Photoperiod-dependent floral reversion in the natural allopolyploid Arabidopsis suecica.

Flower reversion is the result of genetic or environmental effects that reverse developmental steps in the transition from the vegetative to the reproductive phase in plants. Here, we describe peculiar floral abnormalities, homeotic conversions, and flower reversion in several wild-type accessions of the natural allopolyploid Arabidopsis suecica. Microscopy was used to illustrate the phenotype in detail and we experimented with varying photoperiod lengths to establish whether or not the phenotype was responsive to the environment. We also profiled the transcriptional activity of several floral regulator genes during flower reversion using real-time PCR. We showed that the frequency of floral reversion was affected by day length and the position of the flower along the inflorescence axis. In reverting flowers we found unusual gene expression patterns of floral promoters and inflorescence maintenance genes, including lower mRNA levels of AGAMOUS-LIKE-24 (AGL-24), APETALA1 (AP1), and SHORT VEGETATIVE PHASE (SVP), and higher mRNA levels of SUPRESSOR OF CONSTANS1 (SOC1) compared with normal flowers. We conclude that the floral reversion frequency in A. suecica is susceptible to photoperiod changes, and that the floral abnormalities coincide with the competing expression of floral promoters and floral repressors in reverting floral tissue.

Has the impact of heat waves on mortality changed in France since the European heat wave of summer 2003? A study of the 2006 heat wave.

BACKGROUND: In July 2006, a lasting and severe heat wave occurred in Western Europe. Since the 2003 heat wave, several preventive measures and an alert system aiming at reducing the risks related to high temperatures have been set up in France by the health authorities and institutions. In order to evaluate the effectiveness of those measures, the observed excess mortality during the 2006 heat wave was compared to the expected excess mortality. METHODS: A Poisson regression model relating the daily fluctuations in summer temperature and mortality in France from 1975 to 2003 was used to estimate the daily expected number of deaths over the period 2004-2006 as a function of the observed temperatures. RESULTS: During the 2006 heat wave (from 11 to 28 July), about 2065 excess deaths occurred in France. Considering the observed temperatures and with the hypothesis that heat-related mortality had not changed since 2003, 6452 excess deaths were predicted for the period. The observed mortality during the 2006 heat wave was thus markedly less than the expected mortality (approximately 4400 less deaths). CONCLUSIONS: The excess mortality during the 2006 heat wave, which was markedly lower than that predicted by the model, may be interpreted as a decrease in the population's vulnerability to heat, together with, since 2003, increased awareness of the risk related to extreme temperatures, preventive measures and the set-up of the warning system.