Studies in Stomatal Behaviour

Abstract

An apparatus is described enabling light responses of wheat stomata to be followed by periodical porometer readings, between which the substomatal cavities can be swept with carbon dioxide-free air forced in through the stomata. This is held to eliminate the influence of changes in the carbon dioxide content of the intercellular space atmosphere brought about by photosynthesis and respiration in the mesophyll. Using this apparatus in an experiment of ‘Latin square’ design with 6-fold replication of three light treatments, a statistically significant response to light was found in a leaf area subjected to varying light intensities from 90 to 800 f.c. This response was reflected in a similar significant effect, though of smaller magnitude, occurring in a similarly swept ‘control’ area 2 cm. distant and maintained at a constant light intensity of 270 f.c, the intervening portion of leaf being illuminated with 800 f.c. throughout. It is argued that this transmission of a light effect from one area to another does not occur via the intercellular spaces, nor by means of carbon dioxide gradients from cell to cell. It is concluded from the data that there is an indirect effect of light and perhaps also a direct effect upon the guard cells themselves; it is probable that neither of the two effects concerned operates by reduction of the internal carbon dioxide content in the guard cells.