The Mechanisms of Pod Zone Nitrogen Application on Peanut Pod Yield.

Peanut (Arachis hypogaea L.) is a geocarpic plant, which absorbs nutrients not only through roots but also through pods. However, the effect of nitrogen fertilizer application in pod area on pod gene expression and peanut yield is unknown. In this study, we determined the pod yield, dry matter accumulation, nitrogen accumulation in different organs under different nitrogen treatment in root zone and pod zone. The results showed that pod area application of nitrogen led to significantly higher pod yield to compare with the control. The application of 60 kg/hm2 nitrogen at the pod area led to the highest pod yield, full fruit rate and plant nitrogen content. 15N directly absorbed by pods was mainly accumulated in the shell at early stage of pods development, and then transferred to seeds at later period. However, the ratio of 15N absorbed directly by pods from soil was low, only about 10%. To understand the underlying molecular mechanisms, immature pods of different developmental stages were collected for gene expression analysis. The expression levels of several genes encoding ABC type transporter family, nitrate reductase, nitrite reductase and glutamine synthetase increased in different stages of pod development upon pod area nitrogen application. These results indicated that the efficiency of N assimilation and glutamate metabolic cycle in pods was increased under pod nitrogen application. The expression levels of several genes in gibberellin and brassinolide biosynthesis pathways were also up-regulated, suggesting that these two hormones were involved in the promoting effect of pod nitrogen application on pod growth. [ABSTRACT FROM AUTHOR]