Temporal tracing of cell morphology and physiology shifts impacted by nitrate nutrient. (A) Temporal changes of cell morphologies. The circles outline single cells with heterocyst morphology. Spectral responses of heterocysts (B) and vegetative cells (C), and PCA-derived ¹⁵N contents (D) of Anabaena sp. PCC 7120 in RMCS after adding NaNO₃ at different times.