Energy Dissipation In PSII Research Articles

Photosynthetic Performance and Heterogeneous Anatomical Structure in Prunus humilis under Saline–Alkaline Stress

Prunus (P.) humilis is a small woody shrub that has been widely planted in northern China due to its high nutritional value and resistance to environmental abiotic stress. However, little information about the responses of photosynthetic performance and the anatomical structure of P. humilis to saline–alkaline stress (SAS) under field conditions is available. Here, we investigated the behavior of the photosynthetic apparatus of P. humilis by measuring the chlorophyll fluorescence parameters under moderate (MS) and severe (SS) saline–alkaline stress and analyzing their relationship to leaf anatomical traits. The results showed that SAS significantly decreased the net photosynthetic rate (An) but increased the substomatal CO2 concentration (Ci). The maximum photochemical quantum yield of PSII (Fv/Fm) and the efficient quantum yield of PSII [Y(II)] decreased under MS and SS conditions, and this decrease was greater in the distal (tip) than in the proximal (base) leaf. Compared to the leaf tip, the base of P. humilis leaves seemed to have a stronger ability to cope with MS, as was made evident by the increased quantum yield of regulated energy dissipation in PSII [Y(NPQ)] and decreased excitation pressure (1-qP). Under MS and SS conditions, the shapes of the chlorophyll a fluorescence transient (OJIP) changed markedly, accompanied by decreased PSII acceptor-side and donor-side activities. The palisade–spongy tissue ratio (PT/ST) increased significantly with increasing stress and showed a significant correlation with the chlorophyll fluorescence parameters in the leaf base. These results suggested that the activity of PSII electron transfer in the upper leaf position tended to be more sensitive to saline–alkaline stress, and a chlorophyll fluorescence analysis proved to be a good technique to monitor impacts of saline–alkaline stress on photosynthetic function, which may reflect the non-uniformity of leaf anatomy. In addition, among the anatomical structure parameters, the palisade–spongy tissue ratio (PT/ST) can be used as a sensitive indicator to reflect the non-uniform of photosynthetic function and leaf anatomy under stress.

New Data on Phytochemical and Morphophysiological Characteristics of Platycladus orientalis L. Franco and Thuja occidentalis L. Conifer Trees in Polluted Urban Areas of Kazakhstan

The adaptive potential of plants in urban environments, responding to factors like air pollution, electromagnetic radiation, and specific microclimates, remains insufficiently understood. Our study focused on two evergreen Cupressaceae family species, Thuja occidentalis L. and Platycladus orientalis L. Franco, which are commonly found in Kazakhstan’s urban landscapes. Conducted in Almaty, one of Kazakhstan’s most polluted cities, our comparative analysis examined the anatomical features, photosynthetic activity, and secondary metabolite composition of these conifers. Both species exhibited xeromorphic traits, such as submerged stomata, resin passages, and a prominent leaf cuticle. T. occidentalis displayed higher photosynthetic activity values (quantum yield of photosystem II (YII), electron transport rate (ETR), and quantum yield of non-photochemical quenching (Y(NPQ))) than P. orientalis, while P. orientalis exhibited a higher quantum yield of non-regulated energy dissipation in PSII (Y(NO)) values. Chemical analysis revealed 31 components in T. occidentalis and 33 in P. orientalis, with T. occidentalis containing three times more thujone (16.42% and 5.18%, respectively) and a higher monosaccharide content (17.33% and 6.98%, respectively). T. occidentalis also contained 14.53% steroids, whereas P. orientalis showed no steroid presence. The cytotoxic activity of essential oils was determined by the survival of Artemia salina aquatic crustaceans, whereas tested essential oils from both species exhibited acute lethal toxicity to A. salina aquatic crustaceans across all tested concentrations. The connection between physiological traits, adaptation strategies, and cytotoxic effects offers a comprehensive view of the ecological and pharmacological importance of these two observed conifer species, highlighting their diverse roles in urban environments, as well as their potential medical uses.

In vitro regeneration, photomorphogenesis and light signaling gene expression in Hydrangea quercifolia cv. 'Harmony' under different LED environments.

