Biology subjects

Charrier, G.

Publications and source records attributed to Charrier, G..

6 recordsLinked to original sources

bioRxiv2026

Caught a chill? The relationship between canker disease susceptibility and the vulnerability to freeze events in apricot trees.

Bacterial canker remains a major constraint affecting apricot production in South-East of France. It is primarily caused by Pseudomonas syringae, a Gram-negative bacterium, many strains of which exhibit ice nucleation activity. By promoting ice formation at relatively high subzero temperatures, ice nucleation-active bacteria may facilitate tissue disruption and pathogen entry. Concurrently, climate-driven shifts toward warmer winter-spring periods have advanced flowering phenology, increasing exposure to late frost events. Despite breeders having developed less susceptible varieties to bacterial canker and early flowering varieties, the link between these traits and frost sensitivity, an emerging risk in this location, remains unresolved. Here, we have evaluated the links between canker susceptibility and frost sensitivity using three cultivar pairs contrasting in disease response and flowering time. Ice nucleation temperature was measured in excised buds under controlled conditions throughout the frost-risk period, alongside field-based diameter variation monitoring over two years. Disease susceptibility (P < 0.001), phenology (P = 0.003), varieties (P < 0.001), locations (P < 0.001), and sampling date (P < 0.001) significantly affected nucleation temperature, whereas epiphytic bacterial abundance and xylem vessel diameter did not. Trees froze at higher temperatures in situ than in laboratory assays (1 to -2{degrees}C versus -3 to 4{degrees}C, respectively), indicating strong environmental modulation of freezing processes beyond Psy-like bacterial activity, which is reflected in contrasting disease susceptibilities (P < 0.001) and precocities (P < 0.001). These results shed light on the complexity of the freezing process in trees under natural conditions. We discuss the potential roles of microclimatic conditions and alternative ice nucleation sources beyond Psy-like bacteria in driving these physiological processes.

plant biology↗

bioRxiv2024

Differential warming at crown scale impacts walnut primary growth onset and secondary growth rate

Trees are exposed to significant spatio-temporal thermal variations, which can induce intracrown discrepancies in the onset and dynamics of primary and secondary growth. In recent decades, an increase in late winter and early spring temperatures has been observed, potentially accelerating bud break, cambial activation and their potential coordination. Intracrown temperature heterogeneities could lead to asymmetric tree shapes unless there is a compensatory mechanism at the crown level. An original warming experiment was conducted on young Juglans regia trees in a greenhouse. From February to August, the average temperature difference during the day between warmed and control parts was 4{degrees}C. The warming treatment advanced the date of budbreak significantly, by up to 14 days. Warming did not alter secondary growth resumption but increased growth rates, leading to higher xylem cell production (twice as many) and to an increase in radial increment (+80% compared to control). Meristems resumptions were asynchronous without coordination in response to temperature. Buds on warmed branches began to swell two weeks prior to cambial division, which was one week earlier than on control branches. A difference in carbon and water remobilisation at the end of bud ecodormancy was noted under warming. Overall, our results argue for a lack of compensatory mechanisms at the crown scale, which may lead to significant changes in tree architecture in response to intra-crown temperature heterogeneities. Highlight: When tree are submitted to asymmetrical warming, it leads to early budbreak and enhanced cambial activity for warmed branches

developmental biology↗

bioRxiv2023

On the mechanism for winter stem pressure build-up in walnut tree

Xylem embolism is a significant factor in tree mortality. Restoration of hydraulic conductivity after massive embolisation of the vascular system requires the application of positive pressure to the vessels and/or the creation of new conductive elements. Some species generate positive pressure from the root system to propagate pressure in distal, aboveground, organs in spring, whereas other species generate positive pressure locally at the stem level during winter. We provide a mechanistic explanation for winter stem pressure build-up in the walnut tree. We have developed a physical model that accounts for temperature fluctuations and phase transitions. This model is based on the exchange of water and sugars between living cells and vessels. Our computations demonstrate that vessel pressurization can be attributed to the transfer of water between vessels across the parenchyma rays, which is facilitated by a radial imbalance in sugar concentration. The ability to dispose of soluble sugars in living cells, and to transport them between living cells and up to the vessels, are identified as the main drivers of stem pressure build-up in the walnut tree.

plant biology↗

bioRxiv2023

Freeze dehydration vs. supercooling in tree stems: physical and physiological modelling

