Mistletoes breathe differently

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Team of scientists discovers respiratory mechanism that had previously been thought impossible

If we think of plants and metabolism, photosynthesis is what usually comes to mind. Yet plants also have respiratory processes that resemble those of animals in many ways - so-called cell respiration. Here carbon dioxide and water are formed from glucose and oxygen.

A group of scientists led by Prof. Hans-Peter Braun and Dr. Jennifer Senkler from the Institute of Plant Genetics at Leibniz Universität Hannover, in cooperation with Hannover Medical School MHH, has been investigating the respiration of mistletoe and has made a remarkable discovery: mistletoe breathes completely differently from other plants and animals. It lacks an enzyme complex which had so far been regarded as highly significant and essential for the cell respiration of multicellular organisms: the NADH dehydrogenase (also known as complex I of the respiratory chain). "It was thought up to now that higher forms of life cannot exist without this enzyme complex," explains Hans-Peter Braun. The results of the research, which have now appeared in the renowned American journal "Current Biology", are drawing a lot of attention among experts.

The lack of complex I has led to far-reaching changes in the respiratory chain of mistletoe. Investigation of these adaptations is highly relevant, not least because it could lead to a better understanding of dysfunctions in the respiratory chain of humans and animals. "With humans, even tiny impairments in complex I have drastic effects," says Braun. Severe and so far incurable diseases such as Parkinson''s or Leigh Syndrome are related to disorders of complex I. In total, four enzyme complexes are involved in the respiratory chain. Cell respiration occurs in the cytoplasma and the mitochondria of the cells and enables the generation of the energy-rich compound adenosine triphosphate (ATP).

"Mistletoe is a bizarre organism," says plant biochemist Braun. Many people are familiar with it because it grows in large balls as a hemiparasite on trees or bushes. Since ancient times, it has enjoyed medical and symbolic significance, is for example a key ingredient of Getafix''s magic potion in Asterix comics, and even today is used as a medicinal plant against a variety of complaints. Mistletoe is widespread throughout Europe, grows on almost all species of native trees and deprives them of water and minerals. It is called a hemiparasite because as well as acting as a parasite it carries out photosynthesis and is thus able to create many vital nutrients itself.

"We can learn a lot from parasites and hemiparasites, as they do not need to carry out all vital processes themselves," explains Braun. "If certain structures are missing, it becomes clearer what they are for and how exactly they work" How it is that mistletoe manages its respiratory process without NADH dehydrogenase, which is regarded as essential to the energy balance, still requires further clarification. In follow-up projects, the scientists want to carry out more thorough biochemical investigations of the plant to get to the bottom of this mechanism. Apart from other hypotheses, it is conceivable that the missing energy-rich compounds are extracted from the host plants.

The complete article in English is available here:

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Prof. Dr. Hans-Peter Braun, Institute of Plant Genetics, telephone: +49 511 762 2674; e-mail: braun@genetik.uni-hannover.de will be pleased to supply further information.