Search Results (172)

Non-photosynthetic photoreceptors detecting different wavelength ranges in the UV and visible region of spectra may trigger algal acclimation and homeostasis. We studied Plocamium cartilagineum responses based on the saturation of photosynthesis by Amber light and supplementation by different light qualities, applying an experimental design able to simulate a daily cycle in a fully automated system. Thalli were exposed to Amber, Amber + UV-A, Amber + Blue and Amber + Green radiation treatments under two nitrate levels (60 and 240 μM) for enrichment lasting two weeks. P. cartilagineum photosynthesis and biochemistry were measured during different experimental periods. Photosynthesis showed only slight variations, emphasizing that other response variations could be activated by photomorphogenic pathways. Nitrate assimilation was higher in the treatments containing blue and green lights, potentially caused by increasing nitrate reductase activity. Photosynthetic pigments and mycosporine-like amino acids were affected over the two weeks, being mostly influenced by UV-A and blue radiations with the highest nitrate concentration. The shinorine content of thalli under blue radiation with 240 μM of nitrate increased at day 7, possibly modulated by a blue light photoreceptor. The increase in the bioactive compounds in the short-term by specific light qualities under optimal photosynthetic performance was found to be a relevant biotechnological strategy. Full article

Phenotypic plasticity is an important adaptive strategy that enables plants to respond to environmental changes, particularly temperature fluctuations associated with global warming. In this study, the phenotypic plasticity of Iris pumila leaf traits in response to an elevated temperature (by 1 °C) was investigated under controlled experimental conditions. In particular, we investigated important functional and mechanistic leaf traits: specific leaf area (SLA), leaf dry matter content (LDMC), specific leaf water content (SLWC), stomatal density (SD), leaf thickness (LT), and chlorophyll content. The results revealed that an elevated temperature induced trait-specific plastic responses, with mechanistic traits exhibiting greater plasticity than functional traits, reflecting their role in short-term acclimation. SLA and SD increased at higher temperatures, promoting photosynthesis and gas exchange, while reductions in SLWC, LDMC, LT, and chlorophyll content suggest a trade-off in favor of growth and metabolic activity over structural investment. Notably, chlorophyll content exhibited the highest plasticity, emphasizing its crucial role in modulating photosynthetic efficiency under thermal stress. Correlation analyses revealed strong phenotypic integration between leaf traits, with distinct trait relationships emerging under different temperature conditions. These findings suggest that I. pumila employs both rapid physiological adjustments and longer-term structural strategies to cope with thermal stress, with mechanistic traits facilitating rapid adjustments and functional traits maintaining ecological stability. Full article

Low temperatures can significantly affect the growth of ornamental plants, emphasizing the importance of improving their cold tolerance. However, comparative studies on the photosynthetic responses of sun and shade plants to low temperatures remain limited. In this study, gas exchange, chlorophyll fluorescence in Photosystem II (PSII) and Photosystem I (PSI), the antioxidant system, the osmoregulator substance, and lipid peroxidation were investigated in the shade plant Helleborus viridis (Hv) and the sun plant Lupinus polyphyllus (Lp) during cold acclimation (CA) and the freezing–thaw recovery (FTR). The CA treatment significantly declined the net photosynthetic rate (Pn) and the maximum photochemical efficiency of PSII (Fv/Fm) in Hv and Lp, indicating the photoinhibition occurred in both species. However, Hv exhibited a much better photosynthetic stability to maintain Pn, Fv/Fm, and carboxylation efficiency (CE) than Lp during CA, suggesting that Hv had a greater photosynthetic resilience compared to Lp. Furthermore, Hv preferred to maintain Pn, Fv/Fm, the actual photosynthetic efficiency of PSII (Y(II)), and the actual photosynthetic efficiency of PSI (Y(I)) to consistently provide the necessary energy for the carbon assimilation process, while Lp tended to divert and dissipate excess energy by thermal dissipation and cyclic electron flow during CA. Moreover, there were higher soluble sugar contents in Hv in comparison to Lp. These traits allowed Hv to recover photosynthetic efficiency and maintain cellular integrity better than Lp after the freezing stress. In conclusion, CA significantly reduced the photosynthetic capacity and led to the divergent photosynthetic strategies of both species, which finally resulted in a different freezing tolerance after the freezing–thaw recovery. These findings provide insights into the divergent photoprotective strategies of sun and shade plants in response to cold temperatures. Full article