Frost resistance is the major factor affecting the distribution of plant species at high latitude and elevation. The main effects of freeze-thaw cycles are damage to living cells and formation of gas embolism in tree xylem vessels. Lethal intracellular freezing can be prevented in living cells by two mechanisms: dehydration and deep supercooling. We developed a multiphysics numerical model coupling water flow, heat transfer, and phase change, considering different cell types in plant tissues, to study the dynamics and extent of cell dehydration, xylem pressure changes, and stem diameter changes in response to freezing and thawing. Results were validated using experimental data for stem diameter changes of walnut trees. The effect of cell mechanical properties was found to be negligible as long as the intracellular tension developed during dehydration was sufficiently low compared to the ice induced cryostatic suction. The model was finally used to explore the coupled effects of relevant physiological parameters (initial water and sugar content) and environmental conditions (air temperature variations) on the dynamics and extent of dehydration. It revealed configurations where cell dehydration could be sufficient to protect cells from intracellular freezing, and situations where supercooling was necessary. This model, freely available with this paper, could easily be extended to explore different anatomical structures, different species and more complex physical processes.

biophysics↗

bioRxiv2022

Impacts of ocean acidification and warming on post-larval growth and metabolism in two populations of the great scallop (Pecten maximus L.)

Ocean acidification and warming are key stressors for many marine organisms. Some organisms display physiological acclimatisation or plasticity, but this may vary across species ranges, especially if populations are adapted to local climatic conditions. Understanding how acclimatisation potential varies among populations is therefore important in predicting species responses to climate change. We carried out a common garden experiment to investigate how different populations of the economically important great scallop (Pecten maximus) from France and Norway responded to variation in temperature and pCO2 concentration. After acclimation, post-larval scallops (spat) were reared for 31 days at one of two temperatures (13{degrees}C and 19{degrees}C) under either ambient or elevated pCO2 (pH 8.0 and pH 7.7). We combined measures of proteomic, metabolic, and phenotypic traits to produce an integrative picture of how physiological plasticity varies between the populations. The proteome of French spat showed significant sensitivity to environmental variation, with 12 metabolic, structural and stress-response proteins responding to temperature and/or pCO2. Principal component analysis revealed seven energy metabolism proteins in French spat that were consistent with countering ROS stress under elevated temperature. Oxygen uptake in French spat did not change under elevated temperature, but increased under elevated pCO2. In contrast, Norwegian spat reduced oxygen uptake under both elevated temperature and pCO2. Metabolic plasticity seemingly allowed French scallops to maintain greater energy availability for growth than Norwegian spat. However, increased physiological plasticity and growth in French spat may come at a cost, as French (but not Norwegian) spat showed reduced survival under elevated temperature. Summary StatementJuvenile scallops from France and Norway differ in their response to warming and acidification. French scallops show more physiological plasticity, adjusting their proteome and metabolism in order to maintain growth.

evolutionary biology↗

bioRxiv2019

Drought-induced mortality: stem diameter variation reveals a point of no return in lavender species

In the context of climate changes, water availability is expected to severely decline. Consequently, there is a need to predict mortality of woody species, especially to find a physiological threshold to drought-induced mortality. Lavender species (Lavandula angustifolia and Lavandula x intermedia) which are important crops of the Mediterranean region are affected by a decline, notably caused by successive intense drought events. Lavender response to extreme drought events was monitored using continuous stem diameter measurements. Water potential, stomatal conductance, loss of xylem hydraulic conductivity and electrolyte leakage were also measured during desiccation, and recovery was evaluated after rewatering. Two parameters computed from stem diameter variations were related to stress intensity and resilience to stress: PLD (Percentage Loss of Diameter) and stem PLRC (Percentage Loss of Rehydration Capacity of the stem), respectively. We showed that plants did not recover when the PLD reached its maximal value (PLDmax) which was 21.27 {+/-} 0.57% in both lavender species and whatever the growing conditions. This point of no return was associated with a high level of cell lysis evaluated by electrolyte leakage, and occurred far after the xylem hydraulic failure. We discussed the relevance of PLDmax as a threshold for drought-induced mortality and its physiological significance, in relation to the mortality mechanisms. One-sentence summaryUnder extreme drought, lavender death occurs when the water storage of the elastic compartment of the stem is exhausted.

plant biology↗