Coordination in plants means the ability to use different parts of the plant together which is smooth and efficient. This coordination in plants is possible due to the major role played by the plant hormones.

There are four different types of plant hormones that are responsible for control and coordination in plants and they are:

Auxins
Gibberellins
Cytokiins
Abscisic acid
Also, these hormones are responsible for growth of plants in three different stages:

Cell division
Cell enlargement
Cell differentiation
Chemical coordination occurs in plants with the help of fluids secreted in plants known as phytohormones or plant hormones. These hormones regulate the growth of the plants. For example auxin is responsible for the growth of the plants and cytokinin helps in cell division in the fast growing part of the plant such as plant hormones.

Hi buddy... Chemical coordination in plants occurs through phytohormones, which are both growth promoters & growth inhibitors. Hormones like auxin(growth of stem and roots), gibberelins(elongation of cells,germination,flowering), and cytokonin(cell division, helps in delaying age) are growth promoters.
Whereas abcisic acid and ethylene inhibit the growth of plant.. which mainly prevents overgrowth. Abcisic acid promotes seed and bud dormancy and closure of stomatal pores. Ethylene is the only gaseous hormone present in plants. It promotes growth and ripening of fruit and inhibits growth and development of roots, leave and flowers..leaf fall occurs when amount of absicic acid increases which is called abcission..... Apart from that, as we know these inhibitors promote seed dormancy, so the growth promoter hormones like gibberelins and cytokinin have another function of breaking seed dormancy too.
HOPE MY INFO WAS USEFUL :^)