Moniliophthora perniciosa is the causative agent of witches' broom disease in Theobroma cacao. Exogenously provided abscisic acid (ABA), indole-3-acet

Vertical orientation of emerging roots typically is the first response of plants to gravity. Although root gravitropism has been studied extensively, no conclusive data on the onset of gravisensing exist. We determined the inception of gravisensitivity in flax (Linum usitatissimum) roots by clinorotating germinating seeds after various periods of static orientation (gravistimulation) of imbibed seeds. Gravitropic competency was established about 8 h after imbibition, 11 h prior to germination. The time was determined based on 50% of the newly emerged roots curving in the direction of the gravity vector during static imbibition, despite subsequent clinorotation. The threshold value was affected by the orientation of the seeds. Upward orientation of the micropyle/radicle reduced the number of graviresponding roots to about one-half. Prolonged clinorotation weakened the graviresponse. Gravisensing was accompanied by the development of amyloplasts, but the actin cytoskeleton was not involved because imbibition in Latrunculin B did not affect the onset of gravisensitivity or germination, and the development of F-actin in untreated controls was observed only after the onset of gravisensitivity.

A review of past insights of space experiments with plants outlines basic space and gravity effects as well as gene expression. Efforts to grow plants in space gradually incorporated basic question on plant productivity, stress response and cultivation. The prospect of extended space missions as well as colonization of the Moon and Mars require better understanding and therefore research efforts on biomass productivity, substrate and water relations, atmospheric composition, pressure and temperature and substrate and volume (growth space) requirements. The essential combination of using plants not only for food production but also for regeneration of waste, and recycling of carbon and oxygen production requires integration of complex biological and engineering aspects. We combine a historical account of plant space research with considerations for future research on plant cultivation, selection, and productivity based on space-related environmental conditions.

To test if expansins, wall loosening proteins that disrupt binding between microfibrils and cell wall matrix, participate in the differential elongation of graviresponding roots, Zea mays L. cv. Merit roots were gravistimulated and used for immunolocalization with anti-expansin. Western blots showed cross-reaction with two proteins of maize, one of the same mass as cucumber expansin (29 kDa), the second slightly larger (32 kDa). Maize roots contained mainly the larger protein, but both were found in coleoptiles. The expansin distribution in cucumber roots and hypocotyls was similar to the distribution in maize. Roots showed stronger expansin signals on the expanding convex side than the concave flank as early as 30 min after gravistimulation. Treatment with brefeldin A, a vesicle transport inhibitor, or the auxin transport inhibitor, naphthylphthalamic acid, showed delayed graviresponse and the appearance of differential staining. Our results indicate that expansins may be transported and secreted to cell walls via vesicles and function in wall expansion.