Effects of glucose and ethylene on root hair initiation and elongation in lettuce (Lactuca sativa L.) seedlings
Root hair formation occurs in lettuce seedlings after transfer to an acidic medium (pH 4.0). This process requires cortical microtubule (CMT) randomization in root epidermal cells and the plant hormone ethylene. We investigated the interaction between ethylene and glucose, a new signaling molecule in plants, in lettuce root development, with an emphasis on root hair formation. Dark-grown seedlings were used to exclude the effect of photosynthetically produced glucose. In the dark, neither root hair formation nor the CMT randomization preceding it occurred, even after transfer to the acidic medium (pH 4.0). Adding 1-aminocyclopropane-1-carboxylic-acid (ACC) to the medium rescued the induction, while adding glucose did not. Although CMT randomization occurred when glucose was applied together with ACC, it was somewhat suppressed compared to that in ACC-treated seedlings. This was not due to a decrease in the speed of randomization, but due to lowering of the maximum degree of randomization. Despite the negative effect of glucose on ACC-induced CMT randomization, the density and length of ACC-induced root hairs increased when glucose was also added. The hair-cell length of the ACC-treated seedlings was comparable to that in the combined-treatment seedlings, indicating that the increase in hair density caused by glucose results from an increase in the root hair number. Furthermore, quantitative RT-PCR revealed that glucose suppressed ethylene signaling. These results suggest that glucose has a negative and positive effect on the earlier and later stages of root hair formation, respectively, and that the promotion of the initiation and elongation of root hairs by glucose may be mediated in an ethylene-independent manner.
KeywordsCortical microtubule Ethylene Glucose Lettuce (Lactuca sativa L.) Root hair
We thank Prof. Y. Inoue in Tokyo University of Science for providing lettuce seeds.
- Baluška F, Salaj J, Mathur J, Braun M, Jasper F, Šamaj J, Chua NH, Barlow PW, Volkmann D (2000) Root hair formation: F-actin-dependent tip growth is initiated by local assembly of profilin-supported F-actin meshworks accumulated within expansin-enriched bulges. Dev Biol 227:618–632CrossRefPubMedGoogle Scholar
- Cheng WH, Endo A, Zhou L, Penney J, Chen HC, Arroyo A, Leon P, Nambara E, Asami T, Seo M, Koshiba T, Sheen J (2002) A unique short-chain dehydrogenase/reductase in Arabidopsis glucose signaling and abscisic acid biosynthesis and functions. Plant Cell 14:2723–2743CrossRefPubMedPubMedCentralGoogle Scholar
- Dolan L, Duckett CM, Grierson C, Linstead P, Schneider K, Lawson E, Dean C, Roberts K, Poethig S (1994) Clonal relationships and cell patterning in the root epidermis of Arabidopsis. Development 120:2465–2474Google Scholar
- Gális I, Šimek P, Van Onckelen HA, Kakiuchi Y, Wabiko H (2002) Resistance of transgenic tobacco seedlings expressing the Agrobacterium tumefaciens C58-6b gene, to growth-inhibitory levels of cytokinin is associated with elevated IAA levels and activation of phenylpropanoid metabolism. Plant Cell Physiol 43:939–950CrossRefPubMedGoogle Scholar
- Inoue Y, Yamaoka K, Kimura K, Sawai K (1995) Image processing-aided simple analysis method for root hair formation in plants. Bioimages 3:31–36Google Scholar
- Li Y, Lee KK, Walsh S, Smith C, Hadingham S, Sorefan K, Cawley G, Bevan MW (2006) Establishing glucose- and ABA-regulated transcription networks in Arabidopsis by microarray analysis and promoter classification using a relevance vector machine. Genome Res 16:414–427CrossRefPubMedPubMedCentralGoogle Scholar