Armed against salt
When there is an extensive amount of salt plants take action. One of the things they do, as researchers lead by Christa Testerink show in The Plant Cell, is adapting their cell wall. To prevent weakening by sodium ions.
Plants, just like other organisms, don’t like an extensive amount of salt. It damages their cells. When they got the chance they actively grow away from salt. But avoidance is not always possible. That is why the researchers studied the effect of too much salt when the root does not have a chance to grow away.
The first thing they needed was a visible change. This they found in a stress test in which they challenged Arabidopsis roots to a change in gravity and salt stress. Roots that had to deal with both gravity and salt stress grew less quickly downwards again than roots that only had to deal with a gravity challenge.
Subsequently the researchers analysed root growth of 345 different Arabidopsis varieties challenged this way. They noticed that the speed and readjustment to gravity differed between varieties. This the researchers used to identify the genes that contribute to this variety. Narrowing down on one gene ExAD that varied between the different Arabidopsis varieties analysed.
ExADs job is to make sure that in the presence of too much salt the cell wall doesn’t break down
From ExAD it is known that it contributes to the sturdiness of the cell wall. But how this contributes to better salt tolerance was so far unknown. To find this out the researchers exposed seedlings without ExAD to the gravity/salt test. They noticed that the roots of seedlings without ExAD grew quicker downwards again that roots of seedlings with ExAD.
But studying their cell wall showed that this was not due to the fact that they were more salt tolerant. They actually were not. The molecules in their cell walls were less connected to each other. This resulted in a weaker cell wall. Weaker cell walls allow for easier bending of the roots. But they also allow more salt molecules to cross.
ExAD job is to make sure that in presence of salt the cell wall stays strong enough. But more research is needed to analysed how variation in the ExAD gene contribute to salt tolerance. So breeders can use that information in their breeding for salt tolerant crops.
Literature
Yutao Zou, Nora Gigli-Bisceglia, Eva van Zelm, Pinelopi Kokkinopoulou, Magdalena M Julkowska, Maarten Besten, Thu-Phuong Nguyen, Hongfei Li, Jasper Lamers, Thijs de Zeeuw, Joram A Dongus, Yuxiao Zeng, Yu Cheng, Iko T Koevoets, Bodil Jørgensen, Marcel Giesbers, Jelmer Vroom, Tijs Ketelaar, Bent Larsen Petersen, Timo Engelsdorf, Joris Sprakel, Yanxia Zhang, Christa Testerink, Arabinosylation of cell wall extensin is required for the directional response to salinity in roots, The Plant Cell, 2024;, koae135, https://doi.org/10.1093/plcell/koae135
Plant en Zo 