Effects of the Salt Stress Duration and Intensity on Developmental and Physiological Features of the Moss Polytrichum formosum.

The two accessions of the polytrichaceous moss species Polytrichum formosum, namely German and Serbian genotypes, were subjected to salt stress, aiming to study the species' developmental and physiological features. Various concentrations of sodium chloride were applied to an axenic in vitro culture of the two moss genotypes, and the growth parameters as well as physiological feature changes were followed. As inferred by the morpho-developmental parameters and survival index, the Serbian genotype showed higher resistance to salt stress as compared to the German one. However, both moss genotypes survived the highest applied concentration (500 mM). As expected, short exposures to salt were rather easily overcome. No clear patterns in sugar content and changes were observed during the stress, but they are surely included in salt stress response and tolerance in P. formosum. Longer stress increased total chlorophyll content in both genotypes. In short-term applied salt stress, the Serbian genotype had a higher total chlorophyll concentration to control unstressed plants, while the German genotype decreased the total amount of chlorophyll. Similarly, carotenoids were shown to be significantly higher in the Serbian genotype, both in unstressed and treated plants, compared to the German one. The contents of tocopherols were higher in the Serbian genotype in controlled unstressed and subsequently short- and long-stressed plantlets compared to the German accession. In general, we can assume that P. formosum is unexpectedly tolerant to salt stress and that there are differences within various accessions of overall European populations, as referred by two randomly selected genotypes, which is most probably a consequence of different genetic structure.

Impact of Two Brown Seaweed (Ascophyllum nodosum L.) Biostimulants on the Quantity and Quality of Yield in Cucumber (Cucumis sativus L.).

Algal biostimulants are increasingly integral to vegetable cultivation due to their capacity to boost yield, alleviate abiotic and biotic stress, and enhance overall crop quality. This study evaluated the impact of two commercially available algal-based biostimulants on cucumber (Cucumis sativus L.), examining their effects on yield, number of fruits, dry weight, color, flesh thickness, skin thickness, plastid pigments, and tocopherol content. Both biostimulant treatments resulted in a roughly 13% decrease in yield and fruit number compared to the control treatment. Notably, the biostimulants positively influenced the fruit brightness parameter (L*), leading to darker fruits. Fitostim® algal biostimulant exhibited a positive effect on dry weight during the initial harvest. The predominant pigments were chlorophyll a and chlorophyll b (constituting 80% of all analyzed pigments), and the most abundant tocopherol was α-tocopherol, comprising 80% to 90% of tocopherols. Skin tissues contained significantly higher levels of pigments and tocopherols compared to flesh. Both biostimulants caused a notable decrease in total tocopherol content in the skin at the first harvest, with reductions of 19.91 mg/kg DW for Phylgreen® and 9.43 mg/kg DW for Fitostim® algae. The study underscores the variable efficacy of biostimulants, emphasizing their dependence on the specific biostimulant type and fruit part. The application of biostimulants has the potential to substantially enhance the internal quality of cucumbers, particularly in terms of plastid pigments and tocopherols, offering potential health benefits for consumers.

Physio-Biochemical Responses of Sweet Cherry Leaf to Natural Cold Conditions.

Trees of the sweet cherry cultivar 'Grace Star' (Prunus avium L.) were exposed to low temperatures without frost for two consecutive nights under natural conditions 36 d after flowering, to study the effects on the physiological properties and metabolic status of leaves. The response was studied by measuring chlorophyll fluorescence and gas exchange parameters and by analyzing chloroplast pigments (i) immediately after exposure, (ii) 24 h and (iii) 48 h later. The first exposure at 2.4 (±0.2) °C and a minimum of 0.8 °C elicited more changes than the second exposure at 4.9 (±0.3) °C and a minimum of 2.4 °C. After the first exposure, the maximum quantum yield of PS II (Fv/Fm), effective quantum efficiency of PS II, net photosynthesis (PN), stomatal conductance (gs), transpiration, and intercellular CO2 concentration were significantly lower, and after the second exposure, the content of chlorophyll b, total chlorophyll, ß-carotene, and lutein were lower. The content of antheraxanthin and zeaxanthin was higher immediately after both exposures, and that of antheraxanthin was also higher 24 h later. Recovery took longer in trees that were exposed twice. Fv/Fm recovered within 48 h, but the de-epoxidation state of the xanthophyll cycle pool, PN, and gs did not reach the level of controls, indicating that the stress effect lasted several days which is probably sufficient to cause fruit drop and reduce yield.

