Global agriculture faces the dual challenge of increasing productivity to meet the growing demand for food, feed, biofuels, and plant-based biomaterials while coping with soil degradation, climate change, and environmental pollution. Biostimulants have emerged as an innovative and sustainable strategy to enhance plant growth, nutrient uptake, and yield, as well as to mitigate the adverse impacts of abiotic and biotic stresses. Numerous studies show that biostimulant application can prevent 15–50% of potential yield losses caused by stressful environmental conditions. This review classifies major groups of biostimulants and examines mechanisms of their plant growth-promoting action at molecular, biochemical, physiological, and rhizospheric levels. Special emphasis is placed on their role in improving plant tolerance to drought, salinity, cold, heat, metal(loid) toxicity, and pest or pathogen attack. Limitations and challenges, including inconsistent results, variability in product efficiency, and the efforts on standardized formulations and application methods are also discussed. Finally, future research directions are highlighted, focusing on optimizing biostimulant performance to enhance crop resilience, productivity, and environmental sustainability.

Chilling has been recognized as a stress factor adversely impacting plant growth and productivity. Even a slight decrease in temperature may significantly reduce crop yield. Recently, biostimulants have emerged as a new tool for enhancing the chilling tolerance of cold-sensitive plants. The early stages of cucumber growth often occur under suboptimal temperatures, which motivated the aim of the current study to assess the effect of a protein hydrolysate (PH) on the physiological performance of young cucumber plants subjected to chilling stress. The results showed that low temperatures caused severe chilling stress by inducing changes in growth, photosynthesis, and nitrogen assimilation. These adverse effects were mitigated when the PH was supplied. The ameliorating effect could be due to a remedial influence on photosynthetic pigment content, facilitating light harvesting and energy utilization. The potential impact of the PH treatment on the redox balance was demonstrated by the activation of the G6PD gene. The possible effect of the biostimulant on nitrate assimilation was tested by measuring nitrate reductase activity, which improved after application of the biostimulant. Moreover, the activity of phenylalanine ammonia-lyase (PAL) in PH-supplied plants was also increased, further confirming the enhanced protective capacity of the plants. All obtained results indicate the beneficial effect of PH application on cucumber plants and their chilling resilience.

Plants belonging to the genus Cotoneaster can be valuable sources of phytochemicals with potential therapeutic properties. The natural habitats of most of these species are situated in Asia, Africa and southern Europe. Introducing them into other climatic conditions could expose them to abiotic and biotic stresses, affecting their bioactive properties. The aim of this study was to assess and compare the performance of four non-native Cotoneaster species (C. roseus, C. hissaricus, C. hsingshangensis, C. nebrodensis) grown in eastern Poland in terms of leaf morphology, anatomy, and efficiency of the photosynthetic apparatus in relation to lipid peroxidation level, being an indicator of oxidative stress. Photosynthetic pigments concentration and chlorophyll a fluorescence parameters were used to evaluate the photosynthetic capacity. The morphological and anatomical analysis of leaves did not show any anomalies or stress symptoms. Cotoneaster roseus was characterized by the highest chlorophyll concentration, viability index (Rfd) and a moderate lipid peroxidation level. On the other hand, the lowest values of photochemical quenching (qP), maximum fluorescence (Fm), Rfd, and quantum yield of the photosystem II (QY) observed for C. nebrodensis might indicate an inferior efficiency of the photosynthetic apparatus in this species; however, it demonstrated the lowest lipid peroxidation level. Nevertheless, the content and proportion of the photosynthetic pigments as well as overall chlorophyll a fluorescence parameters and lipid peroxidation levels indicate a good physiological condition of all examined plants. The observed differences between the species may be rather species specific and genetically established and not indicate their sensitivity to non-native growth conditions. This is the first report about the physiological parameters of the four Cotoneaster species, proving they are well adapted to growth in the climatic conditions of central Europe providing thus a raw material with potential for pharmaceutical applications.

