Controls on chlorophyll synthesis in barley.

Area of Science:

• Plant Physiology
• Biochemistry
• Molecular Biology

Background:

• Chlorophyll synthesis is essential for photosynthesis and plant development.
• The early steps of chlorophyll biosynthesis involve the production of delta-aminolevulinic acid (ALA).
• Light is a critical environmental factor regulating chlorophyll accumulation.

Purpose of the Study:

• To identify the rate-limiting steps in chlorophyll synthesis in etiolated barley leaves.
• To elucidate the role of protein synthesis in light-induced chlorophyll accumulation.
• To propose a model for the regulation of chlorophyll synthesis.

Main Methods:

• Enzyme activity assays in barley leaves under varying light conditions.
• Use of protein and nucleic acid synthesis inhibitors to study regulatory mechanisms.
• Determination of protein half-life using synthesis inhibitors.

Main Results:

• Enzymes converting ALA to chlorophyll are non-limiting initially.
• A protein (or proteins) involved in ALA synthesis, likely ALA synthetase, is rate-limiting.
• Light-induced chlorophyll synthesis is dependent on protein synthesis but not nucleic acid synthesis.
• The limiting protein has a half-life of approximately 1.5 hours.

Conclusions:

• Chlorophyll synthesis regulation involves light-induced translational activation of ALA synthesis proteins.
• The short half-life of these regulatory proteins contributes to rapid chlorophyll accumulation.
• The holochrome functions enzymatically in protochlorophyllide photoreduction to chlorophyllide.