A proposed role for endomembrane trafficking processes in regulating tonoplast content and vacuole dynamics under ammonium stress conditions in Arabidopsis root cells.

Ammonium (NH) stress has multiple effects on plant physiology, therefore, plant responses are complex, and multiple mechanisms are involved in NH sensitivity and tolerance in plants. Root growth inhibition is an important quantitative readout of the effects of NH stress on plant physiology, and cell elongation appear as the principal growth inhibition target. We recently proposed autophagy as a relevant physiological mechanisms underlying NH sensitivity response in Arabidopsis. In a brief overview, the impaired macro-autophagic flux observed under NH stress conditions has a detrimental impact on the cellular energetic balance, and therefore on the energy-demanding plant growth. In contrast to its inhibitory effect on the autophagosomes flux to vacuole, NH toxicity induced a micro-autophagy-like process. Consistent with the reduced membrane flux to the vacuole related to macro-autophagy inhibition and the increased tonoplast degradation due to enhanced micro-autophagy, the vacuoles of the root cells of the NH-stressed plants showed lower tonoplast content and a decreased perimeter/area ratio. As the endosome-to-vacuole trafficking is another important process that contributes to membrane flux toward the vacuole, we evaluated the effects of NH stress on this process. This allows us to propose that autophagy could contribute to vacuole development as well as possible avenues to follow for future studies.