Light emitting diodes (LEDs) have become an alternative to fluorescent lamps for lighting plant tissue culture due to their low energy consumption, low heat emission, monochromatic spectra and long life. The aim of this study was to investigate the effects of LEDs on the rooting of in vitro cultivated raspberry ( Rubus idaeus L. 'Lloyd George') plants and their subsequent ex vitro acclimatization under sunlight in a greenhouse. The plantlets were cultivated in vitro under an illumination system based on Philips GreenPower LED research module. Four groups of LEDs emitting in white (W), red (R), blue (B), mixed (W:R:B:far-red = 1:1:1:1) spectral regions and fluorescent lamps (control) were used in our studies. Photosynthetic photon flux density (PPFD) of treatments was 87 +/- 7.5 mu mol m(-2) s(-1) for 16 h day(-1). Growth parameters, photosynthetic pigments content, net photosynthesis rate, transpiration, chlorophyll a fluorescence (OJIP testof the plantlets were measured after three weeks on rooting medium under the respective light regimes and three months after transplanting to the greenhouse under sunlight. The results indicated that the best rooting (88.22%) was obtained under mixed LED light. Plants cultivated under red LED light had the lowest percentage of rooting, fresh and dry biomass, but the longest shoots were reported. After acclimatization in the greenhouse, their biomass and leaf area did not differ significantly from the plants grown under white and mixed LED lights. Plants micropropagated and rooted under blue light, showed significantly slower growth and biomass accumulation and did not reach the size of plants from the other light treatments even after 90 days in sunlight in the greenhouse.

An investigation is presented of the uptake of Co, Cs, Mn, Ni and Zn and their effects on L. minor’s growth, photosynthetic pigments, photosynthesis, starch and soluble sugars content. In general, the higher the initial exposure concentration, the lower the removal percentage and bioconcentration factor of the elements. An exponential function fitting was obtained when the total pollutant removal per L. minor dry matter is expressed as function of the initial pollutant concentrations. Based on the maximum removal values the following ordering was obtained: Mn > Cs > Zn > Co > Ni. The essential micronutrient Mn and the non-essential element Cs were highly accumulated. Cs shows major similarities to the essential element K, since both elements are taken up through the same transport channels as K. Both Co and Ni have lower EC50 values resulting in a high toxicity, which can be connected with the low removal rate of these elements. Growth and photosynthetic pigments significantly decreased and starch content significantly increased as a function of the concentration. The photosynthetic capacity of L. minor was the most negatively affected by Zn and was enhanced during Mn exposure.

Taphrina deformans (Berk/Tul) is a causal agent of peach leaf curl that causes severe deformation of leaves and, in some cases, affects plant fruits and shoots, thereby exerting an adverse effect on tree yield and vitality. It has the potential to cause epidemics. The present study indicated ultrastructural alterations in the mesophyll cells of peach leaves, Fayette cultivar, in response to infection by T. deformans. Pathogen-induced hypertrophy and hyperplasia are associated with the unbalanced growth of the infected cells. Changes in the shape of the mesophyll cells from cylindrically oval to isodiametric were found. A strong destruction of the cell compartments was established in a thin parietal cytoplasm. The degradation of chloroplast membrane structures was significant. The regular shape of the chloroplasts was lost with the appearance of concavities. The middle lamella was expanded and exhibited the presence of T. deformans hyphae provoking those alterations. They contacted the cell wall but did not entirely disrupt it. This study confirms and complements the ultrastructural picture of peach leaf curl in the dynamic plant-host system.

The use of herbicides is а traditional method for weed control in crop-producing systems. Along with the high effective weed control, herbicides might cause phytotoxicity for crop plants, due to insufficient herbicide selectivity, combining herbicide treatment with unsuitable meteorological conditions, long-term persistence of herbicide in the soil or off-target transfer of the herbicide – drift. Imazamox is a selective herbicide of imidazolinone group, used to control annual and perennial weeds in imidazolinone-resistant (IMI-R) crops. Protein hydrolysates (PHs) are a group of plant biostimulants containing small peptides and free amino acids, reported to ameliorate plant abiotic stress tolerance, including herbicide phytotoxicity. This report evaluates the damaging effect of simulated imazamox drift on growth, photosynthetic performance and productivity of maize plants as well as the efficiency of foliar application by protein hydrolysates as therapy means. The received results demonstrated that the simulated imazamox herbicide drift has a strong inhibiting effect on maize plants. This is well illustrated by the retarded growth of maize plants, their disrupted photosynthetic activity and productivity losses. The foliar supply of PHs to imazamox damaged maize plants ameliorates their photosynthetic performance, growth and crop productivity.

