Are the green patches on potatoes capable of photosynthesis?

Question

Is it chlorophyll that causes the green patches and does that denote capabillity to photosynthesise, or is it purely due to glycoalkaloid concentrations?

Answer 1

they can be due to either, if potatoes are exposed to sunlight then they begin to prepare for reproduction of new potatoes, this process involves photosynthesis so that it can produce food on its own, and the production of chemicals that protect it from insects and the like, which you mentioned (glycoalkaloids).  Both of these processes can turn the potato green.

so yes the green patches on potatoes are capable of photosynthesis

Answer 2

It is chlorophyll that makes it green, potato tubers are actually modified stems and not roots.

The glycoalkaloids (solanine) are toxic side products of the potato.

Here is an excerpt from wikipedia:

http://en.wikipedia.org/wiki/Solanine

"Solanine occurs naturally in all nightshades, including tomatoes, capsicum, tobacco and eggplant, as well as plants from other species. However, most ingested solanine is from the consumption of potatoes.

Potatoes naturally produce solanine and chaconine, a related glycoalkaloid, as a defense mechanism against insects, disease, and predators. Potato leaves and stems and shoots are naturally high in glycoalkaloids.

When potato tubers are exposed to light, they turn green and increase glycoalkaloid production. This is a natural defense to help prevent the uncovered tuber from being eaten. The green colour is from chlorophyll, and is itself harmless. However, it is an indication that increased level of solanine and chaconine may be present.

Some diseases, such as potato blight, can dramatically increase the levels of glycoalkaloids present in potatoes. Mechanically damaged potatoes also produce increased levels of glycoalkaloids. This is believed to be a natural reaction of the plant in response to disease and damage.

Commercial varieties of potatoes are screened for solanine levels, and most have a solanine content of less than 0.2 mg/g. However, potatoes that have been exposed to light and started to green can show concentrations of 1 mg/g or more. In these situations a single unpeeled potato can result in a dangerous dose.

In potato tubers 30–80% of the solanine develops in and close to the skin.

Showing green under the skin strongly suggests solanine build-up in potatoes although each process can occur without the other. A bitter taste in a potato is another, potentially more reliable indicator of toxicity.

Deep-frying potatoes at 170°C (306°F) is known to effectively lower glycoalkaloid levels, whereas microwaving is only somewhat effective and boiling has no effect."