Eduardo Tambussi

Frequently asked questions about in vivo chlorophyll fluorescence: practical issues

The aim of this educational review is to provide practical information on the hardware, methodology, and the hands on application of chlorophyll (Chl) a fluorescence technology. We present the paper in a question and answer format like frequently asked questions. Although nearly all information on the application of Chl a fluorescence can be found in the literature, it is not always easily accessible. This paper is primarily aimed at scientists who have some experience with the application of Chl a fluorescence but are still in the process of discovering what it all means and how it can be used. Topics discussed are (among other things) the kind of information that can be obtained using different fluorescence techniques, the interpretation of Chl a fluorescence signals, specific applications of these techniques, and practical advice on different subjects, such as on the length of dark adaptation before measurement of the Chl a fluorescence transient. The paper also provides the physiological background for some of the applied procedures. It also serves as a source of reference for experienced scientists.

The Photosynthetic Role of Ears in C3 Cereals : Metabolism, Water Use Efficiency and Contribution to Grain Yield

This review concerns ear photosynthesis and its contribution to grain filling in C3 cereals. Ear photosynthesis is quantitatively important to grain filling, particularly in dry areas where source (i.e., assimilate) limitations can occur. Compared to the flag leaf, ear photosynthesis exhibits higher water stress tolerance. Several factors could be involved in the ears “drought tolerance.” First, although degree of C4 metabolism in ear parts has been reported, current evidence supports only typical C3 metabolism. Second, recycling of respired CO2 (i.e., refixation) could have considerable impact on final crop yield by preventing loss of CO2. Because refixation of CO2 is independent of atmospheric conditions, water use efficiency (measured as total ear photosynthesis divided by transpiration) could be higher in the ear than in the flag leaf. Moreover, ear parts (in particular awns) show higher relative water content and better osmotic adjustment under water stress compared to the flag leaf. This capacity, in addition to persistence of photosynthetic components under drought (delayed senescence), might help the ear to continue to fix CO2 late in the grain filling period.

Photoprotection in water-stressed plants of durum wheat (Triticum turgidum var. durum): changes in chlorophyll fluorescence, spectral signature and photosynthetic pigments

We analysed the photoprotective response in water-stressed plants of durum wheat (Triticum turgidum L. var. durum cv. Mexa). The plants were grown in a greenhouse for 4 weeks and then exposed to water stress by withholding water for 8 d. Development of water stress was monitored as the decrease in relative water content (RWC) and net CO2 assimilation of the last fully developed leaf. The photoprotective response was evaluated in the same leaves by analysing modulated chlorophyll fluorescence, leaf spectroradiometrical changes, and pigment content. Measurements were performed 3, 6 (moderate stress) and 8 (severe stress) d after water-stress treatment began. The non-photochemical quenching of chlorophyll fluorescence (qN), as well as the contents of zeaxanthin and antheraxanthin increased significantly after 6 d of treatment. However, a further rise in these xanthophylls on day 8 was not associated with any increase in qN. In addition, the β-carotene content rose significantly on day 8, suggesting an increase in antioxidant defences. The photochemical index (PI), derived from spectroradiometrical measurements, showed a strong progressive drop on days 6 and 8, which was paralleled by an increase in the de-epoxidation state of the xanthophyll cycle (DPS), in particular by the zeaxanthin content. At midday, PI was strongly (negatively) correlated with DPS and qN. These results suggest that the PI may be a reliable indicator of photoprotection in the study of plant stress, and in breeding programs.

Control of ascorbic acid synthesis and accumulation and glutathione by the incident light red/far red ratio in Phaseolus vulgaris leaves

The effects of red/far red (R/FR) ratios on leaf ascorbate (AA) and glutathione (GSH) accumulation were examined in common bean (Phaseolus vulgaris L.). Growth under low R/FR ratios resulted in a “shade” phenotype and much lower leaf AA and GSH contents than high (R/FR) ratios. Photosynthesis rates were unaffected by changes in the R/FR ratio but leaf respiration rates, pyridine nucleotide pools and antioxidant enzyme activities were decreased under the low R/FR regime. The GSH pool changed slowly in response to altered R/FR ratios but leaf ascorbate acclimated over a single photoperiod. We conclude that light quality signals, particularly R/FR ratios, are important regulators of antioxidant synthesis and accumulation. These acclimatory changes are an early response to changing light environment.

Glyphosate effects on gas exchange and chlorophyll fluorescence responses of two Lolium perenne L. biotypes with differential herbicide sensitivity.

Despite the extensive use of glyphosate, how it alters the physiology and metabolism of plants is still unclear. Photosynthesis is not regarded to be a primary inhibitory target of glyphosate, but it has been reported to be affected by this herbicide. The aim of the current research was to determine the effects of glyphosate on the light and dark reactions of photosynthesis by comparing glyphosate-susceptible and glyphosate-resistant Lolium perenne biotypes. After glyphosate treatment, accumulation of reduced carbohydrates occurred before a decrease in gas exchange. Stomatal conductance and CO(2) assimilation were reduced earlier than chlorophyll fluorescence and the amount of chlorophyll in susceptible plants. In the glyphosate-resistant biotype, stomatal conductance was the only parameter slightly affected only 5 days post-application. In susceptible plants, the initial glyphosate effects on gas exchange could be a response to a feedback regulation of photosynthesis. Since the herbicide affects actively growing tissues regardless of the inhibition of photosynthesis, the demand of assimilates decreased and consequently induced an accumulation of carbohydrates in leaves. We concluded that stomatal conductance could be a very sensitive parameter to assess both the susceptibility/resistance to glyphosate before the phytotoxic symptoms become evident.

