Nitrogen form and root division modifies the nutrimental and biomolecules concentration in blueberry (Vaccinium corymbosum L.)

Blueberry (Vaccinium corymbosum L.) continues to gain importance in the international market due to its effects on the prevention of human diseases. This leads to the need to optimize the production and quality of the fruit. The present research evaluated the effect of NO3- and NH4+, using the split roots technique, in the nutritional status, photosynthetic pigments and total sugars in blueberry leaves. A completely random experiment was established with six greenhouse treatments: three under homogeneous root conduction (HR) and three with split roots (SR). The concentration of N, P, K, Ca, Mg, S, Fe, Cu, Zn, Mn, B and Na, chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (Car) and total sugars were evaluated in the leaves. The exclusive supply of NH4+ led to the largest accumulation of N, P, Mg, S, Cu, Mn and B, compared to plants treated with NO3-. The Chla and total sugars were higher with NH4+ compared to NO3- nutrition. The supply of N separately (SR) had no positive effects on the evaluated variables, however, the SR with half of N, in the form of NH4+, compared to the non-SR with full application of N, has no differences in N-leaf concentration, which implies a higher use in the uptake or accumulation of this macro element in plant. V. corymbosum L. with split root and half of N in the form of NH4+, doubled the N use efficiency, as it matches in yield the complete supply treatment of N-NH4+ without root division.

Feedback inhibition of AMT1 NH4+-transporters mediated by CIPK15 kinase

Background Ammonium (NH4+), a key nitrogen form, becomes toxic when it accumulates to high levels. Ammonium transporters (AMTs) are the key transporters responsible for NH4+ uptake. AMT activity is under allosteric feedback control, mediated by phosphorylation of a threonine in the cytosolic C-terminus (CCT). However, the kinases responsible for the NH4+-triggered phosphorylation remain unknown. Results In this study, a functional screen identified protein kinase CBL-Interacting Protein Kinase15 (CIPK15) as a negative regulator of AMT1;1 activity. CIPK15 was able to interact with several AMT1 paralogs at the plasma membrane. Analysis of AmTryoshka, an NH4+ transporter activity sensor for AMT1;3 in yeast, and a two-electrode-voltage-clamp (TEVC) of AMT1;1 in Xenopus oocytes showed that CIPK15 inhibits AMT activity. CIPK15 transcript levels increased when seedlings were exposed to elevated NH4+ levels. Notably, cipk15 knockout mutants showed higher 15NH4+ uptake and accumulated higher amounts of NH4+ compared to the wild-type. Consistently, cipk15 was hypersensitive to both NH4+ and methylammonium but not nitrate (NO3−). Conclusion Taken together, our data indicate that feedback inhibition of AMT1 activity is mediated by the protein kinase CIPK15 via phosphorylation of residues in the CCT to reduce NH4+-accumulation.