No abstract

The intrinsic variability of volatile organic compound emissions and photosynthetic parameters in response to two drying cycles was investigated on Quercus suber L. saplings originating from three Tunisian populations native to contrasting climates. Emissions mainly included monoterpenes plus traces of sesquiterpenes and methylsalicylate that steadily decreased during the experiment unrelated to treatments. Instead, monoterpene emissions increased by 30% during a first moderate drought and remained enhanced after rewatering, while CO2–H2O gas exchange was reduced by 30%. A second severe drought decreased monoterpene emissions to about two third of controls, strongly inhibited gas exchange and photochemical efficiency, and caused a partial loss of chlorophyll. Rewatering led to only partial recovery of emissions and photosynthetic parameters of stressed plants whose biomasses and leaf nitrogen and chlorophyll contents were lower than in control plants. There was no clear difference among populations in volatile organic compound emissions or photosynthetic parameters. However, the population inhabiting the most arid region had intrinsically smaller leaves with lower specific leaf masses and higher drought-related leaf losses than populations native to less arid climates. These results indicate an adaptive shift from stress-tolerating towards stress-avoiding ecotypes under arid climates involving mainly morphological adaptations without apparent differentiation in volatile organic compound production, probably because of its high phenological plasticity.

Stems of angiosperm trees are affected by gravity. Young poplar stems show primary growth in the top internodes and differential cambium activity in the basal internodes after inclination with some tension wood formed after 45 min. This study was conducted in order to characterize the early changes in poplar gene expression during the early stages of the gravitropic response. Using microarray technology, the expression of 15 000 genes was examined. Approximately 3.1 % of these genes exhibited significant expression changes within the first 45 min of gravity stimulation. Approximately 73 % of the identified genes were found to have a known or predicted molecular function. Many of these genes were involved in secondary wall formation (cellulose synthesis and lignification), cytoskeleton development, signaling, and stress response. Some identified genes seem to play a role in sensing gravitational signals during tension wood formation. A large number of the identified arabinogalactan (AGP) and transcription factor genes were involved in cell wall biosynthesis suggesting that these genes are particularly active in the first phases of signal transduction during tension wood formation.