Chlorophyll fluorescence analysis is one of the most powerful and widely used techniques to study the effect of stresses on the photosynthetic process. From the first utilization, the
/
ratio has ...been largely used as a sensitive indicator of plant photosynthetic performance. Decreases of this index are indicative of the reduction of photosystem II (PSII) efficiency, namely photoinhibition. In the last 20 years, application of chlorophyll fluorescence has been largely improved, and many other informative parameters have been established to detect PSII photochemical efficiency and the partitioning of light energy to alternative dissipative mechanisms (qE, energy-dependent quenching; qZ, zeaxanthin-dependent quenching and qI, photoinhibitory quenching; qH, sustained photoprotective antenna quenching; qM, quenching dependent to chloroplast movement; qT, light harvesting complexes II-I state-transition) such as the recently developed "photoprotective power" of non-photochemical quenching (pNPQ). This review reports a brief description of the main chlorophyll fluorescence parameters and a wide analysis of the current bibliography on the use of different parameters which are useful to detect events of PSII photoinhibition. In addition, in view of the inherent differences in morpho-anatomical, physiological and biochemical features between C3 and C4 metabolism, possible differences in terms of photoinhibition between C3 and C4 plant species under stress conditions are proposed. The attempt is to highlight the limits of their comparison in terms of susceptibility to photoinhibition and to propose direction of future research which, assisted by chlorophyll fluorescence, should improve the knowledge of the different sensitivity of C3 and C4 to abiotic stressors.
The Mediterranean basin is a biodiversity hotspot of wild edible species, and their therapeutic and culinary uses have long been documented. Owing to the growing demand for wild edible species, there ...are increasing concerns about the safety, standardization, quality, and availability of products derived from these species collected in the wild. An efficient cultivation method for the species having promising nutraceutical values is highly desirable. In this backdrop, a hydroponic system could be considered as a reproducible and efficient agronomic practice to maximize yield, and also to selectively stimulate the biosynthesis of targeted metabolites. The aim of this report is to review the phytochemical and toxic compounds of some potentially interesting Mediterranean wild edible species. Herein, after a deep analysis of the literature, information on the main bioactive compounds, and some possibly toxic molecules, from fifteen wild edible species have been compiled. The traditional recipes prepared with these species are also listed. In addition, preliminary data about the performance of some selected species are also reported. In particular, germination tests performed on six selected species revealed that there are differences among the species, but not with crop species. "Domestication" of wild species seems a promising approach for exploiting these "new functional foods".
The hypothesis was tested that isoprenoids and phenylpropanoids play a prominent role in countering photooxidative stress, following the depletion of antioxidant enzyme activity in plants exposed to ...severe drought stress under high solar irradiance and high temperatures.
Platanus × acerifolia, a high isoprene-emitting species, was drought-stressed during summer (WS) and compared with unstressed controls (WW). Water relations and photosynthetic parameters were measured under mild, moderate, and severe drought stress conditions. Volatile and nonvolatile isoprenoids, antioxidant enzymes, and phenylpropanoids were measured with the same time course, but in four different periods of the day.
Drought severely inhibited photosynthesis, whereas it did not markedly affect the photochemical machinery. Isoprene emission and zeaxanthin concentration were higher in WS than in WW leaves, particularly at mild and moderate stresses, and during the hottest hours of the day. The activities of catalase and ascorbate peroxidase steeply declined during the day, while the activity of guaiacol peroxidase and the concentration of quercetin increased during the day, peaking in the hottest hours in both WW and WS plants.
Our experiment reveals a sequence of antioxidants that were used daily by plants to orchestrate defense against oxidative stress induced by drought and associated high light and high temperature. Secondary metabolites seem valuable complements of antioxidant enzymes to counter oxidative stress during the hottest daily hours.
Display omitted
•Photosynthesis is influenced by excess of soluble sugars promoted by girdling.•The increased anthocyanin biosynthesis contributed to lowering the hexose content.•Anthocyanins ...indirectly attenuated the sugar-promoted regulation of photosynthesis.•Anthocyanins protected the PSII from damage caused by excess excitation energy.
The feedback regulation of photosynthesis depends on the cooperation of multiple signals, including sugars. Herein, the effect of shoot girdling was monitored on a daily basis for three days in green- and red-leafed Prunus cerasifera plants (GLP and RLP, respectively). The effect of anthocyanin presence was investigated in terms of photosynthesis, sugar metabolism and photoprotection. Net photosynthesis (A390) and stomatal conductance were reduced on the first day at 12:00 only in the girdled GLP (29 and 33 %, respectively). Moreover, the girdled GLP displayed at 12:00 higher sucrose, glucose and fructose concentrations than control leaves. Conversely, girdled RLP showed the first reduction of A390 at 18:00, with no significant differences at 12:00 in sucrose and glucose concentrations. The increased biosynthesis of anthocyanins that was only detected in girdled RLP contributed to lowering the accumulation of hexoses. Overall, these results revealed a sugar-buffering role exerted by anthocyanins that positively influence the feedback regulation of photosynthesis. Moreover, non-photochemical quenching, namely pNPQ, revealed the ability of anthocyanins to photoprotect photosystem II from supernumerary photons reaching the chloroplast, whose function was compromised by girdling. The present study provides a starting point to understand the possible link between photosynthesis regulation through sugar signalling and anthocyanin upregulation.
