The control of autumn senescence in Swedish Aspen.

FRACHEBOUD YVAN; LUQUEZ VIRGINIA; JANSSON STEFAN

Salzau, Alemania

Workshop; Third European Workshop on Plant Senescence; 2007

Sen Net (European Network on Plant Senescence)

The control of autumn senescence in Swedish aspens Yvan Fracheboud, Virginia Luquez and Stefan Jansson   Department of Plant Physiology, Umeå Plant Science Centre, University of Umeå, Sweden Yvan.fracheboud@plantphys.umu.se   Autumn senescence was studied in 181 aspens (Populus tremula) growing in the region of Umeå, Sweden by the mean of visual scoring between the end of August and the end of October 2006.  A large variation was observed in the population for the start of autumn senescence which ranged from Sep 3 to Oct 11.  The duration of autumn senescence (D) was significantly negatively correlated with the starting date of senescence and with the mean temperature during senescence. Both parameters together explained 85% of the variation of D, indicating that senescence was accelerated at low temperature. Autumn senescence was also investigated in one of the trees over eight years (1999 – 2006). Measurements of chlorophyll content indicated that the starting date of autumn senescence was remarkably constant over the years and largely independent of temperature, suggesting a photoperiodic control for S.  In contrast, the rate of senescence was significantly negatively correlated with temperature, indicating again that autumn senescence proceeds faster at low temperature. The influence of temperature on autumn senescence was further investigated by analyzing micro-arrays gene expression data available for the same tree for four autumns between 1999 and 2004 (Keskitalo, 2006; Sjodin et al., 2006).  The expression of 1864 and 1627 transcripts were respectively positively and negatively correlated with time with R2 > 0.75 during senescence in at least one for the four years, representing c.a. 17% of the ESTs on the array.  From the 1864 up-regulated transcripts, 126 (7%) were in addition also significantly correlated with temperature (p < 0.01). Since the correlation for most of them (120) was negative, we concluded that low temperature stimulates the expression of genes which are up-regulated during autumn senescence. Similarly, 251 (15%) of the 1627 down-regulated transcripts were significantly positively correlated with temperature, while only 3 transcripts were negatively correlated with temperature, implying that the down-regulation of gene expression during autumn senescence is also accelerated at low temperature. Therefore the micro array data confirmed at the gene expression level our physiological observations that autumn senescence is accelerated at low temperature.   References:   Keskitalo J (2006). Constructing a timetable of autumn senescence in aspen. PhD thesis ISBN 91-7264-075-8. Umeå University.   Sjodin A , Bylesjo M, Skogstrom O, Eriksson D , Nilsson P, Ryden P , Jansson S, Karlsson J (2006). UPSC-BASE - Populus transcriptomics online. Plant Journal 48: 806 -817.