Effects of NO (+ NO₂) pollution on growth, nitrate reductase activities and associated protein contents in glasshouse lettuce grown hydroponically in winter with CO₂ enrichment

Abstract

S U M M h R YWinter hydroponic growth of several lettuce cultivars under glass showed considerable inhibition (up to 47 °o) of growth after 6 wk exposure to concentrations of NO ( + NO,; 450 nl P in total) typical of emissions from propane burners used for direct heating and CO., enrichment. After a further 4 wk under similar conditions, however, these growth depressions were replaced by a swing into benefit so that, by harvest, pollutant-exposed lettuces were bigger and had faster assimilation rates than those growing in clean CO.,-enriched air. This adaptation may partly be explained by enhanced use of NOj-derived N by lettuce lea^^es, a consequence of increased nitrate reductase (NaR) activities and amounts of associated NaR proteins, despite adequate nitrate also being available in the hydroponic fluid. Rates of NaR activity in the roots, by contrast, were depressed by NO (-(-NO,) pollution. NaR activities were 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.

Ecological ramifications of the direct foliar uptake of nitrogen

“…Field experiments have shown variable effects of leaf exposure to reactive N on overall plant growth with both increased and decreased growth rates observed (e.g., Adaros et al 1991;Saxe 1994;Hufton et al 1996). However, detrimental physiological responses including decreased photosynthesis (Saxe 1986), effects on plasma membranes (Russell et al 1999) and plant water-use efficiency (Siegwolf et al 2001) have been reported coincident with leaf fumigation with reactive N.…”

“…The primary hypotheses presented have proposed antioxidant compounds in the apoplast facilitating rapid uptake (Ramge et al 1993;Teklemariam and Sparks 2006;Eller and Sparks 2006;Haberer et al 2006) and regulation of the transport and consumption of the apoplastic endpoint products (NO 2 -, NO 3 -, and NH 4 ? ) by downstream enzymatic activity (Zeevaart 1976;Murray and Wellburn 1985;Rowland et al 1987;Bender et al 1991;Thoene et al 1991;Hur and Wellburn 1994;Hufton et al 1996;Wellburn 2002;Eller and Sparks 2006). Eller and Sparks (2006) suggested the uptake of NO 2 to leaves could be predicted with fidelity using a correlative model considering stomatal conductance, apoplastic ascorbate, and leaf nitrate reductase activity.…”

“…However, very little experimental evidence exists for such a scenario. Hufton et al (1996) examined the combined influence of increased CO 2 and NO ? NO 2 fumigation in hydroponically grown lettuce and found a 20% increase in growth in plants experiencing the combined fumigation compared to elevated CO 2 alone.…”

A questão do nitrato em alface hidropônica e a saúde humana

“…Tal fato provoca diminuição da atividade da enzima nitrito redutase pela falta de energia para formação de NADH + . Um ligeiro acúmulo de nitrito ocasiona a inibição da atividade da enzima nitrato redutase, resultando em acúmulo de nitrato nos vacúolos celulares (HUFTON et al, 1996).…”

Atmospheric nitrogenous compounds and ozone – is NOx fixation by plants a possible solution?

“…Young lettuce seedings are strongly retarded in growth by NO whether nitrate is present or absent (see colour plate in Wellburn, 1990Wellburn, , 1994 but lettuce can acclimate to NO over the whole growing period. In Figure 2, which is taken from Hufton, Besford & Wellburn (1996), crop growth and net assimilation rates in the presence of NO were slower initially but, by the time the head of lettuce was formed, they were much faster. This acclimation was traced to a shift from the use of root nitrate reductase (NR) to shoot NR, so that the plants were able to use the NO and NO # of the atmosphere even though plenty of nitrate was available to the roots (Hufton et al 1996).…”