Submitted to: International Journal of Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/19/2004
Publication Date: 5/10/2005
Citation: Healy, R.A., Horner, H.T., Bailey, T.B., Palmer, R.G. 2005. A microscopic study of trichomes on gynoecia of normal and tetraploid clark cultivars of glycine max, and seven near isogenic lines. International Journal of Plant Science. 166:415-425. Interpretive Summary: Hairs or trichomes on plants have many functions. This includes mechanical protection of the female organs from insect or wind damage, production of substances that deters herbivores, attraction of pollinators and/or inhibition of microbes. In soybean, we noticed different types of trichomes on the female organs and at the base of the female organs. Our objective was to study normal soybean and eight different soybean lines that differed only in their type or density of trichomes. We used light and electron microscopy to determine the frequency of trichomes on the female organ (gynoecium). Four trichomes, a two- to four-celled, an elongate a thick-walled, an elongate thin-walled unicellular trichome, an elongate thin-walled bicellular, and a secretory multicellular trichome were observed. The trichome frequency varied considerably among the soybean lines. Of great interest was the secretory multicellular trichomes. Based upon differences in numbers among the eight soybean lines, field studies were conducted to test insect pollinator preference. These field studies will help us select parent lines to use in hybrid soybean seed production. Hybrid soybean will increase yields and contribute to increased farm income.
Technical Abstract: The surfaces of gynoecia of normal Clark, a tetraploid Clark, and seven isolines of soybean display variations in at least four types of trichomes. The normal Clark soybean gynoecium has: a two- to four-celled, elongate thick-walled trichome (TWT), an elongate thin-walled unicellular trichome (UCT), a secretory multicellular trichome (MCT), and an elongate thin-walled bicellular trichome. All these types are present on the gynoecium by one day prior to anthesis. The Clark tetraploid, and the extra-dense, dense 1, dense 2, sharp hair tip, sparse, and puberulent isolines have all four types of trichomes on their gynoecia, although TWTs and UCTs are very short in the puberulent isoline. The glabrous isoline is missing the TWT, but has a short thin-walled trichome that occurs infrequently. The ratio of TWTs on the gynoecium of the normal Clark to those on the isolines is 1:4 on extra-dense, 1:3 on dense 2, 1:1.6 on dense 1, 1:2 on the tetraploid, 1:0.5 on the sparse, and 1:0.2 on the puberulent. There is a positive correlation between the expanded distribution of TWTs onto other parts of the gynoecium and increased pubescence of thick-walled trichomes on the gynoecium. The numbers and morphology of MCTs are similar in the normal Clark, the tetraploid and the seven isolines, except for extra-dense where the numbers of MCTs are suppressed. The numbers of UCTs were significantly greater on the extra-dense, dense 2 and dense 1 isolines than on the normal Clark. No functions are known for any of the types of trichomes on soybean gynoecia but the MCTs may produce a substance that attracts insect pollinators.