Response of chloroplast pigments, sugars and phenolics of sweet cherry leaves to chilling.

The aim of the present study was to evaluate the effect of post-flowering chilling of sweet cherry (Prunus avium L.) on the content of biochemical parameters in the leaf (chloroplast pigments, sugars and phenolics). The effect of chilling was investigated in two experiments. Potted 2-year-old trees of cv. 'Grace Star' and 'Schneiders' were exposed to one, two or three consecutive overnight chillings at an average air temperature of 4.7 °C (Experiment I), but in the following year only trees of 'Grace Star' were chilled at 2.2 °C (Experiment II), 3 to 7 weeks after flowering. The analysis of the biochemical parameters was performed by high performance liquid chromatography combined with electrospray ionization mass spectrometry. Chilling at 4.7 °C caused little or no stress, while 2.2 °C induced more intense stress with increased zeaxanthin, sugar and phenolic content in leaves, while exposure of trees to higher temperatures and closer to flowering showed no changes. Two or three consecutive overnight chilling periods increased the phenolic content and enhanced the accumulation of zeaxanthin in the leaves. Sucrose, sorbitol, fructose, total sugar, and total flavonoid content in leaves increased within 48 h after chilling. Zeaxanthin epoxidized within 24 h after one and 48 h after one and two consecutive overnight chillings.

Physiological and Biochemical Responses of Ungrafted and Grafted Bell Pepper Plants (Capsicum annuum L. var. grossum (L.) Sendtn.) Grown under Moderate Salt Stress.

The response of grafted bell pepper plants (Capsicum annuum L. var. grossum (L.) Sendtn.) to salt stress was investigated by analyzing the photosynthetic traits and mineral content of the plants and the metabolic composition of the fruit. The bell pepper variety "Vedrana" was grafted onto the salt-tolerant rootstock "Rocal F1" and grown at two salinities (20 mM and 40 mM NaCl) and control (0 mM NaCl) during the spring-summer period. On a physiological level, similar stomatal restriction of photosynthesis in grafted and ungrafted plants indicated that grafting did not alleviate water balance disturbances under increased salt exposure. Measurements of midday water potential did not show improved water status of grafted plants. The similar metabolic changes in grafted and ungrafted plants were also reflected in similarly reduced fruit yields. Thus, this grafting did not reduce the risk of ionic and osmotic imbalance in pepper plants grown under moderate salt treatment. Changes in the biochemical profiles of the pepper fruit were seen for both added-salt treatments. The fruit phenolic compounds were affected by rootstock mediation, although only for the July harvest, where total phenolics content increased with 40 mM NaCl treatment. Fruit ascorbic acid content increased with the duration of salt stress, without the mediation of the rootstock. The high salt dependence of this quality trait in pepper fruit appears to lead to more limited rootstock mediation effects.

Physico-chemical characterization of Cornus kousa Burg. fruit: determining optimal maturity for fresh consumption.

BACKGROUND: Japanese dogwood (Cornus kousa Burg.) is a popular ornamental plant which develops edible compound fruit utilized in traditional Asian medicine. Previous compositional studies have focused on a small fraction of secondary metabolites at a single maturity stage. In order to address the question of optimal ripeness of Japanese dogwood fruit for consumption the study provides a comprehensive insight into its primary and secondary metabolic profile. RESULTS: The aim of the study was to investigate biochemical composition and morphological traits of Japanese dogwood (Cornus kousa Burg.) fruit at four maturity stages: GF, green fruit; BF, fruit with a defined red blush; RF, ripe fruit; OF, over-ripe fruit. Fruit was characterized by a nearly spherical shape, decreased water content in later stages of ripeness and highest a* values at RF and OF stages. Total sugars increased significantly from GF to OF stage and total organic acids and vitamin C decreased with maturation. Japanese dogwood fruit was characterized by four major phenolic groups: anthocyanins (three), flavonols (eight) hydroxycinnamic acids (three) and flavonoids (one) as well as by four lipophilic antioxidants: tocopherols (two), xanthophylls (five), carotenes (two) and chlorophylls (two). The progression of fruit ripening caused faster accumulation of individual phenolic compounds and lipophilic antioxidants which resulted in significantly higher total phenolic content at the RF and OF stages. CONCLUSION: Japanese dogwood fruit is a rich alternative source of ascorbic acid, α-tocopherol, flavonols and anthocyanins and should be consumed fresh at fully developed red colour of compound berries when their composition is optimal. © 2020 Society of Chemical Industry.

