Marco Lauteri

Leaf gas exchange, carbon isotope discrimination, and grain yield in contrasting rice genotypes subjected to water deficits during the reproductive stage

Genotypic variations in leaf gas exchange and yield were analysed in five upland-adapted and three lowland rice cultivars subjected to a differential soil moisture gradient, varying from well-watered to severely water-stressed conditions. A reduction in the amount of water applied resulted in a significant decrease in leaf gas exchange and, subsequently, in above-ground dry mass and grain yield, that varied among genotypes and distance from the line source. The comparison between the variable J and the Delta values in recently synthesized sugars methods, yielded congruent estimations of mesophyll conductance (g(m)), confirming the reliability of these two techniques. Our data demonstrate that g(m) is a major determinant of photosynthesis (A), because rice genotypes with inherently higher g(m) were capable of keeping higher A in stressed conditions. Furthermore, A, g(s), and g(m) of water-stressed genotypes rapidly recovered to the well-watered values upon the relief of water stress, indicating that drought did not cause any lasting metabolic limitation to photosynthesis. The comparisons between the A/C(i) and corresponding A/C(c) curves, measured in the genotypes that showed intrinsically higher and lower instantaneous A, confirmed this finding. Moreover, the effect of drought stress on grain yield was correlated with the effects on both A and total diffusional limitations to photosynthesis. Overall, these data indicate that genotypes which showed higher photosynthesis and conductances were also generally more productive across the entire soil moisture gradient. The analysis of Delta revealed a substantial variation of water use efficiency among the genotypes, both on the long-term (leaf pellet analysis) and short-term scale (leaf soluble sugars analysis).

Xanthophyll cycle components and capacity for non-radiative energy dissipation in sun and shade leaves ofLigustrum ovalifolium exposed to conditions limiting photosynthesis.

The relationships between photosynthetic efficiency, non-radiative energy dissipation and carotenoid composition were studied in leaves ofLigustrum ovalifolium developed either under full sunlight or in the shade. Sun leaves contained a much greater pool of xanthophyll cycle components than shade leaves. The rate of non-radiative energy dissipation, measured as non-photochemical fluorescence quenching (NPQ), was strictly related to the deepoxidation state (DPS) of xanthophyll cycle components in both sun and shade leaves, indicating that zeaxanthin (Z) and antheraxanthin (A) are involved in the development of NPQ. Under extreme conditions of excessive energy, sun leaves showed higher maximum DPS than shade leaves. Therefore, sun leaves contained not only a greater pool of xanthophyll cycle components but also a higher proportion of violaxanthin (V) actually photoconvertible to A and Z, compared to shade leaves. Both these effects contributed to the higher NPQ in sun versus shade leaves. The amount of photoconvertible V was strongly related to chla/b ratio and inversely to leaf neoxanthin content. This evidence indicates that the amount of photoconvertible V may be dependent on the degree of thylakoid membrane appression and on the organization of chlorophyll-protein complexes, and possible explanations are discussed. Exposure to chilling temperatures caused a strong decline in the photon yield of photosynthesis and in the intrinsic efficiency of PS II photochemistry in sun leaves, but little effects in shade leaves. These effects were accompanied by increases in the pool of xanthophyll cycle components and in DPS, more pronounced in sun than in shade leaves. This corroborates the view that Z and A may play a photoprotective role under unfavorable conditions. In addition to the xanthophyll-related non-radiative energy dissipation, a slow relaxing component of NPQ, independent from A and Z concentrations, has been found in leaves exposed to low temperature and high light. This quenching component may be attributed either to other regulatory mechanism of PS II efficiency or to photoinactivation.

