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

1.6.3. Leaves of Nuphar lutea

Nuphar lutea plants fixed in early June are characterized by the presence of both floating and submerged leaves (Fig. 1.3.4; see Plate V and subsection 1.3).

The floating leaves exhibit a dorsiventral type of Anatomical Structure (Fig. 1.6.3.1, a, g, d; see Plate X). Cross-sections of the lamina reveal a multi-layered palisade (4–5 layers) and spongy (7–9 layers) parenchyma, as well as large air cavities (aerenchyma strands) penetrating the mesophyll from the upper to the lower epidermis. The average thickness of the leaf lamina varied among plants: in coastal specimens (partially shaded by willows) growing at a depth of about 1.8 m, the thickness reached

300 ± 15 µm. In plants growing at depths of 60 to 80 cm in unshaded areas with a high current velocity (5 m/s), the thickness of the floating leaf laminae was 631 ± 17 µm. It was these specimens that we selected for measurements and the investigation of Anatomical Features (Table 1.6.3.1). Notably, regardless of leaf thickness, the size ratio between epidermal and mesophyll Cells remained unchanged.

The average Cell size of the lower epidermis is larger than that of the upper epidermis. A characteristic feature of floating leaves is the presence of large aerenchyma strands extending from the upper epidermis to the spongy mesophyll, intersecting almost every 2–4 rows of palisade cells (Fig. 1.6.3.1, a, g). In the lower part of the leaf, the aerenchyma divides the entire spongy parenchyma into layers and contacts a continuous subepidermal layer of spongy parenchyma (Fig. 1.6.3.1, d). Stomata are present on both the upper and lower epidermis. The average number of METABOLISM/14.html">Chloroplasts per cell profile is 15 ± 1.2 for palisade cells and 12.0 ± 1.3 for spongy parenchyma cells.

TABLE 1.6.3.1. Anatomical features of Nuphar lutea leaves

The submerged leaves of yellow pond-lily are characterized by an isolateral anatomy with an undifferentiated mesophyll (Fig. 1.6.3.1, b, c; see Plate X). The thickness of the submerged leaf lamina, compared to that of floating leaves from the same plants, is 3.6 times smaller in coastal plants and 5.0–5.4 times smaller in plants growing under direct sunlight in rapid currents. Stomata are absent in submerged leaves. The parenchyma consists of 4–5 cell layers separated by air cavities, which isolate three layers of upper parenchyma from the lower parenchyma layers. The height of the air cavities in cross-section ranges from 17 to 30 µm, whereas their width varies significantly and can exceed 150 µm.

A specific structural feature of submerged leaves is The formation of two loop-like invaginations of The Cell walls in each subepidermal parenchyma cell. These invaginations occur at the junction of two adjacent parenchyma cells in each row along the long axis of the submerged leaf (rather than along its height). As a rule, chloroplasts are absent near these invaginations and are instead localized at the upper and lower poles of the photosynthetic cells.

Thus, it has been established that the submerged Leaves of Sagittaria sagittifolia and Nuphar lutea, regardless of the depth at which they grow, feature thinner laminae compared to the floating leaves of the same individuals. Evidently, the submerged leaves of the studied species undergo

adaptation at the anatomical level, manifesting as a reduction in leaf lamina thickness and an increase in the size of photosynthetic epidermal cells in direct contact with the surrounding aqueous environment. Similar findings have been reported for other hydrophyte species, notably Elodea canadensis Michx. (Rascio et al., 1994), E. densa C.Rich. (Rascio et al., 1991), Hydrilla verticillata (L.) Royle (Magnin et al., 1997), and several Potamogeton species (Rascio, 2002), in which the leaf lamina is only 2–3 cell layers thick, whereas in other species, such as Myriophyllum, Ceratophyllum, or Ranunculus, the leaves become highly dissected and contain numerous elongated air cavities.