Search Results (22)

Zephyranthes tubispatha is an Amaryllidaceae species with high ornamental potential, whose seed dispersal coincides with periods of high temperatures (HTs) and long photoperiods. While supraoptimal temperatures (>28 °C) have been shown to induce thermoinhibition, the effect of light on germination dynamics has not yet been explored. The aim was to study the effect of different exposure times to white light (WL) and different light qualities, as well as the interaction with HT, on seed germination. Changes in the endogenous levels of several phytohormones, responses to pharmacological treatments, and O₂^.− production in the embryo were analyzed to gain an understanding of the underlying physiological mechanisms. Our results suggest the presence of a negative photoblastic response of the high-irradiance (HIR) type. Fluridone (an ABA synthesis inhibitor) restored germination in light-exposed seeds to levels close to the dark control, highlighting the importance of ABA content for photoinhibition. The preincubation period at HT (33 °C) significantly influenced germination behavior and photosensitivity at optimal temperature (20 °C). Thermoinhibition depends on changes in phytohormone balance and/or sensitivity, rather than on their absolute concentration. Unlike thermoinhibition, photoinhibition was not associated with the suppression of O₂^.− production in the embryonic root pole, confirming that these environmental signals utilize different regulatory pathways. Full article

Estimated climate change scenarios demand robust coffee cultivars tolerant to supra-optimal temperatures, water deficit, diseases, and other stresses. Wild Coffea species represent important genetic resources for resilience. The study of variations in morphological structures associated with transpiration control, such as stomata, represents an important approach for identifying genotypes with greater stress tolerance. This study evaluated stomatal density and morphology in 48 wild accessions, 24 of Coffea racemosa and 24 of C. zanguebariae, from provinces of Mozambique. Leaf samples provided microscopic images to assess stomatal traits: density (SD), polar diameter (PD), equatorial diameter (ED), stomatal functionality (SF), and leaf dry mass. Principal components were analyzed for all 48 accessions and separately by species. Mean distribution independence was tested with the Mann–Whitney test (p < 0.05). Results revealed inter- and intraspecific variation. The ability to distinguish accessions varies with the set of traits and species. A significant negative correlation between ED and SF was shared by both species, suggesting a conserved functional pattern. This study discusses the differences in stomatal traits between wild and commercial coffee species and aspects related to possible alterations of stomatal structures during their adaptation to climate change. Additionally, it points to accessions with potential use in genetic breeding programs to increase stomatal function and the possible adaptation of new cultivars. Full article

Temperature and salinity level of the imbibition medium play a crucial role in regulating seed germination and seedling emergence, which is also true in microgreen production, where temperature and water potential may influence seed germination alone and/or in combination. In this study, the effects of different temperatures and water potentials in NaCl, alone or in combination, upon germination and early radicle growth, were assessed in two species for microgreen production (Eruca sativa-rocket, and Raphanus sativus-radish). Seeds were germinated at eight constant temperatures (from 5 to 35 °C) and five water potentials (ψ) in NaCl (from 0 to −1.2 MPa). Final germination percentage (FGP) was maximized at 15–20 °C in rocket, and at 20–25 °C in radish. As the temperature increased or decreased, germination was reduced and became less uniform, to a greater extent, at suboptimal temperatures in both species. Across water potentials, FGP values exceeding 50% at the highest temperature in radish indicated a greater tolerance than rocket to supraoptimal temperatures during germination. Across temperatures, FGP and germination speed in both species were progressively depressed as the water potential decreased. The adverse effects of NaCl progressively increased as the temperature moved away from its optimal value. Overall, rocket seeds were able to germinate well (>80%) at 20 °C at salinity levels down to −0.9 MPa, while radish seeds were able to germinate well (≥90%) at 25 °C at salinity levels down to −0.9 MPa. Salt stress tolerance was higher in rocket and radish at low and high temperatures, respectively. Both thermal time and hydrotime requirements were higher in radish because its seeds took longer to germinate. Thermal time and hydrotime may help to predict the germination capacity and time, once the temperature or water potential of the imbibition substrate is known. The findings of this study have important implications for the large-scale industrial production of microgreens. Full article

