In maize (Zea mays L., cv Contessa), nitrogen (NO3-) limitation resulted in a reduction in shoot growth and photosynthetic capacity and in an increase in the leaf zeaxanthin contents. Nitrogen deficiency had only a small effect on the quantum yield of CO2 assimilation but a large effect on the light-saturated rate of photosynthesis. Linear relationships persisted between the quantum yield of CO2 assimilation and that of photosystem 11 photochemistry in all circumstances. At high irradiances, large differences in photochemical quenching and nonphotochemical quenching of Chi a fluorescence as well as the ratio of variable to maximal fluorescence (Fv/Fm) were apparent between nitrogen-deficient plants and nitrogen-replete controls, whereas at low irradiances these parameters were comparable in all plants. Light intensity-dependent increases in nonphotochemical quenching were greatest in nitrogen-deficient plants as were the decreases in Fv/Fm ratio. In nitrogen-deficient plants, photochemical quenching decreased with increasing irradiance but remained higher than in controls at high irradiances. Thermal dissipative processes were enhanced as a result of nitrogen deficiency (nonphotochemical quenching was elevated and Fv/ Fm was lowered) allowing PSII to remain relatively oxidised even when carbon metabolism was limited via nitrogen limitation.Strong positive correlations have been found between the photosynthetic capacity of leaves and their nitrogen content, most of which is used for synthesis of components of the photosynthetic apparatus (1,6,23,26). Indeed, the availability of nitrogen limits growth in most environments but the restricted development of nitrogen-deficient plants is usually due to a lower rate of leaf expansion rather than a decline in rate of photosynthesis per unit leaf area (22). Evans and Terashima (6) found that the photosynthetic properties of spinach thylakoid membranes were virtually independent of nitrogen treatments. In this case, nitrogen nutrition affected the amount of thylakoids per unit leaf area but not the properties of the membranes (6,27 of photosynthesis (15,17,23,26,27,30), and the incident quantum yield (17) when nitrate was limiting. In developing maize leaves nitrogen deficiency has been found to result in a significant decrease in photosynthesis with a selective reduction in the levels of phosphoenolpyruvate carboxylase, pyruvate orthophosphate dikinase, and ribulose 1,5-bisphosphate carboxylase and a concomitant decrease in level of their respective mRNAs (26). Nitrogen-limited Chiamydomonas cells were found to have a 70% reduction in the Chl content and in this case the Chl a/b ratio increased as a result of Nlimitation (19). Nitrogen-limited plants also accumulate large amounts of carotenoids (12,19). Shade-grown plants grown with limiting nitrogen have been found to be more susceptible to photoinhibition than nitrogen-replete controls (8,25). Damage to the PSII reaction center occurs when the absorption of excitation energy exceeds the capacity for dissipati...

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In order to investigate effects of limited NO3 availability in corn (Zea mays L. cv. Brulouis) 17‐day‐old plants were grown for a further 25 days on sand in a growth chamber. The plants received frequent irrigation with a complete nutrient solution containing 0.2, 0.6, 1.5 or 3.0 mM NO3. With 0.2 mM NO; nitrate levels in both roots and leaves diminished rapidly and were almost zero after 10 days treatment. Concurrently, as signs of nitrogen deficiency appeared, shoot growth was restricted, whereas root growth was enhanced. In addition, the concentration of reduced nitrogen and malate in the leaves declined, and in vitro nitrate reductase activity (NRA. EC 1.6.6.1), soluble protein and chlorophyll levels of leaf tissue were depressed and starch concentration was enhanced. With 0.6 mM NO3 in the nutrient solution, the decrease in NO3 levels in the tissues and the increase in root development were similar to those observed with 0.2 mM NO3. However, shoot growth, reduced nitrogen concentration in leaves, and the above‐mentioned biochemical characteristics were almost identical to those obtained at 1.5 and 3.0 mM NO3. This indicates that when supplied with 0.6 mM NO3, corn plants were able to absorb sufficient NO3 to support maximal biomass production without appreciable NO3 accumulation in roots or shoot. It is, thus, suggested that the plants responded to low NO3, availability in medium by enhancing root growth and by maximizing NO3 reduction relative to NO3 accumulation.

Khamis, S. and Lamaze, T. 1990. Maximal biomass production can occur in corn (Zca mays) in the absence of NO3 accumulation in either leaves or roots. In order to investigate effects of limited NO5 availability in corn (Zea mays L. cv. Brulouis) 17-day-old plants were grown for a further 25 days on sand in a growth chamber. The plants received frequent irrigation with a complete nutrient solution containing 0.2, 0.6, 1.5 or 3.0 mA/ NO5. With 0.2 mM NO;,, nitrate levels in both roots and leaves diminished rapidly and were almost zero after 10 days treatment. Concurrently, as signs of nitrogen deficiency appeared, shoot growth was restricted, whereas root growth was enhanced. In addition, the concentration of reduced nitrogen and malate in the leaves declined, and in vitro nitrate reductase activity (NRA. EC 1.6.6.1), soluble protein and chlorophyll levels of leaf tissue were depressed and starch concentration was enhanced. With 0.6 mM NO3 in the nutrient solution, the decrease in NO5 levels in the tissues and the increase in root development were similar to those observed with 0.2 mM NO,. However, shoot growth, reduced nitrogen concentration in leaves, and the above-mentioned biochemical characteristics were almost identical to those obtained at 1.5 and 3.0 mM NO3. This indicates that when supplied with 0.6 mM NO3, corn plants were able to absorb sufficient NO3 to support maximal biomass production without appreciable NO3 accumulation in roots or shoot. It is, thus, suggested that the plants responded to low NO;, availability in medium by enhancing root growth and by maximizing NOj reduction relative to NO3 accumulation.