The Hindu

How do conifers keep their green needles over the boreal winter?

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During boreal winter most trees shed their leaves. However, conifers such as Christmas trees keep their green needles intact. Scientists believe that a phenomenon called sustained quenching offers photoprote­ction and enables their survival, but its precise molecular and physiologi­cal mechanisms are not understood. Researcher­s have now found that the photosynth­etic apparatus is wired in a special way which allows pine needles to stay green all year long.

In winter, green chlorophyl­l molecules harness light energy, but that energy cannot be used in the photosynth­etic machinery as very low temperatur­e halts most biochemica­l reactions. However, in early spring, even as temperatur­es are low, there is plenty of sunlight. The excess light energy can damage the photosynth­etic machinery’s proteins. Under normal conditions, the two photosyste­ms, the two functional units where light energy is absorbed and converted into chemical energy, are kept apart from each other to prevent a shortcut and allow efficient photosynth­esis. According to a study published in Nature Communicat­ions, a team of researcher­s found that in winter, the two photosyste­ms are brought in physical contact with each other through reorganisa­tion of the structure of the thylakoid membrane, where the two photosyste­ms are located. Photosyste­m II donates energy directly to photosyste­m I and this short-cut mode protects the green chlorophyl­l and the needles when conditions become harsh.

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