Changes in muskmelon perisperm envelope tissue during germination

Muskmelon (<i>Cucumis melo</i> L.) embryos are surrounded by a single layer of endosperm and a two- to four-cell-layered perisperm. The embryonic axis must penetrate the perisperm envelope (perisperm + endosperm) for germination to occur. Radicle emergence could result from increased turgor, weakening of the perisperm tissue, or a combination of both. In a previous report, turgor of the embryonic axis did not increase prior to radicle emergence. This suggests that weakening of the perisperm envelope is a prerequisite for radicle emergence in muskmelon seeds. The changes in cell wall sugars of the perisperm tissue were studied during imbibition using gas chromatography and high performance thin layer chromatography. The major cell wall sugars identified in the micropylar perisperm tissue were glucose, galactose, xylose, and rhamnose. Endo-β-mannanase has been shown to be responsible for endosperm degradation in seeds of Solanaceae, Leguminosae, and Fabaceae. However, the lack of mannose in the cell walls of muskmelon perisperm tissue suggests that this enzyme is not involved in muskmelon seed germination. Structural changes of the micropylar perisperm envelope tissue were visualized during imbibition using electron microscopy. Scanning electron microscope images revealed changes in the perisperm envelope before radicle protrusion. The cell walls of the perisperm envelope tissue were degraded starting 5 h prior to radicle emergence. An Instron was used to measure the mechanical resistance of the perisperm envelope during imbibition. The force and total energy required to penetrate the perisperm tissue of imbibed muskmelon seeds decreased gradually during imbibition. This study confirmed that the perisperm envelope tissue offered mechanical resistance to the expanding embryonic axis. Degradation of the perisperm envelope tissue before radicle protrusion facilitated radicle emergence.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Horticulture

Department dc:contributor.department

Horticulture

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1993

Author dc:creator

• Muthui, Wangechi

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-06302009-040400

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/43496