Seeds in space

Since experimentation with plants began in space, a wide range of information has been gained regarding how this unique environment affects the biology of seeds. Seed biology experiments in this milieu have addressed aspects of seed storage, seed germination and metabolism, seedling orientation and seed production by flowering plants. Construction of hardware that provides a suitable growth environment in microgravity has been especially challenging because of the consequences posed by microgravity for fluid and gas distribution around the plant. Fluid shifting causes seed hydration kinetics to occur at a faster rate in microgravity than in 1 g; however, it also induces hypoxic metabolism during the seed germination process. In the absence of a detectable gravitational force, seedling roots grow according to their embryonic orientation and then initiate random walk movements. Light and oxygen gradients are the primary stimuli that orient root growth in this environment. For seed development to occur in spaceflight, well-ventilated growth chambers are necessary to support the carbohydrate supply needs of the developing embryos, and to provide the necessary humidity gradient for anthers to successfully dehisce and release pollen. The dry weight of seeds formed in space is lower than that in ground controls, and seed storage reserves are altered. Seed storage phenomena in spaceflight depend on whether or not oxygen and moisture are present – if not, viability exceeds that of seeds stored under comparable conditions on the ground. Because of the key role to be played by seeds in future advanced life support scenarios in space, more research is needed on the implications of this unique environment for seed biology.