PLANT HETEROPHILLY - O.M. NEDUKHA - 2011

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

1.7. LEAF EPIDERMIS OF HETEROPHYLLOUS PLANTS

1.7.5. Leaf surface structure in heterophyllous plants

1.7.5.3. Nuphar lutea

Floating leaves. Examination of the upper and lower surfaces of floating Leaves of Nuphar lutea (yellow Water-lily) showed that leaves of this form belong to the amphistomatic type (Fig. 1.7.5.3.1, a-c; see Insert XI). Common features for both epidermises include the stomatal type (paracytic), their shape (round or oval), and the presence of a cuticular groove along the perimeter of all Cells, 2.8 ± 0.7 µm wide (Fig. 1.7.5.3.1, b, f), while distinct features involve stomatal density and dimensions.

Upper leaf surface. Stomata on the upper epidermis are slightly raised above the surface, as are the cuticular ridges. Wavy cuticular ridges extended along the leaf blade, sometimes reaching 100 µm in length. Differences in the Structural Features of the upper and lower epidermises were manifested in stomatal dimensions and density (Table 1.7.5.3.1).

Stomatal density on the lower epidermis is higher than on the upper. Stomata on the upper surface (measuring 12.9 ± 1.3 × 9.9 ± 0.4 µm) vary in shape: round or oval-elongated. Outer stomatal ledges form a spindle-shaped rim. Pore walls of guard cells are smooth. Anticlinal walls of subsidiary cells are wavy. The stomatal index could not be calculated due to the lack of clear demarcation of individual epidermal cells. Therefore, we counted the number of stomata per unit surface area. The average stomatal density per 1 mm² of area was 778 ± 24.

TABLE 1.7.5.3.1. Stomatal characteristics of floating leaves of Nuphar lutea

Note: * P ≤ 0.05 (When comparing CHARACTERISTICS OF THE lower and upper leaf surfaces)

Lower leaf surface. Cells of the lower epidermis of floating leaves of N. lutea are characterized by the presence of high (ranging from 7 to 10 µm) cuticular ridges. Their width also varies from 4 to 8 µm (Fig. 1.7.5.3.1, c-f; see Insert XI). Cup-shaped hydropotes are revealed on the lower epidermis (Fig. 1.7.5.3.1, d, f) with tortuous Cell walls. The average base size of a hydropote is 23 ± 2.1 µm in diameter, with a density of 290 ± 18 items per 1 mm².

The lower surface of the leaf blade is covered with Algae located on and between the cuticular ridges (Fig. 1.7.5.3.1, d, f). Stomata are covered with a cuticle, round or slightly elongated, convex, with the stomatal pore poorly visible; the periphery of the stomata is surrounded by a cuticular ridge that sometimes intersects the center of the stomata. The dimension of stomata along the long axis was ~ 25 µm, and along the short axis ~ 17 µm. The average stomatal density per 1 mm² of area was higher than that on the upper surface. High (10–15 µm) cuticle-like mounds (Fig. 1.7.5.3.1, g) can often be observed on the lower leaf surface; rising above the lower surface, they form an air space that facilitates gas diffusion between the blade surface and the air volume trapped beneath the floating leaf.

Submerged leaves. Ultrastructural studies of submerged leaves of N. lutea showed that stomata are absent on both the upper and lower surfaces of the blade (Fig. 1.7.5.3.2; see Insert XII). Cells of the upper epidermis are irregular in shape, ranging from tetrahedral to polygonal, with anticlinal cell walls slightly rounded at the poles (Fig. 1.7.5.3.2, a, b).

Anticlinal walls are covered with a cuticle layer (2.4 ± 0.4 µm) that forms a ridge above The Cell surface and allows cell margins to be distinguished. The cell dimension along the long axis varies considerably from 20 to 50 µm, with an average short axis dimension of 20 ± 3.4 µm. The cell surface is uneven, showing small cuticular wrinkles (Fig. 1.7.5.3.2, b).

Cells of the lower epidermis are similar to upper epidermal cells in shape and in the presence of cuticular ridges along the cell margins. A distinctive structural feature of the lower surface of submerged water-lily leaves is the presence of cup-shaped hydropotes (Fig. 1.7.5.3.2, c-f) with tortuous thick cell walls forming "cup" depressions similar to those characteristic of hydropotes in the lower epidermis of floating leaves. Submerged leaves (nearly identical in size and shape) from the same plant rosette differed in hydropote Structure.

In some leaves, hydropotes appeared as round (about 15 µm in diameter) or oval cup-shaped structures (measuring ~ 23-26 × 13-15 µm), surrounded by a raised cuticular rim

of principal (adjacent) epidermal cells. Small cuticular wrinkles similar to those on the upper epidermis were revealed On the surface of principal cells (Fig. 1.7.5.3.2, d, e). No structural connections between individual hydropotes were observed.

In other submerged leaves, hydropotes were interconnected and connected to The surface of principal epidermal cells by numerous tentacle-like cuticular strands branching out from the hydropote walls (Fig. 1.7.5.3.2, e, f, arrows). The average density of hydropotes is quite high, reaching 240 ± 21 items/mm² of surface area. The cuticular rim along the periphery of principal epidermal cells was barely noticeable.

It is known that submerged (rosette) leaves in a single specimen of N. lutea can vary in age (Cutter, 1957): some persist from summer and overwinter until the next growing season, while others begin to form only in spring. Furthermore, it is known that the cuticle, participating in plant water transport, can alter its structure, ridge dimensions, and composition with leaf Aging and changes in environmental conditions during leaf development (Frost-Christensen et al., 2003; Frost-Christensen, Floto, 2007; Holloway, 1982, a, b).

According to researchers (Lüttge, Kraft, 1969; Wilkinson, 1979), hydropotes perform secretory and absorptive Functions, transporting ions and water from the aquatic environment into leaves and roots (Lüttge, Kraft, 1983). Considering the aforementioned literature data and our experimental results on The structure of hydropotes in submerged leaves of N. lutea, the following assumptions can be made:

1) cuticular strands connecting hydropotes to each other and to the surface of principal epidermal cell walls serve to increase the surface area for transport processes in "young" submerged leaves;

2) cuticular connections of hydropotes are temporary; in "old" submerged leaves, hydropotes are not interconnected by structural strands;

3) cuticular strands connecting hydropotes are necessary to maintain the cup-shaped Morphology of hydathodes in "young" submerged leaves.

The ultrastructure of hydropotes and the mechanisms of their functioning remain unknown.

Thus, the conducted studies revealed a significant difference in the structural features of emersed and submersed leaves of N. lutea, which manifested in the absence of stomata in submersed leaves. These results are consistent with the data on the structure of submersed leaves of common arrowhead described in the previous subsection.

Considering the data on significant differences in the STRUCTURE OF THE upper and lower surfaces of emersed leaves of N. lutea, as well as literature data

on stomatal and cuticular Transpiration, it can be assumed that in emersed and floating leaves of N. lutea, transpiration occurs predominantly through the upper surface of the epidermis. Water and ion transport in submersed and emersed leaves of water lilies obviously takes place via hydropotes of the lower epidermes, similarly to other species of the family Nymphaeaceae (Luttge, Krapf, 1969; Carpenter, 2006).