Polyhydroxybutyrate Biodegradable Plastic Substrate -

Polyhydroxy alkanoates (PHAs), e.g., polyhydroxybutyrate (PHB), are synthesized from acetyl-CoA used as precursor, and are used for the synthesis of biodegradable plastics with thermoplastic properties. At present, PHAs are produced by bacterial fermentation, and the cost of biodegradable plastic is substantially higher than that of synthetic plastics.

Attempts are being made to produce PHAs in transgenic plants to reduce the cost. Genes encoding the two enzymes, aceto-acetyl-CoA reductase (PhbB) and PHB synthase (phbC), involved in the PHB synthesis from the precursor acetyl-CoA have been transferred from the bacterium Alcaligenes eutrophus and expressed in Arabidopsis thaliana.

When the two enzymes were targetted into the plastids, PHB accumulated in leaves. (About 10 mg PHB/g fresh wt., i.e., 0.1%). PHB production by transgenic plants provides an example of a novel compound synthesized in plants.

Transgenic trees like popular expressing phbB and phbC accumulate PHB in their leaves; the leaves are collected and used for PHB extraction.