Stable Isotope Analysis

Abstract Reports on analytical methods for determining the geographical origin of agricultural products have been increasing since the 1980s [49] . The development of new techniques is highly desirable for consumers, agricultural farmers, retailers and administrative authorities. Various analytical techniques have been studied based on organic constituents, mineral composition, light- and heavy-element isotope ratios or combinations thereof. The analytical techniques that have been applied for the geographical origin discrimination of food may be subdivided into several groups, mainly including spectroscopic techniques and separation techniques. In general, mass spectrometry (MS) is applied to elucidate the composition of a sample by generating spectral information of the components and can be combined with other techniques. For instance, isotope ratio mass spectrometry (IRMS) is a technique that can distinguish chemically identical compounds based on their isotope content. Continuous flow IRMS (CF-IRMS) is the most common type of IRMS used in food analysis. The CF-IRMS offers online sample preparation and the possibility of interfacing with other preparation techniques, including elemental analysis, gas chromatography and high-performance liquid chromatography. In this chapter, IRMS techniques are described on the scope of food analysis, focussing on important aspects ranging from the recommended terms for the expression of stable isotope ratio measurement results to the principles and techniques of IRMS. Special consideration is given to sample preparation procedures for IRMS analysis and to the work with international stable isotope reference materials. Finally, the most recent developments and applications of this MS technique in food traceability are also addressed.

Photosynthetic diffusional constraints affect yield in drought stressed rice cultivars during flowering.

Global production of rice (Oryza sativa) grain is limited by water availability and the low ‘leaf-level’ photosynthetic capacity of many cultivars. Oryza sativa is extremely susceptible to water-deficits; therefore, predicted increases in the frequency and duration of drought events, combined with future rises in global temperatures and food demand, necessitate the development of more productive and drought tolerant cultivars. We investigated the underlying physiological, isotopic and morphological responses to water-deficit in seven common varieties of O. sativa, subjected to prolonged drought of varying intensities, for phenotyping purposes in open field conditions. Significant variation was observed in leaf-level photosynthesis rates (A) under both water treatments. Yield and A were influenced by the conductance of the mesophyll layer to CO2 (g m) and not by stomatal conductance (g s). Mesophyll conductance declined during drought to differing extents among the cultivars; those varieties that maintained g m during water-deficit sustained A and yield to a greater extent. However, the variety with the highest g m and yield under well-watered conditions (IR55419-04) was distinct from the most effective cultivar under drought (Vandana). Mesophyll conductance most effectively characterises the photosynthetic capacity and yield of O. sativa cultivars under both well-watered and water-deficit conditions; however, the desired attributes of high g m during optimal growth conditions and the capacity for g m to remain constant during water-deficit may be mutually exclusive. Nonetheless, future genetic and physiological studies aimed at enhancing O. sativa yield and drought stress tolerance should investigate the biochemistry and morphology of the interface between the sub-stomatal pore and mesophyll layer.

Carbon Isotope Discrimination in Leaf Soluble Sugars and in Whole-Plant Dry Matter in Helianthus annuus L. Grown under Different Water Conditions

Publisher Summary The fractionation of carbon isotopes during photosynthesis involves biochemical and physical processes and is strongly influenced by the environment. Carbon isotope discrimination in whole-plant dry matter represents a long-term integration of the ratio of intercellular to atmospheric partial pressure of CO2 (pi/pa) and consequently of photosynthetic plant transpiration efficiency (W) over the entire plant life cycle. This chapter discusses the possibility of assessing W on different time scales, using the analysis of carbon isotope discrimination in whole-plant dry matter and in leaf soluble sugars. Water-use efficiency and growth characteristics were measured in four sunflower Helianthus annum L. genotypes exposed to either well-watered or drought conditions. The effects of drought on several physiological parameters including gas exchange characteristics, photosystem II photochemical efficiency, photosynthetic capacity, and short-term and long-term carbon isotope fractionation were studied to detect adaptive responses and to determine stomatal and nonstomatal limitations of photosynthesis.

Administration of recombinant human growth hormone on alternate days is sufficient to increase whole body protein synthesis and lipolysis in growth hormone deficient adults

At present, the duration of the effect of recombinant human growth hormone (rhGH) on the rates of protein synthesis and lipolysis in GH deficient (GHD) adults is unknown. This study was designed to establish the frequency of rhGH administration necessary to provide the beneficial metabolic effects of the hormone in GHD adults.

