Tomato Root Penetration in Soil Requires a Coaction between Ethylene and Auxin Signaling1[C][W][OA]

• Published in: Plant physiology (Bethesda) Vol. 156; no. 3; p. 1424
• Main Authors: Santisree, Parankusam, Nongmaithem, Sapana, Vasuki, Himabindu, Sreelakshmi, Yellamaraju, Ivanchenko, Maria G, Sharma, Rameshwar
• Format: Journal Article
• Language: English
• Published: Rockville American Society of Plant Biologists 01.07.2011
• Subjects: Roots; Seed germination; Soil surfaces; Soils; Tomatoes
• ISSN: 0032-0889; 1532-2548

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 DR5::β-glucuronidase auxin-reporter activity and modified the expression of SlIAA3 and SlIAA9 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.