pH Stabilized NH4+-Fed Nutrition Promotes Higher B Uptake and Plant Growth in Rapeseed (Brassica napus L.) by the Upregulation of B Transporters

Abstract

AbstractRapeseed (Brassica napus L.) is a major oilseed crop with high boron (B) requirements. In hydroponic cultivation, B uptake is highly responsive to the media conditions (e.g., pH). Different N sources, such as NH4+ and NO3−, directly affect the media pH. To date, the underlying mechanisms, the role of the buffering at constant N-sources by separating the effects of pH and/or sources of N-form, for the uptake of B remain indistinct under hydroponic cultivation, particularly in rapeseed. Two identical experiments were conducted using (NH4)2SO4 and Ca(NO3)2 as sole N-sources each set were subjected to four treatments viz. non-buffered, buffered pH 5.0, 6.0, and 7.0 at low (1 µM) and high (100 µM) B for 5 days. The novelty of this study demonstrates that NH4+-fed plants prefer buffered pH (6 and 7) for promoting higher plant growth, which was in line with the B concentration, while NO3−-fed plants were not influenced. These aforesaid findings were further supported by the upregulation of BnaNIP5;1 and BnaBOR1;2 in the root and higher expression of BnaNIP5;1 in shoots with buffered pH in NH4+-fed plants. According to our findings, in NH4+-based buffering, B transport channel protein BnaNIP5;1 (through diffusion) facilitated B uptake and distribution from root to shoot while BnaBOR1;2 mediated active uptake of B was in root under low supply of B. In a nutshell, pH buffering in hydroponics is very important in NH4+-based but not in NO3−-based nutrition for the uptake of boron and growth of the rapeseed plants.