Tomato Root Penetration in Soil Requires a Coaction between Ethylene and Auxin Signaling

• Published in: Plant physiology (Bethesda) 2011-07, Vol.156 (3), p.1424-1438
• Main Authors: Santisree, Parankusam, Nongmaithem, Sapana, Vasuki, Himabindu, Sreelakshmi, Yellamaraju, Ivanchenko, Maria G., Sharma, Rameshwar
• Format: Article
• Language: English
• Subjects: Auxins; Biological and medical sciences; Biological Transport - drug effects; Cyclopropanes - pharmacology; DEVELOPMENT AND HORMONE ACTION; Ethylenes - metabolism; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Gene Expression Regulation, Plant - drug effects; Genes, Plant - genetics; Gravitropism - drug effects; Hypocotyls; Indoleacetic Acids - metabolism; Lycopersicon esculentum - drug effects; Lycopersicon esculentum - growth & development; Mechanotransduction, Cellular - drug effects; Mechanotransduction, Cellular - genetics; Meristem - drug effects; Meristem - metabolism; Mutation - genetics; Plant growth regulators; Plant physiology and development; Plant roots; Plant Roots - drug effects; Plant Roots - growth & development; Plants; Receptors; Root growth; Root tips; Seedlings; Seedlings - drug effects; Seedlings - growth & development; Signal Transduction - drug effects; Soil
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.111.177014

During seed germination, emerging roots display positive gravitropism and penetrate into the soil for nutrition and anchorage. Tomato (Solanum lycopersicum) seeds germinated in the presence of 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, failed to insert roots into Soilrite and grew in the air, forming loops. Time-lapse video imaging showed that 1-MCP-grown root tips retained positive gravitropism and made contact with the surface of Soilrite but failed to penetrate into the Soilrite. Time-course studies revealed that the effect of 1-MCP was most prominent when seed imbibition and germination were carried out in the continual presence of 1-MCP. Conversely, 1-MCP was ineffective when applied postgermination after penetration of roots in the Soilrite. Furthermore, treatment with 1-MCP caused a reduction in DRS::β-glucuronidase auxin-reporter activity and modified the expression of SIIAA3 and SIIAA9 transcripts, indicating interference with auxin signaling. The reduced ethylene perception mutant, Never-ripe, displayed decreased ability for root penetration, and the enhanced polar auxin transport mutant, polycotyledon, showed a nearly normal root penetration in the presence of 1-MCP, which could be reversed by application of auxin transport inhibitors. Our results indicate that during tomato seed germination, a coaction between ethylene and auxin is required for root penetration into the soil.