From Molecular Signals to Phenotypic Plasticity: A Critical Synthesis of Structural and Developmental Remodelling in Plant Stress Adaptation

Abstract

Plants respond to environmental stress by altering the structure and the developmental trajectory of their organs, and the molecular pathways connecting stimulus perception to these alterations have been mapped in progressively finer detail over the past three decades. Whether that mechanistic knowledge explains, or predicts, the plasticity observed in plants growing under field conditions remains contested. This critical narrative review examines the evidence linking early signalling events to structural and developmental remodelling, and evaluates how far the resulting phenotypes can reasonably be described as adaptive. Literature was identified through searches of open scholarly databases and supplementary citation searching, and was appraised on design quality, replication and ecological realism rather than on citation frequency. Four judgements emerge from the synthesis. Signal perception remains the weakest link in the causal chain, because few primary sensors for water deficit, salinity or nutrient limitation have been demonstrated directly, and much of the mechanistic architecture is inferred from downstream mutants. Developmental remodelling is best documented for root branching, stomatal patterning, internal aeration tissue and elongation growth, where genetic evidence is strong but was generated largely in a small number of species under controlled conditions. The assumption that plastic responses are adaptive is asserted far more often than it is tested, since fitness measurements under realistic conditions are scarce and evidence for the costs of plasticity is inconsistent. Stress memory is empirically robust at the level of transcription and chromatin, yet its persistence, heritability and agronomic value remain unresolved. The most consequential gap is inferential rather than mechanistic, because the experimental systems that support strong causal claims differ systematically from the environments in which plasticity matters. Progress will depend on fitness-anchored experiments in fluctuating environments, on genetic dissection of plasticity as a trait in its own right, and on phenotyping that resolves developmental trajectories rather than endpoints.