VARIABLE CELL LINEAGES FORM THE FUNCTIONAL PEA EPIDERMIS

Evidence was sought for cellular programs and cellular interactions acting during the formation of stomatal spacing patterns. Daily replicas of the surfaces of Pisum sativum leaves were used to reconstruct the cellular development of specific regions of the epidermis. During the period studied small primordia became mature leaves; this involved a 250-fold increase in area and a 20-fold increase in cell number. The earliest event correlated with the development of a stoma was an unequal division, and such divisions were common in neighbouring and even within the same cells. A distinct cell lineage started with these unequal divisions, forming both a stoma and most of the cells that separated it from its neighbours. Both products of an unequal division became regular epidermal cells only where such development prevented the formation of two stomata that would have been in direct contact with one another. Neighbouring stomata often developed and matured together, indicating that there was no mutual inhibition between developing stomata that were more than one cell apart. It is concluded that stomata are products of an intracellular program which generates stomatal patterns during rather than preceding development. This program can be modified and even stopped during its entire course, allowing for the correction of local 'mistakes' of stomatal patterning. © 1992 Annals of Botany Company.