed for SEM observations and were frozen to monitor Uni gene expression using semiquantitative RT-PCR. Auxin transport was measured in leaf parts of two genotypes using C-14-labeled IAA. All three inhibitors produced similar morphological abnormalities in the four af genotypes used in this study, and the number and severity of abnormalities increased at the higher inhibitor concentrations. The number of pinna pairs produced on leaves was reduced. The proximal compound pinnae had fewer secondary branches and/or congenitally fused margins. Some leaves were converted from pinnately to palmately compound or to simple forms. Others were converted to scale leaves, or the leaf blades were lost, leaving only a pair of stipules. Various terminal pinna conversions occurred. Polar IAA transport was basipetal for all leaf parts and was greater in the petioles of af than wild type. Uni expression was reduced in shoot tips of plantlets grown in 60 muM NPA and TIBA and in the af uni-tac and af tl uni-tac genotypes. These results indicate that both an auxin gradient and the Uni gene play fundamental roles in controlling leaf morphogenesis, and specifically, in the compound pinnae of the af genotypes of pea.