Fig. 3.

Effect of l-glutamate on root architecture in Thlaspi caerulescens. Seed of T. caerulescens was surface-sterilized with Na hypochlorite and germinated on vertical agar plates as previously described for Arabidopsis (Zhang et al., 1999) except that Phytagel™ (1 %, w/v) was used instead of agar and the medium contained 1 mm MgCl₂ and 1 mm CaCl₂ to aid solidification. The background N source was 0.5 mm glutamine. The temperature was 18–23 °C and the photon irradiance was approx. 120 μmol m² s⁻¹ with a 16 : 8-h light–dark regime. After 6 d growth, and before lateral roots had appeared, the seedlings were transferred to fresh plates containing the same medium plus either 1 mm KCl (control) or 1 mm potassium l-glutamate (treated) and incubated for a further 9 d before image capture. Arrows indicate the locations of the primary root tips at the time of transfer.