Inhibition of Pollen Tube Elongation by Microinjected Anti-Rop1Ps Antibodies Suggests a Crucial Role for Rho-Type GTPases in the Control of Tip Growth.

Microinjection of anti-Rop1Ps antibodies was used to assess the function of a tip-localized Rho-type GTPase, Rop, in controlling pollen tube growth. Injected antibodies induced sustained growth arrest within 1 to 2 min after injection but did not affect cytoplasmic streaming. Coinjection with Rop rescued antibody-induced growth inhibition, indicating that injected antibodies specifically block the activity of Rop GTPases. Antibody-induced inhibition was significantly enhanced in the presence of a lower threshold of extracellular [Ca2+] or a subinhibitory dosage of caffeine. In contrast, injection of the C3 toxin, which inactivates a different Rho-type GTPase, arrested tube elongation 10 to 20 min after injection. C3-induced growth arrest was accompanied by the cessation of cytoplasmic streaming. These data suggest that Rho-type GTPases play a pivotal role in the control of pollen tube elongation. We propose that Rop may regulate a Ca2+-dependent pathway involved in vesicle docking/fusion, whereas a C3-sensitive Rho GTPase may mediate cytoplasmic streaming.