PLANT HETEROPHYLLY - 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

1.7.5.1. Sium latifolium

Emergent leaves. For comparative studies, emergent and submerged leaves of S. latifolium (Fig. 1.3.1; see insert II) at the vegetative growth stage (in the first ten days of May) were used. Scanning Electron Cell/15.html">Microscopy of the ULTRASTRUCTURE OF THE upper and lower epidermis in emergent leaves of the greater Water-parsnip demonstrated that these leaves belong to the amphistomatic type (Fig. 1.7.5.1.1). Stomata are of the paracytic type. The contours of the anticlinal walls of leaf epidermal Cells are sinuous. It is not always possible to distinguish the ordinary epidermal cells. The stomatal density on the upper surface was twice as low as that on the lower surface (Table 1.7.5.1.1).

TABLE 1.7.5.1.1. Epidermal features of emergent and submerged Leaves of Sium latifolium

Note: * P ≤ 0.05 (When comparing Features of the lower and upper leaf surfaces)

Stomatal density on 1 μm² of the upper leaf surface was 234 ± 12; on the lower surface, it was 485 ± 21, respectively. The cuticular layer on The Cell surface forms grooves (Fig. 1.7.5.1.1).

Cuticular grooves represent an alternation of wave-like furrows and ridges (about 0.6 ± 0.05 μm wide) distributed across all epidermal cells, including those surrounding the stomata. The height and width of cuticular grooves on the lower surface of ordinary epidermal cells and guard cells are 2.5–3.0 times smaller than those on the upper epidermal surface. The epidermal Cells of the upper epidermis are sinuous. Stomata on the upper surface (15.7 ± 1.2 μm in length; 6.7 ± 0.5 μm in width) are oval and arranged randomly. The outer cuticular ledges form a spindle-shaped rim. The pore walls of guard cells are smooth and non-cutinized. The walls of subsidiary cells are slightly wavy. The grooves are located on all epidermal cells without a specific orientation. On non-specialized epidermal cells located parallel to the long axis of the guard cells of the stomatal pore, the grooves run parallel to the long axis of the stomatal pore.

Fig. 1.7.5.1.1. Structure OF THE upper (a, b) and lower (c, d) surfaces of emergent leaves of Sium latifolium.

Scale bar: a, c - 50 μm; b, d - 5 μm

Stomata on the lower surface (17.1 ± 0.7 μm in length; 13.7 ± 0.9 μm in width) are elongate-oval and arranged irregularly. Most stomatal pores are oriented in the same direction. The cells of the lower epidermis of water-parsnip leaves are covered with a cuticle in the form of grooves, lacking any particular orientation. At the time of fixation, all stomata were open. The pore walls of guard cells are smooth and non-cutinized. The walls of subsidiary cells are slightly wavy. They are characterized by a massive outer stomatal

ledge. On the surface of epidermal cells located parallel to the long axis of the guard cells, the grooves are arranged perpendicular to the long axis of the stomatal pore. T-shaped thickenings are visible at the poles of the stomata, similar to those described by M.A. Baranova (1992) for the leaf epidermis of Austrobaileya scandens C.T. White.

Submerged leaves. Investigation of the ultrastructure of the upper and lower epidermis in submerged leaves of the greater water-parsnip established that submerged leaves are of the amphistomatic type (Fig. 1.7.5.1.2, a–d). The stomata of both upper and lower epidermis in submerged leaves are of the paracytic type. Stomatal density on the upper surface of submerged leaves is nearly half that on the lower surface (Table 1.7.5.1.1). The average number of stomata per 1 mm² of the upper epidermis is 109 ± 11, and per 1 mm² of the lower epidermis, it is 204 ± 20, respectively. The epidermal cells of the upper epidermis are sinuous. Stomata on the upper surface (11.7 ± 0.3 μm in length and 6.2 ± 0.4 μm in width) are oval and arranged irregularly. Stomata on the lower surface (10.4 ± 0.7 μm in length and 5.4 ± 0.4 μm in width) are elongate-oval and distributed randomly. Most stomatal pores are oriented along the leaf blade.

The shape and dimensions of ordinary cells of the upper and lower epidermis cannot be determined due to the presence of large and broad cuticular wrinkles, about 0.1 μm in width, which cover the entire epidermal surface. On the lower epidermis, most stomata are closed, and open stomata can be observed only rarely. The pore walls of guard cells are non-cutinized, similar to those described in studies of the leaf epidermis of Austrobaileya scandens C.T. White (Baranova, 1990). The cuticle surface of ordinary epidermal cells is of the striate type. The outer stomatal ledges form a spindle-shaped rim.

Both epidermal layers of emergent leaves and the upper epidermal layer of submerged leaves in the greater water-parsnip feature the so-called "striate" type of cuticular sculpture According to the Classification of D.L. Dilcher and W. Barthlott (Dilcher, 1974; Barthlott, 1990), which is also typical of the leaves of Austrobaileya maculata and A. scandens (Family Austrobaileyaceae) (Baranova, 1990).

In our opinion, It is interesting that There is a difference in stomatal density per unit surface area between the upper and lower epidermis of amphibious water-parsnip plants, with a higher number of stomata on the lower epidermis compared to the upper. Considering the functional load of stomata, it can be assumed that in emergent leaves of amphibious greater water-parsnip plants, the Transpiration burden is predominantly borne by the lower leaf surface.

Fig. 1.7.5.1.2. Structure of the upper (a, b) and lower (c, d) surfaces of submerged leaves of Sium latifolium.

Scale: a, c = 50 μm; b, d = 10 μm

Thus, a comparative Analysis of the epidermal surface structure of emergent and submerged leaves revealed certain shared and distinct Structural Features of the epidermis. Similar features—such as the amphistomatic type of the leaf blade and the paracytic type of stomata—are taxonomic characteristics of S. latifolium as a representative of dicotyledons (Baranova, 1990). Significant differences were also found in the epidermal structure of submerged leaves of water-parsnip compared to emergent ones, in particular:

- The surface of submerged leaves was characterized by smaller cuticular ridges on the surface of ordinary epidermal cells;

- the stomatal density on the upper epidermis was found to be twice as low;

In the epidermal cells of the floating leaves of Cicuta virosa, the cuticular ridges on both the upper and lower epidermis were observed to be six times larger than those on the epidermis of the submerged leaves of the same individual. It is known that up to 50% of total water transpiration in young leaves occurs through the cuticle (Polevoy 1989). This indicates that cuticular transpiration in floating leaves is quite intense across both the upper and lower leaf surfaces.

The lower stomatal density in the submerged leaves of Cicuta virosa compared to the floating leaves is apparently the result of Gene activity that determines the growth and differentiation of stomatal cells in leaf primordia. The coefficient of variation in the distribution of stomatal numbers on the upper epidermis of both floating and submerged leaves is quite high, indicating the instability of this trait, which varies depending on whether the leaves are surrounded by an aerial or aquatic environment.