Instrumental setup

Transverse relaxation measurements were performed using a mobile NMR lab specifically set up for this purpose (Fig. 1). A commercially available 20 MHz spectrometer (Minispec PC-120, Bruker, Karlsruhe, Germany) equipped with a temperature control device connected to an optical fiber (Neoptix Inc, Canada) allowing ±0.1 °C temperature regulation was placed inside a van. The experimental device was powered by a battery. Such equipped van was positioned in the field close to the plants under investigation. No special care was taken to control the temperature inside the van. The leaf under investigation was cut from the plant (Fig. 2a) without uprooting the plant and, if the leaf was wet, wiped gently. Eight discs 8 mm in diameter were cut from each leaf of the plant studied (Figs. 2b, c). To obtain homogeneous tissues, the discs were cut in the middle of the limb on each side of the central vein and avoiding lateral second order veins. The discs were then placed in NMR tubes which were closed with a 2-cm long Teflon cap to avoid water loss during measurements (Fig. 2d). The temperature of the samples inside NMR probe was set at 18 °C.

Mobile NMR laboratory with the NMR spectrometer including the magnet system and the probe assembly (1), the electronic control NMR unit (2), the battery (3) and a standard laptop computer for measurement control (4)

Oilseed rape plants at the end of stem elongation stage (a), leaf (LR −9) after disc sampling (b), eight discs cut from the leaf for NMR measurement (c) and NMR tube containing 8 discs, closed with a 2-cm long Teflon cap (d)