Red Light-inhibited Mesocotyl Elongation in Maize Seedlings

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Abstract
Red light induces 2 distinct inhibition responses in mesocotyls of etiolated corn [Zea mays] seedlings. A light dose of 10 neinsteins/square cm is saturating for the more sensitive response, whereas doses above 1000 neinsteins/cm2 are required to exceed the threshold sensitivity of the less sensitive one. The sensitive response can be detected within 20 min of the onset of illumination whereas the other response does not become apparent until more than 4 h after the beginning of irradiation. The reciprocity law is valid for the first response, but probably not for the 2nd. An action spectrum for the first response shows 2 maxima, one at 640 nm and the other between 660 and 670 nm, with a pronounced minimum near 650 nm. The effects of both of 640 and 665 nm of light were reversible by far red light, but doses of far red required for full reversibility were almost 3 orders of magnitude greater than the doses of red required either to saturate the initial inhibition or to reverse the effect of far-red light. Possibly, corn may contain a red-absorbing pigment other than phytochrome which in some way interacts with phytochrome in the inhibition of mesocotyl elongation by red light.