Acclimation of potato plants to polyethylene glycol-induced water deficit -: II.: Contents and subcellular distribution of organic solutes

Potato plants (Solanum tuberosum cv, Desiree) were grown hydroponically and subjected to water deficit induced by addition of 10% (w/v) PEG 6000, The potato plants were able to grow under water deficit by accumulating organic solutes (osmoregulation). Osmoregulation occurred in two phases, During the initial 2 d hexoses were accumulated, and after 7 d of PEG treatment osmotic adjustment was mostly due to the accumulation of amino acids, especially proline, which accumulated up to 150 times the control content, Sucrose contents remained unchanged in leaves of PEG-treated plants compared with controls, whereas the starch content decreased during PEG treatment. In control leaves, the hexoses and malate were compartmented in the vacuole and sucrose was found in the cytosol and vacuole, Amino acids were distributed between the cytosol and stroma, but only minor amounts of amino acids could be detected in the vacuole, Under water deficit the subcellular distribution of hexoses, malate and sucrose remained unchanged. Most amino acids showed a slight to moderate higher concentration in the vacuole under water deficit. Proline, the metabolite contributing mainly to osmoregulation, was concentrated mostly in the chloroplast and the cytosol, This underlines the important role of proline as the osmolyte under water deficit.