Additional Nitrogen Fertilization at Heading Time of Rice Down-Regulates Cellulose Synthesis in Seed Endosperm

Abstract

The balance between carbon and nitrogen is a key determinant of seed storage components, and thus, is of great importance to rice and other seed-based food crops. To clarify the influence of the rhizosphere carbon/nitrogen balance during the maturation stage of several seed components, transcriptome analysis was performed on the seeds from rice plants that were provided additional nitrogen fertilization at heading time. As a result, it was assessed that genes associated with molecular processes such as photosynthesis, trehalose metabolism, carbon fixation, amino acid metabolism, and cell wall metabolism were differentially expressed. Moreover, cellulose and sucrose synthases, which are involved in cellulose synthesis, were down-regulated. Therefore, we compared cellulose content of mature seeds that were treated with additional nitrogen fertilization with those from control plants using calcofluor staining. In these experiments, cellulose content in endosperm from plants receiving additional nitrogen fertilization was less than that in control endosperm. Other starch synthesis-related genes such as starch synthase 1, starch phosphorylase 2, and branching enzyme 3 were also down-regulated, whereas some α-amylase and β-amylase genes were up-regulated. On the other hand, mRNA expression of amino acid biosynthesis-related molecules was up-regulated. Moreover, additional nitrogen fertilization caused accumulation of storage proteins and up-regulated Cys-poor prolamin mRNA expression. These data suggest that additional nitrogen fertilization at heading time changes the expression of some storage substance-related genes and reduces cellulose levels in endosperm.

Statement of Foliar Fertilization Impact on Yield, Composition, and Oxidative Biomarkers in Rice

“…5 In this regard, several authors have reported critical differences among cultivars featured by an average protein content, as a consequence of foliar fertilization, upon field trials developed in soils with similar composition. 28 In addition, Bezus et al and Vidal et al evaluated genotypes featured by high protein content and did not observe a statistically significant response to the nitrogen fertilization applied. 30 Additional studies by the same authors evidenced that the response varies according to the genotype, which has been justified because the applied N can be directed to other destinations different from grain, as yield or biomass, for which it is necessary to evaluate higher doses and other moments of application.…”

Effects of Nitrogen Rates on the Physicochemical Properties of Waxy Maize Starch

“…Moderate N rates enhanced starch accumulation in rice, wheat, and normal maize . The high starch content under MN might be attributed to the increased number of cells and starch granules in the endosperm because of the enhanced activities of soluble and bound invertases and sucrose synthase . The activities of adenosine diphosphate‐glucose pyrophosphorylase, starch synthase, starch branching enzyme, and sucrose phosphate synthase involved in starch synthesis were increased under a low N rate in rice .…”

“…The activities of adenosine diphosphate‐glucose pyrophosphorylase, starch synthase, starch branching enzyme, and sucrose phosphate synthase involved in starch synthesis were increased under a low N rate in rice . The low starch content observed under a high N rate might be caused by the downregulation of genes related to starch synthesis . Moreover, a sufficient assimilate supply favoring starch accumulation was demonstrated by N fertilizer additions or ear truncation …”

Feeding the Walls: How Does Nutrient Availability Regulate Cell Wall Composition?

“…This reduction in cell wall components is accompanied by reduced stem mechanical strength, increased lodging, and reduced disease resistance [ 68 , 69 , 70 ]. Similar to roots, expression of cellulose and lignin synthesis genes is reduced in filling seeds in response to high N. This leads to reduced accumulation of both cellulose and lignin in seed endosperms [ 71 ]. In line with this observation, N deficiency leads to an increase in cellulose content in the roots of rice plants [ 72 ].…”