How Roots Branch Out

The expression of aquaporins is locally regulated by the ­increased auxin levels that initiate lateral root formation. These changes ­significantly affect the rate of lateral root emergence.

Plants initiate lateral root formation deep within the primary root. For lateral roots to reach the soil, they first must break through the rigid, overlying tissue layers of the primary root. To initiate lateral root emergence, the plant hormone auxin is required. This also stimulates processes to weaken the cell walls. In the current study, it was found that the increased auxin concentration also causes aquaporin expression to change in the cell membranes of the new organ and the surrounding tissue. Aquaporins facilitate water movement across the cell membranes of plant cells. This regulation is also critical for how rapidly the newly initiated lateral roots can penetrate the tissue. The researchers led by Anton Schäffner at the Institute of Biochemical Plant Pathology have conducted research on this topic together with colleagues from the Centre for Integrative Plant Biology of the University of Nottingham in the UK, the Institut Nationale de la Recherche Agronomique in Montpellier, France, and the Universidad de Extremadura, Badajoz, Spain.

Researchers at Helmholtz Zentrum München investigated in particular the phenotypes of plants whose aquaporin expression had been genetically modified and determined the temporal and spatial expression patterns of aquaporins in the emerging lateral root. The colleagues in France contributed essential physiological data. Mathematical modeling based on the experimentally found expression patterns was also crucial; it enabled enabled the British partners to correctly predict the phenotypic findings. The consortium’s insights gained on the model plant Arabidopsis thaliana (thale cress), may be useful for plant breeding: Through the formation of lateral roots, plants not only have a better grip in the soil but can also absorb more water and minerals. This is a great advantage for plant growth – especially with reduced water availability in soils due to climate change.

Aquaporins are proteins in the cell membrane of organisms that regulate water permeability. Thus, they also influence the rate of pressure changes within plant cells driving their expansion growth.

Experimental system for lateral root formation: Lateral roots are specifically induced at the bend of the primary root, which is formed due to the changed direction of gravity after a 90° ­rotation of the plants. Thus, a synchronous development of the new organ can be achieved, which ­progresses through eight stages, as is depicted in the root longitudinal sections. Source: HMGU