Quantitative NMR microscopy of osmotic stress responses in maize and pearl millet

The effect of osmotic stress (-0.35 MPa) on the cell water balance and apical growth was studied noninvasively for maize (Zea mays L., cv. LG 11) and pearl millet (Pennisetum americanum L., cv. MH 179) by H-1 NMR microscopy in combination with water uptake measurements. Single parameter images of the water content and the transverse relaxation time (T-2) were used to discriminate between the different tissues and to follow the water status of the apical region during osmotic stress. The T-2 values of nonstressed stem tissue turned out to be correlated to the cell dimensions as determined by optical microscopy. Growth was found to be strongly inhibited by mild stress in both species, whereas the water uptake was far less affected. During the experiment hardly any changes in water content or T-2 in the stem region of maize were observed. In contrast, the apical tissue of pearl millet showed a decrease in T-2 within 48 h of stress. This decrease in T-2 is interpreted as an increase in the membrane permeability for water.