Abstract
Leaf epidermal micromorphology and mesophyll structure during the development of Populus euphratica heteromorphic leaves, including linear, lanceolate, ovate, dentate ovate, dentate rhombic, dentate broad-ovate and dentate fan-shaped leaves, were studied by using electron and light microscopy. During development of heteromorphic leaves, epidermal appendages (wax crystals and trichomes) and special cells (mucilage cells and crystal idioblasts) increased in all leaf types while chloroplast ultrastructure and stomatal characters show maximum photosynthetic activity in dentate ovate and rhombic leaves. Also, functional analysis by subordinate function values shows that the maximum adaptability to adverse stress was exhibited in the broad type of mature leaves. The 12 heteromorphic leaf types are classified into three major groups by hierarchical cluster analysis: young, developing and mature leaves. Mature leaves can effectively obtain the highest stress resistance by combining the protection of xerophytic anatomy from drought stress, regulation of water uptake in micro-environment by mucilage and crystal idioblasts, and assistant defense of transpiration reduction through leaf epidermal appendages, which improves photosynthetic activity under arid desert conditions. Our data confirms that the main leaf function is differentiated during the developing process of heteromorphic leaves.
Highlights
During the entire life cycle of higher plants, they are repeatedly subject to diverse environmental stress, especially in desert ecosystems
The cylindrical or ellipsoid cells are closely arranged in the palisade tissue, and no spongy tissue was observed in the mesophyll besides the vascular bundle systems
We found that the epicuticular wax coverage and thickness increased from Pe1 to Pe12 in the development of P. euphratica heteromorphic leaves
Summary
During the entire life cycle of higher plants, they are repeatedly subject to diverse environmental stress, especially in desert ecosystems. Plant response to such unfavorable growth conditions can be a complex combination of physiological activity, individual morphology and longterm adaptive strategy [1, 2]. Previous studies have provided useful information for understanding the adaptation mechanism of P. euphratica to abiotic stress, including eco-hydrological process of the forest community [8], photosynthetic and physiological characteristics of the tree [9,10,11,12], morphological and structural characters of the leaf [13], gene and protein response to stress on a molecular level [7, 14, 15]. Scientists have succeeded in unraveling the whole genome sequence of P. euphratica and the genetic bases underlying the mechanism against salt stress [16]
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