Christmas trees stay green because of photosynthetic shortcut

London

An international team of scientists has deciphered that a short-cut in the photosynthetic machinery allows the needles of Christmas trees to stay green.

In winter, light energy is absorbed by the green chlorophyll molecules but cannot be utilised by the downstream reactions in the photosynthetic machinery as freezing temperatures stop most biochemical reactions.

This is especially a problem in the early spring when temperatures can still be very low, but sunlight is already strong, and the excess light energy can damage the proteins of the photosynthetic machinery.

The researchers led by Umea University on Sweden showed that the photosynthetic apparatus is wired in a special way which allows pine needles to stay green all year long.

"We have followed several pine trees growing in Umea in northern Sweden over three seasons," says Pushan Bag, PhD student at Umea University.

"It was essential that we could work on needles "straight from outdoors" to prevent that they adjusted to the higher temperatures in the lab environment before we analysed them for example with electron microscopy which we used to visualise the structure of the thylakoid membrane".

The study was published in the journal Nature Communications.

The research team combined biochemistry and ultrafast fluorescence analysis, a very sophisticated method that can resolve chlorophyll fluorescence light at a picosecond time scale.

Like this, they could demonstrate how the pine needles deal with excess light energy to protect their sensitive photosynthetic apparatus from damage.

The study was done with pine trees, but the researchers believe that the mechanism is probably similar for other conifer species - like the typical Christmas trees spruces and firs - because their photosynthetic apparatus is similar.

"This remarkable adaptation not only enjoys us during Christmas but is in fact extremely important for mankind," says professor Stefan Jansson from Umea University.