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The superior growth of maize hybrids and some inbreds may be linked to key leaf growth features and critical components in carbon and nitrogen metabolism. Here, we performed simultaneous growth, physiological and heterosis analyses of morpho-physiological traits in four maize inbreds (B73, Mo17, Sids7, Sids63) and two hybrids (B73 × Mo17&Sids7 × Sids63). B73 and Sids7 exhibited alternate superiority over Mo17 and Sids63 in most growth traits. Both hybrids gained an early advantage over their parental inbreds in growth. They showed relatively similar behavior in many growth traits but differed significantly in biomass accumulation. Physiologically, B73 and Sids7 predominated in total pigments. Further, B73 contained the highest levels of sucrose, glucose, amino-N, and total N among inbreds. Both hybrids did not significantly differ in sucrose and total soluble sugars. However, Sids7 × Sids63 had consistently higher N fractions than B73 × Mo17. Both hybrids showed common and specific heterotic patterns. The superior growth of B73, Sids7, and hybrids is positively correlated with a set of leaf morphological (leaf area, leaf breadth, and LAI) and physiological (total chlorophyll, total pigments, and total N) traits. Advantages in these traits and efficient resource utilization support the superior growth of maize genotypes.

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Egyptian Journal of Botany http://ejbo.journals.ekb.eg/ 45 M AIZE grain yield is shaped by source-sink relationships during grain filling. Such relations are driven by complex metabolic changes, responsive to N availability and are not fully understood. Here, the impact of limited and sufficient N fertilization on the metabolic interconversions in the ear leaf of a new maize field-grown hybrid (Tzi8 × Mo17) during its critical transition from assimilation to remobilization were chronologically investigated at 0, 5, 10, 15, and 20 days after pollination. N-deficient plants produced 43% less grain yield and 13% less biomass however, they had 51% higher root dry weight and higher Root/Shoot ratio at anthesis. The low N-induced reduction in yield and biomass accumulation was associated with earlier chlorophyll degradation and overall decrease in leaf chlorophyll, total soluble proteins, carbon (C: sucrose & total soluble sugars), and N assimilates (leaf N, nitrate, ammonia & amino acids). In contrast, N-deficient plants accumulated 18% more starch and 24 % flavonoids than N-sufficient plants and such responses were driven by low N-induced sink limitation. N-deficient plants also had significantly higher activities of N remobilizing (asparaginase & protease) but lower activities of N assimilating (nitrate reductase & glutamine synthetase) enzymes compared to N-sufficient plants. Glutamate and aspartate followed by branched amino acids dominated the amino acids pool under both N conditions. Altogether, the accumulation of starch and flavonoids and the induction of N remobilizing enzymes represent low N-specific responses whereas the rest of responses depict the common metabolic interconversions between adequate and limited N-induced responses during maize grain filling.