TURGOR PRESSURE AND ELONGATION GROWTH IN DEVELOPING SUNFLOWER HYPOCOTYLS

The average turgor pressure of hypocotyl cells of 2-day-old etiolated sunflower seedlings (Helianthus annuus L.) was 0.59 MPa. Turgor pressu re decreased during acceleration of growth in darkness and reached a v alue of 0.5 MPa at days 4 and 5 after sowing (linear phase of growth). Cessation of hypocotyl elongation at day 6 was accompanied by a 40 % drop in cell turgor pressure. We suggest that this loss of cell turgor is the cause of the decline in hypocotyl growth in darkness. Irradiat ion of the etiolated seedlings with white light inhibited hypocotyl gr owth, but turgor pressure was unaffected.