Effects of Isoprenoid Alcohols on Oxygen Exchange of Isolated Chloroplasts in Relation to their Possible Physiological Effects on Stomata

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Abstract
Farnesol accumulates in water-stressed plants of Sorghum, and has been shown to induce closure of stomata in the Commelina bioassay. In the present study we have found that it inhibits bicarbonate- and PGA-stimulated O2 evolution of isolated Pisum chloroplasts. Farnesol apparently disrupts the membranes of isolated plastids and most of the effects that we have observed can probably be attributed to this. Apart from nerolidol, related isoprenoid alcohols had no comparable effects, but the fatty acid linoleic acid appeared to cause damage of a similar nature. These compounds all caused stomata of Commelina to close. It is suggested that, while farnesol causes irreversible damage to membranes when applied exogenously in in vitro systems, it might act in vivo as a regulator of membrane structure and so affect the solute movements on which the turgor changes of guard cells depend.