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Partial nitrate nutrition was testified to improve rice (Oryza sativa L.) growth. However, how partial nitrate nutrition is related to root growth in rice cultivars with different N-use efficiency is still unclear. Two rice cultivars, Nanguang (high N-use efficiency) and Elio (low N-use efficiency), were grown on six ratios of NH 4 + /NO 3 -in the solution. The response of root growth to partial nitrate nutrition was investigated and N status and auxin concentration were recorded in order to elucidate the mechanisms by which the optimal ratio of NH 4 + /NO 3 -that controls the architecture of the root system. The length of adventitious and lateral roots was stimulated only in cv. Nanguang by partial nitrate nutrition. Nitratestimulated root length in Nanguang resulted mainly from root initiation rather than root elongation. Root biomass was similar between two rice cultivars under NH 4 + supplied, while higher root biomass was observed in cv. Nanguang than in cv. Elio under 25% nitrate supplied for 10 weeks. Significant IAA increase was recorded in cv. Nanguang under 25% nitrate presence in the nutrition compared to under sole NH 4 + solution. The presence of nitrate increased root initiation in the rice with high N-use efficiency, which led to faster biomass accumulation and higher N-use efficiency at later growth stages.

SAP and MIZ (SIZ) is a small ubiquitin-related modifier (SUMO) E3 ligase that facilitates conjugation of SUMO to protein substrates. Although there have been a number of reports about the functions of SIZ1 in Arabidopsis in the regulation of diverse life processes, no information regarding the role of SIZ in other plants is available yet. In this work, two homologous genes from rice (Oryza sativa) were isolated and designated as OsSIZ1 and OsSIZ2 based on amino acid sequence homology to AtSIZ1 and their phylogenetic relationship. The function in the vegetative growth and reproductive development in rice was investigated using OsSIZ1 mutants containing a T-DNA insertion. The results showed that the mutant Ossiz1 exhibited the significant changes in several growth and developmental parameters, including primary root length, adventitious root number, plant height, leaf and panicle length, flower formation, and seed-setting rate compared with wild type. Taking together these results indicate that OsSIZ1 plays an important role in regulating growth and development in rice.

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Partial nitrate nutrition (PNN) was found to improve rice (Oryza sativa L. var. japonica) growth. However, how PNN is related to photosynthesis in rice cultivars with different nitrogen use efficiency (NUE) is still not clear. Two rice cultivars, Nanguang (high NUE) and Elio (low NUE), were grown under sole NH 4? and PNN at a total nitrogen concentration of 2.86 mM. The dry weight, leaf area, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and gas exchange parameters were measured. Nitrogen and Rubisco contents in the newly expanded leaves of cv. Nanguang were similar to those of cv. Elio when only NH 4? was supplemented in the nutrient solution. However, in cv. Nanguang, nitrogen and Rubisco contents increased under PNN than under sole NH 4 ? nutrition. Higher nitrogen and Rubisco contents were recorded in cv. Nanguang than in cv. Elio under PNN. The ratio of carboxylation efficiency (CE) to Rubisco content in cv. Nanguang was 11 and 14% higher than that in cv. Elio under NH 4 ? and PNN, respectively. CE was 14% higher in cv. Nanguang than that in cv. Elio. The results suggest that PNN causes an increase in photosynthesis in cv. Nanguang. It is concluded that differences in Rubisco activity, rather than stomatal limitation, are responsible for the differences in photosynthesis between the two cultivars. The presence of nitrate increases Rubisco content in rice with a high NUE, which leads to faster biomass accumulation at later growth stages.

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