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

Potato (Solanum tuberosum L. cv Saturna) plants were grown in pots with varying supplies of K fertilizer (1.25, 5, and 10 grams K(2)O per 12 kilograms soil). Four weeks after midflower, plants were supplied with (14)CO(2) for 12 hours and osmotic and water potential in tubers were determined. Assimilation of (14)CO(2) increased from 504 (K(1)) to 1860 (K(5)) and 1922 kilobecquerels per plant per 12 hours (K(10)). In all treatments, about half of the (14)C 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 (K(1)) to +5.9 (K(5)) and +6.0 bars (K(10)), respectively. Incorporation of (14)C per gram tuber dry weight as well as per gram tuber starch was significantly higher in K(5) than in K(1) and slightly increased even further in the K(10) treatment, where tuber pressure sap contained the highest K concentration (179 millimolar K).