Accurate photosynthetic parameters obtained from photosynthetic light-response curves (LRCs) are crucial for enhancing our comprehension of plant photosynthesis. However, the task of fitting LRCs is still demanding due to diverse variations in LRCs under different environmental conditions, as previous models were evaluated based on a limited number of leaf traits and a small number of LRCs. This study aimed to compare the performance of nine LRC models in fitting a set of 108 LRCs measured from paddy rice (Oryza sativa L.) grown in field across 3 years under different leaf positions, leaf ages, nitrogen levels, irrigation levels, and varieties. The shape of 108 LRCs varies significantly under a range of leaf traits, which can be typed into three leaf light-acclimation types—high-light leaves (HL-1 and HL-2), and low-light leaves (LL). The accuracy of these models was evaluated by (1) LRCs from three acclimation types: HL-1 and HL-2, and LL; and (2) LRCs across three irradiance stages: light-limited, light-saturated, and photoinhibition. Results indicate that the Ye model emerged as the top performance among the nine models, particularly in the photoinhibition stage of LL leaves, with median values of R², SSE, and AIC of 0.99, 2.39, and −14.03, respectively. Furthermore, the Ye model produced the most accurate predictions of key photosynthetic parameters, including dark respiration (R_D), light-compensation point (I_comp), maximum net photosynthetic rate (P_Nmax), and light-saturation point (I_sat). Results also suggest that P_NImax and I_max were the most appropriate parameters to describe photosynthetic activity at the light-saturation point. These findings have significant implications for improving the accuracy of fitting LRCs, and thus robust predictions of photosynthetic parameters in rice under different environmental conditions. Full article

Numerous challenges are posed by the extra-terrestrial environment for space farming and various technological growth systems are being developed to allow for microgreens’ cultivation in space. Microgreens, with their unique nutrient profiles, may well integrate the diet of crew members, being a natural substitute for chemical food supplements. However, the space radiation environment may alter plant properties, and there is still a knowledge gap concerning the effects of various types of radiation on plants and specifically on the application of efficient and rapid methods for selecting new species for space farming, based on their radio-resistance. Thus, the hypotheses behind this study were to explore the following: (i) the pattern (if any) of radio-sensitivity/resistance; and (ii) if the morphological parameters in relation with pigment content may be a feasible way to perform a screening of radiation responses among species. To perform this, we irradiated dry seeds of basil, rocket, radish, and cress with iron (⁵⁶Fe; 1550 MeV/(g/cm²)) and carbon (¹²C; 290 MeV/u, 13 keV/µm) heavy ions at the doses of 0.3, 1, 10, 20, and 25 Gy to investigate the growth responses of microgreens to acute radiation exposure in terms of morphological traits and photosynthetic pigment content. Results indicate that the microgreens’ reaction to ionizing radiation is highly species-specific and that radiation is often sensed by microgreens as a mild stress, stimulating the same morphological and biochemical acclimation pathways usually activated by other mild environmental stresses, alongside the occurrence of eustress phenomena. Over extended periods, this stimulus could foster adaptive changes, enabling plants to thrive in space. Full article

To reveal the global regulation of photosynthetic electron transport (PET) in shade plants, the changes in chlorophyll a fluorescence induction kinetics (CFI) curves and proteomics were investigated using Hosta varieties. There was a significant difference in CFI curves between Hosta ‘Fire Island’ and other varieties (such as Hosta ‘Sum and Substance’) grown under weak light. Weak light induced the appearance of the W phase of CFI curves in the two varieties, which was consistent with a clear decrease in the oxygen-evolving complex and a large upregulation of photosystem (PS) II proteins. In Hosta ‘Fire Island’, the O-J rise of the CFI curves increased faster under weak light than under appropriate light, and this was not only accompanied by a large upregulation of the PS II protein but also a great downregulation in cytochrome b₆/f, plastocyanin, and PS I. Moreover, weak light resulted in a considerable increase in photosynthetic rate and Rubisco abundance in Hosta ‘Fire Island’, yet the non-photochemical quenching and abundance of CP24 declined significantly. By contrast, weak light had fewer effects on these parameters in Hosta ‘Sum and Substance’. Therefore, we suggest that the PET is mainly affected by the abundance of PS II, oxygen-evolving complex, cytochrome b₆/f, plastocyanin, and PS I in Hosta plants grown under weak light; meanwhile, the improved photosynthetic capacity under weak light was mainly related to the enhancement of light energy absorption and capture of PS II as well as the increase in the abundance of Rubisco. Full article