The marine coccolithophore Emiliania huxleyi (strain PnB 272 B10) was grown in a continuous culture system on a 12:12 light:dark cycle at temperatures from 10 °C to 28 °C under either nutrient-replete or nitrate-limited conditions and at either 493 ppmv (low) or 1003 ppmv (high) partial pressures of CO₂ (pCO₂). The maximum and minimum nutrient-replete growth rates were 0.751 d⁻¹ at 20 °C and 0.365 d⁻¹ at 10 °C, respectively. Ratios of particulate organic carbon (POC) to particulate inorganic carbon (PIC) were independent of pCO₂ and of the degree of nitrate limitation but were temperature dependent and lower at 10 °C and 28 °C than at intermediate temperatures. Nutrient-replete growth rates were higher at high versus low pCO₂ at 25 °C but did not differ significantly at other temperatures. Ratios of POC to particulate nitrogen (PN) were independent of temperature under nutrient-replete conditions (mean ± standard deviation = 5.07 ± 0.48 g g⁻¹) and under nitrate-limited conditions at half the nutrient-replete growth rates at the same temperature and pCO₂ (5.52 ± 0.60 g g⁻¹), but POC/PN ratios were significantly higher at low pCO₂ (7.26 ± 0.88 g g⁻¹) versus high pCO₂ (5.52 ± 0.59 g g⁻¹). Ratios of POC to chlorophyll a were positively correlated with temperature under nitrate-limited conditions and negatively correlated with temperature under nutrient-replete conditions. The ratio of productivity indices under nitrate-limited and nutrient-replete conditions was positively correlated with temperature and exceeded 1.0 at temperatures of 15 °C or higher. Growth efficiencies were significantly reduced at suboptimal and supraoptimal temperatures and by a transition from nutrient-replete to nitrate-limited conditions, but they were not significantly different under high and low pCO₂ conditions. Calcification by this strain of E. huxleyi appeared to be very insensitive to environmental conditions over the range of conditions that we examined. Full article

Climate change models predict temperature increases, which may affect germination, an important stage in the recruitment of individuals in agroecosystems. Therefore, it is crucial to conduct research on how temperature will impact the germination of multipurpose native species. Leucaena diversifolia (Schltdl.) Benth. is native to America and is commonly cultivated around the world due to having a high protein content in seeds, and their trees are used in agrosilvopastoral systems because they fix nitrogen and provide shade and cattle feed. However, climate change affects the critical phases of its life cycle and influences its growth, reproduction, phenology, and distribution. To assess the germination performance of Leucaena diversifolia under different temperatures throughout thermal times, we estimated germination variables and determined cardinal temperatures and thermal time; we also analysed germination and potential distribution under two climate change scenarios. We found significant variations in seed germination (78–98%) and differences in cardinal temperatures (Tb = 5.17 and 7.6 °C, To = 29.42 and 29.54 °C, and Tc = 39.45 and 39.76 °C). On the other hand, the sub-optimal and supra-optimal temperature values showed little differences: 51.34 and 55.57 °Cd. The models used showed variations in germination time for the analysed scenarios and the potential distribution. We confirm that the populations and distribution of L. diversifolia will be altered due to climate changes, but the species retains the ability to germinate under warmer conditions. Full article

Atmospheric carbon dioxide (CO₂) concentrations are increasing and may exceed 800 ppm by 2100. This is increasing global mean temperatures and the frequency and severity of heatwaves. Recently, we showed for the first time that the combination of short-term warming and elevated carbon dioxide (eCO₂) caused extreme upward bending (i.e., hyponasty) of leaflets and leaf stems (petioles) in tomato (Solanum lycopersicum), which reduced growth. Here, we examined additional species to test the hypotheses that warming + eCO₂-induced hyponasty is restricted to compound-leaved species, and/or limited to the Solanaceae. A 2 × 2 factorial experiment with two temperatures, near-optimal and supra-optimal, and two CO₂ concentrations, ambient and elevated (400, 800 ppm), was imposed on similarly aged plants for 7–10 days, after which final petiole angles were measured. Within Solanaceae, compound-leaf, but not simple-leaf, species displayed increased hyponasty with the combination of warming + eCO₂ relative to warming or eCO₂ alone. In non-solanaceous species, hyponasty, leaf-cupping, and changes in leaf pigmentation as a result of warming + eCO₂ were variable across species. Full article

