|COMBS, JR, GERALD|
Submitted to: International Conference on Environmental Systems
Publication Type: Proceedings
Publication Acceptance Date: 7/1/1999
Publication Date: N/A
Technical Abstract: Nitrate concentration in spinach and lettuce is known to be influenced by light quantity. The enzyme nitrate reductase is modulated by phytochrome in some species. In the presence of light, electrons that reduce nitrite to ammonium come from photosynthetic electron transport. Because chlorophyll absorbs certain wavelengths more efficiently than others, light tquality as well as light quantity may be used to manipulate nitrate concentration in spinach. To test this hypothesis, narrow-band wavelength light-emitting diode sources (670 nm and 735 nm peak emission) were utilized in combination with cool white fluorescent (CWFL) lamps. Nitrate concentration was compared in spinach seedlings grown for four weeks under CWFL, followed by one of three 5-day pre-harvest light treatments. The three different light quality regimes were 1) CWFL, 2) CWFL + RED (670 nm) LED, and 3) CWFL + FR (735 nm LED). Ion chromatograph analysis of freeze-dried tissue showed a 10-fold increase in nitrate concentration in the CWFL+ FR (0.12 mmoles/g dw) treatment over the CWFL (0.01 mmoles/g dw) and CWFL+Red (0.01 mmoles/g dw) treatments after the 5-day pre-harvest light treatments. There was no significant difference in nitrate concentration between the CWFL and CWFL+Red light treatments after the 5-day exposures.