HETEROBLASTIC FEATURES OF LEAF ANATOMY IN MAIZE AND THEIR GENETIC-REGULATION

Heteroblastic features of leaf anatomy in maize were identified by con ducting a quantitative analysis of leaf anatomy. Heteroblastic variati on in cuticle thickness and epidermal cell shape paralleled changes in previously defined juvenile- and adult-specific traits. The other tra its examined in this study (thickness of the leaf blade, epidermal and bundle sheath cell size, vascular area, interveinal distance, mesophy ll area:bundle sheath area ratio) varied in a more complex fashion. To determine which of these traits are regulated by genes involved in sh oot maturation, we examined the effect of the Teopod2 (Tp2) mutation o n their expression. Tp2 increases the number of leaves that express th e juvenile form of cuticle thickness, epidermal cell shape, and vascul ar area and causes all other leaves to produce intermediate (juvenile/ adult) forms of these traits. It has little or no effect on any of the other traits we examined. Thus, much of the heteroblastic variation i n the internal anatomy of the maize leaf appears to be regulated by fa ctors that are unrelated to the developmental phenomenon of phase chan ge. The effect of Tp2 on leaf anatomy is interesting not only because it provides a criterion for distinguishing between different types of heteroblastic traits, but also because it provides some insight into t he nature of the developmental processes involved in shoot maturation. In particular, the observation that Tp2 leaves are quantitatively int ermediate between juvenile and adult leaves supports the hypothesis th at some phase-specific aspects of leaf identity are regulated in a com binatorial fashion rather than by mutually exclusive patterns of gene expression.