Abstract
Maize (Zea mays) plants exhibit altered carbon partitioning under nitrogen (N) deficiency, but the mechanisms by which N availability affects sugar export out of leaves and transport into developing ears remain unclear. Maize was grown under field conditions with different N supply. Plant growth, sugar movement, and starch turnover in source or sink tissues were investigated at silking and 20 or 21 days after silking. Nitrogen deficiency stunted plant growth and grain yield compared with N-sufficient plants, and resulted in greater starch concentrations in leaves due to more as well as larger starch granules in bundle sheath cells. Transmission electron microscopy revealed an open symplastic pathway for sucrose movement in N-deficient leaves, while the expression levels of transporters responsible for sucrose efflux and phloem loading were lower than in N-sufficient leaves. Nonetheless, greater starch concentrations in the apical cob portion of N-deficient plants implied sufficient carbon supply relative to the diminished sink strength (decreased kernel number and weight). Together with the high sugar concentrations in the developing kernels, the results indicated that reduced sink capacity and sugar utilization during grain filling may limit the yield in N-deficient plants, which in turn imposes a feedback inhibition on sugar export from leaves.
Highlights
In maize (Zea mays), approximately half of the total dry matter at maturity is accumulated between planting and silking and the other half during the reproductive period (Lee and Tollenaar, 2007; Ning et al, 2013)
Together with the high sugar concentrations in the developing kernels, the results indicated that reduced sink capacity and sugar utilization during grain filling may limit the yield in N-deficient plants, which in turn imposes a feedback inhibition on sugar export from leaves
Many studies have shown that more starch is accumulated in Abbreviations BS, bundle sheath; C, carbon; DAS, days after silking; MC, mesophyll cells; N, nitrogen; Pi, inorganic phosphate; VP, vascular parenchyma
Summary
In maize (Zea mays), approximately half of the total dry matter at maturity is accumulated between planting and silking and the other half during the reproductive period (Lee and Tollenaar, 2007; Ning et al, 2013). At the whole plant level, improvement of crop yield may be obtained through increasing carbohydrate production in source leaves (Wang et al, 2015) and/or enhancing the utilization of photoassimilates in sink organs (Sosso et al, 2015). To meet the high N demand of grain filling, large amounts of N are progressively remobilized from vegetative organs during reproductive growth (MasclauxDaubresse et al, 2010). Leaf N is a pivotal factor influencing photosynthesis and carbon (C) production after silking, and an important source of N for grain filling. Many studies have shown that more starch is accumulated in Abbreviations BS, bundle sheath; C, carbon; DAS, days after silking; MC, mesophyll cells; N, nitrogen; Pi, inorganic phosphate; VP, vascular parenchyma
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