STRUCTURE OF POTATO-TUBERS FORMED DURING SPACEFLIGHT

Potato (Solanum tuberosum L. cv. Norland) explants, consisting of a le af, axillary bud, and small stem segment, were used as a model system to study the influence of spaceflight on the formation of sessile tube rs from axillary buds, The explants were flown on the space shuttle Co lumbia (STS-73, 20 October to 5 November 1995) in the ASTROCULTURE (TM ) flight package, which provided a controlled environment for plant gr owth. Light and scanning electron microscopy were used to compare the precisely ordered tissues of tubers formed on Earth with those formed during spaceflight, The structure of tubers produced during spacefligh t was similar to that of tubers produced in a control experiment. The size and shape of tubers, the geometry of tuber tissues, and the distr ibution of starch grains and proteinaceous crystals were comparable in tubers formed in both environments, The shape, surface texture, and s ize range of starch grains from both environments were similar, but a greater percentage of smaller starch grains formed in spaceflight than on Earth, Since explant leaves must be of given developmental age bef ore tubers form, instructions regarding the regular shape and ordered tissue geometry of tubers may have been provided in the presence of gr avity. Regardless of when the signalling occurred, gravity was not req uired to produce a tuber of typical structure.