Response of Pumpkin to Different Concentrations and Forms of Selenium and Iodine, and their Combinations.

The elements selenium (Se) and iodine (I) are both crucial for the normal functioning of the thyroid. Biofortification with these elements is particularly feasible in areas where they show a deficit. Iodine and selenium can have positive effects on different plants when applied at the correct concentrations. The effects of their simultaneous addition on plant physiology and biochemistry, as well as on seed germination and sprout biomass, were studied in pumpkin (Cucurbita pepo L. ssp. pepo). To study the effect of Se and I on sprouts, sprouts were grown from seeds soaked in solutions of different forms of Se, I and their combination in the growth chamber experiment. In the field experiment, pumpkins plants were foliarly treated with the same concentrations and forms of Se and I. The combination of Se and I treatments enhanced the germination of the soaked seeds, with no significant differences between Se and I treatments for sprout mass. The yield of pumpkins and seed production were unaffected by Se and I foliar application. The anthocyanin levels and respiratory potential measured via the electron transport system's activity showed different patterns according to treatments and plant parts (sprouts, leaves, seeds). The redistribution of Se and I from seeds to sprouts was significant. The accumulation of Se was higher in sprouts from the seeds treated with Se together with I, compared to sprouts from the seeds treated with Se alone. Interactions between Se and I were also noted in the seeds, which developed in the treated plants.

Biofortification with selenium and iodine changes morphological properties of Brassica oleracea L. var. gongylodes) and increases their contents in tubers.

Kohlrabi (Brassica oleracea L. var. gongylodes L.) was biofortified with selenium (Se), as selenite and selenate, and iodine (I), as iodide and iodate, and their combinations through foliar spraying, to study absorption of these elements by the plants, separately and in combination. The effects on selected physiological and morphological traits and optical characteristics were monitored. Treatments with Se positively affected total chlorophylls and carotenoids, and leaf stomata dimensions. Addition of I decreased total chlorophylls and increased anthocyanins. In reflectance spectra of the leaves, specific colour regions differed significantly due to the different treatments. Reflectance in the UV correlated positively with Se and I contents of the leaves, which indicated lower demand for production of phenolic compounds. Differences in reflectance in UV part of the spectra could be a consequence of changes in the cuticle. The Se and I levels increased markedly in leaves and tubers, without loss of biomass or yield. Se had antagonistic effects on accumulation of I in leaves. The similar levels of Se and I in the leaves and tubers suggest that the transport of both elements in these plants occurs from the leaves to the tubers through the phloem. According to the Se and I contents in the kohlrabi tubers, biofortification with both elements simultaneously is feasible for human nutrition.

Influence of reflective foil on persimmon (Diospyros kaki Thunb.) fruit peel colour and selected bioactive compounds.

The purpose of this work was to investigate how to overcome the negative effect of anti-hail netting on the photosynthetic photon flux density (PPFD) in persimmon trees and persimmon fruit colour, flesh firmness, total soluble solids (TSS) and individual carotenoid and phenolic compound contents (determined via HPLC-MS) under a hail net with the use of reflective foil. Reflective foil increased the PPFD on the lower side of the fruits, while there was no significant difference on the upper side compared to those of the control group. The CIE colour parameters a* and h° indicated more intense red colouration of the fruits in the foil treatment than those in the control. Among carotenoids, the content of ß-carotene increased, and the content of zeaxanthin decreased in fruits in the reflective foil treatment group, while the content of other carotenoids was not affected by the reflective foil. Among individual phenolic compounds in the persimmon peel, greater light intensity significantly influenced all three phenolic compound subgroups: phenolic acids, flavan-3-ols and flavonols. The content of gallic acid in the persimmon flesh increased the most, while other phenolics did not show any significant differences in concentrations between the foil and control groups. This study is the first to examine the influence of reflective foil on bioactive compounds in persimmon fruit. The use of reflective foil in persimmon orchards improves persimmon fruit colour and selected bioactive compound contents.

Biofortification of common buckwheat microgreens and seeds with different forms of selenium and iodine.

