Gibberellins (GAs) – plant hormone that regulate various developmental processes, including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence.

GA-like substances –

Auxins – Auxins are a powerful growth hormone produced naturally by plants. They are found in shoot and root tips and promote cell division, stem and root growth. They can also drastically affect plant orientation by promoting cell division to one side of the plant in response to sunlight and gravity.

Cytokinins (CKs) – class of plant growth substances (phytohormones) that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence.

CK-like substances –

When plants are cultured with auxin but no cytokinin, they grow large but do not divide. When cytokinin is added, the cells expand and differentiate. When cytokinin and auxin are present in equal levels, the cells form an undifferentiated callus. More cytokinin induces growth of shoot buds, while more auxin induces root formation

Siderophore – small, low molecular-weight chelating agents that are secreted by microorganisms to serve primarily to transport iron across cell membranes.  Limits iron to phytopathogens

ACC (1-aminocyclopropane-1-carboxylate) deaminase – enhances plant growth by lowering plant ethylene levels

Ethylene Gas – mediates many complex aspects of plant growth, development and survival throughout the plant life cycle, including seed germination, root development, shoot and root growth, formation of adventitious roots, abscission of leaves and fruits, flowering, sex determination, and senescence of flowers and leaves [1, 2]. Ethylene also mediates adaptive responses to a variety of stresses, such as drought, flooding, pathogen attack and high salinity. During flooding, for instance, ethylene induces the formation of aerenchyma tissue (consisting of air-filled cavities) for oxygenation. Ethylene is best known, however, for its essential role in the ripening of climacteric fruits, such as tomatoes, bananas, pears and apples. Placing a ripe banana in a paper bag containing unripe avocados, for instance, will hasten ripening of the avocados due to the accumulation of ethylene produced by the banana.

Indoleacetic acid (IAA) – molecule synthesised by plants and a few microbes and plays a key role in root and shoot development.  Is the best known auxin.