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Urea‐based fertilizers are commonly used in the agricultural rice production. Urea produces gaseous ammonia upon contact with plants and soil. Although rice is considered to be a relatively ammonium‐tolerant crop, urea fertilization can have a negative impact on seedling establishment because of tissue ammonia accumulation. We investigated the molecular/genetic regulation of ammonia tolerance in rice using a multidisciplinary approach consisting of high‐resolution LC‐MS/MS analysis and bioinformatics, together with plant molecular physiology and biochemistry. Growth with 10 or 80 mM NH4Cl led to an inhibition of photosynthesis and ROS accumulation. Proteomic analysis revealed changes in the levels of 266 proteins, which function in translation and protein metabolism, amino acid and carbon metabolism/transport, antioxidant and redox metabolism. The abundance of the transcripts encoding these proteins was increased under high ammonium. Data are presented showing that ammonia‐induced changes in metabolism are linked to a strong antioxidant response but little change in secondary metabolism. [ABSTRACT FROM AUTHOR]

Nodule numbers are regulated through systemic auto-regulatory signals produced by shoots and roots. The relative effects of shoot and root genotype on nodule numbers together with relationships to organ biomass, carbon (C) and nitrogen (N) status, and related parameters were measured in pea ( Pisum sativum) exploiting natural genetic variation in maturity and apparent nodulation intensity. Reciprocal grafting experiments between the early (Athos), intermediate (Phönix) and late (S00182) maturity phenotypes were performed and Pearson's correlation coefficients for the parameters were calculated. No significant correlations were found between shoot C/N ratios and plant morphology parameters, but the root C/N ratio showed a strong correlation with root fresh and dry weights as well as with shoot fresh weight with less significant interactions with leaf number. Hence, the root C/N ratio rather than shoot C/N had a predominant influence on plant morphology when pea plants are grown under conditions of symbiotic nitrogen supply. The only phenotypic characteristic that showed a statistically significant correlation with nodulation intensity was shoot length, which accounted for 68.5% of the variation. A strong linear relationship was demonstrated between shoot length and nodule numbers. Hence, pea nodule numbers are controlled by factors related to shoot extension, but not by shoot or root biomass accumulation, total C or total N. The relationship between shoot length and nodule numbers persisted under field conditions. These results suggest that stem height could be used as a breeding marker for the selection of pea cultivars with high nodule numbers and high seed N contents. [ABSTRACT FROM AUTHOR]