Water Deficit and Ethylene Evolution by Young Cotton Bolls

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Abstract
Ethylene evolution and abscission of young cotton (Gossypium hirsutum L.) bolls were shown, in earlier papers, to increase when plants were subjected to conditiions that decreased photosynthesis and sugar content of bolls (dim light, long warm nights). Moisture stress also increased ethylene evolution by young bolls, but it did not decrease their concentration of fructose, glucose or sucrose. When detached bolls were incubated for 16 or 24 h at high or low humidity, their rate of ethylene evolution increased markedly at low humidity and slightly at high humidity. These results suggest that water deficit stimulated ethylene evolution by young bolls directly through partial desiccation, but do not exclude the possibility of a stimulus from moisture-stressed plants. Although attached and detached bolls both lost only a small percentage of their water content, detached bolls lost more for a given rate of ethylene evolution than bolls on moisture-stressed plants. The increased rate of ehtylene evolution by young cotton bolls on plants subjected to a water deficit is probably adequate, in many cases, to cause their abscission.