a, Pollen tubes of Col-0, prk6, prk3 prk6 and prk1 prk3 prk6 growing in the Col-0 pistils. Aniline blue staining was performed 12 or 24 HAP. White arrows indicate the tip of the longest pollen tube in the transmitting tract. Data are representative of three samples for each genotype. Scale bar, 500 μm. b, Length from the top of the stigma to the tip of the longest pollen tube, 12 or 24 HAP with Col-0 and prk mutants. About 2,700 μm is the maximum limit for the length in this measurement. The data are the mean and s.d. of three pistils. ND, no data.