White lupin (Lupinus albus L.) is highly adapted to phosphorus-diminished soils. P-deficient white lupin plants modify their root architecture and physiology to acquire sparingly available soil phosphorus. We employed gas chromatography–mass spectrometry (GC-MS) for metabolic profiling of P-deficient white lupins, to investigate biochemical pathways involved in the P-acquiring strategy. After 14 days of P-deficiency, plants showed reduced levels of fructose, glucose, and sucrose in shoots. Phosphorylated metabolites such as glucose-6-phosphate, fructose-6-phosphate, myo-inositol-phosphate and glycerol-3-phosphate were reduced in both shoots and roots. After 22 days of P-deficiency, no effect on shoot or root sugar metabolite levels was found, but the levels of phosphorylated metabolites were further reduced. Organic acids, amino acids and several shikimate pathway products showed enhanced levels in 22-day-old P-deficient roots and shoots. These results indicate that P-deficient white lupins adapt their carbohydrate partitioning between shoot and root in order to supply their growing root system as an early response to P-deficiency. Organic acids are released into the rhizosphere to mobilize phosphorus from soil particles. A longer period of P-deficiency leads to scavenging of Pi from P-containing metabolites and reduced protein anabolism, but enhanced formation of secondary metabolites. The latter can serve as stress protection molecules or actively acquire phosphorus from the soil.

The relevance of the symbiosis-induced Medicago truncatula sucrose synthase gene MtSucS1 for an efficient arbuscular mycorrhiza (AM) was studied using two independent antisense lines that displayed up to 10-fold reduced SucS1 levels in roots. Mycorrhizal MtSucS1-reduced lines exhibited an overall stunted aboveground growth under inorganic phosphorus limitation. Apart from a reduced plant height, shoot weight, and leaf development, a delayed flowering, resulting in a lower seed yield, was observed. In addition, the root-to-shoot and root weight ratios increased significantly. Gene expression studies demonstrated a major reversion of AM-associated transcription, exhibiting a significant repression of well-known plant AM marker and mycosymbiont genes, together indicating a diminished AM fungus colonization of MtSucS1-antisense lines. Concomitantly, gas chromatography-mass spectrometry-based metabolite profiling revealed that mycorrhizal MtSucS1-reduced lines were affected in important nodes of the carbon, nitrogen, and phosphorus metabolism, accentuating a physiological significance of MtSucS1 for AM. In fact, antisensing MtSucS1 provoked an impaired fungal colonization within the less abundant infected regions, evident from strongly reduced frequencies of internal hyphae, vesicles, and arbuscules. Moreover, arbuscules were early senescing, accompanied with a reduced development of mature arbuscules. This defective mycorrhiza status correlated with reduced phosphorus and nitrogen levels and was proportional to the extent of MtSucS1 knockdown. Together, our results point to an important role for MtSucS1 in the establishment and maintenance of arbuscules in the AM symbiosis.

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Wheat is an important source of proteins and metabolites for human and animal nutrition. To assess the nutritional quality of wheat products, various protein and diverse metabolites have to be evaluated. The grain storage protein family of the α-gliadins are suggested to be the primary initiator of the inflammatory response to gluten in Celiac disease patients. With the technique of RNAi, the α-gliadin storage protein fraction in wheat grains was recently knocked down. From a patient's perspective, this is a desired approach, however, this study aims to evaluate whether such a down-regulation of these problematic α-gliadins also has unintended side-effects on other plant metabolites. Such uncontrolled and unknown arbitrary effects on any metabolite in plants designated for food production would surely represent an avoidable risk for the consumer. In general, α-gliadins are rich in sulfur, making their synthesis and content depended of the sulfur supply. For this reason, the influence of the application of increasing sulfur amounts on the metabolome of α-gliadin-deficient wheat was additionally investigated because it might be possible that e.g., considerable high/low amounts of S might increase or even induce such unintended effects that are not observable under moderate S nutrition. By silencing the α-gliadin genes, a recently developed wheat line that lacks the set of 75 corresponding α-gliadin proteins has become available. The plants were subsequently tested for RNAi-induced effects on metabolites that were not directly attributable to the specific effects of the RNAi-approach on the α-gliadin proteins. For this, GC-MS-based metabolite profiles were recorded. A comparison of wild type with gliadin-deficient plants cultivated in pot experiments revealed no differences in all 109 analyzed metabolites, regardless of the S-nutritional status. No unintended effects attributable to the RNAi-based specific genetic deletion of a storage protein fraction were observed.

Increasing prices for wheat products and fertilisers call for an adjusted agricultural management to maintain yield and to improve product quality. With the increased use of sulfur-free fertilisers in modern cropping systems and the decrease of atmospheric sulfur emissions by industry, sulfur has become a major limiting factor for crop production. The presented data showed that by using GC-MS it was possible to quantitatively detect a set of 72 different metabolites including amino acids, organic acids, sugars, sugar phosphates, and sugar alcohols, phenolic compounds and nucleotides from wheat grains and flag leaves of a pot experiment. A principal component analysis (PCA) revealed a clear separation of flag leaves and grains and a clear separation of non-fertilised and fertilised flag leaves. It could further be shown by PCA, that the low level sulfur fertilisation is also separated from the higher fertilised grains. A considerable influence of the sulfur fertilisation not only on sulfur rich amino acids but also on the sugar metabolism was detected. With increasing sulfur fertilisation six sugars and sugar derivates in the grain such as glucose-6P, galactose, trehalose, cellobiose, melibiose, fumarate, glycerate and the nucleotide uracil were enhanced. Therefore, it was concluded that photosynthesis was limited in developing plants suffering from sulfur deficiency. Late sulfur fertilisation is a procedure that can help to prevent sulfur deficiency. A latent sulfur deficiency at ear emergence can be compensated by late sulfur fertilisation, as wheat plants can replenish sulfate deficits within a short time.

Only little is known about the effect of a varying sulfur (S) nutrition on the pattern of metabolites in different organs of the ears of winter wheat (Tritcum aestivum L.) at final maturity. More insights into the metabolome as influenced by increasing S‐fertilizer rates would, however, be of particular interest in order to unravel S‐dependent physiological processes related to grain filling in wheat. We have therefore investigated the effects of varying sulfur nutrition on metabolite composition and distribution in the organs of the wheat ear and vegetative organs at final maturity. Gas chromatography–mass spectrometry–based metabolite profiles revealed that S deficiency decreased the bulk of metabolites in the straw in favor of an increasing metabolite concentration in the husk, rachis, and grains. Surprisingly, only four out of 109 detectable metabolites, namely N‐acetyl glucosamine, lysine, ferulic acid, and β‐aminoisobutyric acid were most responsible for organ‐specific differences in the metabolite profiles. Under S‐deficient conditions, N‐acetyl‐glucosamine, lysine, and β‐aminoisobutyric were increasingly transferred from source tissues into the ears and grains.

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