Plant growth regulators, sucrose concentration, and light quality significantly impact in vitro regeneration of 'Harmony'. Blue light promotes photomorphogenesis by enhancing light energy utilization, adjusting transcription of light signal genes, and altering hormone levels. Hydrangea quercifolia cv. 'Harmony', celebrated for lush green foliage and clusters of white flowers, has been extensively researched for its regenerative properties. Regeneration in stem segments, leaves, and petioles is facilitated by exogenous auxin and cytokinins (CTKs), with the concentration of sucrose (SC) being a key determinant for shoot regeneration from leaves. The study also highlights the significant impact of light conditions on photomorphogenesis. With an increase in the proportion of red (R) light, there is an inhibitory effect, leading to a reduction in leaf area, a decrease in the quantum yield of PSII (ΦPSII), and an increase in non-photochemical quenching (ΦNPQ) and non-regulated energy dissipation in PSII (ΦNO). Conversely, blue (B) light enhances growth, characterized by an increase in leaf area, elevated ΦPSII, and stable ΦNPQ and ΦNO levels. Additionally, B light induces the upregulation of HqCRYs, HqHY5-like, HqXTH27-like, and HqPHYs genes, along with an increase in endogenous CTKs levels, which positively influence photomorphogenesis independent of HqHY5-like regulation. This light condition also suppresses the synthesis of endogenous gibberellins (GA) and brassinosteroids (BR), further facilitating photomorphogenesis. In essence, B light is fundamental in expediting photomorphogenesis in 'Harmony', demonstrating the vital role in plant growth and development.

Effect of Drought Stress on Chlorophyll Fluorescence Parameters, Phytochemical Contents, and Antioxidant Activities in Lettuce Seedlings

This study monitored changes in chlorophyll fluorescence (CF), growth parameters, soil moisture content, phytochemical content (proline, ascorbic acid, chlorophyll, total phenol content (TPC), and total flavonoid content (TFC)), and antioxidant activities in 12-day-old lettuce (Lactuca sativa L.) seedlings grown under drought stress (no irrigation) and control (well irrigated) treatments in controlled conditions for eight days. Measurements occurred at two-day intervals. Among ten CF parameters studied, effective quantum yield of photochemical energy conversion in PSII (Y(PSII)), coefficient of photochemical quenching (qP), and coefficient of photochemical quenching of variable fluorescence based on the lake model of PSII (qL) significantly decreased in drought-stressed seedlings from day 6 of treatment compared to control. In contrast, maximum quantum yield (Fv/Fm), ratio of fluorescence (Rfd), and quantum yield of non-regulated energy dissipation in PSII (Y(NO)) were significantly affected only at the end. All growth parameters decreased in drought-stressed seedlings compared to control. Proline started increasing from day 4 and showed ~660-fold elevation on day 8 compared to control. Chlorophyll, ascorbic acid, TPC, TFC, and antioxidant activities decreased in drought-stressed seedlings. Results showed major changes in all parameters in seedlings under prolonged drought stress. These findings clarify effects of drought stress in lettuce seedlings during progressive drought exposure and will be useful in the seedling industry.

Effect of exogenously-applied abscisic acid, putrescine and hydrogen peroxide on drought tolerance of barley

The objective of this study was to identify the effect of abscisic acid (ABA), putrescine (Put) and hydrogen peroxide (H2O2) foliar pre-treatment on drought tolerance of barley. Despite water limitation, ABA-sprayed plants preserved increased water content, photosynthetic efficiency of PSII (ΦPSII) and CO2 assimilation rate (Pn) compared to untreated stressed plants. The ABA-treated plants presented also the lowest rate of lipid peroxidation (MDA), lowered the rate of PSII primary acceptor reduction (1 – qP) and increased the yield of regulated energy dissipation (NPQ) with higher accumulation of PGRL1 (PROTON GRADIENT REGULATION LIKE1) protein. These plants preserved a similar level of photochemical efficiency and the rate of electron transport of PSII (ETRII) to the well-watered samples. The significantly less pronounced response was observed in Put-sprayed samples under drought. Additionally, the combined effects of drought and H2O2 application increased the 1 – qP and quantum yield of non-regulated energy dissipation in PSII (ΦNO) and reduced the accumulation of Rubisco activase (RCA). In conclusion, ABA foliar application allowed to balance water retention and preserve antioxidant capacity resulting in efficient photosynthesis and the restricted risk of oxidative damage under drought. Neither hydrogen peroxide nor putrescine has been able to ameliorate drought stress as effectively as ABA.

