*2.6.2 Function*


### **2.7 Salicylic acid (SA)**

#### *2.7.1 Introduction*

Salicylic acid (SA) is a member of the salicylates group of chemicals, which are phenolic compounds generated by plants and have an aromatic ring and a hydroxyl group. Salicylates were used as pain relievers for thousands of years before they were chemically identified.

Salicylic acid and its derivatives, as one of the plant hormones generated naturally, belong to the phenolic acid group and consist of a ring connected to the hydroxyl and carboxyl groups, with cinnamic acid as the starting component. It is mostly produced in cytoplasmic cells of the plant. Symbolised by the symbol SA called chemical orthohydroxybenzoic acid chemical formula is C7H6O3 [30].

#### *2.7.2 Salicylic acid's chemical composition*

#### *2.7.2.1 Function*

Many physiological and biochemical processes, including photosynthesis, ion absorption, membrane permeability, enzyme activity, flowering, heat generation, and plant growth and development, are influenced by Salicylic acid.

Its effects include, among others, the inhibition of root growth, variation in chlorophyll content, carotenoids, and xanthophylls, increased water use efficiency, improved nitrogen uptake by some species, inhibition of ethylene generation, alteration of plant nutrition, inhibition of the absorption of some substances, and regulation of flowering.

Its effects include, among others, the inhibition of root growth, variation in chlorophyll content, carotenoids, and xanthophylls, increased water use efficiency, improved nitrogen uptake by some species, inhibition of ethylene generation, alteration of plant nutrition, inhibition of the absorption of some substances, and regulation of flowering [31].

#### **2.8 Brassinosteroids**

#### *2.8.1 Introduction*

Brasinosteroids, the sixth plant hormone after auxin, gibberellins, cytokinin, abscisic acid, and ethylene, are structurally similar to steroid hormones found in animals. Brassinosteroids are important plant hormones that function similarly to animal hormones in a variety of biological processes, such as cell division, cell elongation, root development, photomorphogenesis, stomatal and vascular differentiation, seed germination, immunity, and reproduction. Brassinosteroids are also involved in regulating the metabolism of plant oxidation radicals, ethylene synthesis and root gravitropic response, and have a role in mediating plant responses to stress, such as freezing, drought, salinity, disease, heat and nutrient deficiency. Depending on growth state, this subfamily of hormones controls a wide variety of activities in plant development and responses to environmental challenges. Analogs of these hormones have been demonstrated to significantly boost grain production.

There are at least 70 polyhydroxylated sterols in the class of Brasinosteroids. These substances are similar in structure to animal steroid hormones that control the function of complex genes is influenced by the expression of several genes metabolic processes, which help to control cell division, differentiation, help in morphogenesis regulation, and regulate certain plant development stages, including blooming and cell expansion [32].
