Plant & zo
The science of plants and more
Only supple cells may stretch
Growth, through making more cells. Or through stretching the cells. Or maybe through something that is a bit in between, what makes it possible for the cells to get even bigger. Endoreplication: the multiplication of the DNA without a cell division following. You would expect that the more DNA copies a cell has, the bigger it is. But this is not completely the case. Researchers from Sweden, Canada, Belgium, and France studied how endoreplication influences cell size.
To study endoreplication the researchers looked at just germinated seedlings. These grow super quickly, through stretching. This happens at one side of the hypocotyl, the part of the stem between the root and the embryogenic leaves, quicker than on the other side. Making the hypocotyl bend, forming a little hook. In this was the seedling protects its growth centre till it sticks its head above the ground.
In the cells at the outside of this hook the researchers observed more DNA than in the cells that were situated at the inside of the hook. But this was not the case in endoreplication deficient plants. In these plants the hypocotyl bends less and straightens more quickly.
Only supple cell walls are allowed to stretch
Zooming in on the hypocotyl cells, the researchers observed that the cell wall of cells of endoreplication deficient plants was much stiffer than that of normal plants. This made the stretching of the cells at the outside of the hook more difficult. This, it turned out, was due to the guard of the cell wall: THESEUS. THESEUS keeps an eye on stiffness of the cell wall, to prevent damage, allowing only supple cell walls to stretch. But absence of THESEUS allows stiff endoreplication deficient plants to stretch out just as easy as plants that could do endoreplication.
Indicating that endoreplication is influencing cell size through regulating the stiffness of the cell wall. Allowing the cell to stretch itself unchecked by THESEUS. This can work two ways. Through promoting endoreplication, a plant can make sure its cells can stretch themselves. But when the plant puts a brake on endoreplication, then it gets smaller, sturdier cells.
Yuan Ma, Kristoffer Jonsson, Bibek Aryal, Lieven De Veylder, Olivier Hamant, Rishikesh P. Bhalerao (2022) Endoreplication mediates cell size control via mechanochemical signaling from cell wall. Sci. Adv., 8 (49), eabq2047 DOI: 10.1126/sciadv.abq2047