Response to Salt Stress in Lettuce: Changes in Chlorophyll Fluorescence Parameters, Phytochemical Contents, and Antioxidant Activities

Chlorophyll fluorescence (CF), growth parameters, phytochemical contents [proline, chlorophyll, ascorbic acid, total phenol content (TPC), total flavonoid content (TFC)], and antioxidant activities were investigated in lettuce (Lactuca sativa L.) seedlings grown under different sodium chloride (NaCl) concentrations (0, 50, 100, 200, 300, and 400 mM) in a controlled environment for eight days. The parameters were evaluated at two days intervals. Almost of the CF and growth parameters as well as phytochemicals were significantly affected by both NaCl concentrations and progressive treatment schedule. The maximum quantum yield (Fv/Fm), effective quantum yield of photochemical energy conversion in PSII [Y(PSII)], coefficient of photochemical quenching (qP), coefficient of non-photochemical quenching (qN), and ratio of fluorescence decline (Rfd) showed decrements only at the highest saline concentration (400 mM), whereas the quantum yield of non-regulated energy dissipation in PSII [Y(NO)] exhibited a dissipation trend. All the growth parameters decreased with increasing NaCl concentrations, showing the highest decrease (~8 fold) in shoot fresh weight, compared to control seedlings. Proline significantly increased with increasing NaCl concentration and treatment time. Other phytochemicals decreased with the increase in NaCl concentration and reached their lowest at 400 mM. Overall, the results showed major changes in all parameters when the seedlings were grown at a NaCl concentration of 400 mM. The present findings will be useful for understanding the differential effect of NaCl concentrations in lettuce seedlings, and also might be useful to optimize the NaCl concentrations in other crops grown in controlled environmental conditions.

Responses of photosystem I compared with photosystem II to combination of heat stress and fluctuating light in tobacco leaves

Moderate heat stress is usually accompanied with fluctuating light in summer. Although either heat stress or fluctuating light can cause photoinhibition of photosystems I and II (PSI and PSII), it is unclear whether moderate heat stress accelerate photoinhibition under fluctuating light. Here, we measured chlorophyll fluorescence, P700 redox state and the electrochromic shift signal under fluctuating light at 25 °C and 42 °C for tobacco leaves. We found that (1) the thylakoid proton conductance was significantly enhanced at 42 °C, leading to a decline in trans-thylakoid proton gradient (ΔpH); (2) this low ΔpH at 42 °C did not decrease donor-side limitation of PSI and thermal energy dissipation in PSII; (3) the activation of cyclic electron flow (CEF) around PSI was elevated at 42 °C; and (4) the moderate heat stress did not accelerate photoinhibition of PSI and PSII under fluctuating light. These results strongly indicate that under moderate heat stress the stimulation of CEF protects PSI under fluctuating light in tobacco leaves.

The root endophytic fungus Serendipita indica improves resistance of Banana to Fusarium oxysporum f. sp. cubense tropical race 4