Analysis of early vigour in twenty modern cultivars of bread wheat (Triticum aestivum L.)

Abstract. Fast development of seedling leaf area is a relevant trait in order to increase early resource acquisition. The use of semi-dwarf genotypes of wheat has decreased early vigour of modern cultivars. We studied early vigour of 20 cultivars cropped in Argentina, and our main objectives were: (i) to analyse the genotypic variability in early vigour; (ii) to study morphological traits that can be good indicators of early vigour, such as seed mass, leaf width, and specific leaf area; and (iii) to determine whether increased dry mass allocation to roots impacts negatively on early vigour. Experiments with non-size-selected and size-selected seeds were carried out in a greenhouse. A field trial was also conducted in order to test the reliability of the greenhouse results. Seeds mass was the main parameter related to early vigour. However, results from the experiment with seeds selected by size (45–50 mg seed–1) showed that seed mass per se only partially explains early vigour, since a significant coefficient of determination was observed between the seedling leaf area of each cultivar in both experiments (i.e. with randomly chosen or size-selected seeds). We observed a high coefficient of determination between net assimilation rate and changes in the ranking of early vigour of the cultivars with time after transplant. Root biomass was positively correlated with leaf area, indicating that the traits were not mutually exclusive. We built simple models by multiple regression to predict early vigour, including some parameters that were easy to measure. Seed mass and leaf width taken together showed better fit than seed mass or leaf width alone. We found a significant coefficient of determination between early vigour in greenhouse and field experiments; thus, screening for early vigour under semi-controlled conditions may be feasible.

Dry mass partitioning and nitrogen uptake by Eucalyptus grandis plants in response to localized or mixed application of phosphorus

Plants respond to nutrient rich patches by changing root morphology and physiology. The aim of this paper was to analyze shoot and root growth of Eucalyptus grandis plants fertilized with the same amount of phosphorus applied in two different ways: thoroughly mixed in the soil or localized in a single hole near the plant. Localized fertilization increased root mass in the zone where fertilizer was applied, but total root mass was not altered by the type of fertilization application. With mixed fertilization plant growth was less than with localized fertilization, and plants showed nitrogen deficiency. Nitrogen uptake was measured in a split-root hydroponics system where phosphate was applied to the whole root system or in part of it. Growth of plants receiving phosphorus in the whole root system was limited by nitrogen uptake, as was revealed by low leaf N and low nitrate uptake. In conclusion, the positive effect of localized application of phosphorus must be ascribed not only to higher phosphorus but also to sustained nitrogen assimilation.

Erratum to: Frequently asked questions about chlorophyll fluorescence, the sequel

Hazem M. Kalaji1 · Gert Schansker2 · Marian Brestic3 · Filippo Bussotti4 · Angeles Calatayud5 · Lorenzo Ferroni6 · Vasilij Goltsev7 · Lucia Guidi8 · Anjana Jajoo9 · Pengmin Li10 · Pasquale Losciale11 · Vinod K. Mishra12 · Amarendra N. Misra13 · Sergio G. Nebauer14 · Simonetta Pancaldi6 · Consuelo Penella5 · Martina Pollastrini4 · Kancherla Suresh15 · Eduardo Tambussi16 · Marcos Yanniccari16 · Marek Zivcak3 · Magdalena D. Cetner1 · Izabela A. Samborska1 · Alexandrina Stirbet17 · Katarina Olsovska18 · Kristyna Kunderlikova18 · Henry Shelonzek19 · Szymon Rusinowski20 · Wojciech Bąba21

Photosynthetic limitations and yield potential in two barley genotypes (Hordeum vulgare L.) subjected to drought

The photosynthetic productivity of plants is determined by the quantity of photosynthetically active radiation intercepted and the efficiency with which it is utilised for net dry matter production. We examine the effects of drought on the photosynthetic capacity of five durum wheat (Triticum turgidum L. var durum) genotypes, grown in a greenhouse. Drought was imposed on five-week-old plants by withholding water. During the onset of water stress, the response of net carbon assimilation by leaves to their intercellular CO2 concentration (A/ci curves, with an LICOR 6400, NB, USA) was measured to examine the limitation imposed by stomata (l), carboxylation velocity (Vc,max) and capacity for ribulose-1,5-bisphosphate regeneration (Jmax) on photosynthesis. Furthermore, simultaneous measurements of modulated chlorophyll fluorescence (MiniPAM, Walz, Effeltrich, Germany) were used to identify changes in the efficiency of light utilisation for electron transport and the occurrence of photoinhibition of photosystem II. At moderated water stress (y w » -1 MPa and RWC ³ 65%), the light-saturated net CO2 assimilation rate (Asat) decreased by ca. 56% in water-stressed plants of all genotypes, accompanied by decreases in Vc,max and Jmax by ca. 35% and 45%, respectively, and increases in stomatal limitation (by ca. 30%), indicating inactivation or loss of Rubisco and other key Calvin cycle enzymes (i.e. sedoheptulose-1,7-bisphosphate), and stomatal closure. As water-stress progressed (y w £ -2 MPa and RWC £ 65%), further decreases were found in Asat accompanied with large decreases on in Vc,max and Jmax (and increases in stomatal limitation) for all varieties. The exponential decline of Asat vs. y w were fitted by non-linear regression using the model y = a*e-b(x), where b can be taken as an index of sensitivity to drought. However, no significant differences were found in this parameter for any genotype studied. Furthermore, decreases in the quantum yield of photosystem II were accompanied with decreases in the efficiency of energy capture by open PSII reaction centres (Fv?/Fm?) without major changes in the photochemical quenching (qp) in water-stressed plants of all varieties, indicating down regulation of electron transport.