EFFECT OF NITROGEN APPLICATION ON REDISTRIBUTION AND TRANSFORMATION OF PHOTOSYNTHESIZED ¹⁴C DURING GRAIN FORMATION IN TWO MAIZE CULTIVARS WITH DIFFERENT SENESCENCE APPEARANCE

ABSTRACT

A field trial was conducted to investigate the effect of nitrogen (N) application on redistribution and transformation of photosynthesized ¹⁴C during grain formation in two maize (Zea mays L.) cultivars with different senescence appearance, ¹⁴CO₂ was introduced to ear leaf of maize at vegetative growth stage and grain-filling stage, respectively, the ¹⁴C-distribution to respired CO₂, vegetative mass and grain as well as to crude chemical components including sugar, polysaccharide, organic acids, amino and protein in ear leaf of maize and grain at grain-filling stage was determined. Two maize hybrids included “Danyu 13”, an early senescence hybrid, and “Zhongdan 306”, a stay-green hybrid. There were four N treatments: [1] N1: 0 kg N ha⁻¹; [2] N2: 250 kg N ha⁻¹ (1/5 N as basal application and 4/5 N as top-dressing at stalk elongation stage only); [3] N3: 250 kg N ha⁻¹ (1/5 N as basal, 2/5 N as top-dressing at stalk elongation stage and tasselling stage, respectively); [4] N4: 400 kg N ha⁻¹ (1/5 N as basal and 4/5 N as top-dressing at stalk elongation stage). For Zhongdan 306, a higher grain yield was ascribed to the less respiratory loss of C, larger translocation of current photosynthesized C during ripening, and smaller translocation of C existed in vegetative mass, while grain formation for Danyu 13 depended upon the larger translocation of C existed in vegetative mass and smaller translocation of current photosynthesized C during ripening. Percentage of photosynthetically fixed ¹⁴C distributed in both sugar and polysaccharide in ear leaf and grain for Zhongdan 306 was significantly larger than Danyu 13, while that in organic acids, amino and protein for Zhongdan 306 were markedly smaller than Danyu 13. The highest percentage of ¹⁴C distributed in sugar, the main carbohydrate translocated from leaf to grain, could be achieved in N3 treatment for Zhongdan 306 and in N2 treatment for Danyu 13, respectively, which consequently benefited to grain formation. This distribution of photosynthesized ¹⁴C between C-pool and N-pool may be related to the ratio of sucrose phosphate synthase (SPS) to phospho enol pyruvate carboxylase (PEPC) in leaf of maize at grain-filling stage.

ACKNOWLEDGMENTS

This research was supported by National Natural Science Foundation of China (Grant No.30000098) and International Foundation for Science (IFS, the Research Agreement Grant No. C/2965-1), and were carried out in Key Laboratory of Plant Nutrition Research, Ministry of Agriculture, China.