Researchers describe how Vitamin E works in plants under extreme conditions
Vitamin E is a powerful antioxidant that could act as a sentinel in plants, sending molecular signs of the chloroplast, a cellular organelle, to the nucleus under extreme environmental conditions. This is one of the conclusions of an article published in Trends in Plant Science by Sergi Munné-Bosch and Paula Muñoz of the Faculty of Biology at the University of Barcelona (UB).
This flow of information reaching the cell nucleus, retrograde signalling, is a molecular mechanism that facilitates the adaptive response of plants in situations of physiological stress (salinity, lack of nutrients, drought, senescence, etc.).
Communication pathway between the chloroplast and the cell nucleus
Vitamin E is a group of naturally occurring molecules, lestocopherols and tocotrienols, synthesized by photosynthetic organisms. These molecules, which have similar chemical functions and structures, differ from each other in their distribution and location. While tocopherols are distributed globally in the plant kingdom, tocotrienols are present only in certain species and organs, and are considered secondary metabolites.
The new study highlights the biological role of vitamin E in the cellular communication process between the chloroplast and the cell nucleus. "The role of vitamin E would be to send signals from the chloroplast to the nucleus to do cellular reprogramming at the molecular level and trigger appropriate responses to several stress situations. This flow of information to the cell nucleus would regulate key aspects of plant development, such as organ senescence (leaves, flowers) or fruit ripening," explains Sergi Munné-Bosch, professor in the Department of Evolutionary Biology, Ecology and Environmental Sciences and at the ICREA Academy.
Chlorophyll degradation pathway
The best characterized vitamin E synthesis so far combines two pathways: the non-mévalonate pathway, which generates phytyl or geranylgeranyl in the chemical structure of tocopherols and tocotrienols, respectively, and shikimic acid, which produces a homogeneous acid, and the chromanol ring in both antioxidants.
There is also another way of synthesizing vitamin E with the degradation of chlorophyll. "This is a biologically important pathway in the plant domain and therefore a chemical compound is created: phytol. It would finally make it possible to obtain the phytyl without the participation of methylerythritol phosphate," the authors write.
The new pathway is possible when VTE5 and VTW6, two kinase-active enzymes, are activated and facilitate the conversion of phytol to phytyl diphosphate, and thus, the entry of this molecule into tocopherol biosynthesis. "We know little about the regulation of this alternative biosynthetic pathway, but we do know that it acts in situations of stress and senescence related to active degradation of chlorophyll," explains Sergi Munné Bosch, head of the UB's ANTIOX research group.
Vitamin E is involved in the physiological processes related to growth, photoprotection, flowering, longevity and senescence of plants. "It is an essential factor in the protection of photosynthetic and non-photosynthetic tissues. In the case of vitamin E deficiency, the effects on plants may be more or less significant depending on the species, the organ studied and especially the conditions under which the experiment is carried out in the case of a research study. In general, the higher the stress on the plant, the greater the effect."
A better understanding of the role of vitamin E in the non-photosynthetic tissues of plants - roots, nodules, reserve tissues, some flowers and fruits - is one of the future areas of work of the UB ANTIOX Research Group, which will work on new research in the fields of biotechnology, food and ecophysiology.
"All these discoveries are relevant to fundamental biology and biotechnology as they will change aspects such as fruit ripening and flower longevity, both before and after harvest," the authors conclude.