BACKGROUND: The biofortification of crops can counteract human diseases, including selenium (Se) and iodine (I) deficiencies in the diet. Little is known about the effects of combinations of Se and I on microgreens and seeds, or on their accumulation in these tissues. The present study aimed to evaluate Se (SeO3 2- , SeO4 2- ) and I (I- , IO3 - ) biofortification of common buckwheat microgreens and seeds with respect to the effects of the addition of Se, I and Se + I on yield and on physiological and biochemical characteristics. RESULTS: In combination treatments, microgreens yield (600-800 g m-2 ) was 50-70% higher than for Se and I alone. The respiratory potential also increased by 60-120%. Fv /Fm was close to 0.8 in all samples. Se content [0.24 µg g-1 dry weight (DW)] was 50% higher for combination treatments than for Se and I alone. I content was highest for IO3 - treatment (216 µg g-1 DW) and decreased in combination treatments with Se by 50%. CONCLUSION: Biofortification of buckwheat microgreens with Se and I should be performed with care because there are synergistic and antagonistic effects of these elements with respect to their accumulation. IO3 - for the biofortification of microgreens should be kept low to prevent exceeding the recommended daily intake of I. © 2019 Society of Chemical Industry.

Is foliar enrichment of pea plants with iodine and selenium appropriate for production of functional food?

Pea (Pisum sativum L.) plants were sown in a field and foliar sprayed at blooming stage with solutions of different forms of iodine (I) - I- and IO3- and selenium (Se) - SeO32- and SeO42-. The possibility of enrichment of pea seeds to nutritionally important levels of both elements and their distribution through the plant parts were studied. To evaluate stress caused by application of I and Se, some morphological, physiological and biochemical characteristics were determined. The results showed elevated concentrations of both elements in all parts of pea plants. In seeds, I content was more than 6-fold higher, while Se content was up to 12-fold higher than in control plants. Although the plants were in good condition, some differences in pod characteristics and electron transport system activity were observed. Glutathione content was not affected by any treatment and only the I- + SeO42- combination decreased the amount of anthocyanins in plants.

Photosynthetic Traits of Plants and the Biochemical Profile of Tomato Fruits Are Influenced by Grafting, Salinity Stress, and Growing Season.

Changes in the photosynthetic traits of plants and metabolic composition of fruits of two tomato cultivars, grafted onto two rootstocks, grown in three salinity levels were studied in two growing periods during the season. Increased salinity stress conditions lowered water potential, stomatal conductance, and transpiration rate of grafted tomato plants, in both growing periods. Water deficit induced stomatal closure, which resulted in stomatal limitation of photosynthesis. The proline content in tomato leaves increased and was closely correlated with salinity. Some of the quality parameters of tomato fruits were affected by rootstock. The sugar/acid ratio was the highest in fruits of 'Belle'/'Maxifort' grafts. With increasing salt stress conditions from 40 to 60 mM NaCl, the lycopene content increased and ascorbic acid content decreased in fruits of 'Gardel'/'Maxifort' grafts, indicating the ability of this scion/rootstock combination to mitigate the toxicity effect of salinity stress. A higher phenolics concentration in fruits from the first growing period may be an additional indicator of stress, caused by higher temperatures and solar radiation, compared with the later period.

Sorbus aucuparia and Sorbus aria as a Source of Antioxidant Phenolics, Tocopherols, and Pigments.

Due to its nutritive and medicinal properties, berries of some Sorbus species are used for the preparation of jams and jelly as well as in traditional medicine. On the other hand, their chemical composition is not much studied especially of those grown in Balkan Peninsula. We have analyzed individual phenolics, tocopherols, carotenoids and chlorophylls using HPLC in berries from Sorbus aucuparia and Sorbus aria collected in different localities in Serbia and Montenegro together with the amounts of total phenolics and proanthocyanidins as well as their radical scavenging activity against DPPH radical. Berries of S. aucuparia were richer source of polyphenolics in comparision with S. aria and, regardless the species and locality, caffeoylquinic acids such as neochlorogenic and chlorogenic acid were the most abundant compounds. Among analyzed tocopherols the most abundant in all samples was α-tocopherol (0.48 - 19.85 µg/g dw) as it was ß-carotene among carotenoids (mean concentration of 0.98 µg/g dw in S. aucuparia and 0.40 µg/g dw in S. aria, respectively). Correlation between total phenolics and DPPH radical scavenging activity was noticed. Our study represents comprehensive report on chemical composition of S. aucuparia and S. aria which could contribute to a better understanding of their quality.

Seed soaking in I and Se solutions increases concentrations of both elements and changes morphological and some physiological parameters of pea sprouts.

