Metabolic responses to potassium availability and waterlogging in two oil-producing species: sunflower and oil palm

Abstract

Oil palm and sunflower are important major oil-producing crops at the global scale, with 70 Mt oil produced each year. Although they have been studied for decades for their agronomical aspects, their metabolism is poorly documented, in particular situations such as low potassium. In fact, these species are strong potassium (K)-demanding species cultivated in regions where soil K availability is generally low and waterlogging caused by tropical heavy rains or poor drainage system can limit further nutrient absorption. That is, K deficiency and waterlogging are common stresses that can occur simultaneously and impact on crop development and yield. They are both known to impact on catabolism, with rather opposite effects: inhibition of glycolysis and higher glycolytic fermentative flux, respectively. However, the metabolic effects of K and waterlogging have never been assessed precisely. This is very surprising because most tropical or wet areas where rice, sunflower, oil palm and other important crops are cultivated combine these two environmental constraints. The aim of this study was to understand the overall impact of waterlogging and limited K availability on metabolism, and to understand how such advert environmental conditions reshape the carbon balance in two-oil producing species (sunflower and oil palm). Here, we examined the metabolic response of sunflower seedlings and oil palm saplings in the greenhouse under controlled conditions (nutrient composition with low or high K availability, with or without waterlogging) using gas exchange, metabolomics, proteomics, elemental quantitation, isotope and major flux analyses at different sampling times. While separate K deficiency and waterlogging caused well-known effects like polyamines production and sugar accumulation, respectively, waterlogging altered K-induced respiration enhancement and polyamine production, and K deficiency tended to suppress waterlogging-induced accumulation of Krebs cycle intermediates in leaves, stems and roots. Furthermore, the natural 15N/14N isotope composition (15N) in leaf, stem and root compounds shows that there was a change in nitrate circulation, with less nitrate influx to leaves and stems under low K availablity combined with waterlogging, and more isotopic dilution of lamina nitrates under high K. Our results also show that both low K and waterlogging have a detrimental effect on photosynthesis but clearly stimulate leaf respiration, thereby impacting the carbon use efficiency. Omics analyses show differential accumulation of typical metabolic intermediates and enzymes not only of the Krebs cycle but also of alternative catabolic pathways. In addition, we found a strong relationship between metabolic composition and the rate of leaf dark respiration. Finally, based the results we have and from literature, in the last chapter of this thesis, we briefly describe potential roles of putrescine, and then review data that help defining the most likely specific role of putrescine under K deficiency. Overall, advert environmental conditions (here, low K and waterlogging) have an enormous impact on respiration in oil producing species (sunflower and oil palm here). Leaf metabolome and proteome appear to be good predictors not only of K availability but also of CO2 efflux, and this opens avenues for cultivation biomonitoring using functional genomics technologies. Show more