Plant Physiology - Musienko M. M. 2001

General principles of regulation of plant growth and morphogenesis
Application of phytohormones and other synthetic growth regulators in crop production

Exogenous application of phytohormones is necessary when plants experience a deficiency. Most commonly, this occurs during specific, critical Stages of Ontogeny (e.g., seed germination, flowering, fruiting) or when the integrity of the plant Organism is compromised (e.g., during plant propagation via cuttings or tissue culture). Occasionally, growing conditions (such as moisture stress or a shortage of certain mineral nutrients) hinder the synthesis of endogenous Hormones, making exogenous application equally essential.

It should be noted that Cells, Tissues, and Organs must be receptive to exogenous phytohormones, meaning they must be competent. Competence is determined by the presence of specific receptor Proteins and the overall state of intracellular processes. A Cell may be competent to the action of a given phytohormone at one stage of growth, but not at another.

The Physiological Effect of all phytohormones depends on their concentration and mutual ratios. An elevated concentration typically leads not to stimulation, but to metabolic inhibition and organism death.

As is known, endogenous phytohormones are localized in specific cellular compartments; therefore, exogenous application cannot fully replace them, since external application results in a different distribution pattern.

Auxins

In agricultural and horticultural practice, they are most commonly used for:

·stimulating ROOT formation in cuttings and restoring The Root System. For instance, treating the lower ends of cuttings with IAA at a concentration of 50 mg/L induces an influx of nutrients and enhances Respiration, which positively affects root development;

·inducing parthenocarpic fruit set. Spraying tomato plants during the flowering phase leads to The formation of seedless fruits with an increased sugar content;

·preventing fruit drop. The application of auxins promotes additional nutrient transport to the fruits and prevents the Formation of the abscission layer in pedicels;

·at high concentrations, 2,4-D (2,4-dichlorophenoxyacetic acid) can be used as a selective herbicide;

Cytokinins

Cytokinins make it possible to:

·regulate growth and Organogenesis in isolated cell and organ cultures;

·overcome apical dominance, thereby stimulating the growth of lateral shoots;

·delay senescence processes;

·enhance Plant resistance to adverse environmental conditions.

Gibberellins

Under METABOLISM/18.html">The Influence of gibberellins, it is possible to:

·increase green mass yield through accelerated stem elongation;

·break dormancy in potato tubers and the seeds of certain plant species;

·ensure synchronized germination of barley seeds to produce high-quality malt in brewing;

·improve the productivity and quality of grapes by forming dense, seedless clusters.

Abscisic acid

A promising application of ABA involves reducing Transpiration rates and increasing plant drought resistance.

Ethylene

In practice, ethylene is widely used to accelerate the ripening of many fruits.

Currently, many substances have been synthesized that are also capable of regulating plant growth processes because their Structure is similar to that of native phytohormones. These include, for example, indolebutyric, indolepyruvic, and naphthylacetic acids—auxin analogues—among Other Compounds.