Interaction of Slicing and Osmotic Stress on Proline Metabolism in Jerusalem Artichoke Tuber Tissue

Abstract

Information was sought to explain the changes with time and with osmotic stress in the rate of ¹⁴C transfer from added L-[U-¹⁴Carginine to proline in slices of tubers from Jerusalem artichoke (Helianthus tuberosus¹⁴ L.). Using osmotically stressed tubers, the transfer rates were shown to be independent of the size of the free proline pool, and of the net rate of proline accumulation. In osmotically stressed and in turgid slices, the rates of transfer increased after slicing, but decreased after 24 h. Only in freshly cut slices were the rates higher for stressed slices. Proline and hydroxy- proline in protein increased with time from slicing in both turgid and stressed slices, and proline and hydroxyproline in protein were labelled when L-[U-¹⁴C]arginine was added. However, no correlation could be shown between ¹⁴C in protein-bound proline plus hydroxyproline, and the net increase in these with time. It is concluded that externally added arginine donates carbon to proline in reactions whose rates do not determine the net rate of proline accumulation or the net rate of synthesis of proline destined for protein.

The metabolism of L-[U-¹⁴C]glutamate added to discs was also studied. [¹⁴C]proline was a minor product of glutamate metabolism at all times.