Plant Physiology - Musiyenko M.M. 2001

Physiology of Plant Growth and Development
The concepts of plant "growth" and "development"

The capacity for growth is one of the defining characteristics of All living organisms. A plant absorbs Water and nutrients, harnesses solar energy, and sustains numerous metabolic reactions that drive its GROWTH AND DEVELOPMENT. The Development of a mature plant from a single seed is an exceptionally wondrous and complex process. It involves Cell Division, cell enlargement via elongation, the differentiation of Cells and individual Organs (roots, stems, leaves, flowers), and ultimately, a sequence of intricate, highly coordinated chemical transformations.

The ultimate form of a plant is shaped by both its genetic program and environmental factors that influence its expression. While the genotype sets the boundaries of a plant's phenotypic plasticity, the environment dictates how its developmental pathway unfolds within those limits.

Growth is an irreversible increase in the size of a plant (or its organs) resulting from the de novo formation of organs, cells, or their individual structural elements driven by biosynthetic processes.

Development is the sum of qualitative morphological and physiological changes occurring in a plant at various stages of its life cycle (ontogeny), governed by the interplay of genotype and phenotype.

All stages of growth are linked to the biochemical activity of metabolic cycles, primarily Protein Synthesis, through which the Genetic information encoded in DNA is translated into specific enzyme complexes, structural Proteins, and other cellular components. These Enzymes, in turn, regulate the functional activity of The Cell.

Changes occurring at THE CELLULAR LEVEL influence The formation of both individual organs and the Organism as a whole. This process is known as morphogenesis; thus, plant development encompasses the initiation, growth, and differentiation of cells (cytogenesis), Tissues (histogenesis), and organs (Organogenesis).

Growth can be positive, when anabolism prevails over Catabolism, and negative, when catabolism outweighs anabolism. For instance, during seed germination and seedling establishment, the number of cells, their size, and structural complexity increase, yet dry mass decreases; therefore, germination represents a period of negative growth. Another example of growth is The Emergence of new leaves on shoots.

The appearance of flowers, however, marks a qualitatively new physiological state of the plant, indicating profound biochemical and physiological shifts. Thus, flowering serves as an indicator of plant development. At the same time, the fundamental unity of these processes must be emphasized. The emergence of a flower or novel leaves is invariably accompanied by the enlargement of leaf primordia and floral buds, accompanied by cell proliferation—in other words, growth. The Physiology of Plant Growth and Development is one of the most actively investigated fields, closely intertwined with agronomy and modern biotechnology.

The primary criteria used to determine the rates of growth and development differ. Growth rates are typically measured by The rate of biomass accumulation, volume increase, and dimensional expansion of the plant. Conversely, the rate of development is gauged by the plant's transition to reproduction. This distinction further underscores that these concepts are not identical, allowing us to examine the processes of growth and development sequentially.