Modelling the relative contribution of seed nitrogen reserves and external nitrogen uptake during heterotrophic growth in Medicago truncatula

Background and aims Heterotrophic growth relies on remobilisation of seed reserves and mineral absorption. We used a compartmental model to investigate the fluxes of N absorption and remobilisation of N reserves in a legume seed with high protein content. Methods Seedling growth was studied during the heterotrophic stage in two genotypes of Medicago truncatula as a function of N supply. N absorption and seed remobilisation fluxes were distinguished in a 15 N labelling experiment. Results Remobilisation of seed N reserves was high during germination, but N uptake started as soon as the radicle protruded. Both sources contributed to high elongation rates of the radicle and hypocotyl. When organ lengths stabilised, there was an efflux of N from the cotyledons and roots indicating that seedling growth was limited by carbohydrate production. No significant differences between genotypes were observed except for early N uptake, which was lower in the genotype with the highest initial seed N content. Conclusions N fluxes were similar to those of other non-legume dicotyledonous species but differed from monocotyledonous species. These results improve our understanding of the effects of mineral fertilisation on crop establishment. The compartmental model is a useful tool to analyse N fluxes patterns within and between diverse species, in relation to seed characteristics and soil N availability

QTL analysis of seed germination and pre-emergence growth at extreme temperatures in Medicago truncatula

Enhancing the knowledge on the genetic basis of germination and heterotrophic growth at extreme temperatures is of major importance for improving crop establishment. A quantitative trait loci (QTL) analysis was carried out at sub- and supra-optimal temperatures at these early stages in the model Legume Medicago truncatula. On the basis of an ecophysiological model framework, two populations of recombinant inbred lines were chosen for the contrasting behaviours of parental lines: LR5 at sub-optimal temperatures (5 or 10°C) and LR4 at a supra-optimal temperature (20°C). Seed masses were measured in all lines. For LR5, germination rates and hypocotyl growth were measured by hand, whereas for LR4, imbibition and germination rates as well as early embryonic axis growth were measured using an automated image capture and analysis device. QTLs were found for all traits. The phenotyping framework we defined for measuring variables, distinguished stages and enabled identification of distinct QTLs for seed mass (chromosomes 1, 5, 7 and 8), imbibition (chromosome 4), germination (chromosomes 3, 5, 7 and 8) and heterotrophic growth (chromosomes 1, 2, 3 and 8). The three QTL identified for hypocotyl length at sub-optimal temperature explained the largest part of the phenotypic variation (60% together). One digenic interaction was found for hypocotyl width at sub-optimal temperature and the loci involved were linked to additive QTLs for hypocotyl elongation at low temperature. Together with working on a model plant, this approach facilitated the identification of genes specific to each stage that could provide reliable markers for assisting selection and improving crop establishment. With this aim in view, an initial set of putative candidate genes was identified in the light of the role of abscissic acid/gibberellin balance in regulating germination at high temperatures (e.g. ABI4, ABI5), the molecular cascade in response to cold stress (e.g. CBF1, ICE1) and hypotheses on changes in cell elongation (e.g. GASA1, AtEXPA11) with changes in temperatures based on studies at the whole plant scale

Modelling Memory: do crop models need to become nostalgic?

International audienceIncreased frequency of stress events such as heat waves has been observed for the last decades. Based on the last IPCC report, they are expected to be more frequent, to last longer and to increase in intensity during the reproductive phase of economically important crops. Many recent studies pointed out induced memory effects of stressing events when plants are challenged several times with similar stresses throughout the crop season. These memory effects were shown to be potentially beneficial since the plants are 'primed' and thus more prepared to develop an earlier, more rapid, intense and/or sensitive response when the stress recurs [1]. Therefore, the new climatic patterns prompts to take into account stress memory into predictive crop modelling approaches so as to estimate the effects of repeated stresses and their consequences on crop yield, quality of harvested products. During the last decades, the use of crop models have been enlarged to climate change driven predictions [2]. While evidence for improving crop climate models and especially the temperature response functions in order to reduce uncertainty in yield simulations before any decision making in agriculture, no modelling studies have attempted to decipher and interpret simulation bias in the light of stress memory nor they focused on methodologies to take into account stress memory effects

Modelling Memory: do crop models need to become nostalgic?

