title: Surface charge on isolated maize-coleoptile amyloplasts.
abstract: Whole amyloplasts were isolated from Zea mays L. coleoptiles. Electron microscopy confirmed that their envelopes consisted of two intact membranes. Their surface charge was quantified through electrokinetic measurements employing a vertically oriented cataphoresis cell. Amyloplasts from coleoptiles of different ages (5-9 d) and degree of exposure to light (0-9 d) all had negative zeta potentials (mean of -19.4 mV). Isolated starch granules had comparable values. The net negative surface charge was confirmed ultrastructurally by the binding of cationised ferritin to both amyloplasts and starch grains. Cationised ferritin tagged with a fluorescent label (fluorescein isothiocyanate) showed binding to some amyloplasts but not to starch grains. These results are discussed in the context of a hypothesized role for statolith charge in plant graviperception.
authors.affiliation: Boyce Thompson Institute for Plant Research, Cornell University, 14853, Ithaca, NY, USA.
authors.forename: F D
authors.initials: FD
authors.lastname: Sack
authors.forename: D A
authors.initials: DA
authors.lastname: Priestley
authors.forename: A C
authors.initials: AC
authors.lastname: Leopold