Resurrection plants present an attractive model for studying the mechanisms of desiccation tolerance. In addition to drought, the presence of light during desiccation is extremely dangerous. In the present study, we investigated the effect of light during the desiccation of shade and sun Haberlea rhodopensis from two different habitats by measuring the changes in electrolyte leakage, malondialdehyde and proline content, and photosynthetic and antioxidant activities. Moreover, the plasticity and acclimation ability of plants to changing light intensities were studied by desiccating shade plants under high light and sun plants under low light. The most significant differences between shade and sun plants were observed under moderate dehydration. Regardless of some decline in PSII activity in sun plants, it was much higher compared to shade plants. The lower PSII efficiency in the latter was accompanied by a higher extent of excitation pressure and consequently significant enhancement in non-photochemical quenching, Y(NPQ), and especially in the fraction of energy that is passively dissipated as heat and fluorescence, Y(NO). The activity of antioxidant enzymes remained high during the desiccation of H. rhodopensis, being higher in the sun compared to shade plants in an air-dried state. In addition, shade and sun plants showed high acclimation capacity when desiccated at opposite light intensities. Full article

Photoinhibition, a common physiological obstacle in forest regeneration, results from rapid light elevations after removing upper-layer trees, thereby impeding sapling growth and survival. The leaf mass per area (LMA), which reflects the current light environment, may predict saplings’ responses to future elevations in light intensity. However, the relationship between the LMA and photoinhibition sensitivity in boreal forest evergreen conifers remains unclear. In this study, we explored whether the LMA was related to photoinhibition sensitivity in A. sachalinensis saplings. Saplings with a high LMA exhibited higher excitation pressure (1−qP) under the current light environment, leading to increased stress even at low relative light intensities of 3%–17%. A model illustrating the dependence of photosynthetic physiological parameters on the photosynthetic photon flux density (PPFD) revealed that 1−qP significantly decreased with an increasing LMA, while the electron transfer rate (ETR) and non-photochemical quenching (NPQ) significantly increased. Additionally, regardless of the LMA, 1−qP reached near saturation (≈1.0) at a PPFD of 1000 μmol m⁻² s⁻¹, likely owing to the inefficient consumption of excess energy by electron transfer, as indicated by the low maximum ETR (approximately 25 μmol m⁻² s⁻¹). These findings suggest that although A. sachalinensis exhibits high sensitivity to photoinhibition, a high LMA may reflect physiological acclimation to forthcoming elevations in light exposure, thereby reducing the susceptibility to photoinhibition at present and in the future. Full article

The estuarine anemone Anthopleura hermaphroditica and its symbiont Philozoon anthopleurum are continuously exposed to intense fluctuations in solar radiation and salinity owing to tidal changes. The aim of this study was to evaluate the effects of the tidal cycle, solar radiation, and salinity fluctuations on the photosynthetic and cellular responses (lipid peroxidation, total phenolic compounds, and antioxidant activity) of the symbiont complex over a 24 h period in the Quempillén River Estuary. Additionally, laboratory experiments were conducted to determine the specific photobiological responses to photosynthetically active radiation (PAR), ultraviolet radiation (UVR), and salinity. Our field results showed that the photosynthetic parameters of the symbiont complex decreased with increasing ambient radiation; however, no relationship was observed with changes in salinity. Increased peroxidative damage, total phenolic compound levels, and antioxidant activity were mainly related to increased UVR and, to a lesser extent, PAR. During the dark period, only PAR-exposed organisms returned to the basal levels of photosynthesis and cell damage. Laboratory exposure confirmed the deleterious effects of UVR on the photosynthetic response. The present study suggests that the ability of A. hermaphroditica to acclimate to natural radiation stress is mediated by the concerted action of various physiological mechanisms that occur at different times of the day, under varying levels of environmental stress. Full article

Climate change has emerged as a crucial global issue that significantly threatens the survival of plants. In particular, low temperature (LT) is one of the critical environmental factors that influence plant morphological, physiological, and biochemical changes during both the vegetative and reproductive growth stages. LT, including abrupt drops in temperature, as well as winter conditions, can cause detrimental effects on the growth and development of tomato plants, ranging from sowing, transplanting, truss appearance, flowering, fertilization, flowering, fruit ripening, and yields. Therefore, it is imperative to understand the comprehensive mechanisms underlying the adaptation and acclimation of tomato plants to LT, from the morphological changes to the molecular levels. In this review, we discuss the previous and current knowledge of morphological, physiological, and biochemical changes, which contain vegetative and reproductive parameters involving the leaf length (LL), plant height (PH) stem diameter (SD), fruit set (FS), fruit ripening (FS), and fruit yield (FY), as well as photosynthetic parameters, cell membrane stability, osmolytes, and ROS homeostasis via antioxidants scavenging systems during LT stress in tomato plants. Moreover, we highlight recent advances in the understanding of molecular mechanisms, including LT perception, signaling transduction, gene regulation, and fruit ripening and epigenetic regulation. The comprehensive understanding of LT response provides a solid basis to develop the LT-resistant varieties for sustainable tomato production under the ever-changing temperature fluctuations. Full article

