Lucia Guidi

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 effect of nitrogen deficiency on leaf gas exchange and chlorophyll fluorescence parameters in sunflower

Abstract Fully expanded leaves of sunflower ( Helianthus annuus L.) growing with either complete or nitrogen-deficient nutrition solution were analysed for gas exchange and chlorophyll fluoresence after 24 days from the transplanting. Under N-stress the decline in photosynthesis and the rise in stomatal conductance determined at light saturation level were accompanied by an increase of the intercellular CO 2 concentration (about +60%). This indicates that the decline in A max (photosynthetic activity at light saturation level) was due to limitation related to a reduced mesophyllic activity, rather than to stomatal limitation. At low light intensity photosynthetic efficiency of PSII was not affected. In N-stressed plants starch content decreased significantly in leaves. The sucrose/starch ratio rose in N-stressed plants, indicating that the carbon partitioning trend had shifted towards sucrose. This result is in accordance with the lower shoot/root ratio observed in nitrogen-stressed plants.

Arabidopsis thaliana MYB75/PAP1 transcription factor induces anthocyanin production in transgenic tomato plants

Tomato (Solanum lycopersicum L.) cv. Micro-Tom plants were transformed with the Arabidopsis thaliana (L.)Heyhn. MYB75/PAP1 (PRODUCTION OF ANTHOCYANIN PIGMENT 1) gene. This gene encodes for a well known transcription factor, which is involved in anthocyanin production and is modulated by light and sucrose. Transgenic tomato plants expressing AtMYB75 were characterised by a significantly higher anthocyanin production in leaves, stems, roots and flowers under normal growth conditions. Further, they also exhibited anthocyanins in fruits. Anthocyanin accumulation was not widespread but took place in specific groups of cells located in epidermal or cortical regions or in proximity of vascular bundles. In all the organs of the transgenic plants, where AtMYB75 overexpression was determined, a clear increase in the accumulation of DFR (DIHYDROFLAVONOL 4-REDUCTASE) transcript was also detected. The expression of the tomato MYB-gene ANT1 (ANTHOCYANIN1), which had previously been identified as a transcriptional endogenous regulator of anthocyanin biosynthesis, was not altered. The higher basal content of anthocyanins in the leaves of the transgenic plants could be further increased in the presence of high light conditions and contributed to mitigate photobleaching damages under high irradiance.

Effect of chronic ozone fumigation on the photosynthetic process of poplar clones showing different sensitivity.

Rooted cuttings from two poplar clones (Populus x euramericana, I-214, and Populus deltoides x maximowiczii, Eridano) were exposed for 15 days to diurnal square-wave treatment with ozone (60 nL L-1 for 5 h day-1). Completely fully expanded leaves exposed to ozone showed a reduction in net CO2 assimilation rate as compared to the control leaves during whole exposure period in both the clones. The reduction was related to a strong stomatal closure in clone I-214, but also to an altered mesophyll activity ascribed to limitation of the dark reactions of photosynthetic process. The results obtained in leaves of I-214 subjected to long-term fumigation seem to support the view that the decrease in quantum yield of electron transport may be a mechanism to down-regulate photosynthetic electron transport so that production of ATP and NADPH would be in equilibrium with the decreased demand in the Calvin cycle. In Eridano the CO2 assimilation was reduced because of the exposure and any alteration in stomatal conductance was observed. Thus, chlorophyll fluorescence parameters showed that an inhibition of photosystem II had occurred (reduction in Fv/Fm ratio), while no alterations in quenching parameters were observed upon illumination. The results seem to indicate that an alternative sink for reducing equivalent, other than carbon metabolism is present.

The effect of salinity on photosynthetic activity in potassium-deficient barley species

The interactive effects of salinity and potassium deficiency on the growth, mineral elements and photosynthetic performance were investigated in wild (Hordeum maritimum L.) and cultivated barley (Hordeum vulgare L. var. Manel). At 28 d of growth, plants were treated with 3 mM K and 0 mM NaCl (3-0); 3 mM K and 100 mM NaCl (3-100); 0 mM K and 0 mM NaCl (0-0), 0 mM K and 100 mM NaCl (0-100) for 14 d. In both species, biomass production decreased considerably when the two constraints were applied simultaneously. Salinity affected shoots more than roots, whereas for potassium deficiency, the reverse occurred. Generally, potassium uptake was more affected in wild than in cultivated barley and, independent of potassium availability, 100 mM NaCl increased Na+ content in both species, whereas K+ deprivation increased Na(+) content only in H. maritimum shoots (0-0). Potassium-use efficiency (KUE) increased in all treated plants. Potassium deficiency increased the negative effects induced by salt in the photosynthetic process of H. vulgare, and this species seemed to be unable to counteract the negative effects of salinity. H. maritimum showed limitation in CO2 photoassimilation, but this species displayed mechanisms that play a role in avoiding PSII photodamage aimed to dissipate the excess energy.

Drought stress has contrasting effects on antioxidant enzymes activity and phenylpropanoid biosynthesis in Fraxinus ornus leaves: an excess light stress affair?

