The vegetative growth of plant shoots and leaves is controlled by the rapidly developing roots. New leaf tissue provides auxin, one of the key plant hormones, to the roots to maintain a balance with another key hormone, cytokinin, for cell division in the root tips. When vigorous root growth occurs, roots require more auxin from the plant’s leaves. In response, the plant produces new vegetative growth to supply the roots with the auxin needed to sustain the growth of new root caps every seven to 14 days.
When temperatures are above 90°F (31°C) or below 68°F (20°C), the enzyme activity needed for hormone production becomes limited and cell division is impaired. During temperature extremes, additional plant hormones and/or hormone cofactors must be applied to the plant or cell division and growth will stop.
When dry and wilting conditions exist, a combination of plant hormones and hormone cofactors can be applied to maintain cellular respiration, enabling plants to continue to producer intercellular water.