Differential modulation of crassulacean acid metabolism according to macronutrient deficiencies in C ₄ Portulaca oleracea

C ₄ photosynthesis and the crassulacean acid metabolism (CAM) rarely co-evolved in a single lineage, but Portulaca can switch from C ₄ to CAM under drought stress. Little is known about CAM responses to nutrient availability, hence the goal of this work was to assess the influence of macronutrients over C ₄ -CAM.

P. oleracea was grown hydroponically and subjected to treatments (+/− PEG) for: nitrate deficiency (−NO ₃ ⁻ ), ammonium (NH ₄ ⁺ ), NO ₃ ⁻ + NH ₄ ⁺ , magnesium (−Mg), phosphorus (−P), calcium (−Ca), potassium (−K), and sulphur (−S) deficiencies, and salt stress. Samples were monitored for diurnal titratable acidity (ΔH ⁺ ), osmotic potential, and gene relative expression for core C ₄ /CAM and signaling genes.

-NO ₃ ⁻ induced CAM even without PEG, a process probably without the mediation of abscisic acid (ABA). Notably, −P showed a trend to induce CAM without PEG and −Ca prevented CAM induction even with PEG. Salt stress induced CAM, and NH ₄ ⁺ was not toxic for P. oleracea . Other treatments showed less conspicuous responses.

This work brings an unprecedented overview of the nutrition of C ₄ and CAM, suggesting perspectives for deepening the study of C ₄ -CAM. Understanding the molecular mechanisms and environmental signaling of C ₄ -CAM is essential for realizing the evolution of two CCMs in a single plant.