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Water Relationships and Incorporation of ¹⁴C Assimilates in Tubers of Potato Plants Differing in Potassium Nutrition

Agricultural Research Station Büntehof, Bünteweg 8, D-3000 Hannover 71, Federal Republic of Germany

Potato (Solanum tuberosum L. cv Saturna) plants were grown in pots with varying supplies of K fertilizer (1.25, 5, and 10 grams K₂O per 12 kilograms soil). Four weeks after midflower, plants were supplied with ¹⁴CO₂ for 12 hours and osmotic and water potential in tubers were determined. Assimilation of ¹⁴CO₂ increased from 504 (K₁) to 1860 (K₅) and 1922 kilobecquerels per plant per 12 hours (K₁₀). In all treatments, about half of the ¹⁴C was translocated to the tubers within 12 hours, although calculated turgor pressure in tubers which could be considered as a potential counter-pressure to phloem unloading increased from +5.3 (K₁) to +5.9 (K₅) and +6.0 bars (K₁₀), respectively. Incorporation of ¹⁴C per gram tuber dry weight as well as per gram tuber starch was significantly higher in K₅ than in K₁ and slightly increased even further in the K₁₀ treatment, where tuber pressure sap contained the highest K concentration (179 millimolar K).