DIURNAL FLUCTUATIONS IN NITRATE ACCUMULATION AND REDUCTASE ACTIVITY IN LETTUCE (LACTUCA SATIVA L.) GROWN USING NUTRIENT FILM TECHNIQUE

The aim of this study was to use Nutrient Film Technique (NFT) to investigate the accumulation of nitrate (NO₃) within the lettuce (Lactuca sativa L.) plants. For health reasons lettuce should be produced with a low NO₃ content. NO₃ accumulation is influenced by radiation and NO₃ content through the induction of NO₃ reductase activity (NRA). Observers have found there are diurnal and annual fluctuations of NO₃ accumulation and NRA. Where plants were given nutrient solution (10mM NO₃), NO₃ accumulated during the early part of the dark period. If nutrient were withheld then the levels of NO₃ accumulation decreased and where light (100umol m^-2s^-1) was given during the normal dark period, NO₃ levels remained constant throughout the night. At sunrise levels of NO₃ increased where nutrient solution was combined with a dark night but decreased where light had been given. Withholding nutrients from the solution led to the depletion of NO₃ in the roots. The level of NRA had some relationship to the levels of NO₃ in the plant. There was a relationship between NO₃ in the leaf tissue and NO₃ uptake by the roots.