Regulation of respiratory metabolism in germinating seeds

Germination and early seedling growth are critical periods in the life cycle of plants. Starting from a quiescent dry state in the seed, embryos and seedlings need to maintain an efficient heterotrophic metabolism and cope with often stressful conditions, in order to rapidly reach autotrophy and start competing for nutriments and space. These processes are almost entirely dependent on mitochondrial respiration, which provides cellular energy as well as a metabolic platform involved in the conversion of seed reserves into building blocks for growth metabolism. It is therefore no surprise that seed mitochondria exhibit unusual properties in respect of desiccation and temperature tolerance. Stress proteins such as LEA (late embryogenesis abundant) proteins and sHSPs (small heat shock proteins) are involved in the protection of mitochondria in the dry state, and likely contribute to their thermal tolerance during germination. In many cases, fast germination increases the chances of successful emergence and establishment of seedlings, and this requires an efficient energy metabolism. Oxygen availability for respiration can be a challenge because of limiting oxygen diffusion rates in large seeds and/or within soils. It appears that, at least in legume seeds, mitochondria are able to self-adjust their oxygen consumption with the support of nitric oxide (NO) metabolism. This allows maximal energy production to be achieved under hypoxic conditions, without subjecting tissues to deleterious anoxia. In the context of ongoing and future climate change, it is of general importance to understand how mitochondrial functions have evolved to maintain energy homeostasis in organisms and tissues exposed to extreme environmental conditions such as desiccation. Such traits could offer interesting targets for plant adaptation and improvement

Simple system using natural mineral water for high-throughput phenotyping of Arabidopsis thaliana seedlings in liquid culture

Background: Phenotyping for plant stress tolerance is an essential component of many research projects. Because screening of high numbers of plants and multiple conditions remains technically challenging and costly, there is a need for simple methods to carry out large-scale phenotyping in the laboratory.Methods: We developed a method for phenotyping the germination and seedling growth of Arabidopsis (Arabidopsis thaliana) Col-0 in liquid culture. Culture was performed under rotary shaking in multiwell plates, using Evian natural mineral water as a medium. Nondestructive and accurate quantification of green pixels by digital image analysis allowed monitoring of growth. Results: The composition of the water prevented excessive root elongation growth that would otherwise lead to clumping of seedlings observed when classic nutrient-rich medium or deionized water is used. There was no need to maintain the cultures under aseptic conditions, and seedlings, which are photosynthetic, remained healthy for several weeks. Several proof-of-concept experiments demonstrated the usefulness of the approach for environmental stress phenotyping. Conclusion: The system described here is easy to set up, cost-effective, and enables a single researcher to screen large numbers of lines under various conditions. The simplicity of the method clearly makes it amenable to high-throughput phenotyping using robotics

Plasmatic concentration of organochlorine lindane acts as metabolic disruptors in HepG2 liver cell line by inducing mitochondrial disorder.

Lindane (LD) is a persistent environmental pollutant that has been the subject of several toxicological studies. However, concentrations used in most of the reported studies were relatively higher than those found in the blood of the contaminated area residents and effects of low concentrations remain poorly investigated. Moreover, effects on cell metabolism and mitochondrial function of exposure to LD have received little attention. This study was designed to explore the effects of low concentrations of LD on cellular metabolism and mitochondrial function, using the hepatocarcinoma cell line HepG2. Cells were exposed to LD for 24, 48 and 72 h and different parameters linked with mitochondrial regulation and energy metabolism were analyzed. Despite having any impact on cellular viability, exposure to LD at plasmatic concentrations led to an increase of maximal respiratory capacity, complex I activity, intracellular ATP and NO release but decreased uncoupled respiration to ATP synthesis and medium lactate levels. In addition, LD exposure resulted in the upregulation of mitochondrial biogenesis genes. We suggest that, at plasmatic concentrations, LD acts as a metabolic disruptor through impaired mitochondrial function and regulation with an impact on cellular energetic metabolism. In addition, we propose that a cellular assay based on the analysis of mitochondria function, such as described here for LD, may be applicable for larger studies on the effects of low concentrations of xenobiotics, because of the exquisite sensitivity of this organelle

Integrative analysis of acquired thermotolerance in developmentally arrested Arabidopsis seedlings. Implication of energy metabolism

In the context of climate change, the increased frequency and intensity of heat waves will likely have a negative impact on plant physiology, due to the structural destabilization of proteins and membranes caused by high temperatures. As part of this thesis, we developed and characterized an original experimental setup in which Arabidopsis thaliana seedlings are arrested in their development because of mineral starvation. These seedlings exhibit a high metabolic plasticity, especially for energy metabolism, which allows them to survive in a steady state for weeks. Then, we performed an integrative analysis of the processes that allow these seedlings to survive an otherwise lethal heat stress (43°C, 2 h), thanks to a priming treatment at a nonlethal temperature (38°C, 2 h). Priming protects the energy metabolism and permits the recovery of organelle dynamics after stress. At the transcriptional level, primed seedlings overexpress many chaperone proteins and genes involved in photosynthesis, and in the regulation of the expression of mitochondrial and plastidial genomes. At the protein level, the accumulation of HSPs and other stress proteins favour seedling recovery, whereas in the absence of acclimation, heat shock provokes the decrease of ribosomal proteins and the accumulation of proteins implicated in protein degradation. This study highlights the relevance of multi-scale analysis to decipher mechanisms of stress response in plants