Lateral mechanical impedance rather than frontal, promotes cortical expansion of roots

Abstract

<jats:title>Abstract</jats:title><jats:p>It has long been considered that mechanical impedance on root will restrict root elongation and consequently promote radial growth. However, we did observe radial expansion but not elongation restriction in maize seedlings after short growth in sands. Mechanical impedance of soil can be classified into frontal- and lateral-type based on the interaction site of root. Therefore, we suspected that radial expansion might be mainly stimulated by lateral rather than frontal impedance. To verify our speculation, frontal and lateral impedance was provided separately. Small plastic caps were used to provide unique frontal impedance on root tip and cylindrical plastic containers were used to provide lateral impedance. Plastic caps could reduce root length remarkably. However, the radial expansion of plastic-cap-fitted roots was significantly inferior to that of the sand-cultured roots. Microstructural analysis revealed that sand-condition thickened root largely dependents on cortical expansion, whereas plastic cap did it mainly by thickening stele. In cylindrical plastic containers, mechanical impedance came only from the lateral direction and promoted the expansion of cortex just as sand-condition. Thus, we proposed that the expansion of the cortex and the consequent radial growth is mainly due to lateral impedance when growing in sands.</jats:p>

How plants get round problems: new insights into the root obstacle avoidance response

“…Mechanical impedance generated by obstacles or by the mechanical properties of the growth medium can have dramatic effects on the root. Frontal tip impedance inhibits root growth and increases root hair formation, whereas lateral impedance induces root thickening and can even change stem cell niche organization (Potocka et al ., 2011; Feng et al ., 2020). In this issue of New Phytologist , Jacobsen et al .…”