The secret of evergreen conifers revealed

The secret of evergreen conifers revealed
The secret of evergreen conifers revealed
Anonim

Biophysicists have found an answer to the question of why conifers remain green all year round. The reason is in the short cycle of photosynthesis, which they switch to in winter, according to the authors of the study, the results of which are published in the journal Nature Communications.

Scientists from the Swedish University of Umeå, together with colleagues from the Free University of Amsterdam and the Canadian University of Western Ontario, deciphered the mechanism of photosynthesis in pine needles and found that in winter it proceeds according to a shortened cycle.

In winter, light energy is absorbed by green chlorophyll molecules, but is not used in subsequent reactions of the photosynthetic mechanism, since low temperatures stop most biochemical reactions.

In bright sun and low temperatures, excess light energy can damage the proteins of the photosynthetic mechanism. Therefore, most trees shed their leaves for the winter. But in a pine or spruce, the photosynthetic apparatus is arranged in a special way, due to which their needles remain green throughout the year.

“We have observed several pine trees growing in Umeå in northern Sweden for three seasons,” the first author of the article, PhD student Pushan Bag, said in a press release from the University of Umeå, who collected needle samples and conducted analyzes all year round. that we could work with the needles "straight from the street" so that they did not have time to adapt to the higher temperatures in the laboratory before we analyze them, for example, using electron microscopy, which we used to visualize the structure of the thylakoid membrane."

The authors found that in winter, the structure of the thylakoid membrane of chloroplasts, in which light-dependent reactions of photosynthesis occur, is reorganized, which leads to physical contact between two photosystems - functional units in which light energy is absorbed and converted into chemical energy.

It turned out that in warm conditions photosystems I and II are located separately from each other to ensure effective photosynthesis, and in winter photosystem II gives energy directly to photosystem I. Thus, pine needles cope with excess light energy and protect their sensitive photosynthetic apparatus from damage during extreme northern winter.

“The pine needles have given us the opportunity to study this highly adaptable contraction or spill-over mechanism,” says study author Alfred Holzwarth of the Free University of Amsterdam, who developed a special fluorescence analysis method for the project.

“This wonderful adaptation not only makes us happy during Christmas, but is actually extremely important for human development,” continues Professor Stefan Jansson of Umeå University, who led the study. “If conifers could not survive in the harsh winter climate, vast areas in the northern hemisphere might not have been colonized by humans, as conifers provided firewood, shelter and other necessities. And today they form the basis of the economy of most circumpolar countries."

The authors note that the study was carried out on pines, but they believe that a similar mechanism applies to other types of conifers.

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