Partners and International Organizations
(English)
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AT, BE, BG, DK, FI, FR, DE, EL, HU, IE, IT, LT, NO, PT, SI, ES, SE, CH, UK
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Abstract
(English)
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Mechanical interference of insects or environmental conditions with plants induces reactions in plant cells, which influence plant morphology and often lead to the formation of lignin and callose. For example, bending of tree stems provokes the formation of reaction wood with changed morphology of xylem and xylem parenchyma cells and altered cell wall compositions. In our studies we address the question, whether secondary cell wall formation in vessel and fibre cells is induced by mechanical pressure. In the inflorescence stem of Arabidopsis, collateral vascu-lar bundles are arranged in a circle and are separated by interfascicular fibres. Lignification of xylem and interfascicular fibre cells starts at the bottom of the inflorescence stem. It has been proposed that secondary cell wall formation and lignification of xylem and interfascicular fibres were induced by the weight of the inflorescence stem and it has been shown, that increased weight at the top of inflorescences increased lignification in the stem (Ko et al., 2004). In order to apply a continuous pressure on the top of inflorescence stems, we have fixed Arabidop-sis plants horizontally in a centrifuge with the shoot tips towards the center, and have centrifuged the plants at 11 ms-2 (1.12g) when the inflorescence stem started to grow. Longitudinal stem growth was severely reduced in centrifuged plants. In addition, secondary growth was slightly in-duced.In a second series of experiments we centrifuged Arabidopsis plants at 11 ms-2 without protecting the inflorescence stem from wind created by centrifugation. Centrifuged plants had heavily lignified vessel and fibre cells in the inflorescence stem and cell size was reduced. Furthermore, secondary growth was induced and xylem and phloem developed also in the interfascicular space. These ob-servations suggest that bending of the stem may have additional effects to pressure applied from the top. At present we are analysing stem growth and secondary xylem formation after mechanical stimula-tion in the ethylene insensitive mutant ein2. Results obtained so far point to a function of ethylene in stem growth reduction and secondary growth induction after mechanical stimulation. Reference:Ko JH, Han KH, Park S, Yang J (2004) Plant Physiol 135: 1069-1083
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