The perisperm-endosperm envelope in Cucumis: structure, proton diffusion and cell wall hydrolysing activity

Area of Science:

• Plant biology
• Seed germination
• Biochemistry

Background:

• The seed envelope in cucurbits, comprising endosperm cells and lipid/callose layers, acts as a semi-permeable barrier to radicle emergence.
• Investigating the structure, development, permeability, and cell wall hydrolase activity of this envelope is crucial for understanding seed germination.

Purpose of the Study:

• To investigate the structure, development, and permeability of the cucurbit seed envelope.
• To analyze the activity of cell wall hydrolases during seed germination.

Main Methods:

• Seed sections were stained (aniline blue, Sudan III).
• Proton diffusion and enzyme activity (endo-beta-mannanase, beta-glucanase) were detected using tissue printing and gel-diffusion assays.
• Enzyme activity was quantified via substrate hydrolysis and glucose formation measurement.

Main Results:

• The perisperm-endosperm (PE) envelope, with differentiated lipid and callose layers, was identified.
• Reduced lipid staining (chloroform treatment) increased envelope permeability.
• Proton diffusion occurred unidirectionally (inner to outer surface), and enzyme activity increased during germination.

Conclusions:

• The lipid layer of the PE envelope contributes to its semi-permeability.
• Proton diffusion may create an acidic environment, promoting cell wall hydrolase activity (endo-beta-mannanase, beta-glucanase).
• These hydrolases likely weaken the PE envelope, facilitating radicle protrusion in cucumber and muskmelon seeds.