In recent years, light emitting diodes (LEDs), due to their low energy consumption, low heat emission and specific wavelength irradiation, have become an alternative to fluorescent lamps (FLs) in plant tissue culture. The aim of this study was to investigate the effects of various LED light sources on the in vitro growth and rooting of plum rootstock Saint Julien (Prunus domestica subsp. insititia). The test plantlets were cultivated under a Philips GreenPower LEDs research module illumination system with four spectral regions: white (W), red (R), blue (B) and mixed (W:R:B:far-red = 1:1:1:1). The control plantlets were cultivated under fluorescent lamps (FL) and the photosynthetic photon flux density (PPFD) of all treatments was set at 87 ± 7.5 μmol m−2 s−1. The effect of light source on the selected physiological, biochemical and growth parameters of plantlets was monitored. Additionally, microscopic observations of leaf anatomy, leaf morphometric parameters and stomata characteristics were carried out. The results showed that the multiplication index (MI) varied from 8.3 (B) to 16.3 (R). The MI of plantlets grown under mixed light (WBR) was 9, lower compared to the control (FL) and white light (W), being 12.7 and 10.7, respectively. In addition, a mixed light (WBR) favored plantlets’ stem growth and biomass accumulation at the multiplication stage. Considering these three indicators, we could conclude that under the mixed light, the microplants were of better quality and therefore mixed light (WBR) was more suitable during the multiplication phase. A reduction in both net photosynthesis rate and stomatal conductance in the leaves of plants grown under B were observed. The quantum yield (Yield = FV/FM), which represents the potential photochemical activity of PS II, ranged from 0.805 to 0.831 and corresponded to the typical photochemical activity (0.750–0.830) in the leaves of unstressed healthy plants. The red light had a beneficial effect on the rooting of plum plants; the rooting was over 98%, significantly higher than for the control (FL, 68%) and the mixed light (WBR, 19%). In conclusion, the mixed light (WBR) turned out to be the best choice during the multiplication phase and the red LED light was more suitable during the rooting stage.

The aim of this study was to investigate the response of in vitro cultivated highbush blueberry (Vaccinium corymbosum 'Bluecrop') to lighting from different light-emitting diodes (LEDs). The plantlets were cultivated in vitro under an illumination system based on Philips GreenPower LED research module. Four groups of LEDs emitting in white (W), red (R), blue (B), mixed (W:R:B:far-red = 1:1: 1:1) were studied. Growth parameters, content of photosynthetic pigments and chlorophyll a fluorescence of the plants grown under different LED light were measured. LED lighting affects plant growth, morphogenesis and pigments content of highbush blueberry in vitro. The best results with highest fresh and dry weight, multiplication index and number of leaves were obtained under mixed LEDs.

This study aimed to evaluate the effects of the protein hydrolysate Naturamin WSP on the antioxidant defense system and oxidation-related damage of young cucumber plants exposed to chilling stress. Low positive temperatures have a negative effect on plant growth and performance, and besides visible alterations, such as inhibited growth, significant changes occur at the cellular level. Plants grown at low temperature typically suffer from oxidative damage, which leads to increased lipid peroxidation. Moreover, chilling-stressed plants accumulate more proline to protect their cell membranes. The application of biostimulants such as the protein hydrolysate Naturamin WSP can alleviate some of the adverse effects caused by low temperature. Our results indicated an increased activity of guaiacol peroxidase (GPOD) in all plants treated with the biostimulant regardless of the temperature of cultivation. The mitigation of damages caused by chilling stress might be explained by an enhanced anti-oxidative defense, as demonstrated by the activity of guaiacol peroxidases and increased proline concentrations in Naturamin WSP-treated plants.

Maize is one of the most sensitive industrial crops of zinc supply. Questions about fertilisation methods and the type of fertilisers used are the subject of serious scientific discussion. The key objective of this paper was to evaluate the possibilities to recover the yielding potential of Zn-deficient young maize plants by application of nanosized Zn-containing foliar fertilisers. The agronomic response of Zn-deficient maize plants to foliar fertilisation with nanoscale zinc-containing foliar fertilisers was investigated. The study was conducted in two stages: i) planting and growing the plants under controlled conditions in a zinc-deficient environment for three months; and ii) moving the plants and continuing the experiment in field conditions. A single spray with two nanosized zinc-containing foliar fertilisers was carried out. The physiological status of the plants and the dynamic of zinc and micro- and macroelements concentration in plant organs were monitored. The influence of foliar zinc fertilisation on yield and grain structural components has been determined. Our results indicated that zinc fertilisation throughout the initial growth stages plays a decisive role in the formation of the reproductive organs of maize plants. Foliar zinc fertilisers can entirely recover the physiological performance of plants grown under conditions of zinc deficiency.