Pea (Pisum sativum L., cv. 'Petit Provencal') seeds were soaked in solutions of different iodine (I) and selenium (Se) forms (1000 mg I L-1 and 10 mg Se L-1). Iodine and selenium content in different parts of pea sprouts, as well as morphological, biochemical and physiological characteristics were measured in sprouts. The results showed increased concentrations of both elements in sprouts grown from treated seeds. Soaking influenced the biomass and height of the sprouts. Significant differences between plants grown from treated seeds in comparison with control plants were also observed for electron transport system activity and concentrations of tocopherol and glutathione. On the other hand, the content of photosynthetic pigments and anthocyanins remained similar as in control plants. Potential photochemical efficiency of photosystem II was close to theoretical maximum 0.8 in all samples. From the pattern of changes of stress indicators we suppose that plants adapted to the stress earlier in the experiment, i.e. before they were sampled for physiological measurements.

Influence of Yellow Light-Emitting Diodes at 590 nm on Storage of Apple, Tomato and Bell Pepper Fruit.

The objective of this study is to investigate the effects of irradiation from light-emitting diodes (LEDs) on several fruits during storage. To improve storage and increase the contents of some bioactive compounds, apple, tomato and red bell pepper fruits were exposed to yellow light emitted from the diodes at 590 nm. The contents of ascorbic acid, total phenolics, total flavonoids and several pigments were investigated, along with the antioxidant potential. The colour parameters (L*, a* and b*) and firmness of the fruit were also determined. After 7 days of LED light irradiation, there was significantly higher total phenolic content and antioxidant potential in apple peel extracts. The irradiated fruit of tomato had significantly higher levels of total phenolic compounds, and the fruit of red bell pepper had significantly higher antioxidant potential. LED light had no effects on the colour parameters, although there was a tendency to accelerate colour development. Apple fruit irradiated with LED light was significantly less firm. Among twelve analysed pigments, significantly more ß-carotene was detected in LED light-irradiated apple and bell pepper fruit, more α-tocopherol and γ-tocopherol in bell pepper fruit, and more lutein in apple peel and bell pepper fruit. The applied LED light slightly accelerated the ripening of the studied fruit, and affected the synthesis of some of the secondary metabolites.

Wild Prunus Fruit Species as a Rich Source of Bioactive Compounds.

Sugars, organic acids, carotenoids, tocopherols, chlorophylls, and phenolic compounds were quantified in fruit of 4 wild growing Prunus species (wild cherry, bird cherry, blackthorn, and mahaleb cherry) using HPLC-DAD-MSn. In wild Prunus, the major sugars were glucose and fructose, whereas malic and citric acids dominated among organic acids. The most abundant classes of phenolic compounds in the analyzed fruit species were anthocyanins, flavonols, derivatives of cinnamic acids, and flavanols. Two major groups of anthocyanins measured in Prunus fruits were cyanidin-3-rutinoside and cyanidin-3-glucoside. Flavonols were represented by 19 derivatives of quercetin, 10 derivatives of kaempferol, and 2 derivatives of isorhamnetin. The highest total flavonol content was measured in mahaleb cherry and bird cherry, followed by blackthorn and wild cherry fruit. Total phenolic content varied from 2373 (wild cherry) to 11053 mg GAE per kg (bird cherry) and ferric reducing antioxidant power antioxidant activity from 7.26 to 31.54 mM trolox equivalents per kg fruits.

Carotenoid and chlorophyll composition of commonly consumed leafy vegetables in Mediterranean countries.

Major chloroplast pigments in five leafy vegetables (chicory-Cichorium intybus, cv. 'Anivip' and cv. 'Monivip', dandelion-Taraxacum officinale, garden rocket-Eruca sativa and wild rocket-Diplotaxis tenuifolia), commonly consumed in Mediterranean countries, have been separated by high-performance liquid chromatography (HPLC) on a reversed-phase column. Three classes of pigments were identified and quantified: xanthophylls (oxygenated carotenoids), carotenes (hydrocarbon carotenoids) and chlorophylls. The contents of the pigments in the analysed leafy vegetables varied significantly. The results indicated that selected leafy vegetables were moderately rich in xanthophylls, primarily lutein (3.87-7.44mg/100g fwt). Other xanthophylls were detected in relatively small quantities. The provitamin A carotenoids (α- and ß-carotene) were also detected, but α-carotene were not present in chicory cultivars and in dandelion. The ratio of chlorophyll a/b varied from 2.44 to 2.67 depending on the species. The highest content of all the analysed constituents was found in the garden rocket.

