Leaf RGR patterns (a, c, e) and root velocity patterns (b, d, e) acquired simultaneously for N. tabacum seedlings under three different conditions for the root system. (a, b) Roots are growing in the dark at 22°C substrate temperature (control, n = 3). (c, d) Roots growing in the dark at 10°C substrate temperature (root cooling, n = 4). (e, f) Roots subjected to diel light–dark cycles at 22°C substrate temperature (root illumination, n = 4). Error bars are S.E.