EFFECTS OF NO (+NO2) POLLUTION ON GROWTH, NITRATE REDUCTASE ACTIVITIES AND ASSOCIATED PROTEIN CONTENTS IN GLASSHOUSE LETTUCE GROWN HYDROPONICALLY IN WINTER WITH CO2 ENRICHMENT
Ca. Hufton et al., EFFECTS OF NO (+NO2) POLLUTION ON GROWTH, NITRATE REDUCTASE ACTIVITIES AND ASSOCIATED PROTEIN CONTENTS IN GLASSHOUSE LETTUCE GROWN HYDROPONICALLY IN WINTER WITH CO2 ENRICHMENT, New phytologist, 133(3), 1996, pp. 495-501
Winter hydroponic growth of several lettuce cultivars under glass show
ed considerable inhibition (up to 47%) of growth after 6 wk exposure t
o concentrations of NO (+ NO2; 450 nl l(-1) in total) typical of emiss
ions from propane burners used for direct heating and CO2 enrichment.
After a further 4 wk under similar conditions, however, these growth d
epressions were replaced by a swing into benefit so that, by harvest,
pollutant-exposed lettuces were bigger and had faster assimilation rat
es than those growing in clean CO2-enriched air. This adaptation may p
artly be explained by enhanced use of NO2-derived N by lettuce leaves,
a consequence of increased nitrate reductase (NaR) activities and amo
unts of associated NaR proteins, despite adequate nitrate also being a
vailable in the hydroponic fluid. Rates of NaR activity in the roots,
by contrast, were depressed by NO (+ NO2) pollution. NaR activities we
re highest in early afternoon in clean or polluted air but these daily
patterns did not coincide with the content of NaR-associated proteins
determined by ELISA. Other mechanisms of modulating NaR activity must
therefore be responsible.