PLANT HETEROPHYLLY - O.M. NEDUKHA - 2011

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

1.9. FUNCTIONAL CHARACTERISTICS OF LEAVES

1.9.3. Energy and Carbohydrate Metabolism

Due to the fact that flooding conditions restrict gas availability and significantly reduce light intensity, higher aquatic plants have adapted to such constraints. For instance, The rate of gas diffusion between submersed plant Organs and the environment is 10⁴ times lower than that between terrestrial plants and the air (Jackson, 1985). Consequently, this drastic restriction leads to reduced Gas Exchange in the aquatic environment, especially in the dark (Rijnders et al., 2000). This results in energy and carbohydrate deficits, as well as the inhibition of oxygen-dependent processes (Mommer, Visser, 2005). Anaerobic processes can be partially compensated for by low ATP levels (Gibbs, Greenway, 2003) and the rapid depletion of carbohydrate reserves (Laan, Blom, 1990; Guglielminetti et al., 1997). In addition, oxygen reserves in submersed plants can be replenished through diffusion from the Water directly into submersed organs, most commonly via The ROOT System, which is characterized by the presence of aerenchyma. Such a mechanism has been identified in Rumex crispus and Eriophorum angustifolium Honck. Therefore, the oxygen deficit typically observed in terrestrial plants during flooding is accompanied by energy and carbohydrate shortages, as the latter are intensively consumed by flooded plants for Respiration (Mommer, Visser, 2005).

It has been proven that under sufficient illumination, the carbohydrate content in flooded plants increases by 30-160% compared to simultaneously flooded yet shaded plants (Ram et al., 2002). A similar response has been observed in Rumex crispus, where starch concentration was significantly higher (approximately 70%) in flooded and illuminated plants compared to flooded and shaded ones (Laan, Blom, 1990).

In submersed leaves of many hydrophytes, a high rate of carbohydrate accumulation is observed compared to aerial leaves (Mommer et al., 2005). This has been described in Rumex palustris, Ranunculus sceleratus (Kende et al., 1998; Sauter, 2000; Voesenek et al., 2004; 2006), Nymphoides peltata (S.G. Gmel.) Kuntze (Mommer et al., 2005), Oryza sativa L., Potamogeton pectinatus, and P. distinctus (Sato et al., 2002; Ishizawa et al., 1999; Summers et al., 2000).

It is known that during the Photosynthesis of angiosperms, alongside primary photosynthetic products, plants also synthesize sucrose, starch, Amino Acids, hydroxy acids, and keto acids (Kursanov, 1976). In Plants with C₃ photosynthesis, Oligosaccharides (raffinose, stachyose, verbascose) are also detected In addition to the aforementioned photosynthetic products (Nekrasova et al., 2003). In mesophytes, the content and composition of photosynthetic products vary depending on leaf age (Mokronosov, Nekrasova, 1977), light intensity (Voskresenskaya, 1965), Temperature (Pyankov, 1983), and CO₂ concentration (Nekrasova, 1971).