Peptidases in germinating barley grain: properties, localization and possible functions

Area of Science:

• Plant Biology
• Biochemistry
• Molecular Biology

Background:

• Barley grains store approximately 10% insoluble reserve proteins.
• During germination, these proteins are hydrolyzed into amino acids for seedling development.
• In resting grains, reserve proteins are stored in the starchy endosperm.

Purpose of the Study:

• To investigate the hydrolysis and absorption of reserve proteins during barley germination.
• To characterize the enzymatic activities within the starchy endosperm and scutellum.
• To understand the transport mechanism of nutrients to the growing seedling.

Main Methods:

• Analysis of proteinase and carboxypeptidase activities in the starchy endosperm.
• Assay of peptidase activities (acid and alkaline) in the scutellum.
• pH optimum determination for key enzymes involved in protein hydrolysis.

Main Results:

• The starchy endosperm exhibits high proteinase and carboxypeptidase activity with pH optima between 4 and 6.
• The scutellum displays significant acid carboxypeptidase activity and alkaline peptidase activity (leucine aminopeptidase, dipeptidase) with pH optima at 8-10.
• Enzyme profiles suggest a sequential hydrolysis process within the grain.

Conclusions:

• The starchy endosperm functions similarly to a lysosome during germination, breaking down proteins.
• The scutellum plays a crucial role in absorbing and further hydrolyzing peptides into amino acids.
• This efficient nutrient processing ensures adequate amino acid supply for seedling growth.