What are the main plant hormones involved in growth and development?

The main plant hormones involved in growth and development are auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

Auxins are a group of plant hormones that play a crucial role in coordinating growth and behavioural processes in the plant's life cycle. They are primarily involved in cell elongation, which is a key aspect of plant growth. Auxins also play a role in phototropism, the process by which plants grow towards light, and gravitropism, the way plants respond to gravity.

Gibberellins are another group of plant hormones that are involved in promoting stem elongation, triggering the germination of seeds and breaking of bud dormancy, and stimulating flowering and fruit development. They work in conjunction with auxins to regulate growth and development in plants.

Cytokinins are hormones that promote cell division and shoot formation. They are primarily involved in cell growth and differentiation, and they work together with auxins to control cell division and differentiation in plant roots and shoots. Cytokinins also help delay the ageing process in plants, keeping them fresh and green.

Abscisic acid (ABA) is a plant hormone that plays a key role in seed dormancy and the closing of stomata. It is often referred to as the "stress hormone" because it helps plants respond to environmental stressors like drought and cold. ABA also plays a role in inhibiting growth, counteracting the growth-promoting activities of hormones like auxins and gibberellins.

Lastly, ethylene is a gaseous plant hormone that is involved in fruit ripening, flower wilting, and leaf fall. It is unique among plant hormones because it is a gas and can diffuse through the air. Ethylene also plays a role in the plant's response to mechanical stress, and it can stimulate the opening of flowers, the shedding of leaves, and the ripening of fruit.

In summary, these five hormones - auxins, gibberellins, cytokinins, abscisic acid, and ethylene - are the main players in plant growth and development. They each have unique roles but also work together to ensure the plant grows and develops properly.