Cell wall and membrane-associated exo-beta-D-glucanases from developing maize seedlings.

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Cell Wall Biology

Background:

• Maize (Zea mays L.) shoots contain a beta-D-glucan exohydrolase (ExGase) in their cell walls.
• This enzyme hydrolyzes beta-D-glucans, with preferential activity against (1-->3)-beta-D-glucans and varying activity against other linkages.

Purpose of the Study:

• To purify and characterize a beta-D-glucan exohydrolase from developing maize shoots.
• To determine the molecular structure and identify different forms of the enzyme.
• To investigate the enzyme's localization and potential roles in cell wall metabolism and elongation.

Main Methods:

• Enzyme purification from maize cell walls.
• Polyclonal antisera generation and use for cDNA clone selection.
• Nucleotide sequencing to deduce the full amino acid sequence.
• Northern and immunogel-blot analyses to study transcript and polypeptide expression and localization.

Main Results:

• Purification of a beta-D-glucan exohydrolase (ExGase) from maize.
• Deduced sequence of 622 amino acids.
• Detection of three distinct ExGase polypeptides: one constitutive in the cell wall, a second appearing during elongation and linked to mixed-linkage beta-D-glucan disappearance, and a third associated with the plasma membrane.
• Membrane-associated ExGase shows limited activity against (1-->4)-beta-D-glucan linkages.

Conclusions:

• Maize possesses a novel ExGase with multiple forms and distinct cellular localizations.
• The enzyme's expression and localization suggest roles in regulating cell elongation and potentially other membrane-wall interface processes.
• Further investigation is needed to elucidate the specific functions of the different ExGase forms at the membrane-wall interface.