Transport of organic anions in root cells and its role in cell signaling in higher plants

The organic anion balance is critical for metabolic, bioenergetic, and electrochemical processes in plant cells, controlling the quality and quantity of yield and plant stress resistance. Nevertheless, the redistribution and membrane transport of these substances in plant tissues have not been investigated in detail. The mechanism of passive anion efflux from a plant cell through the ion channels has not been established so far. Here, using the patch-clamp technique, we have characterized the ion channel-mediated conductances of ascorbate, malate, gluconate, citrate, fumarate, and pronionate in the root cells of Arabidopsis thaliana, Triticum aestivum, and Helianthus annuus. These conductances showed high permeability to ascorbate, malate, and citrate, as well as low permeability to fumarate, propionate, and gluconate. Anion channel conductances of root cells showed rapid activation kinetics and low potential dependence. They were also inhibited by 9-anthracenecarboxylic acid, suggesting that they belong to the ALMT family of anion channels found only in higher plants. Aequorin chemilu minometry was used to test the effect of organic anions on the Ca2+ signaling in root cells. Among four organic anions tested, only ascorbate induced a significant increase in the cytosolic Ca2+ activity at physiological levels (1 and 10 mM). This effect may underlie the previously unknown functions of exogenous ascorbate related to short- and long-distance signaling in higher plants.

1. López-Bucio J., Nieto-Jacobo M. F., Ramı́rez-Rodrı́guez V., Herrera-Estrella L. Organic acid metabolism in plants: from adaptive physiology to transgenic varieties for cultivation in extreme soils. Plant Science, 2000, vol. 160, no. 1, pp. 1–13. https://doi.org/10.1016/s0168-9452(00)00347-2

2. Igamberdiev A. U., Bykova N. V. Role of organic acids in the integration of cellular redox metabolism and mediation of redox signalling in photosynthetic tissues of higher plants. Free Radical Biology and Medicine, 2018, vol. 122, pp. 74–85. https://doi.org/10.1016/j.freeradbiomed.2018.01.016

3. Meyer S., Scholz-Starke J., De Angeli A., Kovermann P., Burla B., Gambale F., Martinoia E. Malate transport by the vacuolar AtALMT6 channel in guard cells is subject to multiple regulation. Plant Journal, 2011, vol. 67, no. 2, pp. 247–257. https://doi.org/10.1111/j.1365-313x.2011.04587.x

4. Canarini A., Kaiser C., Merchant A., Richter A., Wanek W. Root exudation of primary metabolites: mechanisms and their roles in plant responses to environmental stimuli. Frontiers in Plant Science, 2019, vol. 10, art. 157. https://doi.org/10.3389/fpls.2019.00157

5. Barbier-Brygoo H., De Angeli A., Filleur S., Frachisse J.-M., Gambale F., Thomine S., Wege S. Anion channels/transporters in plants: from molecular bases to regulatory networks. Annual Review of Plant Biology, 2011, vol. 62, no. 1, pp. 25–51. https://doi.org/10.1146/annurev-arplant-042110-103741

6. Hedrich R., Geiger D. Biology of SLAC1-type anion channels – from nutrient uptake to stomatal closure. New Phytologist, 2017, vol. 216, no. 1, pp. 46–61. https://doi.org/10.1111/nph.14685

7. Wang C., Zhang J., Wu J., Brodsky D. E., Schroeder J. I. Cytosolic malate and oxaloacetate activate S‐type anion channels in Arabidopsis guard cells. New Phytologist, 2018, vol. 220, no. 1, pp. 178–186. https://doi.org/10.1111/nph.15292

8. Diatloff E., Roberts M., Sanders D., Roberts S. K. Characterization of anion channels in the plasma membrane of Arabidopsis epidermal root cells and the identification of a citrate-permeable channel induced by phosphate starvation. Plant Physiology, 2004, vol. 136, no. 4, pp. 4136–4149. https://doi.org/10.1104/pp.104.046995

9. Zhang W.-H., Ryan P. R., Tyerman S. D. Citrate-permeable channels in the plasma membrane of cluster roots from white lupin. Plant Physiology, 2004, vol. 136, no. 3, pp. 3771–3783. https://doi.org/10.1104/pp.104.046201

10. Demidchik V. Non-selective cationic channels of the plasma membrane of root cells of higher plants. Minsk, 2014. 172 p. (in Russian).

11. Sharma T., Dreyer I., Kochian L., Piñeros M. A. The ALMT family of organic acid transporters in plants and their involvement in detoxification and nutrient security. Frontiers in Plant Science, 2016, vol. 7, art. 1488. https://doi.org/10.3389/fpls.2016.01488

12. Miller A. J., Smith S. J. Cytosolic nitrate ion homeostasis: could it have a role in sensing nitrogen status? Annals of Botany, 2008, vol. 101, no. 4, pp. 485–489. https://doi.org/10.1093/aob/mcm313

13. Lipton D. S., Blanchar R. W., Blevins D. G. Citrate, malate, and succinate concentration in exudates from p-sufficient and p-stressed Medicago sativa L. seedlings. Plant Physiology, 1987, vol. 85, no. 2, pp. 315–317. https://doi.org/10.1104/pp.85.2.315

14. Demidchik V. Mechanisms of oxidative stress in plants: from classical chemistry to cell biology. Environmental and Experimental Botany, 2015, vol. 109, pp. 212–228. https://doi.org/10.1016/j.envexpbot.2014.06.021

15. Demidchik V., Shabala S., Isayenkov S., Cuin T. A., Pottosin I. Calcium transport across plant membranes: mechanisms and functions. New Phytologist, 2018, vol. 220, no. 1, pp. 49–69. https://doi.org/10.1111/nph.15266