Chlorophyll Fluorescence of the Desert Plant Calotropis Procera Grown Under Water Deficit Stress

Abdellah Akhkha

Department of Biology, Faculty of Science, Taibah University, Al-Madinah Al-Munawwarah, Kingdom of Saudi Arabia.

Corresponding Author E-mail: abdellah99@gmail.com

ABSTRACT: The effectiveness of the photosynthetic machinery of the desert plant Calotropis procera grown under different water deficit regimes was investigated by chlorophyll fluorescence technique in order to understand how such desert plant withstand water limitations without a irreversible damage to the integrity of the Photosystem II of the photosynthetic apparatus. At the onset of stress (first harvest), all chlorophyll fluorescence parameters Fo, Fm, Fv / Fm and Fv / Fo, were reduced in both low and mild water deficit regimes 30% and 50% respectively. However, in the second harvest, stressed leaves showed some recovery and maximal fluorescence Fm was increased at the low water regime. All chlorophyll fluorescence ratios were also increased in both low and mild water deficit regimes. At the third harvest, Fo and Fm were still higher in low water regime, but decreased or reached a level similar to that of well-watered plants respectively at mild water regime. Chlorophyll fluorescence ratios at low water regime were similar to that of the well-watered plants but higher at mild water regime. Generally, the photosynthetic apparatus was reversibly affected by both limited water regimes on the onset of water stress; however, stressed leaves were recovered and the photosynthetic machinery became sometimes similar to that of well-watered plants or even more efficient at other times. Chlorophyll Index was increased in all water regimes and at all harvests. The relationships between Chlorophyll Index and the different chlorophyll fluorescence parameters are discussed.

KEYWORDS: Chlorophyll fluorescence; Calotropis procera; water deficit regimes

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