Melatonin (MT) is considered as an antistress molecule that plays a constructive role in the acclimation of plants to both biotic and abiotic stress conditions. In the present study, we assessed the impact of 10 and 100 μM MT foliar spray, on chlorophyll content, and photosystem II (PSII) function, under moderate drought stress, on oregano (Origanum vulgare L.) plants. Our aim was to elucidate the molecular mechanism of MT action on the photosynthetic electron transport process. Foliar spray with 100 μM MT was more effective in mitigating the negative impact of moderate drought stress on PSII function, compared to 10 μM MT. MT foliar spray significantly improved the reduced efficiency of the oxygen-evolving complex (OEC), and PSII photoinhibition (Fv/Fm), which were caused by drought stress. Under moderate drought stress, foliar spray with 100 μM MT, compared with the water sprayed (WA) leaves, increased the non-photochemical quenching (NPQ) by 31%, at the growth irradiance (GI, 205 μmol photons m⁻² s⁻¹), and by 13% at a high irradiance (HI, 1000 μmol photons m⁻² s⁻¹). However, the lower NPQ increase at HI was demonstrated to be more effective in decreasing the singlet-excited oxygen (¹O₂) production at HI (−38%), in drought-stressed oregano plants sprayed with 100 μM MT, than the corresponding decrease in ¹O₂ production at the GI (−20%), both compared with the respective WA-sprayed leaves under moderate drought. The reduced ¹O₂ production resulted in a significant increase in the quantum yield of PSII photochemistry (Φ_PSII), and the electron transport rate (ETR), in moderate drought-stressed plants sprayed with 100 μM MT, compared with WA-sprayed plants, but only at the HI (+27%). Our results suggest that the enhancement of PSII functionality, with 100 μM MT under moderate drought stress, was initiated by the NPQ mechanism, which decreased the ¹O₂ production and increased the fraction of open PSII reaction centers (qp), resulting in an increased ETR. Full article

Water limits may have a disastrous impact on agricultural productivity, and the current climate change scenario presents additional problems for crops that rely on regular rainfall. Reactive oxygen species, such as hydrogen peroxide (H₂O₂), are a recognized stress-sensing mechanism in plants, and may be investigated as an approach for reducing stress impact via systemic acquired acclimation. Here, we looked at how H₂O₂ foliar application impacts tomato plants’ photosynthetic activity, antioxidant system, sugar chemical profile, and osmotic adjustment during drought and recovery. The experiment was in randomized blocks, 3 × 2 factorial design, with no, one, or two foliar application of 1 mM H₂O₂, on plants that were either continually watered or subjected to drought. The plants were tested both during the drought period and after they had resumed irrigation (recovered). Leaf water potential, chlorophyll a fluorescence, gas exchange, lipid peroxidation, H₂O₂ concentrations, phenols, proline, antioxidant enzyme activity, and sugar chemical profile were all measured. Our findings showed that H₂O₂ application generated metabolic alterations in tomato plants independent of water status, and that two applications in drought plants resulted in a 30% decrease in oxidative stress during drought and faster recovery following irrigation return, with greater production of defence-related molecules such as the APX enzyme, phenols, arabinose, and mannose. Continually watered plants also benefited from H₂O₂ application, which increased carbon assimilation by 35%. Full article

