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Spanish scientists shed light on the unknown 'menopause' of plants

Although it sounds strange, some plants go through a kind of 'menopause'. Known as proliferative stop , it affects annual plants that only bloom once – known as monocarpic plants – and then die. The first part, that of flowering, is a highly studied process: it has been analyzed in depth how light influences, seasonal changes, temperature or the age of the plant in which the flowers appear. However, there is a gap in the investigation of how it ends. Now, a group of researchers from the Institute of Molecular and Cellular Plant Biology (IBMCP), a joint center of the Higher Council for Scientific Research (CSIC) and the Polytechnic University of Valencia (UPV), publishes the analysis in the journal 'Current Biology' more complete of this process that, if it can be controlled, would be an opportunity to, for example, extend the reproductive phase of crops as important as legumes or cereals.

Even though they only flower once, monocarpic plants can live for years. In fact, flowering does not by itself result in the death of the plant, although it is true that the production of fruits and seeds causes changes that will lead to death. These changes are induced by hormones that divert the resources of the roots and leaves towards the production of fruits and seeds.

«This process that we could call the vegetable menopause – explains in a statement Cristina Ferrándiz Maestre , a researcher at the IBMCP and one of the authors of the study – constitutes a great evolutionary adaptation since, by not forming new organs such as flowers and fruits, the redistribution of nutrients towards the production of seeds is ensured, allowing their optimal development and thus perpetuating the species ”, clarifies Ferrándiz.

However, despite its ecological and economic importance, little is known about the factors that control the stop of proliferation. Using molecular and cellular biology techniques, genetics and image analysis to the model species Arabidopsis thaliana -a herbaceous plant, the first from which its complete genome was obtained- to define with high spatio-temporal resolution the sequence of molecular and cellular events that trigger the stop of proliferation.

How to control vegetable menopause

The investigation is twofold. On the one hand, the changes that occur in the meristem – tissues responsible for plant growth – before the proliferative stop have been analyzed: how and when the cells stop dividing, when they begin to be seen signs of aging, when stem cell activity disappears … “It's like zooming in on the meristem to understand what phases take place and what characterizes them,” says Paz Merelo , researcher of the IBMCP that leads the study.

Image of an inflorescence (left), of the meristem in 3D (center) and, on the right, fluorescent proteins (green, red and yellow) in longitudinal sections of the meristem –

«On the other hand, we have studied some important plant hormones to maintain proliferation, the cytokinins . With fluorescent markers that allow us to follow their activity, we have seen that their activity is completely blocked at the moment of the stop, so, probably, the cytokinins are the triggers of the stop -reveals Merelo-. In addition, we have verified that, if we treat the meristems with cytokinins externally, they do not stop producing stem cells.

Longer harvests

According to its authors, the study is pioneering because, for the first time, it has been seen up close how these tissues responsible for growth change near plant 'menopause'. “This will allow us to design new experiments to control the flowering period and its end, or to identify more factors involved in its control”, assures Ferrándiz. The stop of proliferation is a common process in a wide range of species, so the processes described are relevant for new biotechnological approaches aimed at increasing the yield in crops by extending the duration of the flowering period, or delaying the stop of proliferation. .

“As this study shows that cytokinins prevent the arrest of proliferation and, therefore, extend the production period, the pathways related to these hormones would be promising targets in improvement programs,” says Ferrándiz. In addition, the yield of many crops depends to a great extent on environmental conditions, so obtaining plant varieties with a longer reproductive phase, or with a late stop of proliferation, would allow adjusting production in the face of specific climatic changes.

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