Navigating shoot apical meristem plasticity for plant adaptation.

Plants exhibit striking developmental plasticity, driven by stem cell populations within meristematic tissues such as the shoot apical meristem (SAM). While the genetic networks governing stem cell homeostasis are well-characterized, recent studies reveal that the SAM also functions as an active environmental sensor to modulate growth plasticity. This Tansley review synthesizes advances in how the SAM perceives and integrates key environmental signals - including light, temperature, oxygen, and humidity - to direct adaptive growth. We detail the molecular mechanisms, such as photoreceptor-mediated activation, thermal resilience pathways, hypoxia sensing, hydraulic dynamics, and mechanical signalling, that regulate stem cell activity. Furthermore, we explore how these environmental cues couple with developmental programs to fine-tune meristem function and organogenesis. By drawing parallels to the environmental regulation of root meristem development, we highlight conserved sensing and signalling modules within meristematic tissues that influence plant growth plasticity. Examining this interplay both in shoot and in root meristems, from evolutionary and applied perspectives, underscores how environmental responsiveness of stem cell niches regulates plant adaptation, informing strategies for engineering climate-resilient crops.