Impaired cell growth under ammonium stress explained by modeling the energy cost of vacuole expansion in tomato leaves

Abstract

Ammonium (NH 4 +)-based fertilization efficiently mitigates the adverse effects of nitrogen fertilization on the environment. However, high concentrations of soil NH 4 + provoke growth inhibition, partly caused by the reduction of cell enlargement and associated with modifications of cell composition, such as an increase of sugars and a decrease in organic acids. Cell expansion depends largely on the osmotic-driven enlargement of the vacuole. However, the involvement of subcellular compartmentation in the adaptation of plants to ammonium nutrition has received little attention, until now. To investigate this, tomato (Solanum lycopersicum) plants were cultivated under nitrate and ammonium nutrition and the fourth leaf was harvested at seven developmental stages. The vacuolar expansion was monitored and metabolites and inorganic ion contents, together with intracellular pH, were determined. A data-constrained model was constructed to estimate subcellular concentrations of major metabolites and ions. It was first validated at the three latter developmental stages by comparison with subcellular concentrations obtained experimentally using nonaqueous fractionation. Then, the model was used to estimate the subcellular concentrations at the seven developmental stages and the net vacuolar uptake of solutes along the developmental series. Our results showed ammonium nutrition provokes an acidification of the vacuole and a reduction in the flux of solutes into the vacuoles. Overall, analysis of the subcellular compartmentation reveals a mechanism behind leaf growth inhibition under ammonium stress linked to the higher energy cost of vacuole expansion, as a result of alterations in pH, the inhibition of glycolysis routes and the depletion of organic acids.

Nitrate alleviates ammonium toxicity in Brassica napus by coordinating rhizosphere and cell pH and ammonium assimilation

“…However, high conditions inhibited rapeseed growth, as indicated by a decrease in root and shoot dry weight, total root length, and total root volume (Figure 1). Such phenomena are frequently observed in other plant species when is used alone (Li et al., 2014; Poucet et al., 2022). Compared to the sole conditions, and amino acids accumulated in the sole conditions, whereas organic acids declined (Figures 6, 7 and 9).…”

“…Compared to the sole conditions, and amino acids accumulated in the sole conditions, whereas organic acids declined (Figures 6, 7 and 9). These results indicate that toxicity in B. napus might be associated with the accumulation of (Britto & Kronzucker, 2002; Hachiya et al., 2012), the accumulation of phenolics (Podgórska et al., 2017; Royo et al., 2016), the depletion of organic acids which in turn suppressed the TCA cycle and glycolysis (Li et al., 2021; Poucet et al., 2022). Some recent researches suggest that rhizosphere and apoplast acidification is one of the most important causes of ammonium toxicity (Hachiya et al., 2021; Xiao et al., 2022).…”

“…There is a slight but statistically significant pH decrease in the cytosol of rapeseed root treated with ammonium, but a remarkable decrease was observed in the rapeseed vacuole under sole ammonium treatment (Figure 5). In tomato, there was no significant pH change in the leaf cytosol under sole ammonium or nitrate treatments but a remarkable decrease in the vacuole of leaves treated with ammonium compared to nitrate (Poucet et al., 2022). However, a slight alkalinization of the cytoplasm and/or vacuole was even observed in maize root that were exposed to high levels of exogenous (Gerendás et al., 1990; Gerendás & Ratcliffe, 2000).…”