Stomatal closure by ultraviolet-radiation
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The effect of ultraviolet radiation (UV) (255-325 nm) on stomatal closure was investigated on tef (Eragrostis tef (Zucc) Trotter) in the presence of white light (ca 50 .mu.mol m-2 s-1). The action spectrum showed that UV (ca 2 .mu.mol m-2 s-1, half band width about 10 nm) of 285 nm or shorter wavelengths was very efficient in causing stomatal closure. The effectiveness decreased sharply towards longer wavelengths. Radiation of 313 nm or longer wavelengths was practically without effect. Increasing UV intensity increased stomatal resistance. When stronger white light (5 to 9 times stronger than the one used during irradiation) was administered stomates re-opened rapidly irrespective of whether the UV was on or off, although a subsequent gradual closing tendency was observed when the UV was on.