Water Potential Gradients between Old and Developing Leaves in Lithops (Aizoaceae).

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Lithops plants consist of a pair of opposite succulent leaves inserted on a short stem. The apical meristem produces a new pair of leaveswithin the old one every growing season, recycling water from the old leaves. Since there are no data on water relations between the twopairs of leaves, we measured leaf water potential at different stages of development with a pressure chamber. Osmotic potential of cell sapwas measured with a cryoscopic osmometer and turgor pressure was calculated indirectly. Leaf water potentials were never very low eventhough plants were not irrigated. In old leaves water potential ranged between -0.5 and -0.28 MPa. In young leaves water potentialincreased with size from -1.05 to -0.5 MPa and was always lower than in the corresponding old leaves. The water potential gradientbetween old and new leaves was steeper in the early stages of development (0.6 MPa) and gradually decreased (0.15 MPa) when youngleaves had almost completed their expansion. Our data show that in Lithops water movement from old to young leaves occurs accordingto a water potential gradient. The maintenance of this gradient may be ascribed to differences in turgor pressure, due to the more elasticand plastic walls of cells of young leaves. The possibility to perform a complete life cycle without external water supply is an extremeadaptation to the arid environment where Lithops grows.
Lingua originaleEnglish
pagine (da-a)366-368
Stato di pubblicazionePublished - 2007


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