Abstract
Rice (Oryza sativa L.) seedlings grown under nitrogen (N) deficiency conditions show a foraging response characterized by increased root length. However, the mechanism underlying this developmental plasticity is still poorly understood. In this study, the mechanism by which N deficiency influences rice seminal root growth was investigated. The results demonstrated that compared with the control (1 mM N) treatment, N deficiency treatments strongly promoted seminal root growth. However, the N deficiency-induced growth was negated by the application of zeatin, which is a type of cytokinin (CK). Moreover, the promotion of rice seminal root growth was correlated with a decrease in CK content, which was due to the N deficiency-mediated inhibition of CK biosynthesis through the down-regulation of CK biosynthesis genes and an enhancement of CK degradation through the up-regulation of CK degradation genes. In addition, the N deficiency-induced decrease in CK content not only enhanced the root meristem cell proliferation rate by increasing the meristem cell number via the down-regulation of OsIAA3 and up-regulation of root-expressed OsPLTs, but also promoted root cell elongation by up-regulating cell elongation-related genes, including root-specific OsXTHs and OsEXPs. Taken together, our data suggest that an N deficiency-induced decrease in CK content promotes the seminal root growth of rice seedlings by promoting root meristem cell proliferation and cell elongation.
Highlights
Rice (Oryza sativa L.) is one of the most important food crops in the world [1]
In order to investigate the effect of N deficiency on rice seminal root growth, rice seedlings were cultivated hydroponically under control (1 N) and N deficiency (1/4 N, 1/16 N, and 0 N) conditions
We found that the CK contents in rice seminal roots in the N deficiency treatment groups were lower than those of the control, and that a decrease in the concentration of N was accompanied by a decrease in the content of CKs as well as a longer seminal root (Figure 1, Table 1)
Summary
Rice (Oryza sativa L.) is one of the most important food crops in the world [1]. In the past 50 years, rice yield has steadily increased worldwide, partly owing to an increase in nitrogen (N) application.at present, the average recovery efficiency of N fertilizer (the percentage of fertilizer N recovered in aboveground plant biomass at the end of the cropping season) is only 33% at the field level [2]. Rice (Oryza sativa L.) is one of the most important food crops in the world [1]. In the past 50 years, rice yield has steadily increased worldwide, partly owing to an increase in nitrogen (N) application. At present, the average recovery efficiency of N fertilizer (the percentage of fertilizer N recovered in aboveground plant biomass at the end of the cropping season) is only 33% at the field level [2]. High N input and low N use efficiency increase crop production costs and. Decreasing N application is an important goal of sustainable agriculture. Decreasing N application may lead to N deficiency and affect rice root growth, and the underlying mechanism by which N deficiency affects rice root growth is still poorly understood
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