What are the main plant hormones and their functions?

The main plant hormones are auxins, gibberellins, cytokinins, abscisic acid, and ethylene, each with unique functions in plant growth and development.

Auxins are a group of hormones that play a crucial role in the growth and development of plants. They are primarily involved in cell elongation, apical dominance (the suppression of growth of lateral buds), and the formation of roots. Auxins also play a role in phototropism, the growth of a plant towards light, and gravitropism, the growth of a plant in response to gravity.

Gibberellins are another group of hormones that stimulate stem elongation, germination, and flowering. They are particularly important in breaking dormancy, a resting stage seen in seeds and buds. Gibberellins also promote the growth of leaves and stems, and can cause an increase in the size and number of fruits.

Cytokinins are hormones that promote cell division and differentiation. They are primarily involved in promoting lateral bud growth, delaying leaf senescence (ageing), and enhancing nutrient mobilisation. Cytokinins also work in conjunction with auxins to control the growth and development of roots and shoots.

Abscisic acid (ABA) is a hormone that plays a key role in stress responses. It is involved in the closing of stomata (small openings on the leaf surface) during drought conditions to prevent water loss. ABA also plays a role in seed dormancy, ensuring that the seed does not germinate until conditions are favourable.

Ethylene is a gaseous hormone that is involved in the ripening of fruits. It also plays a role in leaf abscission (the shedding of leaves), flower wilting, and the response of plants to mechanical stress. Ethylene can stimulate or inhibit growth and development depending on the species and stage of development.

In summary, plant hormones are vital for the growth, development, and survival of plants. They regulate a wide range of processes, from cell division and elongation to stress responses and fruit ripening.