Tissue patterning of Arabidopsis cotyledons.

•  Trichome and stomatal patterning are not independent events because trichomes form before stomata. We thought trichome genes might provide spatial referents to ensure proper distribution of stomata for gas exchange, and therefore studied mutants of GL1 and TRY using stomatal pattern of the entire cotyledon surface as the indicator. •  Mature cotyledons were imaged by SEM, stomatal maps were generated, and data were spatially analysed. Expression of GL1 and TRY was determined in wild type and mutant samples by reverse transcriptase-PCR (RT-PCR) analysis. •  At the tissue level, findings showed wild type cotyledons had a random stomatal pattern, whereas gl1-1 and try240 cotyledons had ordered and clustered stomatal patterns, respectively. Regardless of overall pattern type, c. 10% of the stomatal population - those closest to one another - were always ordered, the result of genes regulating cellular differentiation. •  These results indicate epidermal cells respond to GL1 and TRY signals that affect distribution of both stomata and trichomes in postembryogenic events. The GL1 and TRY genes play dual roles in the epidermis, one role regulating epidermal tissue patterning and a second role connected with trichome development.