PLANT HETEROPHYLLY - O.M. NEDUKHA - 2011

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

Conclusions

We adhere to the theoretical framework that heterophylly in aquatic and terrestrial plants is a manifestation of heteroblastic leaf primordium development, heredity, and METABOLISM/18.html">The Influence of exogenous factors. In light of E. Sinnott's morphogenesis concept (Sinnott, 1940; 1963), the shape of the leaf blade is determined by the primordial form and the Regulation of Cell division and elongation rates during the juvenile phase of leaf development. Given that recent studies on Arabidopsis thaliana, Ranunculus palustris, and Oryza sativa have proven that Cell Division and elongation are driven by the activation

of specific genes that regulate proliferative activity and cell expansion within primordia, as well as alter leaf metabolic rates (Fukao et al., 2006; Xu et al., 2006; Bailey-Serres, Voesenek, 2008), it is hypothesized that heterophylly represents a hereditary trait manifested through The regulation of structural and metabolic changes during early ontogenetic phases across all levels of organismal Organization.

Investigations into the evolutionary ORIGIN OF HETEROPHYLLY using molecular Methods—specifically the positive Selection analysis of chloroplast rbcL (RuBisCO) Gene sequences in ecologically diverse Japanese aquatic plants, namely species of the genus Potamogeton, which exhibit considerable morphological and growth Variability—suggest that homophylly in this genus is ancestral, whereas heterophylly is also genetically transmitted and exists as a case of parallel evolution (Iida et al., 2004; 2006).

Based on extensive literature data and our own research on the Structural and functional organization of submerged and floating leaves in heterophyllous species such as Sium latifolium, Nuphar lutea, and Sagittaria sagittifolia, it has been established that the functioning and adaptation of higher aquatic plants to submersed life lead to The Emergence of distinct morphological and Anatomical Features of heterophylly, alongside the cellular mechanisms driving its formation. Regardless of whether it arises in terrestrial, aquatic, or flooded environments, or during the emergence of plants from Water (such as reservoir shallowing), heterophylly is accompanied by anatomical and structural differences in leaves and stems, as well as shifts in their functional traits. Submerged leaves of heterophyllous plants differ from floating or aerial ones by several key characteristics, namely:

✵ alterations in the shape, area, and Structure OF THE leaf blade: the leaf shape typically becomes dissected, elongated, or fan-like, which helps withstand water resistance and pressure. The area and perimeter of the leaf blades increase, thereby enhancing gas diffusion into the leaf, while the blade thickness is reduced several-fold, facilitating optimal diffusion of CO₂ dissolved in the surrounding aqueous medium. Most submerged leaves feature an isolateral or centric anatomy with an undifferentiated mesophyll and a well-developed aerenchyma; epidermal Cells generally contain well-developed grana-rich Chloroplasts;

✵ the absence or reduction of Stomata in the epidermis; reduced thickness or complete absence of the wax layer and cuticular ridges on both surfaces of the blade, which promotes

accelerated gas Transport Across the epidermal cell walls (epidermis ^ aquatic environment);

✵ The formation of aerenchyma not only in leaves but also in roots, facilitating the accumulation and transport of oxygen and other gases from the leaves to the roots, as well as in the reverse direction from the roots to stems, petioles, and leaf blades;

✵ Changes in the ultrastructure of photosynthetic cells: the formation of chloroplasts with abundant thylakoids in grana, resembling those of shade-tolerant plants; decreased starch content in Plastids, and an increased population of Peroxisomes, which enhances Photorespiration;

✵ alterations in Photosynthesis—reduced activity of RuBisCO, PEP carboxylase, and Pyruvate kinase; lowered chlorophyll content per unit of leaf area, and a modified ratio of chlorophylls (a+b) to carotenoids. This shift in pigment composition enables submersed Organs to regulate Light absorption efficiency under attenuated underwater light to optimize assimilation;

✵ depletion of carbohydrate reserves and suppression of aerobic Respiration.

Overall, based on theoretical models and experimental data, it can be concluded that heterophylly in higher aquatic and terrestrial plants is driven by specialized cellular mechanisms that govern the Cytology/cytology/16.html">Early stages of primordium formation. Differences in Anatomical Structure, ultrastructure, and the functioning of photosynthetic cells in submerged leaves compared to floating/aerial leaves of heterophyllous aquatic plants clearly demonstrate the direct dependence of plant survival on environmental conditions.