Understanding the dynamics of physiological changes involved in the acclimation responses of plants after their exposure to repeated cycles of water stress is crucial to selecting resilient genotypes for regions with recurrent drought episodes. Under such background, we tried to respond to questions as: (1) Are there differences in the stomatal-related and non-stomatal responses during water stress cycles in different clones of Coffea canephora Pierre ex A. Froehner? (2) Do these C. canephora clones show a different response in each of the two sequential water stress events? (3) Is one previous drought stress event sufficient to induce a kind of “memory” in C. canephora? Seven-month-old plants of two clones (’3V’ and ‘A1’, previously characterized as deeper and lesser deep root growth, respectively) were maintained well-watered (WW) or fully withholding the irrigation, inducing soil water stress (WS) until the soil matric water potential (Ψ_msoil) reached ≅ −0.5 MPa (−500 kPa) at a soil depth of 500 mm. Two sequential drought events (drought-1 and drought-2) attained this Ψ_msoil after 19 days and were followed by soil rewatering until a complete recovery of leaf net CO₂ assimilation rate (A_net) during the recovery-1 and recovery-2 events. The leaf gas exchange, chlorophyll a fluorescence, and leaf reflectance parameters were measured in six-day frequency, while the leaf anatomy was examined only at the end of the second drought cycle. In both drought events, the WS plants showed reduction in stomatal conductance and leaf transpiration. The reduction in internal CO₂ diffusion was observed in the second drought cycle, expressed by increased thickness of spongy parenchyma in both clones. Those stomatal and anatomical traits impacted decreasing the A_net in both drought events. The ‘3V’ was less influenced by water stress than the ‘A1’ genotype in A_net, effective quantum yield in PSII photochemistry, photochemical quenching, linear electron transport rate, and photochemical reflectance index during the drought-1, but during the drought-2 event such an advantage disappeared. Such physiological genotype differences were supported by the medium xylem vessel area diminished only in ‘3V’ under WS. In both drought cycles, the recovery of all observed stomatal and non-stomatal responses was usually complete after 12 days of rewatering. The absence of photochemical impacts, namely in the maximum quantum yield of primary photochemical reactions, photosynthetic performance index, and density of reaction centers capable of Q_A reduction during the drought-2 event, might result from an acclimation response of the clones to WS. In the second drought cycle, the plants showed some improved responses to stress, suggesting “memory” effects as drought acclimation at a recurrent drought. Full article

Cold acclimation before winter has been shown to enhance the cold tolerance of evergreen conifers, including Pinus massoniana Lamb., a characteristic heteroblastic foliage tree in the conifer. In the initial growing season of P. massoniana, both primary needle seedlings (PNSs) and secondary needle seedlings (SNSs) are generated. While previous research has highlighted differences in the morphological structure and photosynthetic physiological functions of primary and secondary needles, their response to cold acclimation remains poorly understood. This study aimed to investigate the changes in morpho-anatomical structure, starch grain accumulation, and lignin deposition in the roots, stems, and leaves of PNSs and SNSs during cold acclimation using solid potassium iodide and hydrochloric acid phloroglucinol double-staining techniques. The results revealed that, during cold acclimation, the leaves and stems of PNSs exhibited sensitivity to low-temperature stress, resulting in noticeable shrinkage and fracture of mesophyll and cortical parenchyma cells. Furthermore, the early stages of cold acclimation promoted the accumulation of starch grains and lignin in the seedling tissues. In contrast to PNSs, the leaves and stems of SNSs exhibited a shorter cold acclimation period, attributed to the hydrolysis of starch grains in the epidermal cell walls and the transformation of xylem lignin, which supports cell structure stability and enhances cold resistance. In conclusion, these findings suggest that SNSs displayed a superior cold resistance potential compared to PNSs following cold acclimation, providing a significant theoretical basis for the further screening of cold-tolerant germplasm resources of P. massoniana and the analysis of cold resistance traits in heteroblastic foliage. Full article

The success of using active restoration in Mediterranean-type climate zones mostly depends on an appropriate matching of plant species and specific management prescriptions upon establishment. In this study, we assessed the early growth and short-term physiological acclimation of seven common species found in the sclerophyllous forests in central Chile to water restriction and shading. We established a nursery experiment that included three treatments (T0: sun-exposed and water-restricted, T1: sun-exposed and fully irrigated, and T2: shaded and fully irrigated) and seven tree species differing in their shade and drought tolerance (Quillaja saponaria Molina, Aristotelia chilensis (Mol.) Stuntz, Peumus boldus Molina, Lithraea caustica (Mol.) Hook. and Arn, Luma apiculata (DC.) Burret, Colliguaja odorifera Molina, and Escallonia pulverulenta (Ruiz and Prav.) Pers). We measured the increment in seedling height and different leaf morpho-physiological traits during two months in the dry season. Based on the measured traits, none of the species took advantage of the higher water availability in T1 relative to T0, but most of the species responded to the shade in T2, regardless of their shade or drought tolerance. Height increments due to shade varied from 0% in P. boldus to 203% in L. apiculata. Overall, all the species responded similarly to the treatments in specific leaf area, chlorophyll content index, photosynthetic rate, stomatal conductance, and intrinsic water use efficiency. This suggests that the species exhibited similar acclimation patterns of these parameters to shade and drought, even regarding the variation in midday xylem water potential found in the water-restricted treatment T0 (from −1.5 MPa in P. boldus to −3.1 MPa in E. pulverulenta). In this study, shading had a higher positive effect on the seedling performance of sclerophyllous species than watering, which at operational level highlights the need for investing in tree shelters when using these species in restoration programs. Full article