The experiment was conducted using Fraxinus ornus plants grown outside under full sunlight irradiance, and supplied with 100% (well-watered, WW), 40% (mild drought, MD), or 20% (severe drought, SD) of the daily evapotranspiration demand, with the main objective of exploring the effect of excess light stress on the activity of antioxidant enzymes and phenylpropanoid biosynthesis. Net CO₂ assimilation rate at saturating light and daily assimilated CO₂ were significantly smaller in SD than in WW and MD plants. Xanthophyll-cycle pigments supported nonphotochemical quenching to a significantly greater extent in SD than in MD and WW leaves. As a consequence, the actual efficiency of PSII (Φ(PSII)) was smaller, while the excess excitation-energy in the photosynthetic apparatus was greater in SD than in WW or MD plants. The concentrations of violaxanthin-cycle pigments relative to total chlorophyll (Chl(tot)) exceeded 200 mmol mol⁻¹ Chl(tot) in SD leaves at the end of the experiment. This leads to hypothesize for zeaxanthin a role not only as nonphotochemical quencher, but also as chloroplast antioxidant. Reductions in ascorbate peroxidase and catalase activities, as drought-stress progressed, were paralleled by greater accumulations of esculetin and quercetin 3-O-glycosides, both phenylpropanoids having effective capacity to scavenge H₂O₂. The drought-induced accumulation of esculetin and quercetin 3-O-glycosides in the vacuoles of mesophyll cells is consistent with their putative functions as reducing agents for H₂O₂ in excess light-stressed leaves. Nonetheless, the concentration of H₂O₂ and the lipid peroxidation were significantly greater in SD than in MD and WW leaves. It is speculated that vacuolar phenylpropanoids may constitute a secondary antioxidant system, even on a temporal basis, activated upon the depletion of primary antioxidant defences, and aimed at keeping whole-cell H₂O₂ within a sub-lethal concentration range.

Bilingualism provides a neural reserve for aging populations.

It has been postulated that bilingualism may act as a cognitive reserve and recent behavioral evidence shows that bilinguals are diagnosed with dementia about 4-5 years later compared to monolinguals. In the present study, we investigated the neural basis of these putative protective effects in a group of aging bilinguals as compared to a matched monolingual control group. For this purpose, participants completed the Erikson Flanker task and their performance was correlated to gray matter (GM) volume in order to investigate if cognitive performance predicts GM volume specifically in areas affected by aging. We performed an ex-Gaussian analysis on the resulting RTs and report that aging bilinguals performed better than aging monolinguals on the Flanker task. Bilingualism was overall associated with increased GM in the ACC. Likewise, aging induced effects upon performance correlated only for monolinguals to decreased gray matter in the DLPFC. Taken together, these neural regions might underlie the benefits of bilingualism and act as a neural reserve that protects against the cognitive decline that occurs during aging.

Growth and photosynthesis of Lycopersicon esculentum (L.) plants as affected by nitrogen deficiency

Fully expanded leaves of tomato (Lycopersicon esculentum) growing with either complete or nitrogen-deficient nutrient solution were analysed for leaf water status, gas exchange and chlorophyll fluorescence during the vegetative and reproductive phases. N-deficiency did not affect leaf water relations but did decrease light saturated photosynthetic rate as well as stomatal conductance in the vegetative stage. A lower variable to maximum fluorescence ratio (Fv/Fm) was found in N-limited plants which also showed an increase in leaf starch content and in starch to sucrose ratio. The inhibition of photosynthesis and the alteration of photosynthates partitioning were responsible for the growth reduction in N-stressed plants. During the reproductive phase the limitation of photosynthesis may be due to a large accumulation of starch which determines both a decrease in the carbon demand from the sinks and a decrease in CO2 conductance in the mesophyll.

Photosynthetic response of tomato plants to vascular wilt diseases

Greenhouse experiments were conducted to study the chronology of effects on gas exchange and chlorophyll-a fluorescence, visible symptoms and hyphal colonization in plants of the susceptible tomato cultivar Bonny Best inoculated with tracheomycotic fungi Fusarium oxysporum f. sp. lycopersici or Verticillium albo-atrum. The net photosynthetic rates and related parameters of healthy (uncolonized and asymptomatic) leaves of infected plants were affected by both the parasites. In the first uncolonized leaf, net photosynthesis was depressed in different ways: in Fusarium-infected individuals, the maximum detrimental effect was observed a week after inoculation, while in Verticillium-infected plants the most severe depression was detected 21 days after inoculation. The behaviour of the physiological parameters investigated, together with the data relative to chlorophyll fluorescence measurements highlighted the fact that the depression in photosynthetic activity was caused by different concomitant factors in Verticillium-infected plants and was due mainly to drought stress in plants inoculated with Fusarium.

Screening of bean cultivars for their response to ozone as evaluated by visible symptoms and leaf chlorophyll fluorescence.

Fourteen Italian cultivars of Phaseolus vulgaris were exposed to a single pulse of ozone (O(3), 150 nl l(-1)) or to filtered air (<3 nl l(-1)) for 3.5 h. O(3) sensitivity was assessed by recording the extent of visible symptoms, effects on chlorophyll (Chl) content and changes in Chl a fluorescence parameters. This paper reports the results of an initial screening of 14 bean cultivars that was used to select a small number of cultivars for further work. Seven cultivars showed visible symptoms of injury in the range of 2-60 h after the end of the O(3) fumigation. O(3) significantly depressed total Chl content in most cultivars and a significant correlation was found between Chl content and visible symptoms. Most cultivars showed a significant change in the F(v)/F(m) ratio, even when there were no visual symptoms. There was no relationship between the extent of visual symptoms and quenching coefficients, indicating that these parameters were of no use in the determination of sensitivity to O(3) stress.