The movement and endogenous levels of plant growth regulators during water-stress-induced abscission in cotton

Abscission and the movement of, as well as the endogenous levels of, plant growth regulators was investigated in cotyledons of cotton (Gossypium hirsutum L. cv. Stoneville 213) before, during and after periods of moisture deficit. Abscission of cotyledons was observed during and after 24 hrs after various levels of plant water stress were achieved. The threshold plant water potential at which abscission was induced was approximately -13 bars. There was a dramatic increase in abscission up to 75 to 80% of the cotyledons within each pot, as plant water potential decreased to approximately -20 bars. Further increases in water stress did not appreciably increase the level of abscission (75 to 80%). Basipetal and acropetal transport of ¹�C-labeld plant growth regulators, indole acetic acid (IAA), abscisic acid (ABA), kinetin, and gibberellin A₃ (GA₃), were examined independent of uptake or exit from 20 mm petiole sections. ¹�C-IAA transport was both polar and active, and water stress has a marked effect on basipetal transport. The capacity of the petioles of plants grown under well-watered conditions to transport ¹�C-IAA was approximately 60% of the label transported over a 2 hr period. This level of transport was constant in a range of water potentials from -4 to -9 bars. The transport capacity was reduced to approximately 30%/2 hr in plants with water potentials ranging from -9 to -12 bars respectively. ..