Serendipita indica is a root-colonizing basidiomycete that has received considerable attention in recent decades on account of its wide host range and the diverse benefits it imparts to host plants, including banana (Musa spp.). Banana is globally threatened by the fungal pathogen Fusarium oxysporum f. sp. cubense (Foc). In this study, to examine whether S. indica can improve the Foc resistance of banana, S. indica colonized (S+) and non-colonized (CK) ‘Tianbaojiao’ banana plants were inoculated with Foc tropical race 4 (TR4). Chlorophyll fluorescence parameters in leaves and antioxidant enzyme activities in roots of S+, CK, FocTR4-inoculated S+ plants (SF), and FocTR4-inoculated CK plants (F+) were determined and symptom appearance in corms of SF and F+ plants was observed. An analysis of antagonistic activity between S. indica and FocTR4 was performed and results showed that no significant differences in chlorophyll fluorescence parameters were displayed between CK and S+. No significant differences in Y(II) (effective quantum yield of photochemical energy in PSII) and Y(NPQ) (quantum yield of regulated energy dissipation in PSII) were exhibited among the four groups. However, the Fv/fm (ratio of variable to maximal fluorescence) values were significantly decreased (p < 0.01) in F+ and SF, and the Fv/fm value of SF was significantly improved than that of F+ (p < 0.05). The Y(NO) (quantum yield of non-regulated energy dissipation in PSII) was remarkable improved (p < 0.01) in F+ but not in SF. Although infection symptoms in SF were significantly alleviated compared with those of F+, no obvious antagonistic effect was observed between S. indica and FocTR4, indicating that the enhancement of FocTR4 resistance in banana was not directly induced by S. indica. Colonization by S. indica increased superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities in S+. After FocTR4 inoculation, SOD activity was significantly compromised in F+ but not in SF; POD activity was drastically increased in both F+ and SF, and that in SF was significantly higher than in F+; CAT activity was significantly improved in S+, but no obvious change was observed in F+ and SF when compared with CK. Moreover, APX and glutathione reductase (GR) activities were enhanced dramatically in SF but not in F+ compared with CK. Results obtained in this study indicated that the beneficial effect of S. indica colonization on FocTR4 resistance of banana might be achieved, at least partly, through regulation of antioxidant enzyme activities.

Dynamics of regulated YNPQ and non-regulated YNO energy dissipation in sunflower leaves exposed to sinusoidal lights

Better understanding of photosynthetic efficiency under fluctuating light requires a specific approach to characterize the dynamics of energy dissipation in photosystem II. In this study, we characterized the interaction between the regulated YNPQ and non-regulated YNO energy dissipation in outdoor- and indoor-grown sunflower leaves exposed to repetitive cycles of sinusoidal lights of five amplitudes (200, 400, 600, 800, 1000µmolm-2s-1) and periods (20, 40, 60, 90, 120s). The different light cycles induced various patterns of ChlF emission, from which were calculated the complementary quantum yields of photochemical energy conversion YII, light-regulated YNPQ, and non-regulated YNO non-photochemical energy dissipation. During the light cycles, YNO varied in complex but small patterns relative to those of YNPQ, whose variations were mostly mirrored by changes in YII. The YNO patterns could be decomposed by fast Fourier transform into a main (MH) and several upper harmonics (UH). Concerning YNPQ dynamics, they were described by sinusoidal regressions with two components, one constant during the light cycles but increasing with the average light intensity (YNPQc), and one variable (YNPQv). Formation and relaxation of YNPQv followed the intensity of the sinusoidal lights, with lags ranging from 5 to 13s. These lags decreased with the amplitude of the incident light, and were shorter by 37% in outdoor than indoor leaves. YNPQv and UHs responses to the growth conditions, amplitudes, and the periods of the sinusoidal light were closely correlated (r = 0.939), whereas MH and YNPQc varied similarly (r = 0.803). The analysis of ChlF induced by sinusoidal lights may be a useful tool to better understand the dynamics of energy dissipation in PSII under fluctuating lights.

The positive regulation of putrescine on light-harvesting complex II and excitation energy dissipation in salt-stressed cucumber seedlings

Non-photochemical quenching (NPQ) is an important mechanism employed by higher plants to protect themselves against the adverse effects of excess excitation energy. The regulatory mechanism of exogenous putrescine (Put) on the status of light-harvesting complex II (LHCII) and its dissipation of excess excitation energy in cucumber seedlings (Cucumis sativus L.) were investigated under salt stress in this study. Put significantly increased the maximum quantum photochemical efficiency in photosystem II (Fv/Fm), NPQ, and the actual yield of PSII (ΦPSII) under salt stress. Quantum yield of regulated energy dissipation in PSII (ΦNPQ) significantly increased and non-regulated energy dissipation (ΦNO) decreased when was sprayed on stressed plants. Put increased the expression levels of D1, D2, Lhcb4 and PsbS, thereby minimizing degradation to the monomeric and trimeric states of LHCII in the thylakoid membranes of salt-stressed cucumber leaves. In addition, Put up-regulated the activity of transglutaminase (TGase) and significantly increased the levels of total endogenous polyamines in monomeric and trimeric LHCII under salt stress. These results suggest that Put could play a crucial role in dissipating excess excitation energy by regulating endogenously increased polyamines to alter the adaptation of LHCII, which are most probably involved in an improvement of photochemical efficiency in salt stressed-cucumber seedlings.

