Studies in Stomatal Behaviour

Abstract

An experiment was carried out to investigate stomatal responses in wheat to four ‘closing treatments’, viz. high carbon dioxide concentration, darkness, dry air and nil, each given under both aerobic and anaerobic conditions. Thus the effect of lack of oxygen on the closing (or opening) tendency was estimated. Changes in $(conductance)3$ calculated from resistance porometer readings were used as data and reasons are given for thinking this is the best available measure for investigating stomatal dynamics in wheat. Williams's hypothesis demands that lack of oxygen should cause stomatal opening or prevent closure; the present experiment shows that anaerobic conditions significantly increase the closing tendency when ‘closing treatments’ are first applied. There is also some suggestion that oxygen-lack itself tends to cause closure in the absence of any other ‘closing treatment’. Williams's hypothesis in its original form is thus disproved (for wheat) but the present results would be consistent with an ‘active’ uptake of water by the guard cells contributing to stomatal opening. A nearly significant interaction between carbon dioxide and oxygen suggests that under anaerobic conditions a ‘closing substance’ may perhaps be formed, for example, by the union of some intermediate in glycolysis with carbon dioxide.