PLANT HETEROPHYLLY - O.M. NEDUKHA - 2011

CHAPTER ONE. MORPHOLOGICAL AND STRUCTURAL-FUNCTIONAL CHARACTERISTICS OF VEGETATIVE ORGANS IN HETEROPHYLLOUS PLANTS

1.6. ANATOMICAL STRUCTURE OF LEAVES AND STEMS IN HETEROPHYLLOUS PLANTS

1.6.2. Leaves of Sagittaria sagittifolia

In S. sagittifolia (common arrowhead) growing in the Psel River (Velyka Bahachka urban-type settlement, Poltava Region), both emergent (floating/aerial) and submerged leaves were present in May and early June (Fig. 1.3.3, a, b; see Insert IV and description in Section 1.3). The emergent leaves of each individual exhibited two forms: 2-7 leaves had a sagittate blade, while one or two leaves possessed an oblong blade. Furthermore, 5-12 submerged leaves exhibited an elongated linear blade. The petiole length of emergent leaves ranged from 23 to 35 cm depending on the Water depth at which the plants grew, whereas the submerged leaves were sessile (lacking a petiole). In individuals growing at depths up to 30 cm, the dimensions of the submerged leaves along the long axis were 25-40 cm, and along the short axis, 1.2-1.8 cm.

Emergent sagittate leaves. The leaf blades of S. sagittifolia were characterized by a dorsiventral Anatomical Structure, containing a single-layered upper and lower epidermis, a two-layered palisade parenchyma, and 4-7 layers of spongy parenchyma (Fig. 1.6.2.1, a, b; see Insert IX). Leaf thickness was approximately 300 µm. Stomata were visible on both the upper and lower epidermis; they were spaced 14-18 epidermal Cells apart at a distance of about 500 µm from one another (in transverse leaf sections). The cells of both epidermal layers fit tightly together. METABOLISM/14.html">Chloroplasts were detected in the Cells of the upper and lower epidermis (Fig. 1.6.2.1, c, d). Nuclei in the cells of both the upper and lower epidermis were positioned on the proximal side.

The cells of the two-layered palisade parenchyma were nearly cylindrical in shape, with their height being four times greater than their width (Table 1.6.2.1). Heterogeneity in Cell density was observed: 2-15 densely packed palisade cells alternated with aerenchyma, which could extend from the guard cells of the stomata to the spongy parenchyma. On the lower side of the leaf, aerenchyma strands about 50 µm long extended between the epidermis and the first or second layers of spongy parenchyma (Fig. 1.6.2.1, d). Chloroplasts were located along the periphery of the palisade cells. The cells of the spongy parenchyma varied in shape: rounded, oval, or irregular. Chloroplasts were also distributed along The Cell periphery, and their number per cell section was 1.8 times lower compared to the palisade cells. In shape, the lower epidermal cells resembled those of the upper epidermis, but their dimensions differed (Table 1.6.2.1).

TABLE 1.6.2.1. Morphological and anatomical parameters of Sagittaria sagittifolia leaves

Emergent oblong leaves. In terms of anatomical structure, the blades of oblong leaves closely resemble the sagittate leaves (Fig. 1.6.2.1, e, f; see Insert IX), but they differed in blade and palisade cell dimensions (Table 1.6.2.1): blade thickness was 1.3 times smaller, while the height and width of palisade cells were 1.3 and 1.7 times smaller, respectively, compared to sagittate leaves. These leaves are similar to sagittate leaves in stomatal distribution and the presence and localization of aerenchyma strands. Spongy parenchyma cells varied in shape: rounded, oval, or irregular. Chloroplasts were also located along the cell periphery.

Submerged leaves. Leaf blades immersed in water were characterized by an isolateral anatomical structure, lacking any division of the mesophyll into palisade and spongy parenchyma (Fig. 1.6.2.1, g, h; see Insert IX). The thickness of the leaf blade was half that of the emergent sagittate leaves. Stomata were absent in both the upper and lower epidermis. Epidermal cells were larger than parenchymal cells (Table 1.6.2.1). The photosynthetic parenchyma, located between the epidermal layers, consisted of a single cell layer or was entirely absent, whereas 4-5 layers of parenchymal cells could be distinguished at or near vascular bundle locations. Large air cavities were visible between the epidermal cells, measuring up to 400-500 µm in length and up to 100 µm in height. Chloroplasts were located in the cells of both epidermal layers (from 10 to 13 per cell section), with a similar number of chloroplasts found in the central parenchymal cells; chloroplasts in the epidermal cells were positioned on the outer side of the cells near the cell walls contacting the aqueous medium, whereas in parenchymal cells, chloroplasts were distributed evenly throughout the entire cell volume.