The strange and "noisy" method in which leaves are used to grow

The study, carried out by researchers from the Hebrew University and published in the journal Communications Physics, also found that normal growth of a leaf is based on sharp changes in the growth field, both in time and place - changes that apparently help the tissue "feel itself"

Tissue growth is one of the unsolved mysteries of science. How do a collection of cells connected to each other manage to grow in a coordinated manner, so that a properly shaped organ develops? Who coordinates between them and what is coordinated through them? How do they know where, how much and in what direction to grow? Indeed, the growth process is complex and involves different fields of knowledge. It is driven by a complex network of biological and chemical factors, but also obeys the laws of physics and mechanics, all in order to produce geometry, which is sometimes not flat - called non-Euclidean geometry. From this it follows that for the purpose of understanding growth-control mechanisms, a good choice of the system is necessary, so that its biology, mechanics and geometry will be measurable and interpretable.

A plant leaf can serve as a good system for studying these questions. The leaf can multiply its area a hundred times and maintain a correct shape, mostly flat. The leaves are surface-like, and their growth is mainly in two dimensions, therefore the shape of their surface, which can be measured, contains most of the information regarding the growth process. Moreover, it is known that diseases, genetic manipulations and pesticides can interfere with normal growth and then the leaf distorts into three-dimensional shapes, as expected from a thin sheet of material - that is, the geometry of the leaf is very sensitive to inaccuracies in growth. Finally, leaves grow easily in free air and therefore constitute a reliable and accessible model system.

A common hypothesis was that a leaf soon grows like a flat balloon - its area increases gradually and moderately in a similar way in different areas, and thus it maintains its shape, while growing. In such a scenario, growth control and coordination are delicate and slow processes that have to "correct" abnormalities (or errors) that accumulate over large area cells. This is also the picture obtained when leaf growth is measured with low resolution in time and space, that is, measurements of large surface cells at long time intervals.

Changes that make the tissue "feel itself"

A new study conducted under the leadership of Dr. Shaf Amron, in the laboratory of Prof. Eran Sharon at the Rakah Institute of Physics at the Hebrew University, in collaboration with Dr. Michael Moshe, also from the Rakah Institute, shows that exactly the opposite is true - normal growth of a leaf is based on sharp changes in a field The growth, both in time and in place, changes that apparently help the tissue "feel itself". The study was published last month in the scientific journal Communications Physics. Dr. Amron built a system that measures the growth of the leaf in 10D with high resolution, and analyzed its measurements with the help of techniques accepted in the fields of non-linear physics, statistical physics and differential geometry. The first measurements surprised the researchers - it seemed that during growth, the small surface cells of the leaf (consisting of 50-XNUMX cells) swell and contract at enormous rates and alternately. Why would a leaf that grows shrink?

Dr. Amron devoted half a year to searching for the source of the "error" and "fixing" the measurement system. Finally she understood That the "noisy" growth field it measures is real and reliable. It turns out that this is how a leaf develops and grows - at any given moment, the growth field looks like a big mess where areas swell and shrink, and only on average, over a long time and a large area, is the "smooth" and coordinated field obtained. Dr. Amron performed statistical analyzes and identified the typical times and distances for fluctuations (oscillations) in growth. With the help of these sizes, she was even able to show the existence of substantial differences between the growth of the leaf during the day and at night. In a theoretical analysis of the growth fields, Dr. Moshe showed that The measured mess cannot be random And it must be coordinated in short times and distances.

This discovery offers a new picture of the growth control mechanism. These are not gentle and mild corrections for (almost) uniform growth. On the contrary, the leaf cells forcefully push each other, push and release repeatedly and create a mechanical stress field that changes in time and space. Thus, the entire tissue is organized in a coordinated manner, preventing the accumulation of mechanical efforts over a large area. In a sense, the cells communicate with each other by clicks and relaxes, and this is how information about the state of the leaf is formed.

Plants do not have a central brain

Prof. Sharon adds and explains: "It is important to understand that this information is not processed by a central 'brain', but by the tissue itself, locally. This picture fits into new approaches that suggest that plant (and not just plant) tissues are able to process environmental information collectively. Indeed, if millions of cells that are sensitive to their environment (light, heat, humidity, etc.) are in mutual interaction (by the effort field), then they are able to translate external signals into common states. This fact points to the blurring between the concepts of 'growth' and 'behaviour', which characterizes the plant world."

These days, Prof. Sharon's research group is conducting follow-up experiments, investigating the physical mechanisms involved in the control of leaf growth and their relationship to the biological mechanisms in the plant.

for the scientific article