Plant Physiology - Musiyenko M.M. 2001

Physiology of Excretion in Plants

A plant Organism is an open system that continuously exchanges matter and energy with its environment. A vital component of plant Homeostasis is The excretion of metabolic byproducts. The physiology of plant excretion remains insufficiently understood due to experimental challenges; notably, in plants, the excretory function is frequently carried out by Cells and Tissues that show no morphological differences from surrounding non-secretory cells. Furthermore, the quantities of secreted substances can be extremely small, necessitating highly sensitive analytical techniques. In addition, these products are often sequestered into internal compartments, making it difficult to isolate them in pure form.

The excretion or secretion of substances in plants, much like in animals, is performed by specialized cells and tissues. However, unlike in animals, every plant Cell exhibits secretory capabilities over the course of its ontogeny. A clear distinction should be made between secretion and excretion.

Secretion is The Active Transport of specific metabolic products from metabolically active cellular compartments into metabolically less active ones. This process invariably involves Active transport MECHANISMS, which require an input of metabolic energy.

Excretion, by analogy with animal organisms, refers to the elimination of terminal metabolic products that are no longer utilized in METABOLISM.

It should be noted that drawing a strict boundary between secretion and excretion is difficult. This is because the roles of many metabolic byproducts remain unknown, and because excretory products, alongside physiologically active substances (those fulfilling specific physiological Functions), are frequently released into the same compartments.

The term “excretion” broadly encompasses the elimination from the organism of metabolic products, excess Water, salts, BIOLOGICALLY ACTIVE SUBSTANCES, and foreign or toxic compounds generated during the vital activity of the plant (Salamatova, 1991).

Excretory processes occur at the cellular, tissue, and organ levels, as well as at the whole-organism level. To date, there is no comprehensive Classification of all plant secretions; therefore, O. A. Zauralov (1985) proposed dividing all plant-derived products into two main groups: internal secretions and external secretions (which are released from the plant into the environment) (Table 19).

Table 19. Classification of Plant Excretions (Zauralov, 1985)

Various terms are used in literature to describe excreted substances, such as “exometabolites,” “stress metabolites,” “pathological secretions,” among others. Here, we will focus specifically on those phenomena that pertain to excretory processes regulated by the plant's regulatory systems.