Sufficient potassium supply enhances tolerance of potato plants to PEG-induced osmotic stress

Potassium (K) plays a crucial role in reducing the severity of drought stress. Potatoes are considered drought sensitive crops due to their shallow root system. In this study, potato cultivars 'Milva' and `Agria' grown under -K (75 mu M) and +K (1000 mu M) supply in a hydroponic system were examined under greenhouse conditions. Half of the plants for each cultivar and K supply were treated for two weeks with polyethylene glycol (PEG) to induce osmotic stress at 67 days after planting (dap). For recovery, plants grew two more weeks without PEG. Plant height, biomass, and water consumption were measured weekly. Leaflets were analysed before, during, and after PEG addition to subsequently determine parameters, for example, total free amino acids and metabolites. Additionally, the K allocation in plant parts was determined. K supply and PEG positively affected biomass production, and the production of side shoots was enhanced with -K and PEG. The water consumption increased with PEG addition in Milva, which was not observed in Agria. K and sugars accumulated in side shoots, showing cultivar and treatments specific reactions. Individual amino acids, including isoleucine, leucine, valine, and alanine, accumulated under low K supply and PEG-induced osmotic stress, and functional characterization could provide information on the response to drought stress. However, K remained an important variable, providing functions of other osmolytes to maintain plant metabolism. The results revealed morphophysiological and biochemical indications for adaption mechanisms against osmotic stress and may help to identify drought stress tolerant cultivars.