PT  - JOURNAL ARTICLE
AU  - Xuanjun Feng
AU  - Jing Xiong
AU  - Yue Hu
AU  - Liteng Pan
AU  - Zhengqiao Liao
AU  - Xuemei Zhang
AU  - Wei Guo
AU  - Fengkai Wu
AU  - Jie Xu
AU  - Erliang Hu
AU  - Hai Lan
AU  - Yanli Lu
TI  - Lateral mechanical impedance rather than frontal, promotes cortical expansion of roots
AID  - 10.1101/860155
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 860155
4099  - http://biorxiv.org/content/early/2019/11/29/860155.short
4100  - http://biorxiv.org/content/early/2019/11/29/860155.full
AB  - 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.