EFFECT OF IRRADIANCE AND LIGHT QUALITY ON STARCH SYNTHESIS BY ISOLATED CHLOROPLASTS OF CODIUM FRAGILE

Area of Science:

• Marine Botany
• Photosynthesis Research
• Biochemistry

Background:

• The intertidal alga Codium fragile possesses unique light-harvesting pigments.
• Understanding starch synthesis is key to comprehending algal carbon fixation in fluctuating environments.

Purpose of the Study:

• To quantify net starch synthesis in isolated Codium fragile chloroplasts.
• To investigate the role of specific light intensities and accessory pigments in this process.

Main Methods:

• Enzymic hydrolysis (amyloglucosidase/α-amylase) of chloroplast samples.
• Measurement of glucose yields using coupled enzyme reactions (hexokinase/glucose-6-phosphate dehydrogenase).
• Assessment of starch synthesis under varying photosynthetically active radiation (PAR) levels and pigment inactivation.

Main Results:

• Net starch synthesis occurred between 100 and 375 μmol m^-2 s^-1 PAR.
• Inactivation of siphonoxanthin and siphonein reduced net starch synthesis by 68%.
• Optimal starch synthesis correlated with saturating or super-saturating photosynthetic rates.

Conclusions:

• Codium fragile chloroplasts exhibit light-dependent starch synthesis.
• Accessory carotenoids play a vital role in optimizing starch production for photosynthesis in intertidal zones.