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Non-photochemical quenching (NPQ) is an important mechanism employed by higher plants to protect themselves against the adverse effects of excess excitation energy. The regulatory mechanism of exogenous putrescine (Put) on the status of light-harvesting complex II (LHCII) and its dissipation of excess excitation energy in cucumber seedlings (Cucumis sativus L.) were investigated under salt stress in this study. Put significantly increased the maximum quantum photochemical efficiency in photosystem II (Fv/Fm), NPQ, and the actual yield of PSII (ΦPSII) under salt stress. Quantum yield of regulated energy dissipation in PSII (ΦNPQ) significantly increased and non-regulated energy dissipation (ΦNO) decreased when was sprayed on stressed plants. Put increased the expression levels of D1, D2, Lhcb4 and PsbS, thereby minimizing degradation to the monomeric and trimeric states of LHCII in the thylakoid membranes of salt-stressed cucumber leaves. In addition, Put up-regulated the activity of transglutaminase (TGase) and significantly increased the levels of total endogenous polyamines in monomeric and trimeric LHCII under salt stress. These results suggest that Put could play a crucial role in dissipating excess excitation energy by regulating endogenously increased polyamines to alter the adaptation of LHCII, which are most probably involved in an improvement of photochemical efficiency in salt stressed-cucumber seedlings.

Impact of weak water deficit on growth, photosynthetic primary processes and storage processes in pine and spruce seedlings.

We investigated the influence of 40 days of drought on growth, storage processes and primary photosynthetic processes in 3-month-old Scots pine and Norway spruce seedlings growing in perlite culture. Water stress significantly affected seedling water status, whereas absolute dry biomass growth was not substantially influenced. Water stress induced an increase in non-structural carbohydrate content (sugars, sugar alcohols, starch) in the aboveground part of pine seedlings in contrast to spruce seedlings. Due to the relatively low content of sugars and sugar alcohols in seedling organs, their expected contribution to osmotic potential changes was quite low. In contrast to biomass accumulation and storage, photosynthetic primary processes were substantially influenced by water shortage. In spruce seedlings, PSII was more sensitive to water stress than PSI. In particular, electron transport in PSI was stable under water stress despite the substantial decrease of electron transport in PSII. The increase in thermal energy dissipation due to enhancement of non-photochemical quenching (NPQ) was evident in both species under water stress. Simultaneously, the yields of non-regulated energy dissipation in PSII were decreased in pine seedlings under drought. A relationship between growth, photosynthetic activities and storage processes is analysed under weak water deficit.

Response of photosynthetic capacity of tomato leaves to different LED light wavelength

Light-emitting diodes (LEDs) are widely used in horticultural facilities in recent years. However, the influence of light quality on photosynthesis still calls for further exploration. This study comprehensively analyzed the influence of different LED lighting (white: W, combination of red and blue 1:1: RB, blue: B, purple: P and red: R) on photosynthetic electron transport in tomato leaves. Plant height under B and P treatments was significantly higher than the other treatments and showed more compact development. Photosynthetic pigment content and net photosynthetic rate (Pn) of B and P treatments were significantly lower than the W treatment. The redox state of photosystem I was repressed by blue and purple light while the intrinsic PSII activity was not altered by the treatments. The ETR (II) and ETR (I) under B and P treatment were lower than the other treatments, while the cyclic electron flow (CEF), the quantum yield of regulated energy dissipation in PSII [Y(NPQ)] and the quantum yield of PSI non-photochemical energy dissipation due to the donor-side limitation [Y(ND)] were higher, indicating that B and P treatment induced non-photochemical quenching of PSII and excitation of PSI’s self-protection mechanisms in tomato plants. Blue and purple light exposure resulted in a higher proton gradient (ΔpH), leading to impaired thylakoid membrane integrity and inhibited the activity of ATP-synthase. In conclusion, the blue and purple light significantly reduced photosynthesis efficiency, enhancing CEF and inducing NPQ for photoprotection of PSII and PSI via lumen acidification.

Efficient modulation of photosynthetic apparatus confers desiccation tolerance in the resurrection plant Boea hygrometrica.

