Dear Ali Safaa ,

Secondary metabolites are organic compounds that are generally not involved directly in the growth and development of plants but play important roles in their ecological interactions. However, There are some exceptional cases, where secondary metabolites such as alkaloids and flavonoids can directly influence plant growth and development. For example, alkaloids such as nicotine and caffeine can act as growth inhibitors or stimulators, depending on their concentrations and the species of plants. Flavonoids can also play a role in plant growth and development by regulating auxin transport and modulating the activity of plant hormones. Additionally, some secondary metabolites can indirectly affect plant growth and development by protecting them from pests and pathogens, regulating hormone levels, and modulating stress responses.

Nevertheless, it's important to remember that phytohormones, signal molecules, and primary metabolites are the main compounds that directly contribute to the growth and development of plants, while secondary metabolites primarily play roles in plant defense, signaling (here's the overlap), and ecological interactions.

I suggest to look into the concept of plant biostimulant as well.

Nicolò M. Villa yes, Thank you very much

They play a role e.g. for keeping insects away or helping with symbiosis of root to mycorrhysa.

S. Wenkart yes I know like Phytoalexins and plant toxins in plant defenses, Thank you very much

Yes directly by interaction with plant hormones , indirectly by inversion to aplant protection compounds

Secondary metabolites have complex chemical composition and are produced in response to various forms of stress to perform different physiological tasks in plants. They are used in pharmaceutical industries, cosmetics, dietary supplements, fragrances, flavors, dyes, etc. Primary metabolites are compounds that are directly involved in the growth and development of a plant whereas secondary metabolites are compounds produced in other metabolic pathways that, although important, are not essential to the functioning of the plant. Secondary metabolites, at least the major ones present in a plant, apparently function as defence (against herbivores, microbes, viruses or competing plants) and signal compounds (to attract pollinating or seed dispersing animals). They are thus important for the plant's survival and reproductive fitness.

When applied to other crops, secondary metabolites obtained from plants serve distinct purposes. Some might stimulate. Some may have a detrimental impact. Some might offer protection. Some act as tolerant. Some retort. When they are applied to other crops, the functions change. Hence, in order to use it, we must first employ GCMS to identify the phytocompounds and their significance.

Abdulsattar Alrijabo Rk Naresh Swaminathan C. yes, Thank you very much