Estimation of polymer rigidity in cell walls of growing and nongrowing celery collenchyma by solid-state nuclear magnetic resonance in vivo

When the growth of a plant cell ceases, its walls become more rigid and lose the capacity to extend. Nuclear magnetic resonance relaxation methods were used to determine the molecular mobility of cell wall polymers in growing and nongrowing live celery (Apium graveolens L.) collenchyma. To our knowledge, this is the first time this approach has been used in vivo. Decreased polymer mobility in nongrowing cell walls was detected through the C-13-nuclear magnetic resonance spectrum by decreases in the proton spin-spin relaxation time constant and in the intensity of a subspectrum corresponding to highly mobile pectins, which was obtained by a spectral editing technique based on cross-polarization rates. Flexible, highly methyl-esterified pectins decreased in relative quantity when growth ceased. A parallel increase in the net longitudinal orientation of cellulose microfibrils was detected in isolated cell walls by polarized Fourier-transformed infrared spectrometry.