Brassinosteroid hormones (BRs) multitask to smoothly regulate a broad spectrum of vital physiological processes in plants, such as cell division, cell expansion, differentiation, seed germination, xylem differentiation, reproductive development and light responses (photomorphogenesis and skotomorphogenesis). Their importance is inferred when visible abnormalities arise in plant phenotypes due to suboptimal or supraoptimal hormone levels. This group of steroidal hormones are major growth regulators, having pleiotropic effects and conferring abiotic stress resistance to plants. Numerous abiotic stresses are the cause of significant loss in agricultural yield globally. However, plants are well equipped with efficient stress combat machinery. Scavenging reactive oxygen species (ROS) is a unique mechanism to combat the deleterious effects of abiotic stresses. In light of numerous reports in the past two decades, the complex BR signaling under different stress conditions (drought, salinity, extreme temperatures and heavy metals/metalloids) that drastically hinders the normal metabolism of plants is gradually being untangled and revealed. Thus, crop improvement has substantial potential by tailoring either the brassinosteroid signaling, biosynthesis pathway or perception. This review aims to explore and dissect the actual mission of BRs in signaling cascades and summarize their positive role with respect to abiotic stress tolerance. Full article

Industrial hemp (Cannabis sativa L.) as a grain and fiber crop is experiencing a resurgence in North America. Due to governmental prohibition, there has been limited information on regional agronomic production systems including basic information on seed germination. This study was initiated to provide basic information on the relationship between temperature and germination in hemp seed. Germination was measured at constant temperatures ranging from 3 to 42 °C. Cardinal temperatures were determined for two industrial oil crop hemp cultivars (‘Georgina’ and ‘Victoria’). The optimal germination temperature indicated by a high mean germination percentage and rate was between 19 and 30 °C. Optimal (29.6 °C), base (3.4 °C) and ceiling (42.6 °C) temperatures were calculated from a linear regression of the germination rates to reach 50% germination for each temperature. The thermal time for ‘Georgina’ and ‘Victoria’ to reach 50% germination at suboptimal temperatures was 694 and 714 °C h, respectively. The osmotic and solid matrix-primed hemp seeds germinated faster than the untreated seeds, but the final germination percentages were not different. The primed seeds germinated faster at supraoptimal temperatures but did not impact final germination percentages in the thermally inhibited seeds. Full article

