Blue light regulation of stomata in wheat seedlings. II. Action spectrum and search for action dichroism

The stomatal conductance response to low intensity blue light was studied in wheat seedlings (Triticum aestivum L. cv. Starke II, Weibull) under red background illumination. Reciprocity was shown to be valid for illumination times from 10 s up to about 2 min. The action spectrum, constructed from fluence rate response curves, showed a maximum peak at 445–450 nm, another peak at 470 nm, a slight shoulder at 420 nm and a plateau between 370–400 nm. The relationship with action spectra for other blue light responses is discussed. The blue light response of wheat stomata did not exhibit action dichroism (the direction of the electrical vector of polarized blue light did not influence the response of the guard cells).