Water permeability of chloroplast envelope membranes

Abstract

In tulip tree (Liriodendron tufipifera) leaves, the proton NMR signal from chloroplast water is resolved from that of water in other leaf compartments. We used the saturation-transfer NMR method to measure the mean water molecule residence time within a chloroplast, (88 f 17) ms at 20°C. From the measured chloroplast dimensions, we calculate an effective permeability coefficient of (9 + 2) x 10-4cm/s for the chloroplast envelope membrane. This is the first in vivo measurement of chloroplast water permeability. ChloroplastWater exchange Membrane permeability Water compartment

Molecular aspects of plastid envelope biochemistry

“…In vivo measurement by saturation-transfer NMR of water permeability of chloroplast envelope membranes indicated, however, that the inner membrane presents a non-negligible barrier to water diffusion [214]. C 0 2 diffuses very rapidly across the plastidial inner membrane, whereas the bicarbonate anion (HCO;) does not.…”

“…In contrast to the outer membrane, which contains a nonspecific pore protein allowing the passage of water and certain ions and molecules smaller than 9 -10 kDa [213], the permeability of the inner membrane is limited to small uncharged molecules such as H 2 0 , NH3, 0 2 , and lipophilic molecules. In vivo measurement by saturation-transfer NMR of water permeability of chloroplast envelope membranes indicated, however, that the inner membrane presents a non-negligible barrier to water diffusion [214]. C 0 2 diffuses very rapidly across the plastidial inner membrane, whereas the bicarbonate anion (HCO;) does not.…”

Changes in water content and distribution in Quercus ilex leaves during progressive drought assessed by in vivo 1H magnetic resonance imaging.

“…Of the different plant organs and tissues, leaf has been noticeably less studied by MRI than the other plant organs, in spite of previous studies that have proved that NMR is suitable to study leaf water content [11]. Nuclear magnetic resonance spin-lattice relaxation time (T 1 ) has proved to be useful to determine water exchange time and permeability coefficient of membranes during storing after harvest [12] and to study chloroplast membrane permeability [13]. Proton spin-spin relaxation time (T 2 ) has been successfully used to detect water compartment in wheat leaves [14].…”

Using Bulk Magnetic Susceptibility to Resolve Internal and External Signals in the NMR Spectra of Plant Tissues

“…The remaining question is whether signals from outside leaves of certain plants (10), and these have been exploited to follow the movement of water across the chloroplast memthe cells but inside root and shoot tissue (i.e., in the intercellular spaces, cell walls, and the lumen of xylem tubes) are brane (27,28).…”