Impact of nitrogen supply on growth, steviol glycosides and photosynthesis in Stevia rebaudiana Bertoni

This work investigated the agronomic, physiological and biochemical response of Stevia rebaudiana Bertoni grown under different nitrogen (N) rates. A pot trial in open air conditions was set up in 2012 with the aim to evaluate the effect of four N rates on the biometric and productive characteristics, steviol glycoside (SG) content as well as on leaf gas exchanges, chlorophyll fluorescence, photosynthetic pigments, Rubisco activity and N use efficiency. N deficiency caused a decrease in leaf N content, chlorophylls and photosynthetic CO2 assimilation, resulting in a lower dry matter accumulation as well as in reduced SG production. The application of 150 kgNha21 seems to be the most effective treatment to improve rebaudioside A (Reb A) content, Reb A/stevioside ratio, photosynthetic CO2 assimilation, stomatal conductance, N use efficiency, ribulose-1,5-bis-phosphate carboxylase/oxygenase (Rubisco) and PSII efficiency. The results demonstrate that by using an appropriate N rate it is possible to modulate the SG biosynthesis, with a significant increase in the Reb A content and in the ratio between Reb A and stevioside. This finding is of great relevance in order to obtain a raw material designed to meet consumer needs and bio-industry requirements for high-quality, Reb A content, and safe and environmentally friendly products

Agronomical evaluation and chemical characterization of Linum usitatissimum L. as oilseed crop for bio-based products in two environments of Central and Northern Italy

In the recent years, new perspectives for linseed (Linum usitatissimum L.) are open as renewable raw material for bio-based products (Bb), due to its oil composition, and the interesting amounts of coproducts (lignocellulosic biomass). Therefore, the possibility to introduce linseed crop in two environments of central and northern Italy, traditionally devoted to cereal cultivation, has been evaluated. Twoyears field trials were carried out in the coastal plain of Pisa (Tuscany region) and in the Po valley (Bologna, Emilia Romagna region), comparing two linseed varieties (Sideral and Buenos Aires). Agronomical evaluation (yield and yield components), seed and oil characterization (oil, protein content, and fatty acid composition), together with carbon (C) and nitrogen (N) content of the residual lignocellulosic biomass were investigated. The two varieties, grown as autumn crop, showed a different percentage of plant survival at the end of winter, with Sideral most resistant to cold. The achieved results showed significant influence of cultivar, location and growing season on yield and yield components, as well as on chemical biomass composition. In particular, Sideral appeared to be the most suitable variety for tested environments, since higher seed yield (3.05 t ha–1 as mean value over years and locations) and above-ground biomass (6.98 t ha–1 as mean value over years and locations) were recorded in comparison with those detected for Buenos Aires (1.93 and 4.48 t ha–1 of seed production and lignocellulosic biomass, respectively). Interestingly, in the northern area, during the 1st year, Buenos Aires was the most productive, despite its low plant survival at the end of winter, which determined a strong reduction in plant density and size. In such conditions, the plants produced a larger number of capsules and, consequently, high seed yield (3.18 t ha–1). Relevant differences were also observed between the two years, due to the variability of climatic characteristics (temperature levels, and moisture regimes). All these findings confirmed as, in linseed, yield and yield components are quantitatively inherited and influenced by both genotype and environment (location and climate). Varietal and environmental effects were also recorded for oil content and yield, and, generally, good oil percentages, for both genotypes, were found (ranging from 44 to 49% on dry matter basis). Oil from the two varieties was characterized by a stable proportion of polyunsaturated fatty acids with a high content of alpha-linolenic acid (more than 57%), that makes this oil suitable to be used in paints, resins, varnishes, linoleum, polymers and oleochemicals. Finally, our results pointed out as above- and below-ground biomasses, were different in terms of quantity, and chemical characteristics (N, C and C/N ratio). Interesting amounts of N and C could return into the soil by crop residues (stem portions and roots), thus underling the possibility to maintain and/or increase the soil organic matter pool

Ramie fibers in a comparison between chemical and microbiological retting proposed for application in biocomposites