Herbicides are powerful means for weed control in modern agriculture. However, in some cases they can negatively affect the crops, for example after herbicide drift. One suitable approach, aimed to improve recovery of herbicide-damaged crops, is the therapeutic biostimulant application. The aim of our study was to evaluate the potential of the plant biostimulant Amino Expert((R)) to ameliorate recovering of florasulam + aminopyralid-potassium (Derby((R)) Super) - damaged oilseed rape plants. The experiment included five treatments: 1. Untreated plot, accepted as a control. Treatments 2 and 3 represented Derby((R)) Super 100% (of the registered rate) and Derby((R)) Super 20% respectively. The treatments 4 and 5 included two applications - first by the herbicide and second - by the biostimulant four days later. The observations showed that the herbicide drift caused negative effect on oilseed rape plants distinguished by yellowing and growth retardation, which was visible to the beginning of flowering. On the contrary, the plants received an additional therapeutic application by Amino Expert((R)) Impuls recovered faster and finally developed a higher silique number plant(-1) as well as biological yield. The physiological parameters such as photosynthetic rate and pigments content also confirmed the ameliorative effect of the plant biostimulant application.

This work focuses on developing light environments for the effective regulation of morphogenesis and ex vitro conditions adaptation in micropropagated raspberry plants on the basis of photomorphogenetic control of physiological processes using light-emitting diodes (LEDs). In experiments with cloned plants growing ex vitro in stressful conditions during acclimation, the effects of optical radiation of various spectral combinations from different photosynthetically active radiation (PAR) spectral regions were studied. The data on the plant development and state of the photosynthetic apparatus, features of photosynthetic gas exchange and transpiration, accumulation of photosynthetic pigments, light curves of photosynthesis, and data on growth processes in light modes using combined quasimonochromatic radiation (either mixture of red, green, and blue light or red, far-red, and blue light) with various ratio of the distinct spectral regions were obtained. Photosynthetic apparatus functional activity under different light conditions was studied with chlorophyll fluorescence determination, and plant stress responses to growing under artificial spectral light conditions were characterized. The experiments were accompanied by detailed plant phenotyping at the structural and functional levels. Plant acclimation and photosynthetic improvements in response to added far-red and green light wavelengths to the main red-blue spectrum have been elucidated.

In recent years, the light emitting diodes (LED) have become an alternative to the fluorescence lamp source of light for plant tissue culture, due to their low energy consumption, low heat emission, specific wavelength irradiation etc. The aim of this study was to investigate the effect of LEDs on the growth of in vitro cultivated raspberry (Rubus idaeus L. ‘Lloyd George’). The plantlets were cultivated in vitro under an illumination system based on Philips GreenPower LED research module. Four groups of LEDs emitting in white (W), red (R), blue (B), mixed (W:R:B:far-red=1:1:1:1) lights and fluorescent lamps (control) were used in our studies. Growth parameters, some physiological and biochemical characteristics of the plantlets were measured after three four weeks passages under corresponding light treatment. Our results indicated that different LEDs specifically influence the growth and development of in vitro cultivated raspberry plantlets and could be applied as an efficient lighting system for rapid in vitro micropropagation of Rubus idaeus L. The combination of blue, red, far red and white LEDs (1:1:1:1) stimulated the growth and biomass accumulation, as well as the intensity of net photosynthesis. For optimal results, it would be advisable to shorten the culture period to 3 weeks. This effective and affordable protocol would support the commercial micropropagation of raspberries and other soft fruits.

The object of the experiment was the walnut cultivar Izvor 10, grafted on a walnut rootstock (Juglans regia L.). The plants were propagated by the "Hot Callus" method and grown in containers (501) with peat-pearlite mixture (2:1). The impact of nitrogen fertilization on the growth and the physiological characteristics of young walnut plants was studied Variants of the experiment were: Control (not fertilized). Variant II - 2 g N/ container and Variant III- 4 g N container. The height of the fertilized plants varied from 86 to 107 cm and the stem diameter - from 12.76 to 13.61 mm, while the control plants reached average values of 49.33 cm in height and 10.53 mm in stem diameter and the differences were statistically proven. It was found that fertilization with ammonium nitrate (NH4NO3), in the range of 2 - 4g N/container contributes to a more efficient development and structuring of the photosynthetic apparatus, which, on the other hand is a prerequisite for more intensive photoassimilation and biomass accumulation. It was concluded that fertilization is mandatory for the production of walnut planting material in containers.

