Abstract
Abstract. Kalanchoe pinnata (Lam.) Pers., a plant having crassulacean acid metabolism (CAM), was grown in high light (16–23 mol photons m−2 d−1) and in the shade (0.8–2.1 mol photons m−2 d−1), respectively. Plants were stressed in three ways, i.e. by transfer from high light to shade or vice versa just before measurements, and by withholding nitrogen and/or water. During the day‐night cycle of CAM, K. pinnata showed day‐night changes of citrate levels (Δ citrate) in addition to malate changes (Δ malate). Changes of leaf‐cell sap osmotic pressure. Δπ, were linearly correlated with these changes of organic‐acid anion levels with a relation of Δπ/(Δ citrate +Δ malate) = 1/1. The environmental stressor, i.e. limited N‐nutrition, drought and higher or lower irradiance than experienced during growth, affected the absolute and relative contributions made by Δ citrate and Δ malate to total nocturnal organic‐acid accumulation. In the high‐light‐grown plants transferred to the shade, changes of citrate levels were much less affected than changes of malate levels by the generally decreased metabolic activity and inhibition of CO2 uptake. In the shade‐grown plants, Δ citrate increased in response to stress imposed by interactive effects of the three stressors.
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