Authentication and traceability of Italian extra-virgin olive oils by means of stable isotopes techniques

Authentication of food origin is relevant to avoid food fraud. This work aimed to explore the variation of isotopic compositions (δ(13)C, δ(18)O) of extra-virgin olive oils from Italy growing in different environmental conditions. A total of 387 oil samples from nine different regions (from North to South), produced on 2009, 2010 and 2011, were analysed. Statistical analysis showed correlations among oil isotope compositions and latitude, mean annual temperature, mean annual precipitation and xerothermic index. No correlation was found comparing isotope compositions with elevation and longitude. An observed shift of the oil δ(18)O per centigrade degree of the mean annual temperature is congruent with literature. The year effect was significant for both δ(18)O and δ(13)C. Samples from Sicilia and Sardegna were higher in (13)C and (18)O than oils from northern regions.

Comparing integrated stable isotope and eddy covariance estimates of water-use efficiency on a Mediterranean successional sequence

Water-use efficiency (WUE), thought to be a relevant trait for productivity and adaptation to water-limited environments, was estimated for three different ecosystems on the Mediterranean island of Pianosa: Mediterranean macchia (SMM), transition (STR) and abandoned agricultural (SAA) ecosystems, representing a successional series. Three independent approaches were used to study WUE: eddy covariance measurements, C isotope composition of ecosystem respired CO2, and C isotope discrimination (Δ) of leaf material (dry matter and soluble sugars). Seasonal variations in C–water relations and energy fluxes, compared in SMM and in SAA, were primarily dependent on the specific composition of each plant community. WUE of gross primary productivity was higher in SMM than in SAA at the beginning of the dry season. Both structural and fast-turnover leaf material were, on average, more enriched in 13C in SMM than SAA, indicating relatively higher stomatal control and WUE for the long-lived macchia species. This pattern corresponded to 13C-enriched respired CO2 in SMM compared to the other ecosystems. Conversely, most of the annual herbaceous SAA species (terophytes) showed a drought-escaping strategy, with relatively high stomatal conductance and low WUE. An ecosystem-integrated Δ value was weighted for each ecosystem on the abundance of different life forms, classified according to Raunkiar’s system. Agreement was found between ecosystem WUE calculated using eddy covariance and those estimated using integrated Δ approaches. Comparing the isotopic methods, Δ of leaf soluble sugars provided the most reliable proxy for short-term changes in photosynthetic discrimination and associated shifts in integrated canopy-level WUE along the successional series.

The impact of winter flooding with saline water on foliar carbon uptake and the volatile fraction of leaves and fruits of lemon (Citrus × limon) trees

We investigated the consequences of recurrent winter flooding with saline water on a lemon (Citrus×limon (L.) Burm.f.) orchard, focussing on photosynthesis limitations and emission of secondary metabolites (isoprenoids) from leaves and fruits. Measurements were carried out immediately after flooding (December), at the end of winter (April) and after a dry summer in which plants were irrigated with optimal quality water (September). Photosynthesis was negatively affected by flooding. The effect was still visible at the end of winter, whereas the photosynthetic rate was fully recovered after summer, indicating an unexpected resilience capacity of flooded plants. Photosynthesis inhibition by flooding was not due to diffusive limitations to CO2 entry into the leaf, as indicated by measurements of stomatal conductance and intercellular CO2 concentration. Biochemical and photochemical limitations seemed to play a more important role in limiting the photosynthesis of flooded plants. In young leaves, characterised by high rates of mitochondrial respiration, respiratory rates were enhanced by flooding. Flooding transiently caused large and rapid emission of several volatile isoprenoids. Emission of limonene, the most abundant compound, was stimulated in the leaves, and in young and mature fruits. Flooding changed the blend of emitted isoprenoids, but only few changes were observed in the stored isoprenoids pool.

An Evaluation of the Effect of Salinity on Photosynthesys

Exposure to salinity causes large effects on higher plants, both halophytes and glycophytes. In glycophytes the rate of photosynthetic CO2 assimilation (A) is generally reduced by salinity. This reduction has been partly attributed to stomatal closure (e.g.: 1, 2). Salt induced non-stomatal: inhibition of photosynthesis has also been observed in several plant species (2, 3, 4, 5, 6). This inhibition has been attributed to a reduction in the activity of ribulose-1,5-bisphosphate (RuBP) carboxylase when RuBP is in limiting supply (6), to reduced RuBP regeneration capacity (5, 6), or to the sensitivity of photosystem II (PSII) to NaCl (7).