title: Xylem development and cell wall changes of soybean seedlings grown in space.
abstract: OBJECTIVE
  Plants growing in altered gravity conditions encounter changes in vascular development and cell wall deposition. The aim of this study was to investigate xylem anatomy and arrangement of cellulose microfibrils in vessel walls of different organs of soybean seedlings grown in Space.
  
  
  METHODS
  Seeds germinated and seedlings grew for 5 d in Space during the Foton-M2 mission. The environmental conditions, other than gravity, of the ground control repeated those experienced in orbit. The seedlings developed in space were compared with those of the control test on the basis of numerous anatomical and ultrastructural parameters such as number of veins, size and shape of vessel lumens, thickness of cell walls and deposition of cellulose microfibrils.
  
  
  RESULTS
  Observations made with light, fluorescence and transmission electron microscopy, together with the quantification of the structural features through digital image analysis, showed that the alterations due to microgravity do not occur at the same level in the various organs of soybean seedlings. The modifications induced by microgravity or by the indirect effect of space-flight conditions, became conspicuous only in developing vessels at the ultrastructural level. The results suggested that the orientation of microfibrils and their assembly in developing vessels are perturbed by microgravity at the beginning of wall deposition, while they are still able to orient and arrange in thicker and ordered structures at later stages of secondary wall deposition.
  
  
  CONCLUSIONS
  The process of proper cell-wall building, although not prevented, is perturbed in Space at the early stage of development. This would explain the almost unaltered anatomy of mature structures, accompanied by a slower growth observed in seedlings grown in Space than on Earth.
authors.affiliation: Laboratorio di Botanica ed Ecologia Riproduttiva, Dip. Arboricoltura, Botanica e Patologia Vegetale, Università degli Studi di Napoli Federico II, via Università, 100, I-80055 Portici (NA), Italy.
authors.forename: Veronica
authors.initials: V
authors.lastname: de Micco
authors.forename: Giovanna
authors.initials: G
authors.lastname: Aronne
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Joseleau
authors.forename: Katia
authors.initials: K
authors.lastname: Ruel
mesh_terms: D005118:Extraterrestrial Environment; D036226:Seedlings / Q000254:growth & development* / Q000648:ultrastructure*; D013025:Glycine max / Q000254:growth & development*; D014893:Weightlessness; D052584:Xylem / Q000254:growth & development*