The final developmental stage of the woody tissues is the cell death of the xylem elements. Xylem-cell death involves a range of morphological and nuclear changes. Accumulation of hydrolytic enzymes and secondary cell wall synthesis is followed by tonoplast disruption and finally the autolytic loss of the cell contents. Xylem-cell death is reminiscent of other physiological cell death processes that are known to be apoptotic in nature. However, it is obvious that xylem-cell death of plants with extensive secondary growth, such as trees, is regulated by factors that are unique. As other processes of secondary xylem development, xylem-cell death occurs in a highly co-ordinate manner in the three different dimensions of the stem; the radial, the tangential and the longitudinal dimension. Further regulatory complexity is conferred be the fact that different types of xylem elements, the fibers and the vessels of the angiosperm trees, die at a different age and therefore seemingly according to different programmes. The main objective of my work is to identify novel regulators of xylem-cell death in hybrid aspen, Populus tremula x tremuloides. The first approach is to identify genes that are differentially expressed in xylem tissues undergoing cell death by a cDNA microarray analysis. The function and the expression pattern of the candidate regulatory genes in xylem-cell death is characterized in Arabidopsis thaliana. The second approach is to analyze genetic mutants of Arabidopsis. At the moment, there are no known Arabidopsis mutants affected in the xylem-cell death.

 

Selected publications:

 

Tuominen, H., Puech, L., Fink, S. and Sundberg, B. () A radial concentration gradient of indole-3-acetic acid is related to secondary xylem development in hybrid aspen. Plant Physiology, 115: 577-585.

 

Regan, S., Bourquin, V., Tuominen, H., and Sundberg, B. () Accurate and high resolution in situ hybridization analysis of gene expression in secondary stem tissues. Plant Journal, 19: 363-369.

 

Tuominen, H., Puech, L., Regan, S., Fink, S., Olsson, O. and Sundberg. B, () Cambial-region-specific expression of the Agrobacterium iaa genes in transgenic aspen visualized by a linked uidA reporter gene. Plant Physiology, 123: 531-541.

 

Overmyer, K., Tuominen, H., Kettunen, R., Betz, C., Langebartels, C., Sandermann, H., Kangasjärvi, J. () Ethylene regulation of ozone-induced superoxide radical accumulation and cell death in the Arabidopsis rcd1 mutant. Plant Cell, 12:.

 

Tuominen, H., Olsson, O., Sundberg, B. () Genetic engineering of wood formation. In Molecular Biology of Woody Plants Vol 1 (SM Jain and SC Minocha, eds.). Kluwer Publishers, pp. 155-180.

 

Kangasjärvi, J., Tuominen, H., Overmyer, K. () Ozone-induced cell death: Reactive oxygen species as signal molecules regulating cell death. In Trends in European Forest Tree Physiology Research, Cost Action E6: EUROSILVA (S. Huttunen, H. Heikkilä, J. Bucher, B. Sundberg, P. Jarvis, and R. Matyssek, eds). Kluwer Academic Publishers, pp. 81-92.

 

Kangasjärvi, J., Overmyer, K., Tuominen, H., Keinänen, M. () The role of ethylene in regulating reactive oxygen species-mediated cell death. In.Biology and Biotechnology of the Plant Hormone Ethylene (M. Vendrell, H. Klee, J.C. Pech, F. Romojaro, F., eds) III, pp. 328-334.

Tuominen, H., Overmyer, K., Kollist, H., Keinänen, M., Kangasjärvi, J. () Mutual antagonism between ethylene and jasmonic acid regulate ozone-induced spreading cell death in Arabidopsis. Plant Journal, 39: 59-69.

 

Ahlfors, R., Lång, S., Overmyer, K., Jaspers, P., Brosché, M., Tauriainen, A., Belles-Boix, E., Kollist, H., Tuominen, H., Piippo, M., Inzé, D., Palva, E.T., Kangasjärvi, J. () Arabidopsis thaliana RADICAL INDUCED CELL DEATH 1 belongs to the WWE protein-protein interaction-domain and modulates abscisic acid, ethylene and methyl jasmonate responses. Plant Cell, 16:.

 

Overmyer, K., Brosché, M., Pellinen, R., Kuittinen, T., Tuominen, H., Ahlfors, R., Keinänen, M., Saarma, M., Scheel, D., Kangasjärvi, J. . Ozone-induced programmed cell death in the Arabidopsis rcd1 (radical-induced cell death1) mutant. Plant Physiology, in press.