Microinjection of guanine nucleotide analogues into lily pollen tubes results in isodiametric tip expansion

Heterotrimeric and small G-proteins are supposed to participate in tip grow th of plant cells. Quantitative changes in tip growth rate after introducti on of non-hydrolysable guanine nucleotide analogues (NA) into lily pollen t ubes have been interpreted as support for the hypothesis that heterotrimeri c G-proteins regulate tube elongation (Ma et al., 1999([11])). Here, we rep ort that microinjection of guanine NA into lily pollen tubes causes loss of growth polarity, resulting in isodiametric tip swelling. Our results are c ompatible with current models suggesting an involvement of plant Rho-relate d small G-proteins (Rop) in the maintenance of pollen tube polarity and in tip morphogenesis.