Flavonoids have recently been suggested to have the potential to serve as antioxidants other than effective UV attenuators in photoprotection. Here, we tested the hypothesis that flavonoids ...accumulate in response to “excess light” in the presence or in the absence of UV radiation. In a UV exclusion experiment, we grew
Ligustrum vulgare plants outdoors under 30% or 100% sunlight irradiance, by cutting-off the whole UV waveband. These plants were also exposed to UV irradiance or supplied with 125
mM NaCl at the root zone. Leaves of plants under 100% sunlight irradiance suffered from excess light, which was exacerbated greatly by root zone salinity stress. Salinity stress repressed the activities of antioxidant enzymes, particularly in full sunlight, and led to severe leaf oxidative damage. Dihydroxy B-ring-substituted flavonoids, namely quercetin 3-O- and luteolin 7-O-glycosides, accumulated steeply in response to sunlight irradiance in the absence of UV radiation. UV radiation and root zone NaCl increased, to a similar degree, the concentration of these flavonoids, which have a great potential to scavenge various forms of reactive oxygen. Treatment-induced changes in leaf phenylpropanoid concentration affected antioxidant activities to a greater extent than the UV-screening capacities of leaf extracts. Early responses to an abrupt increase in sunlight irradiance included a steep increase in the concentrations of quercetin derivatives and cyanidin 3-O-glucoside, with the latter negligibly absorbing in the UV-spectral region. In contrast, effective UV attenuators, such as hydroxycinnamates and monohydroxy B-ring flavonoids, were unresponsive to the light treatments. Overall, these findings lead to the hypothesis that flavonoids may have an important antioxidant function in photoprotection. This hypothesis is further corroborated by the large distribution of quercetin and luteolin derivatives in the vacuoles of mesophyll, not only in the corresponding compartments of epidermal cells, but also in full sunlight-treated leaves in the absence of UV radiation. Future experiments aimed at evaluating the relative contribution of flavonoids within the complex antioxidant defense systems operating in the leaf are needed to help conclusively address the relevance of their antioxidant functions in photoprotection.
Despite the huge biodiversity characterizing the Mediterranean environment, environmental constraints, such as high sunlight and high temperatures alongside with dry periods, make plant survival ...hard. In addition, high irradiance leads to increasing ozone (O3) concentrations in ambient air. In this era of global warming, it is necessary to understand the mechanisms that allow native species to tolerate these environmental constraints and how such mechanisms interact. Three Mediterranean oak species (Quercus ilex, Quercus pubescens and Quercus cerris) with different features (drought tolerant, evergreen or deciduous species) were selected to assess their biometrical, physiological and biochemical responses under drought and/or O3 stress (80–100 nl l−1 of O3 for 5 h day−1 for 77 consecutive days). Leaf visible injury appeared only under drought stress (alone or combined with O3) in all three species. Drought × O3 induced strong reductions in leaf dry weight in Q. pubescens and Q. cerris (−70 and −75%, respectively). Alterations in physiological (i.e. decrease in maximum carboxylation rate) and biochemical parameters (i.e. increase in proline content and build‐up of malondialdehyde by‐products) occurred in all the three species, although drought represented the major determinant. Quercus ilex and Q. pubescens, which co‐occur in dry environments, were more tolerant to drought and drought × O3. Quercus ilex was the species in which oxidative stress occurred only when drought was applied with O3. High plasticity at a biochemical level (i.e. proline
content) and evergreen habitus are likely on the basis of the higher tolerance of Q. ilex.
Hyperkalemia is a major concern in chronic kidney disease and in end-stage renal disease, representing a predictor of hospitalization and mortality. To prevent and treat hyperkalemia, dietary ...management is of great clinical interest. Currently, the growing use of plant-based diets causes an increasing concern about potassium load in renal patients. The aim of this study was to assess the bioaccessibility of potassium in vegetables, concerning all aspects of the plants (fruit, flower, root, tuber, leaf and seed) and to what extent different boiling techniques affect potassium content and bioaccessibility of plant-based foods. Bioaccessibility was evaluated by an in vitro digestion methodology, resembling human gastro-intestinal tract. Potassium content was higher in seeds and leaves, despite it not being possible to define a common “rule” according to the type of organ, namely seed, leaf or fruit. Boiling reduced potassium content in all vegetables excluding carrot, zucchini, and cauliflower; boiling starting from cold water contributed to a greater reduction of the potassium content in potato, peas, and beans. Bioaccessibility after in vitro digestion ranged from 12 (peas) to 93% (tomato) regardless of species and organs. Higher bioaccessibility was found in spinach, chicory, zucchini, tomato, kiwi, and cauliflower, and lower bioaccessibility in peas. Potassium from leaf resulted in the highest bioaccessibility after digestion; as a whole potassium bioaccessibility in the fruits and vegetables studied was 67% on average, with differences in relation to the different organs and species. Further, considering the method of boiling to reduce potassium content, these data indicate that the effective potassium load from plant-based foods may be lower than originally expected. This supports the clinical advices to maintain a wide use of plant-based food in the management of renal patients.
PDF
