Tracing development of soybean leaf primordia by marking progenitor cells with mutant markers

Marking cells with genetic marker is a useful way to study plant development. A heterozygous (Y11y11) strain of soybean was exposed to X rays or 14 MeV neutrons before, or 1-7 days after, sowing. Clones of dark-green (due to reversion of the Xantha-like allele y11) or yellow (due to loss of the wild-type allele y11) cells were produced in the first and second compound leaves. Of these clones, none extended beyond the mid-vein. In the first leaf, about half the clones produced by marking before sowing were delimited by the mid-vein but extended beyond the main lateral veins; whereas, about 20% were bounded by small lateral veins, indicative that in the first-leaf primordium of the dormant embryo the mid-vein is already differentiated, but that only about half of the main lateral veins are. After marking on day 7, 99% of the marked clones in the first leaf were bounded by small lateral veins. This and the preceding results indicate that most small lateral veins develop during the first seven days after sowing, together with development of the leaf lamina. Primordia of the 6th or later leaves in dormant seeds exposed to neutrons produced two marked clones that extended over the mid-vein, showing that the mid-vein and lamina are not completely differentiated at this early stage.