Dynamics of Storage Reserve Deposition during Brassica rapa L. Pollen and Seed Development in Microgravity

Abstract

Pollen and seeds share a developmental sequence characterized by intense metabolic activity during reserve deposition before drying to a cryptobiotic form. Neither pollen nor seed development has been well studied in the absence of gravity, despite the importance of these structures in supporting future long-duration manned habitation away from Earth. Using immature seeds (3-15 d postpollination) of Brassica rapa L. cv. Astroplants produced on the STS-87 flight of the space shuttle Columbia, we compared the progress of storage reserve deposition in cotyledon cells during early stages of seed development. Brassica pollen development was studied in flowers produced on plants grown entirely in microgravity on the Mir space station and fixed while on orbit. Cytochemical localization of storage reserves showed differences in starch accumulation between spaceflight and ground control plants in interior layers of the developing seed coat as early as 9 d after pollination. At this age, the embryo is in the cotyledon elongation stage, and there are numerous starch grains in the cotyledon cells in both flight and ground control seeds. In the spaceflight seeds, starch was retained after this stage, while starch grains decreased in size in the ground control seeds. Large and well-developed protein bodies were observed in cotyledon cells of ground control seeds at 15 d postpollination, but their development was delayed in the seeds produced during spaceflight. Like the developing cotyledonary tissues, cells of the anther wall and filaments from the spaceflight plants contained numerous large starch grains, while these were rarely seen in the ground controls. The tapetum remained swollen and persisted to a later developmental stage in the spaceflight plants than in the ground controls, even though most pollen grains appeared normal. These developmental markers indicate that Brassica seeds and pollen produced in microgravity were physiologically younger than those produced in 1 g. We hypothesize that microgravity limits mixing of the gaseous microenvironments inside the closed tissues and that the resulting gas composition surrounding the seeds and pollen retards their development.

Plant cell gravisensitivity and adaptation to microgravity

“…Using cytochemistry, a delay in accumulation of storage nutrients in embryo cotyledon and root cells of seeds was found 13 days after pollination (Kuang et al . ). In the ground‐based controls, embryonic cells contain only protein bodies and a few starch grains in plastids, while in seeds developed during spaceflight embryonic cells only contained abundant starch grains in plastids (Fig.…”

Microgravity effects on different stages of higher plant life cycle and completion of the seed‐to‐seed cycle

“…; Kuang et al . ), it still remains that plants in Space are subjected to multiple stressors (some triggered by altered gravity) that often determine lower reproductive fitness. Consider pollen viability, which is really sensitive to different combinations of temperature and humidity; moreover the period of time when pollen is viable can quickly shorten if environmental conditions are not appropriate for the species (Bassani et al .…”

Assessing diet and seasonality in the Lower Pecos canyonlands: an evaluation of coprolite specimens as records of individual dietary decisions

“…However, a recent study suggests that natural starch rain may be a more common environmental contaminant than has been previously realized in archaeological starch research (Laurence 2010). While this remains unresolved, it is clear that starch frequently enters the atmosphere through pollen grain rupture associated with precipitation and other weather patterns (Currie et al 2000;D'amato et al 2007;Erpenbeck et al 2005;Garcia 2010;Kuang et al 2005;Pacini 2006;Wang et al 2004;Zona 2001).…”