A short-reduce in photosynthetic equipment can permit needles of pine bushes to live green

Overview

• Post By : Kumar Jeetendra


• Source: Umea University


• Date: 24 Dec,2020

How do conifers which are used for example as Christmas trees keep their green needles over the boreal winter when many trees drop their leaves?

Science hasn’t provided a good response to this question but now an international group of scientists, including researchers in Umeå University, has deciphered that a short-cut in the photosynthetic machinery allows the needles of pine trees to stay green. The study was published in the journal Nature Communications.

In winter, light energy is absorbed by the green chlorophyll molecules but can’t be properly used by the downstream reactions from the photosynthetic machinery as freezing temperatures prevent most biochemical reactions.

This is particularly an issue in the early spring when temperatures can still be very low, but sunlight is currently powerful, and the extra light energy can damage the proteins of the photosynthetic machinery. The researchers showed that the photosynthetic apparatus is wired in a special way that allows pine needles to stay green throughout the year.

Under normal conditions, both photosystems, the two functional units where light energy is absorbed and converted to chemical energy, are kept apart from each other to avoid a short-cut and allow efficient photosynthesis.

In winter, the structure of the thylakoid membrane, where the two photosystems are located, is reorganized which brings the two photosystems in bodily contact. The researchers showed that photosystem II donates energy directly to photosystem I and this short-cut mode protects the green chlorophyll and the needles when conditions become unpleasant.

“It was essential that we could work on needles”straight from outdoors” to prevent that they adjusted to the higher temperatures at the laboratory environment before we examined them for example with electron microscopy which we used to visualize the structure of the thylakoid membrane”.

All plants have safety valves to take care of the excess light energy that’s either dissipated as heat or as fluorescence light. However, only conifers seem to have such strong valves that they can keep the photosynthetic apparatus intact within the intense boreal winter.

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 can demonstrate how the pine needles deal with excess light energy to secure their sensitive photosynthetic apparatus from damage.

“We needed to adjust the equipment to study pine needles in cold temperatures in order to trap the unique mechanism,” explains Volha Chukhutsina from Vrije Universiteit Amsterdam, who has performed much of the ultrafast fluorescence analysis. “We also tried spruce needles but they were hard to match in a good way into the equipment.”

Alfred Holzwarth, who has developed the time-resolved fluorescence measurements adds:”The pine needles gave us the opportunity to examine this shortcut mechanism – also called spill-over – as they really show an extreme adaptation”.

The research was performed with pine trees, but the researchers believe that the mechanism is most likely like other conifer species – like the standard 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. Hadn´t conifers been able to survive in extremely harsh winter climates vast areas in the northern hemisphere may not have been colonized as conifers provided firewood, housing, and other necessities? Still today they form the basis of the economy in most of the circumpolar taiga region.”

Stefan Jansson, Professor, Umeå University