ARREST OF STOMATAL INITIALS IN TRADESCANTIA IS LINKED TO THE PROXIMITY OF NEIGHBORING STOMATA AND RESULTS IN THE ARRESTED INITIALS ACQUIRING PROPERTIES OF EPIDERMAL-CELLS

We examined spatial relations of arrested stomatal initials and their differentiated state on leaves of the monocotyledon Tradescantia. The placement and proximity of stomata and arrested stomatal initials to t he five nearest stomata were studied to test the hypothesis that if de veloping stomatal initials occur too close to one another, initials wi ll arrest. The results showed that arrested stomatal initials were not randomly placed, but were closely associated with another stoma, most often in an adjacent cell file. The distance to their nearest stomata l neighbors was less than the equivalent distance between stomata that mature. After stomatal initials form, their position within or across cell files was not adjusted by cell division or expansion. Synergisti c effects from several neighboring stomata could not be linked to stom atal arrest; rather, arrest was associated only with the nearest stoma tal neighbor. Since the arrest of stomatal initials was distance depen dent, a failure intrinsic to the arrested initials is not solely respo nsible for halting stomatal development. These data show that an inhib itory mechanism adjusts stomatal development to influence the final di stribution of Tradescantia stomata. The pigmentation and expansion cha racteristics of arrested stomatal initials were like those of epiderma l cells, indicating that the initials did not remain halted at a speci fic point in their development. The capacity of arrested initials to d ifferentiate in the epidermal cell pathway indicates that they remain pluripotent after their initial specification and that the opportunity for patterning is long enough to permit their entry into the epiderma l cell pathway. (C) 1995 Academic Press, Inc.