Due to light weight, renewability, sustainability and generally moderate costs, natural fibers are addressed for the production of composites for application in packaging, automotive and other indus- tries. Several approaches are under investigation to improve compatibility with polymer matrices and improve mechanical performances of composites with natural fibers. The retting process is the major limitation to efficient and high-quality natural fiber production. The conventional retting is normally done chemically by treatment of decorticated fibers with hot alkaline solutions. Such a process requires high energy input and produces hazardous wastes. Microbiological and enzymatic methods represent a reliable replacement, however their application on ramie (Boehmeria nivea (L.) Gaud.) has not yet been optimized and tuned for use on a large scale. Consequently, the aim of this work was to evaluate the role of microbiological retting on the morphological, chemical and physical–mechanical properties of the derived ramie fibers for application in biocomposites. The decorticated ramie fibers, obtained by mature crop stands grown at the experimental station of the Department of Agriculture, Food and Environment (DAFE) of the University of Pisa, were subjected to a water based microbiological degumming performed with the use of two selected strains of Clostridium felsineum L. at 30◦C for 7 days. The results obtained with this method were compared with those recorded adopting the conventional chemical process with NaOH water solution at 100 ◦ C for 2 h. The morphological, chemical (hemicellulose, cellulose, lignin and ash) and physico-mechanical (tensile strength, elastic modulus and elongation at break) properties of retted ramie fibers were investigated. The fibers produced were evaluated for the production of compos- ites by using polyhydroxyalkanoates (PHAs) as polymeric matrix, as targeted in the EC running project OLI-PHA. Significant differences were observed between the two types of degumming in terms of yield and quality of the fibers. Even if the highest fiber yields were recorded with chemical retting, the perfor- mances of fibers modified by microbiological treatments were comparable with those of the composite prepared with fibers modified by chemical treatment. Scanning electron microscopy analysis revealed a good removal of non-cellulosic gummy material from the surface of ramie fibers. According to the mechanical properties, the ramie fibers obtained by both degumming processes, were suitable for use in PHAs composites

The positive role of steviol glycosides in stevia (Stevia rebaudiana Bertoni) under drought stress condition

Steviol glycosides (SVglys) are a group of diterpenoids mainly present in the leaves of stevia (Stevia rebaudiana Bertoni). An experiment was conducted to find the functional role of SVglys compounds in stevia affected by drought stress. In this study, a liquid blend of SVglys (200 ppm) was sprayed on stevia plants grown in well-watered (90% field capacity) and drought-stress conditions (45% field capacity) and then the morphological traits and metabolites were evaluated. It was observed that leaf losses caused by drought stress were stopped through external application of SVglys and consequently the harvest index of stevia was increased. Metabolite analysis of stevia leaves showed that the total SVglys content was significantly decreased due to drought stress, but was compensated by external application of SVglys. Among the SVglys, Rebaudioside A responded more to external SVglys. A slight promotion in total antioxidant activity of stevia leaves was observed when external SVglys was applied. The glucose availability in stevia leaves was increased by external application of SVglys but only in well-watered plants. According to our findings, it can be concluded that in stevia, SVglys may have a positive function in drought stress tolerance by exerting a protective role under such conditions

Plant growth retardants (PGRs) affect growth and secondary metabolite biosynthesis in Stevia rebaudiana Bertoni under drought stress

