Storage of Osmotically Active Compounds in the Taproot ofDaucus carotaL.

Abstract

The osmotic potential of cell sap from the storage root, lateral roots and shoots of carrot (Daucus carota L., cv. Amsterdamse Bak) was calculated from the concentration of osmotically active compounds in these tissues. The osmotic potential of the taproot did not change with age prior to and during the storage of osmotically active sugars, as sucrose and reducing sugars. The increased contribution of soluble sugars in the osmotic potential was accompanied by a proportionally decreased contribution of potassium and organic acids. Before storage of soluble sugars in the taproot occurred, potassium and organic acids contributed 80% to the total osmotic value, in contrast with lateral root tissue, where potassium and nitrate were the main osmotic solutes. The concentration of osmotically active solutes was lower in lateral root tissue than in storage root tissue. Shoot tissue resembled taproot tissue before storage, in having potassium and organic acids as the main osmotic solutes. The concentration of osmotically active solutes was highest in shoot tissue and it increased towards the end of the experimental period. The calculated osmotic potentials were in good agreement with the experimental values, as determined from the molecular depression of the freezing point of cell sap. Storage of reducing sugars and sucrose is discussed in relation to acid and neutral invertase activities.