Photosynthetic determinants of growth in maize plants: Effects of nitrogen nutrition on growth, carbon fixation and photochemical features

Maize(Zea mays L.) plants were grown in a greenhouse with different levels of nitrate-N (2 to 20 millimolar). Nitrogen nutrition had dramatic effects on plant growth and photosynthetic characteristics of mature leaves. Increasing nitrogen resulted in greater biomass production, shoot/root ratios, and rates of leaf expansion during the day. The elongating zone of high-N plants had higher activities (per gram fresh weight) of sucrose synthase and neutral invertase than low-N plants, suggesting that increased leaf growth was related to a greater biochemical capacity for sucrose metabolism.Mature leaves of high-N plants had higher rates of photosynthesis and assimilate export (sucrose formation), and partitioned more carbon into sucrose relative to starch. Increased photosynthetic rates (leaf area basis) were associated with higher levels of ribulose-l,5-bisphosphate carboxylase, phosphoenolpyruvate carboxylase and pyruvate, phosphate dikinase (determined immunochemically). In addition, N-nutrition affected the functional organization of chlorophyll in the leaves. Large increases in the number of PS I reaction centers were observed which fully accounted for increases in leaf chlorophyll content with increasing nitrate supply.Collectively, the results suggest that increased growth of maize plants at high light and optimal nitrogen nutrition is related to greater capacity for photosynthesis and translocation in mature leaves, and possibly increased capacity for sucrose metabolism in expanding leaves.