FATTY-ACID COMPOSITION OF MICROSOMAL PHOSPHOLIPIDS AND H-ATPASE ACTIVITY IN THE ROOTS OF SCOTS PINE-SEEDLINGS GROWN AT DIFFERENT ROOT TEMPERATURES DURING FLUSHING()

The fatty acid composition of phospholipids in the microsomes and the vanadate-sensitive H+-ATPase activity of the roots of one-year-old Sco ts pine (Pinus sylvestris L.) seedlings were studied during flushing i n spring. The seedlings in hydroponic cultures were subjected to diffe rent root temperatures (5, 12 or 20 degrees C). The shoot was maintain ed at 20/15 degrees C (day/night) during the 35 d experiment. After 35 d at 5 degrees C, root growth was totally inhibited and shoot growth partly inhibited. In roots grown at 5 degrees C the fatty acid composi tion of the microsomal phospholipids and the degree of fatty acid unsa turation (bond index) were unchanged, while in roots grown at 12 and 2 0 degrees C the fatty acid composition changed and bond index decrease d. At those root temperatures, the most obvious change was a decline i n the proportion of linolenic acid (C18:3). In the new white roots gro wn either at 12 degrees C or 20 degrees C the proportion of C18:2 was higher and the proportion of C18:3 lower than in 1-year-old roots. Ind ependently of root temperature, H+-ATPase activity, determined on a fr esh weight basis, declined to half of the original activity during the experiment. The decline in H+-ATPase activity was most rapid during t he first week. In the old roots the decline in H+-ATPase activity foll owed closely the decline in amount of membrane protein. In new roots H +-ATPase activity was high and increased with increasing root temperat ure. These results suggest that in the roots of Scots pine seedlings, vanadate-sensitive H+-ATPase activity is dependent on age, while chang es in the microsomal fatty acid composition of phospholipids are regul ated mainly by root temperature.