Table 1.
Summary of the action of the main phytohormones on root development and nodulation in legumes and root development in Arabidopsis or other non-legume dicot species (when specified).
| Hormone | Action on Root Development in Legumes | Action on Nodulation | Action on Root Development in Arabidopsis or Other Dicots | References |
|---|---|---|---|---|
| Auxin | + on LRF at low doses, − at higher doses | + at low doses on indeterminate nodules | + on LRF at low doses, − at higher doses | [6,7,8,9] |
| Cytokinins | − on LRF | + on nodulation | − on LRF | [10,11,12] |
| Abscisic acid (ABA) | + on LRF at low doses (≤ 10−7 M), − at higher doses + on intermediate LRF stages and meristematic activity |
− on nodule development and NF signaling | − on LRF at 10−7 M − on LRP emergence and meristematic activity |
[5,13,14,15,16] |
| Ethylene | + on LRF at low doses, − at higher doses. Inhibits primary root length |
− | − on LRF and primary root growth through auxin interaction | [17,18,19,20,21] |
| Nitric oxide | Present in LRP. Necessary downstream of auxin for LRF? |
Necessary for early infection and nodule primordia formation. Accelerates nodule senescence | + on LRF through reactivation of cell cycle genes in tomato, downstream of auxin. + on LRF in sunflower seedlings | [8,22,23,24,25,26,27] |
| Jasmonic acid | + on LRF, − on primary root length | − on nodulation by acting on NF signaling | + on LRF and − on primary root length | [28,29] |
| Brassinosteroids | − on primary root length and LRF | ± (cf. [30], for review) | Promote LR emergence at low doses (10−8 M) Promote LRF and root apical meristem maintenance |
[31,32] |
| Gibberelic acid | Pea biosynthetic mutants are dwarf with fewer LR | May require an optimum concentration + on pea, − on lotus [33] |
Inhibits LRF (in poplar) | [31,34] |
| Strigolactones | Reduce LRF from 10−7 M | + at low doses in M. truncatula and in pea, lotus; − at higher doses | − on LRF (phosphate dependent conditions) | [35,36,37,38] |
| CLE/CLV1 | − on LRF (dependent on nitrate status in the shoot) | − on nodulation through the AON pathway | − on LRF in nitrate limiting conditions | [39,40,41,42] |
| CEP/LRR-RLK | Reduces LRF | Enhances nodulation in a systemic pathway | Reduces LRF in nitrate limiting conditions (systemic action) | [43,44,45] |
Data is compiled for legumes from literature in M. truncatula, L. japonicus, Glycine max (soybean) and Pisum sativum (pea). LRF: Lateral Root Formation. CLE: CLAVATA3/EMBRYO-SURROUNDING REGION peptides; CLV1: Clavata 1; CEP: C-terminally Encoded Peptide; LRR-RLK: Leucine Rich Repeat Receptor Like Kinase.