Local inhibition of nitrogen fixation and nodule metabolism in drought-stressed soybean

Drought stress is a major factor limiting symbiotic nitrogen fixation (NF) in soybean crop production. However, the regulatory mechanisms involved in this inhibition are still controversial. Soybean plants were symbiotically grown in a split-root system (SRS), which allowed for half of the root system to be irrigated at field capacity while the other half remained water deprived. NF declined in the water-deprived root system while nitrogenase activity was maintained at control values in the well-watered half. Concomitantly, amino acids and ureides accumulated in the water-deprived belowground organs regardless of transpiration rates. Ureide accumulation was found to be related to the decline in their degradation activities rather than increased biosynthesis. Finally, proteomic analysis suggests that plant carbon metabolism, protein synthesis, amino acid metabolism, and cell growth are among the processes most altered in soybean nodules under drought stress. Results presented here support the hypothesis of a local regulation of NF taking place in soybean and downplay the role of ureides in the inhibition of NF

Drought Stress Causes a Reduction in the Biosynthesis of Ascorbic Acid in Soybean Plants

Drought provokes a number of physiological changes in plants including oxidative damage. Ascorbic acid (AsA), also known as vitamin C, is one of the most abundant water-soluble antioxidant compound present in plant tissues. However, little is known on the regulation of AsA biosynthesis under drought stress conditions. In the current work we analyze the effects of water deficit on the biosynthesis of AsA by measuring its content, in vivo biosynthesis and the expression level of genes in the Smirnoff-Wheeler pathway in one of the major legume crop, soybean (Glycine max L. Merr). Since the pathway has not been described in legumes, we first searched for the putative orthologous genes in the soybean genome. We observed a significant genetic redundancy, with multiple genes encoding each step in the pathway. Based on RNA-seq analysis, expression of the complete pathway was detected not only in leaves but also in root tissue. Putative paralogous genes presented differential expression patterns in response to drought, suggesting the existence of functional specialization mechanisms. We found a correlation between the levels of AsA and GalLDH biosynthetic rates in leaves of drought-stressed soybean plants. However, the levels of GalLDH transcripts did not show significant differences under water deficit conditions. Among the other known regulators of the pathway, only the expression of VTC1 genes correlated with the observed decline in AsA in leaves

Root architecture of Medicago Truncatula: response to drought of the primary and secondary root

Trabajo presentado en el XIII Congresso Luso-Espanhol de Fisiologia Vegetal, celebrado en Lisboa del 24 al 28 de julio de 2013.Forage legumes are important in agricultural systems as feed sources for livestock and raw food materials for humans. Medicago truncatula, considered as a model legume, is phylogenetically related to some of the most economically important European legume crops. However, legumes show inconsistent production rates, mostly due to abiotic factors and particularly drought (Zahran, 1999), one of the major factor affecting crop productivity. The more severe the water deficit, the larger the number of cellular processes affected, starting with inhibition of plant cell growth, followed by inhibition of cell division, cell wall formation and protein biosynthesis (Hsiao, 1973). The second most important consequence of decreased water availability is a reduction of leaf C fixation due to either CO2 diffusion and/or metabolic disruption processes. Due to the importance of the photosynthetic process for ecosystem productivity, plant research has been highly focused to photosynthetic aboveground organs and only in the last decades root research is emerging. The present study aims to analyze the response of the root of M. truncatula to drought stress. To do so, root architecture analysis and metabolic profiling of primary and secondary roots were carried out. The primary root system of legumes has been described as a prominent, central taproot that penetrates to different depths in unrestricted soil. However, M. truncatula taproot become early branched with numerous lateral roots. Under controlled conditions, the taproot develops at the upper part of the root and represents around 5-10% of the root biomass in plants at the late vegetative stage. Preliminary results suggest that the primary and secondary root respond differently to drought. Total carbon (C) and nitrogen (N) content was not affected in the primary root of drought stressed plants when a significant decline was observed in the secondary roots. The C decline agrees with the reduction of the starch in drought stress secondary roots and the accumulation of soluble C compounds as sucrose, glucose, malate, and citrate. However, the decline of N content could not be explained in base to the soluble protein content which was unaffected. Besides, a general accumulation of amino acids was detected in the secondary roots of drought stressed plants. Amino acids, sugars and organic acids, are compatible solutes which can exert a role on turgor maintenance and also stabilizing proteins and cell structures under stress conditions. Response to drought of the different root parts of this forage legume will be discussed.Spanish Ministry of Economy and Competitiveness (AGL2011-23738), Public University of Navarre and Basque Government.N

Impact of innovative and sea-shell amendments in Bradyrhizobium and soybean symbiotic relationship

Trabajo presentado en el 8th International Symposium of Interactions of Soil Minerals with Organic Components and Microorganisms (ISMOM), celebrado en Sevilla (España), del 23 al 28 de abril de 201

Analysis of the effect of temperature on yield components and starch concentration in tritordeum and wheat

Resumen del trabajo presentado en el II Simposio Español de Fisiología y Mejora de Cereales, celebrado en Córdoba (España), los días 6 y 7 de marzo de 2019Cereal production is highly dependent on environmental conditions. Elevated temperature is a key factor currently affecting crop yield and grain quality. Tritordeum is fertile amphiploid derived from the crosses between Hordeum chilense, and Triticum durum (tetraploid or hexaploid). This cereal has been described to display important grain nutritional properties. One high yielded bread wheat genotype (Togano) and four tritordeum lines (HTC15432, HT435, HT621, Bulel T1) were selected for this study. Bulel T1 is the commercial tritordeum line, HTC15432 is a new line with high yield and both HT435, HT621 were selected for their high lutein content. These plants were grown in greenhouses under two temperature levels (ambient temperature, Tambient versus elevated temperature, Tambient +4ºC) in order to test the impact of temperature increase on crop productivity and nutritional traits. Together with the agronomic characterization (aboveground biomass, grain yield, kernel number/plant, spike number/plant, thousand kernel weight (TKW) and harvest index (HI), starch, C/N % and protein concentration were determined in grains. Grain yield analyses showed that temperature effect on crop production varied depending on the analysed variety. While HT15432, yield decreased, HT435 production significantly increased. In other cases, no significant effects were observed