Remediation of Cu-contaminated soil using chelant and EAOP.

An electrochemical advanced oxidation process (EAOP) was used for treatment of the washing solution obtained during leaching of Cu (364 +/- 2 mg kg(-1)) contaminated soil, with chelant S,S isomer of ethylenediamine disuccinate ([S,S]-EDDS). In the EAOP (constant current density 40 mA cm(-2)), a boron-doped diamond anode was used for the generation of hydroxyl radicals and oxidative decomposition of [S,S]-EDDS-metal complexes in the washing solution. The released Cu was mostly electro-deposited on the stainless-steel cathode. Three consecutive additions of 5 mmol kg(-1) [S,S]-EDDS removed 46% of the Cu from the soil, mostly from carbonate and oxide soil fractions (87 and 99% Cu reduction). The soil Cu oral availability in the simulated stomach and intestinal phases (in vitro physiologically based extraction test) was reduced by 5.5 and 4.6-times. Cu plant availability (in vitro diethylenetriamine pentaacetate test) was reduced by 3.6-times. The discharge solution was clear, almost colorless, with pH 8.4, 0.45 mg L(-1) Cu and 0.01 mM EDDS.

Biochemical responses in leaves of two apple tree cultivars subjected to progressing drought.

The influence of water deprivation on potted apple trees (Malus domestica Borkh.) was investigated. Biochemical responses including ascorbic acid, glutathione (GSH), tocopherols, chlorophylls, carotenoids, free amino acids, and soluble carbohydrates were measured in leaves of diploid 'Elstar' and triploid 'Jonagold Wilmuta' subjected to progressive drought. Leaf water potential was chosen to be the primary indicator of water stress in tested plants. Time courses of measured biochemical parameters showed that mild drought did not significantly affect the chosen stress indicators. Moderate drought increased the concentrations of ascorbic acid, total GSH, beta-carotene, zeaxanthin and alpha-tocopherol, indicating the adaptation to oxidative stress in apple trees. Moderate drought also increased concentration of soluble carbohydrates, mostly due to increased sorbitol concentration. Severe drought negatively affected vitality of apple trees, and caused a decrease in sorbitol concentration. Severe drought also caused decreases in ascorbic acid, total GSH, beta-carotene, alpha-tocopherol and chlorophyll concentrations, which, together with the increase in oxidised GSH concentration, indicated severe damage due to oxidative stress. Severe drought increased free amino acid concentration, which was probably the result of increased proteolysis. Zeaxanthin concentration remained high even in leaves of apple trees subjected to severe drought stress. The results were similar for both tested apple cultivars.

The glutathione system as a stress marker in plant ecophysiology: is a stress-response concept valid?

Environmental stress impacts cause an increased formation of reactive oxygen species (ROS) in the chloroplasts (photo-oxidative stress). The role of glutathione in the antioxidative defence system provides a rationale for its use as a stress marker. However, responses of glutathione concentrations and redox states are not consistent among the large number of available publications. In the present review the hypothesis that stress responses of the glutathione system follow a general ecophysiological stress-response concept is investigated. In this view, an initial response phase would be followed by an acclimation phase where a new steady-state is established. Alternatively, if successful acclimation is not achieved, degradation of the system will follow. Recent publications dealing with responses to photochilling, salinity, and drought are analysed as to whether the results fit the concept. In general, an initial stress response was related to changes in the glutathione redox state, whereas acclimation was marked by increased glutathione concentrations, increased related enzyme activities, and/or a more reduced redox state of glutathione. The latter was interpreted as overcompensation leading to enhanced regeneration of glutathione. Deterioration effects upon strong stress impacts were related to progressive degradation and oxidation of the glutathione pool. A time-course analysis, which has rarely been done in the published literature, showed this sequence of events. When apple trees were subjected to progressing drought, the initial response was a slight oxidation of the glutathione pool, followed by increased glutathione concentrations. When the stress increased, glutathione concentrations dropped and redox state became more oxidized, which marked the degradation of the system. In spite of the general congruency of these results with the suggested stress-response concept, several limitations have to be highlighted: The importance of the glutathione system relative to other components of the photoprotective and antioxidative defence system, as well as relative to stress avoidance strategies, has to be established. It is suggested that a variety of parameters taking into account alternative protection pathways (e.g. photorespiration, light dissipation) and other components of the antioxidative systems should be measured. Within such response patterns the glutathione system is a valuable stress marker in ecophysiological studies.