The turgor pressure of growing lily pollen tubes

Abstract

The turgor pressure of growing pollen tubes of the lily (Lilium longiflorum Thunb.) has been recorded using a turgor pressure probe. Insertion of the probe's micropipette was routinely accomplished, providing recording periods of 20 to 30 min. Probe insertion did not affect tube growth. The stable turgor values ranged between 0.1 and 0.4 MPa, the mean value being 0.209 ± 0.064 MPa (n = 106). A brief increase in turgor, generated by injection of oil through die pressure probe, caused the tube to burst at its lip. Burst pressures ranged between 0.19 and 0.58 MPa, that is, individual lily pollen tubes do not withstand turgor pressure approaching twice their regular turgor pressure. In contrast, parallel experiments using the incipient plasmolysis technique yielded a mean putative turgor pressure of 0.79 MPa either using sucrose (n = 24) or mannitol (n = 25). Surprisingly, turgor pressure was not significantly correlated with tube growth rate which ranged from zero to 13 μm/min. Nor did it correlate with tube length over the tested range of 100 to 1600 μm. In addition the influence of the medium's osmolality was surprisingly low: raising the external osmotic pressure from 0.36 to 1.08 MPa, with sucrose or mannitol, only caused mean turgor pressure to decline from 0.27 to 0.18 MPa. We conclude that growing lily pollen regulates its turgor pressure remarkably well despite substantial variation in tube growth rate, tube length, and osmotic milieu.