Can Plants Normally Produce Seeds under Microgravity in Space?

Abstract

Growth analysis was performed on a barley (Hordeum vulgare L.) mutant line showing an abnormal gravity response, and also on the original normal line. The reproductive structures of mutant plants were quite different from the original normal plants. Analysis by stratified clip method revealed difference in distribution of leaves, stems, and heads, as well as leaf area index (LAI) in the mutant line caused by diagravitropic or plagiogravitropic growth. Mutant plants showed an abnormal gravity response even in the seedling stage. In mutant but not normal plants, the direction of first-leaf growth depended on the position of the embryo. Seed production of mutant plants was about 60% compared with normal plants, even though net assimilation rate (NAR) and relative growth rate (RGR) were not decreased. Seed fertility of mutant plants was correlated with the angle between heads and ground level. However, when plants were turned upside down, all heads, both mutants and normal, were nearly vertical, and seed fertility recovered to a level that not significantly different from normal plants. From these results, it was predicted that barley plants may not produce seeds normally under microgravity.