V31M235R1128 - J. King Saud Univ., Vol. 16, Science (1),...

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Unformatted text preview: J. King Saud Univ., Vol. 16, Science (1), pp. 19-29, Riyadh (1423/2003) Ecological Anatomy of Xerophytic Leaves from Qatar Hussain A. Abulfatih University of Qatar, Faculty of Science, Department of Biological Sciences, P. O. Box: 11828, Doha, Qatar e-mail: [email protected] (Received 27-2-1422 H; accepted for publication 29-12-1422 H) Abstract . Leaf anatomy of 11 of the most common xerophytic species found in Qatar were investigated, including: Acacia ehrenbergiana , Calotropis procera , Cyperus conglomeratus , Fagonia ovalifolia, Glossonema edule, Heliotropium bacciferum , Lycium shawii , Ochradenus baccatus , Sporobolus arabicus , Tamarix rosmarinus and Ziziphus nummularia . Under the extreme arid conditions leaf anatomy revealed the following features: most investigated species have flattened leaves, coated with a layer of cuticle and one row of epidermal cells. Guard cells are present commonly at the level of the epidermal layer or slightly depressed. Monocot species maintain bulliform cells (motor cells) which play a major role in folding and unfolding of the leaf corresponding with the changes in the environmental conditions, as in Sporobolus arabicus . Trichomes were present with different proportions in different species, as shown in Glossonema edule , Heliotropium bacciferum , Lycium shawii , Sporobolus arabicus , and Ziziphus nummularia . Calotropis procera had a high density of scales on the leaf surface. Palisade tissue is well developed, and characterized by having many layers of elongated cells, rich with chloroplasts. Intercellular spaces are limited in the palisade and spongy tissues. Spongy tissues occupy much less volume if compared with mesophytes and hydrophytes. Vascular bundles usually distributed across the width of the leaf. Vascular bundles are surrounded by a bundle sheath of parenchyma cells in the case of Sporobolus arabicus . Such bundle sheath is known to play an important role in the process of photosynthesis under extreme arid conditions. Leaves in many instances maintained strengthening tissues (fibers), especially in Sporobolus arabicus . Introduction Xerophytes are those plants that live in arid conditions, and have elaborate structural and physiological modifications that reduce water loss. Xerophytic annuals, which depend solely on sporadic rainfall are shallow-rooted and perennials which depend mainly on the subsoil moisture are deep-rooted [1, 2]. Desert plants show high stomatal resistance, to reduce water loss. Many desert plants have evolved specific types of photosynthetic pathways to cope with the scarcity of water, high temperature and intense solar radiation, as in C 4 and CAM plants [3]. 19 Hussain A. Abulfatih Drought resistant plants in the Arabian Peninsula are commonly found in the interior dry areas in diverse habitats, extending over Qatar, United Arab Emirates, Bahrain, Kuwait, Oman, Saudi Arabia, and Republic of Yemen [1-10]....
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V31M235R1128 - J. King Saud Univ., Vol. 16, Science (1),...

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