Figure 1.

Representative in vivo ¹³C-NMR spectra obtained from sycamore cells. The spectra, recorded at 20°C, are the result of 900 transients (1 h). A, Control cells at pH 6.0; B, cells incubated for 12 h with 100 μm homoserine at pH 6.0; C, cells incubated for 12 h with 100 μm homoserine at pH 8.0. Note that the C1 resonance of homoserine (carboxyl group) is smaller than those of C2 to C4. This is attributable to the fact that the relaxation time of the carboxyl groups exceeds the duration of induction decays, resulting in a saturation of the signal. In addition, the C1 peak is broadened because of interaction of the carboxyl group with divalent cations. cit, Citrate; Hser, homoserine; mal, malate; PCA, perchloric acid; P-Hser, phosphohomoserine; ref., reference signal; and s, Suc.