Imidazolinone herbicides combined with imidazolinone resistant (IMI-R) crops provide a tool for solving the important problem of the occurrence of weeds during the early growth stages of sunflower.These herbicides inhibit the synthesis of branched chain amino acids by interrupting the key enzyme acetohydroxyacid synthase (AHAS).We studied the imazamox detoxification in an IMI-R sunflower hybrid together with plant growth and photosynthetic performance.Inhibition of photosynthesis and growth were observed as initial effects of imazamox application.A slight decrease in AHAS activity was also noticed.These effects disappeared within two weeks after application.A fast and well-functioning detoxification mechanism for the herbicide, of which the content decreased for about 90 % at 14 d after application, seems to be responsible for this.The activity of the xenobiotic detoxifying enzyme glutathione S-transferases (GSTs) significantly increased after imazamox application.Our results suggest that the metabolite glutathione serves as an auxiliary tool for imazamox detoxification through conjugation reactions realized by the GSTs, thereby taking part in the non-target mechanisms of resistance in IMI-R sunflower hybrids.

A strategy to alleviate soil toxicity, which is gaining popularity in the last years, is bioremediation by inoculation with specific microorganisms. In the present study, we tested the influence of a mixture of four microalgae strains (Scenedesmus incrassatulus, Trachydiscus minutus, Chlorella sp. and Phormidium sp.) on some biochemical parameters of barley plants cultivated on soil contaminated with petroleum products. The aim was to evaluate the effect of microalgae suspension treatment on soil health and on the potential for phytoremediation. For the purpose, the nitrogen assimilation capacity, the levels of oxidative stress as well as the state of both enzymatic and non-enzymatic antioxidant systems in plants were measured. The results clearly show that petroleum-contaminated soil adversely affects the growth and development of the model culture, while treating the soil with the microalgae suspension significantly mitigates the negative impact. This is supported by the lower levels of stress markers and the increasing of some antioxidants in the plants grown on microalgae-treated soil. Therefore, the application of microalgae is an environmentally friendly strategy for improving soil health in areas affected by petroleum pollution.

Biostimulants offer a novel approach for the regulation of crucial physiological processes in plants. Recently, it has been observed that the application of biostimulants on both seeds and plants may ameliorate to some extent the negative effects of abiotic stresses such as drought, heat, salinity, and others. In the climate conditions of Bulgaria, the early developmental stages of warm climate crops, like maize, often occur under suboptimal temperatures. Although the mitigation of abiotic stress is perhaps the most frequently cited benefit of biostimulant formulations, little is known about their influence on chilling-stressed plants. The aim of our study was to evaluate the effects of a biostimulant from the group of protein hydrolysates on both the growth and the photosynthetic performance of chilling-exposed young maize plants grown in controlled environment. Here, we report that application of a protein hydrolysate increased the performance of chilled maize plants, as demonstrated by leaf gas exchange, photosynthetic pigment content, and chlorophyll fluorescence, but did not affect their growth. Nevertheless, based on the better preserved photosynthetic performance of the biostimulant-treated maize plants exposed to chilling, we assume that under subsequent favorable conditions their growth would recover more quickly as compared to the untreated ones.

A comparative study of the effects of exposure to high Cd2+ (50 µM) and excess Zn2+ (600 µM) on photosynthetic performance of hydroponically-grown durum wheat seedlings was performed. At day 8, Cd and Zn were added to the nutrient solution. After 7-days exposure, the chosen concentrations of both metals resulted in similar relative growth rate (RGR) inhibitions of about 50% and comparable retardations of the CO2 assimilation rates (about 30%) in the second developed leaf of wheat seedlings. Analysis of chlorophyll a fluorescence indicated that both metals disturbed photosynthetic electron transport processes which led to a 4- to 5-fold suppression of the efficiency of energy transformation in Photosystem II. Non-specific toxic effects of Cd and Zn, which prevailed, were an inactivation of part of Photosystem II reaction centres and their transformation into excitation quenching forms as well as disturbed electron transport in the oxygen-evolving complex. The specificity of the Cd and Zn modes of action was mainly expressed in the intensity of the toxicity effects: despite the similar inhibitions of the CO2 assimilation rates, the wheat photochemistry showed much more sensitivity to Cd than to Zn exposure.