The ratio of auxin to cytokinin controls leaf development and meristem initiation in Physcomitrium patens.

The article focuses on the interaction between the plant hormones auxin and cytokinin in regulating development of the moss Physcomitrium patens, particularly in gametophore (shoot) architecture. It demonstrates that the ratio of auxin to cytokinin, rather than their absolute concentrations, critically influences phyllid (leaf-like structure) outgrowth, cell proliferation, and branch stem cell initiation. Experimental treatments show that high auxin levels inhibit phyllid development, but this effect can be partially reversed by simultaneous cytokinin application, while inhibition of auxin synthesis mimics cytokinin effects. Additionally, cytokinin-insensitive mutants exhibit altered auxin responses and hypersensitivity to auxin, indicating complex crosstalk between these hormones in moss development that parallels but also differs from angiosperm models.