Effect of Light Quality on Stomatal Opening in Leaves of Xanthium strumarium L.

Abstract

Flux response curves were determined at 16 wavelengths of light for the conductance for water vapor of the lower epidermis of detached leaves of X. strumarium L. An action spectrum of stomatal opening resulted in which blue light (wavelengths between 430-460 nm) was nearly 10 times more effective than red light (wavelengths between 630-680 nm) in producing a conductance of 15 cmol/m2 per s. Stomata responded only slightly to green light. An action spectrum of stomatal responses to red light corresponded to that of CO2 assimilation; the inhibitors of photosynthetic electron transport, cyanazine (2-chloro-4[1-cyano-1-methylethylamino]-6-ethylamino-s-triazine) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, eliminated the response to red light. This indicates that light absorption by chlorophyll is the cause of stomatal sensitivity to red light. Determination of flux response curves on leaves in the normal position (upper epidermis facing the light) or in the inverted position (lower epidermis facing the light) led to the conclusion that the photoreceptors for blue as well as for red light are located on or near the surfaces of the leaves; presumably they are in the guard cells themselves.