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Choline oxidation by intact spinach chloroplasts.

P Weigel¹, C Lerma, A D Hanson

¹MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824.

Plant Physiology

|January 1, 1988

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Spinach chloroplasts directly from leaves oxidize choline to betaine aldehyde more rapidly in light than dark. This light-stimulated choline oxidation requires oxygen and reducing power from Photosystem I.

Area of Science:

Plant Physiology
Photosynthesis
Biochemistry

Background:

Plants synthesize betaine through a two-step oxidation of choline.
Chloroplasts are involved in choline oxidation, with faster rates observed in light.

Purpose of the Study:

To investigate the light-stimulated oxidation of choline in spinach chloroplasts isolated directly from leaves.
To determine the factors influencing choline oxidation rates and identify the primary product.

Main Methods:

Isolated spinach chloroplasts were used to measure choline oxidation rates in dark and light conditions.
The effects of hypoxia, uncouplers, inhibitors (DCMU, dibromothymoquinone), electron donors (reduced diaminodurene), and substrates (dihydroxyacetone phosphate) were assessed.
Product analysis identified betaine aldehyde as the main product.

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Main Results:

Chloroplasts from intact leaves showed significantly higher choline oxidation rates (20-fold) compared to protoplast-derived chloroplasts.
Light-stimulated choline oxidation was dependent on oxygen and Photosystem I (PSI) activity, indicated by inhibition with PSII inhibitors and partial restoration with PSI electron donors.
Choline oxidation was not limited by Calvin cycle activity or light saturation for CO2 fixation.

Conclusions:

Choline oxidation in spinach chloroplasts is an oxygen-dependent process.
The light stimulation of choline oxidation is driven by reducing power generated from PSI.
Betaine aldehyde is the primary intermediate in this light-enhanced pathway.