Boea hygrometrica (B. hygrometrica) can tolerate severe desiccation and resume photosynthetic activity rapidly upon water availability. However, little is known about the mechanisms by which B. hygrometrica adapts to dehydration and resumes competence upon rehydration. Here we determine how B. hygrometrica deals with oxidative stress, excessive excitation/electron pressures as well as photosynthetic apparatus modulation during dehydration/rehydration. By measuring ROS generation and scavenging efficiency, we found that B. hygrometrica possesses efficient strategies to maintain cellular redox homeostasis. Transmission electron microscopy (TEM) analysis revealed a remarkable alteration of chloroplast architecture and plastoglobules (PGs) accumulation during dehydration/rehydration. Pulse-amplitude modulated (PAM) chlorophyll fluorescence measurements, P700 redox assay as well as chlorophyll fluorescence emission spectra analysis on leaves of B. hygrometrica during dehydration/rehydration were also performed. Results showed that the photochemical activity of PSII as well as photoprotective energy dissipation in PSII undergo gradual inactivation/activation during dehydration/rehydration in B. hygrometrica; PSI activity is relatively induced upon water deficit, and dehydration leads to physical interaction between PSI and LHCII. Furthermore, blue-native polyacrylamide gel electrophoresis (BN-PAGE) and immunoblot analysis revealed that the protein abundance of light harvesting complexes decrease markedly along with internal water deficit to restrict light absorption and attenuate electron transfer, resulting in limited light excitation and repressed photosynthesis. In contrast, many thylakoid proteins remain at a basal level even after full dehydration. Taken together, our study demonstrated that efficient modulation of cellular redox homeostasis and photosynthetic activity confers desiccation tolerance in B. hygrometrica.

Allocation of Absorbed Light Energy in Photosystem II in NPQ Mutants of Arabidopsis.

To analyze changes of energy allocation in PSII at non-steady state photosynthesis, the induction and relaxation of non-photochemical quenching of Chl fluorescence was re-evaluated with the use of Arabidopsis thaliana mutants in which the ability to induce non-photochemical quenching was either enhanced (npq2) or suppressed (npq1 and npq4). When dark-treated leaves of the wild type (WT) were illuminated, very high Φf,D, which represents the loss of excitation energy via non-regulated dissipation, at the beginning of light illumination was gradually decreased to the steady-state level. In contrast, ΦNPQ, representing regulated energy dissipation in PSII, was relatively constant after a significant change in the first 10 min. In npq1 and npq4 mutants, lower ΦNPQ resulted in much higher Φf,D than in the WT. Comparison of npq1 and npq4 mutants showed a kinetic difference of two types of non-photochemical quenching. Because non-photochemical quenching calculated as NPQ = Fm - Fm')/Fm' was determined by the interplay between ΦNPQ and Φf,D, NPQ and ΦNPQ, both of which represent regulatory heat dissipation, were not linearly correlated. We showed that the kinetics of NPQ formation in the light and relaxation in the dark were affected by drastic changes in Φf,D We discuss the nature of a high level of Φf,D at the dark-light transition. We also point out an unavoidable problem of applying the energy allocation model when the Fv/Fm value changes during a photoinhibiotry illumination.

Expression of OsCAS (Calcium-Sensing Receptor) in an Arabidopsis Mutant Increases Drought Tolerance.

