Effect of decreased irradiance on N and C metabolism in leaves and roots of maize |
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Authors: | Lucia Merlo Massimo Ferretti Calvino Passera Rossella Ghisi |
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Affiliation: | Dept of Agricultural Biotechnology, Univ. of Padova, Via Gradenigo 6, 1-35131 Padova, Italy;Dept of Agrobiology and Agrochemistry, Univ. of Viterbo, Via De Lellis, 1-01100 Viterbo, Italy. |
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Abstract: | The effects of decreased irradiance on fresh and dry weight, root respiration, levels of carbohydrates and N-compounds, and extractable activities of enzymes involved in C and N metabolism were evaluated in maize ( Zea mays L. cv. Plauto) seedlings during the 7 days following transfer from 450 to 200 μmol m−2 s−1 PAR. The fresh weight of roots and stems, the initiation of new leaves, root respiration rate, and the accumulation of dry matter, soluble sugars, starch, malate and amino acids in both leaves and roots were strongly reduced at low irradiance. In contrast, the level of nitrate was increased in leaves and only marginally affected in roots. Leaf phosphoenolpyruvate carboxylase (EC 4.1.1.31) activity started to decrease after 24–34 h, whereas ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) activity and chlorophyll content were unaffected or only slightly reduced. In both leaves and roots, the adjustment of N metabolism to low irradiance occurred through a relatively rapid (30% after 10 h) and large (60% after 3 days) decrease of nitrate reductase (NR; EC 1.6.6.1) activity, followed by slower and smaller changes in the activity of nitrite reductase (EC 1.7.7.1), glutamine synthetase (EC 6.3.1.2) and NAD-dependent glutamate dehydrogenase (EC 1.4.1.2). We suggest that the preferential decrease of NR activity relative to other N-assimilating enzymes may be important for preventing the accumulation of toxic N-compounds like ammonia in both leaf and root tissues. |
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Keywords: | Carbohydrates enzyme activities irradiance maize N-compounds nitrate reductase root respiration Zea mays |
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