Endophytic Microbiome Responses to Sulfur Availability in Beta vulgaris (L.).

Sulfur is an essential plant macronutrient, and its adequate supply allows an efficient root storage and sugar extractability in sugar beets (Beta vulgaris L.). In this study, we investigated the effect of changes in sulfur availability on the endophytic community structure of sugar beets. Plants were hydroponically grown in a complete nutrient solution (S-supplied), a nutrient solution without MgSO4 (S-deprived), and a nutrient solution without MgSO4 for six days and resupplied with 100 µM MgSO4 for 48 h (S-resupplied). The sulfur status was monitored by inductively coupled plasma ICP-OES, and combustion analysis together with the evaluation of microRNA395 as a biomarker for sulfate status. Metabarcoding of the bacterial 16S rRNA gene was carried out in order to determine leaf endophytic community structure. The Shannon diversity index significantly differed (p < 0.05) between sulfate-supplied and sulfate-deprived seedlings. Validation by Real-Time PCR showed a significant increase (p < 0.05) of Burkholderia spp. in sulfate-deprived plants as compared to sulfate-supplied ones. The study sheds new light on the effects of nutrient deficiency on the microbiome of sugar beet plants.

Molecular and Morphological Changes Induced by Leonardite-based Biostimulant in Beta vulgaris L.

Humic substances extracted from leonardite are widely considered to be bioactive compounds, influencing the whole-plant physiology and the crop yield. The aim of this work was to evaluate the effect of a new formulate based on leonardite in the early stage of growth of sugar beet (Beta vulgaris L.). A commercial preparation of leonardite (BLACKJAK) was characterized by ionomic analysis, solid-state 13C MAS NMR spectroscopy. Seedlings of sugar beet were grown in Hoagland's solution under controlled conditions. After five days of growth, an aliquot of the concentrated BLACKJAK was added to the solution to obtain a final dilution of 1:1000 (0.5 mg C L-1). The sugar beet response in the early stage of growth was determined by evaluating root morphological traits as well as the changes in the expression of 53 genes related to key morphophysiological processes. Root morphological traits, such as total root length, fine root length (average diameter < 0.5 mm), and number of root tips, were significantly (p < 0.001) increased in plants treated with BLACKJAK, compared to the untreated plants at all sampling times. At the molecular level, BLACKJAK treatment upregulated many of the evaluated genes. Moreover, both Real Time PCR and digital PCR showed that genes involved in hormonal response, such as PIN, ARF3, LOGL 10, GID1, and BRI1, were significantly (p < 0.05) upregulated by treatment with BLACKJAK. Our study provides essential information to understand the effect of a leonardite-based formulate on plant growth hormone metabolism, although the molecular and physiological basis for these complicated regulatory mechanisms deserve further investigations.

Innovative Approaches to Evaluate Sugar Beet Responses to Changes in Sulfate Availability.

In this study, a system based on omics profiling was set-up for sugar beet (Beta vulgaris L. subsp. vulgaris) evaluation after changes in sulfate availability. Seedlings were grown on sulfate-deprived Hoagland solution. Six days after germination, 100 µM MgSO4 was added to the solution. Root samples were collected 36 h after treatments. WinRHIZO root-scanning approach was used for the automated image analysis of plant root morphology. Inductively Coupled Plasma Spectrometry (ICP-OES) and quadrupole-time-of-flight mass spectrometry (Q-TOF) were used for ionomic and metabolic analysis, respectively. Nanofluidic real-time PCR (OpenArray system) was used for molecular profiling. OpenArray chips were designed with TaqMan probes for 53 sugar beet genes putatively involved in sulfate nutrition. At morphological level treated seedlings showed significantly higher values (P < 0.01) than untreated plants for root traits related to soil exploration and nutrient uptake, such as total root length, fine roots length and root tips number. ICP-OES, Q-TOF and transcriptomic data revealed changes due to sulfate availability in sugar beet samples. Two key results are highlighted in sulfate-supplied roots and leaves. Firstly, high expression levels of auxin efflux carrier component 1 (PIN) and 5-phosphoribosyl-anthranilate, precursor of tryptophan and auxin synthesis, were observed in roots. Secondly, high levels of 2-Cys peroxiredoxin BAS1, chloroplastic, thioredoxin reductase (NADPH) and cysteine synthase, chloroplastic/chromoplastic, O-acetylserine sulfhydrylase, involved in protection against oxidative stress and cysteine synthase activity, respectively, were observed in leaves. Based on our findings, the combination of evaluated omics approaches could become a key system for the evaluation of the nutritional status of sugar beet under different nutrient availability conditions.

Arsenic uptake and speciation and the effects of phosphate nutrition in hydroponically grown kikuyu grass (Pennisetum clandestinum Hochst).

BACKGROUND: This work focuses on the accumulation and mobility properties of arsenic (As) and the effects of phosphate (P) on its movement in Pennisetum clandestinum Hochst (kikuyu grass), grown hydroponically under increasing arsenate (As(V)) concentrations. The uptake of both ions and the relative kinetics show that phosphate is an efficient competitive inhibitor of As(V) uptake. The P/As uptake rate ratios in roots indicate that P is taken up preferentially by P/As transporters. An arsenite (As(III)) efflux from roots was also found, but this decreased when the arsenate concentration in the solution exceeded 5 µM. METHODS: Increases in both arsenite and arsenate concentrations in roots were observed when the arsenate concentration in the solution was increased, and the highest accumulation of As(III) in roots was found when plants were grown at 5 µM As(V). The low ratios of As accumulated in shoots compared to roots suggest limited mobility of the metalloid within Kikuyu plants. RESULTS: The results indicate that arsenic resistance in kikuyu grass in conditions of moderate exposure is mainly dependent on the following factors: 1) phosphate nutrition: P is an efficient competitive inhibitor of As(V) uptake because of the higher selectivity of membrane transporters with respect to phosphate rather than arsenate; and 2) a detoxification mechanism including a reduction in both arsenate and arsenite root efflux. CONCLUSIONS: The As tolerance strategy of Kikuyu limits arsenate uptake and As translocation from roots to shoots; therefore, this plant cannot be considered a viable candidate for use in the phytoextraction of arsenic from contaminated soils or water.