The calcium-sensing receptor (CaS), which is localized in the chloroplasts, is a crucial regulator of extracellular calcium-induced stomatal closure in Arabidopsis. It has homologs in Oryza sativa and other plants. These sequences all have a rhodanese-like protein domain, which has been demonstrated to be associated with specific stress conditions. In this study, we cloned the Oryza sativa calcium-sensing receptor gene (OsCAS) and demonstrated that OsCAS could sense an increase of extracellular Ca2+ concentration and mediate an increase in cytosolic Ca2+ concentration. The OsCAS gene was transformed into an Arabidopsis CaS knockout mutant (Salk) and overexpressed in the transgenic plants. OsCAS promoted stomatal closure. We screened homozygous transgenic Arabidopsis plants and determined physiological indices such as the oxidative damage biomarker malondialdehyde (MDA), relative membrane permeability (RMP), proline content, and chlorophyll fluorescence parameters, after 21 days of drought treatment. Our results revealed lower RMP and MDA contents and a higher Proline content in transgenic Arabidopsis plants after drought stress, whereas the opposite was observed in Salk plants. With respect to chlorophyll fluorescence, the electron transport rate and effective PSII quantum yield decreased in all lines under drought stress; however, in the transgenic plants these two parameters changed fewer and were higher than those in wild-type and Salk plants. The quantum yield of regulated energy dissipation and nonregulated energy dissipation in PSII were higher in Salk plants, whereas these values were lower in the transgenic plants than in the wild type under drought stress. The above results suggest that the transgenic plants showed better resistance to drought stress by decreasing damage to the cell membrane, increasing the amount of osmoprotectants, and maintaining a relatively high photosynthetic capacity. In conclusion, OsCAS is an extracellular calcium-sensing receptor that helps to compensate for the absence of CaS in Arabidopsis and increases the drought stress tolerance of transgenic plants.

Quantum yield of non-regulated energy dissipation in PSII (Y(NO)) for early detection of leaf rust (Puccinia triticina) infection in susceptible and resistant wheat (Triticum aestivum L.) cultivars

The development and optimization of protocols for the precise and pre-symptomatic detection of diseases, and non-invasive evaluation of genotype-specific pathogen resistance enabling selection of the more promising genotypes in breeding programmes are important and often overlooked topics in precision agriculture. The increasing pressure to minimize both production costs and the environmental impact of pesticides forces the search for rapid and objective methods of screening pathogen resistance. Using the non-destructive pulse amplitude modulated (PAM) chlorophyll fluorescence imaging technique, we hypothesized that not only disease detection but also discrimination between differences in the level of resistance of wheat cultivars to the leaf rust (Puccinia triticina Erics.) pathogen can be achieved. Experiments were conducted using the cultivars Dekan and Retro as representatives of a susceptible and a highly resistant genotype, respectively. Fluorescence measurements were carried out daily on the control and on plants inoculated with P. triticina until the first small red-brown pustules appeared in the centre of chlorotic spots. In response to pathogen inoculation, the fluorescence readings showed an early characteristic increase in Y(NO) in both resistant and susceptible cultivars. The susceptible cultivar, however, showed a more pronounced difference between Y(NO) values measured on the control and inoculated leaves as well as a distinct evolution over time. Accordingly, our results indicate that Y(NO) might be suitable for discriminating between wheat genotypes as early as 2 days after inoculation. Thus, the proposed protocol might be adopted as an additional tool for the early screening of new genotypes, especially in breeding programs that aim for high resistance to disease and low crop variability for precision agriculture. However, its implementation in experimental field plots requires improvement of the measurement system and establishment of appropriate algorithms for disease pattern recognition and data analysis.

Seasonal differences in xanthophyll cycle characteristics and antioxidants in Mahonia repens growing in different light environments.

We investigated differences between summer and winter in photosynthesis, xanthophyll cycle-dependent energy dissipation, and antioxidant systems in populations of Mahonia repens (Lindley) Don growing in the eastern foothills of the Colorado Rocky Mountains in deep shade, full exposure, and under a single-layered canopy of Pinus ponderosa (partially shaded). In summer, increasing growth irradiance (from deep shade to partial shade to full exposure) was associated with increased xanthophyll cycle-dependent energy dissipation in PSII and an increased capacity to detoxify reactive reduced oxygen species, as measured by increases in the activities of ascorbate peroxidase, superoxide scavenging, glutathione reductase, and monodehydroascorbate reductase, as well as increases in leaf ascorbate and glutathione content. Leaves of exposed and partially shaded plants exhibited decreased capacities for photosynthetic O2 evolution in winter compared to summer, while in the deeply shaded plants this parameter did not differ seasonally. Seasonal differences in the levels of antioxidants generally exhibited an inverse response to photosynthesis, being higher in winter compared to summer in the exposed and partially shaded populations, but remaining unchanged in the deeply shaded population. In addition, total pool size and conversion state of the xanthophyll cycle were higher in winter than in summer in all populations. These trends suggest that both xanthophyll cycle-dependent energy dissipation in PSII and the capacity to detoxify reactive reduced oxygen species responded to the level of excess light absorption.