EFFECT OF LIGHT QUALITY AND TEMPERATURE ON FE3+ REDUCTION, AND CHLOROPHYLL CONCENTRATION IN PLANTS

Plant species differ in their response to light; some grow best in full sunlight, some in partial shade and others in full shade. Inside, under growth chamber conditions, cool white fluorescent (CWF) lamps, in combination with supplemental incandescent (Inc) lamps, were a satisfactory light source. Low pressure sodium (LPS) lamps were also used. The spectral radiant power curve for the CWF lamps extends from 350 (includes UV and blue) to above 700 nm, whereas the spectral curve for LPS lamps is 560-610 nm (no UV or blue) with no radiation below 550 nm. The effect of LPS and CWF lamps, alone and in combination with Inc lamps, on plant growth and reduction of Fe3+ to Fe2+ was investigated. Lettuce (Lactuca sativa L. ''Grand Rapids''), cotton (Gossypium hirsutum L. ''M8'') and petunia (Petunia hybrida Vilm. ''Pink Cascade'') were grown in environmental control cabinets at 22 and 28.degree. C under LPS or CWF lamps, with and without Inc lamps. Reduction of Fe3+ to Fe2+ was determined as Fe2+ ferrozine [disodium salt of 3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine] in solution under all light treatments to determine if chlorophyll concentration in plant tops was related to Fe3+ reduction in solution. Cotton was observed to be chlorotic under LPS, but not under CWF lamps. Only small amounts of Fe3+ were reduced to Fe2+ at wavelengths above 420 nm, and more Fe3+ was reduced to Fe2+ in solution under CWF than under LPS lamps. Chlorophyll concentration in lettuce and cotton leaves followed about the same pattern as Fe3+ reduced to Fe2+ in solution. Chlorophyll levels were greater in leaves grown under CWF than under LPS lamps, and generally greater in leaves grown at 28 than at 22.degree. C. If CWF light mediates reduction of Fe3+ to Fe2+ in plant foliage as it does in Fe2+-ferrozine solutions, then it could make Fe2+ available for biochemical reactions related to chlorophyll synthesis. Petunia did not respond to the light regimes and temperature as did lettuce and cotton.