Abstract Beyond the inhibitory action against the gibberellin biosynthesis, some plant growth retardants (PGRs) can play an important role in regulating plant responses to abiotic stress through the induction of different tolerance mechanisms. The aim of the present study was the exploitation of the potential of PGRs in enhancing the resistance to drought stress in Stevia rebaudiana Bert. Therefore, the effects of three PGRs on stevia plants grown under drought stress condition were investigated. Stevia plants were first subjected to water stress and, second, treated with PGRs to detect PGRs effect on biometric, productive and phytochemical characteristics of drought stressed-plants. The control plants were uniformly irrigated at 3-day intervals, while water-stress conditions were imposed by watering the plants at 12-day intervals. Subsequently, the Chlorocholine chloride (CCC, as Copalyl diphosphate synthase inhibitor and Kaurene synthase inhibitor), Paclobutrazol (PBZ, as Kaurene oxidase inhibitor) and Daminozide (DAM, as anti-gibberellins) were applied in drought stressed-plants. The CCC and DAM were sprayed on stevia shoots, while PBZ was drenched. The obtained results showed that leaf dry weight of stevia plants was significantly reduced by drought stress, but this parameter increased as a consequence of CCC and PBZ treatments. Drought stress also caused a significant reduction in total steviol glycoside (SVglys) content. This reduction was more pronounced in drought stressed-plants treated with CCC, while PBZ was able to counteract the SVglys reduction, with SVgly content similar to that observed in the control. Similarly, PBZ was able to increase the soluble sugar production and total antioxidant capacity in the leaves of stressed-stevia plants. These findings suggested that CCC and, in particular, PBZ had a protective effect on stevia growth under drought stress by induction of antioxidant defenses and soluble sugar production. CCC seems to inhibit gibberellin biosynthesis, preventing the SVglys production, while DAM and PBZ, as gibberellin inhibitors, didn't have a negative effect on SVglys production in drought stressed-plants. This observation seems to emphasize their role in limiting the rate of target enzymes of CCC in SVglys biosynthetic pathway. Moreover, the induction of glucose production, as a substrate for SVglys biosynthesis, could be a convincing evidence for SVglys promotion in PBZ treated-plants

Unmanned aerial vehicle to estimate nitrogen status of turfgrasses

Spectral reflectance data originating from Unmanned Aerial Vehicle (UAV) imagery is a valuable tool to monitor plant nutrition, reduce nitrogen (N) application to real needs, thus producing both economic and environmental benefits. The objectives of the trial were i) to compare the spectral reflectance of 3 turfgrasses acquired via UAV and by a ground-based instrument; ii) to test the sensitivity of the 2 data acquisition sources in detecting induced variation in N levels. N application gradients from 0 to 250 kg ha-1 were created on 3 different turfgrass species: Cynodon dactylon x transvaalensis (Cdxt) Patriot, Zoysia matrella (Zm) Zeon and Paspalum vaginatum (Pv) Salam. Proximity and remote-sensed reflectance measurements were acquired using a GreenSeeker handheld crop sensor and a UAV with onboard a multispectral sensor, to determine Normalized Difference Vegetation Index (NDVI). Proximity-sensed NDVI is highly correlated with data acquired from UAV with r values ranging from 0.83 (Zm) to 0.97 (Cdxt). Relating NDVI-UAV with clippings N, the highest r is for Cdxt (0.95). The most reactive species to N fertilization is Cdxt with a clippings N% ranging from 1.2% to 4.1%. UAV imagery can adequately assess the N status of turfgrasses and its spatial variability within a species, so for large areas, such as golf courses, sod farms or race courses, UAV acquired data can optimize turf management. For relatively small green areas, a hand-held crop sensor can be a less expensive and more practical option

Anti-nutritive constituents in oilseed crops from Italy

Eight different oilseed crops (Brassica carinata, Camelina sativa, Coriandrum sativum, Euphorbia lagascae, Lepidium sativum, Lesquerella fendleri, Madia sativa, Vernonia galamensis) grown in Italy were investigated regarding anti-nutritive compounds, such as glucosinolates, sinapine, inositol phosphates and condensed tannins, which can adversely affect the nutritional value of residues from the oilseed processing. In all seeds at least one anti-nutritive compound was found, which possibly could lower the nutritive value, but in most cases a real negative effect is not to be expected. The existence and the concentration of the different anti-nutritive components varied in the different seeds. Glucosinolates and sinapine were found only in seeds of B. carinata, L. sativum, C. sativa and L. fendleri, whereas condensed tannins and inositol phosphates appeared in all seeds. In the different seeds the amount ranged from 0.2 mg/g (L. fendleri) to 13.1 mg/g (L. sativum) for sinapine, from 0.4 mg/g (E. lagascae) to 19.6 mg/g (L. fendleri) for condensed tannins, from 6.6 mg/g (E. lagascae) to 23.1 mg/g (B. carinata) for inositol hexa-phosphate as well as from 18.7 μmol/g (C. sativa) to 164.6 μmol/g (L. sativum) for glucosinolates