PLANT REPRODUCTION DURING SPACEFLIGHT - IMPORTANCE OF THE GASEOUS ENVIRONMENT

Plant reproduction is a complex developmental process likely to be dis rupted by the unusual environmental conditions in orbital spacecraft. Previous results, reviewed herein, indicated difficulties in obtaining successful seed production in orbit, often relating to delayed plant development during the long-term growth necessary for a complete plant life cycle. Using short-duration exposure to spaceflight, we studied plant reproduction in Arabidopsis thaliana (L.) Heynh. during three fl ight experiments: CHROMEX-03 on STS-54 (6 d), CHROMEX-04 on STS-51 (10 d), and CHROMEX-05 on STS-68 (11 d). Plants were 13-14 d old (rosette s) at time of launch and initiated flowering shoots while in orbit. Pl ants were retrieved from the orbiters 2-3 h after landing and reproduc tive material was immediately processed for in-vivo observations of po llen viability, pollen tube growth, and esterase activity in the stigm a, or fixed for later microscopy. Plants produced equal numbers of flo wers to those controls growing on the ground but required special envi ronmental conditions to permit fertilization and early seed developmen t during spaceflight. In CHROMEX-03, plants were grown in closed plant growth chambers (PGCs), and male and female gametophyte development a borted at an early stage in the flight material. In CHROMEX-04, carbon dioxide enrichment was provided to the closed PGCs and reproductive d evelopment proceeded normally until the pollination stage, when there was an obstacle to pollen transfer in the spaceflight material. In CHR OMEX-05, an air-exchange system was used to provide a slow purging of the PGCs with filtered cabin air. Under these conditions, the spacefli ght plants apparently had reproductive development comparable to the g round controls, and immature seeds were produced. In every aspect exam ined, these seeds are similar to those produced by the ground control plants.