International audienceIncreased frequency of stress events such as heat waves has been observed for the last decades. Based on the last IPCC report, they are expected to be more frequent, to last longer and to increase in intensity during the reproductive phase of economically important crops. Many recent studies pointed out induced memory effects of stressing events when plants are challenged several times with similar stresses throughout the crop season. These memory effects were shown to be potentially beneficial since the plants are 'primed' and thus more prepared to develop an earlier, more rapid, intense and/or sensitive response when the stress recurs [1]. Therefore, the new climatic patterns prompts to take into account stress memory into predictive crop modelling approaches so as to estimate the effects of repeated stresses and their consequences on crop yield, quality of harvested products. During the last decades, the use of crop models have been enlarged to climate change driven predictions [2]. While evidence for improving crop climate models and especially the temperature response functions in order to reduce uncertainty in yield simulations before any decision making in agriculture, no modelling studies have attempted to decipher and interpret simulation bias in the light of stress memory nor they focused on methodologies to take into account stress memory effects

Nitric Oxide (NO) in Plant Heat Stress Tolerance: Current Knowledge and Perspectives

High temperature is one of the biggest abiotic stress challenges for agriculture. While, Nitric oxide (NO) is gaining increasing attention from plant science community due to its involvement in resistance to various plant stress conditions, its implications on heat stress tolerance is still unclear. Several lines of evidence indicate NO as a key signaling molecule in mediating various plant responses such as photosynthesis, oxidative defense, osmolyte accumulation, gene expression, and protein modifications under heat stress. Furthermore, the interactions of NO with other signaling molecules and phytohormones to attain heat tolerance have also been building up in recent years. Nevertheless, deep insights into the functional intermediaries or signal transduction components associated with NO-mediated heat stress signaling are imperative to uncover their involvement in plant hormone induced feed-back regulations, ROS/NO balance, and stress induced gene transcription. Although, progress is underway, much work remains to define the functional relevance of this molecule in plant heat tolerance. This review provides an overview on current status and discuss knowledge gaps in exploiting NO, thereby enhancing our understanding of the role of NO in plant heat tolerance

Drought or/and Heat-Stress Effects on Seed Filling in Food Crops: Impacts on Functional Biochemistry, Seed Yields, and Nutritional Quality

Drought (water deficits) and heat (high temperatures) stress are the prime abiotic constraints, under the current and climate change scenario in future. Any further increase in the occurrence, and extremity of these stresses, either individually or in combination, would severely reduce the crop productivity and food security, globally. Although, they obstruct productivity at all crop growth stages, the extent of damage at reproductive phase of crop growth, mainly the seed filling phase, is critical and causes considerable yield losses. Drought and heat stress substantially affect the seed yields by reducing seed size and number, eventually affecting the commercial trait ‘100 seed weight’ and seed quality. Seed filling is influenced by various metabolic processes occurring in the leaves, especially production and translocation of photoassimilates, importing precursors for biosynthesis of seed reserves, minerals and other functional constituents. These processes are highly sensitive to drought and heat, due to involvement of array of diverse enzymes and transporters, located in the leaves and seeds. We highlight here the findings in various food crops showing how their seed composition is drastically impacted at various cellular levels due to drought and heat stresses, applied separately, or in combination. The combined stresses are extremely detrimental for seed yield and its quality, and thus need more attention. Understanding the precise target sites regulating seed filling events in leaves and seeds, and how they are affected by abiotic stresses, is imperative to enhance the seed quality. It is vital to know the physiological, biochemical and genetic mechanisms, which govern the various seed filling events under stress environments, to devise strategies to improve stress tolerance. Converging modern advances in physiology, biochemistry and biotechnology, especially the “omics” technologies might provide a strong impetus to research on this aspect. Such application, along with effective agronomic management system would pave the way in developing crop genotypes/varieties with improved productivity under drought and/or heat stresses

How does early leaf reduction impact on development of adaptation strategies to low phosphorus availability in Zea Mays L.?

National audienc

Impact of early growth traits on further genotypic performance during the vegetative growth of maize (Zea mays L.) in response to phosphorous (P) availability

International audienc

How does early leaf reduction impact on development of adaptation strategies to low phosphorus availability in Zea Mays L.?

National audienc