Climate changes with global warming associated with rising atmospheric [CO₂] can strongly impact crop performance, including coffee, which is one of the most world’s traded agricultural commodities. Therefore, it is of utmost importance to understand the mechanisms of heat tolerance and the potential role of elevated air CO₂ (eCO₂) in the coffee plant response, particularly regarding the antioxidant and other protective mechanisms, which are crucial for coffee plant acclimation. For that, plants of Coffea arabica cv. Geisha 3, cv. Marsellesa and their hybrid (Geisha 3 × Marsellesa) were grown for 2 years at 25/20 °C (day/night), under 400 (ambient CO₂, aCO₂) or 700 µL (elevated CO₂, eCO₂) CO₂ L⁻¹, and then gradually submitted to a temperature increase up to 42/30 °C, followed by recovery periods of 4 (Rec4) and 14 days (Rec14). Heat (37/28 °C and/or 42/30 °C) was the major driver of the response of the studied protective molecules and associated genes in all genotypes. That was the case for carotenoids (mostly neoxanthin and lutein), but the maximal (α + β) carotenes pool was found at 37/28 °C only in Marsellesa. All genes (except VDE) encoding for antioxidative enzymes (catalase, CAT; superoxide dismutases, CuSODs; ascorbate peroxidases, APX) or other protective proteins (HSP70, ELIP, Chape20, Chape60) were strongly up-regulated at 37/28 °C, and, especially, at 42/30 °C, in all genotypes, but with maximal transcription in Hybrid plants. Accordingly, heat greatly stimulated the activity of APX and CAT (all genotypes) and glutathione reductase (Geisha3, Hybrid) but not of SOD. Notably, CAT activity increased even at 42/30 °C, concomitantly with a strongly declined APX activity. Therefore, increased thermotolerance might arise through the reinforcement of some ROS-scavenging enzymes and other protective molecules (HSP70, ELIP, Chape20, Chape60). Plants showed low responsiveness to single eCO₂ under unstressed conditions, while heat promoted changes in aCO₂ plants. Only eCO₂ Marsellesa plants showed greater contents of lutein, the pool of the xanthophyll cycle components (V + A + Z), and β-carotene, compared to aCO₂ plants at 42/30 °C. This, together with a lower CAT activity, suggests a lower presence of H₂O₂, likely also associated with the higher photochemical use of energy under eCO₂. An incomplete heat stress recovery seemed evident, especially in aCO₂ plants, as judged by the maintenance of the greater expression of all genes in all genotypes and increased levels of zeaxanthin (Marsellesa and Hybrid) relative to their initial controls. Altogether, heat was the main response driver of the addressed protective molecules and genes, whereas eCO₂ usually attenuated the heat response and promoted a better recovery. Hybrid plants showed stronger gene expression responses, especially at the highest temperature, when compared to their parental genotypes, but altogether, Marsellesa showed a greater acclimation potential. The reinforcement of antioxidative and other protective molecules are, therefore, useful biomarkers to be included in breeding and selection programs to obtain coffee genotypes to thrive under global warming conditions, thus contributing to improved crop sustainability. Full article

With the burgeoning population of the world, the successful germination of seeds to achieve maximum crop production is very important. Seed germination is a precise balance of phytohormones, light, and temperature that induces endosperm decay. Abscisic acid and gibberellins—mainly with auxins, ethylene, and jasmonic and salicylic acid through interdependent molecular pathways—lead to the rupture of the seed testa, after which the radicle protrudes out and the endosperm provides nutrients according to its growing energy demand. The incident light wavelength and low and supra-optimal temperature modulates phytohormone signaling pathways that induce the synthesis of ROS, which results in the maintenance of seed dormancy and germination. In this review, we have summarized in detail the biochemical and molecular processes occurring in the seed that lead to the germination of the seed. Moreover, an accurate explanation in chronological order of how phytohormones inside the seed act in accordance with the temperature and light signals from outside to degenerate the seed testa for the thriving seed’s germination has also been discussed. Full article

The selection of most suitable propagation material, as well as the adjustment of existing seedling management practices, are gaining increasing importance to ensure the best outcomes under the long-term setting of climate change. One of the factors to consider is a predicted increase in the frequency and duration of high-temperature periods. Since heat often coincides with drought, these factors are typically assessed together, yet heat stress on its own has received less attention. In this study, we examined the effect of supra-optimal ambient temperature on nine Salix alba clone cuttings wilting under greenhouse conditions and sufficient moisture levels. Most plants are especially vulnerable to extreme conditions in early stages of development. Response to heat varied between clones but, overall, shoots that were taller than 350 mm were more sensitive to heat stress. The pruning of excess lateral shoots did not show significant improvement in heat tolerance. In total, 96% of the wilted cuttings proceeded to produce lateral shoots after the cessation of heat stress. It should be studied further if similar patterns are evident in field conditions and if earlier outplanting has a positive effect on cutting vitality. Full article

Green algae are fast-growing microorganisms that are considered promising for the production of starch and neutral lipids, and the chlorococcal green alga Parachlorella kessleri is a favorable model, as it can produce both starch and neutral lipids. P. kessleri commonly divides into more than two daughter cells by a specific mechanism—multiple fission. Here, we used synchronized cultures of the alga to study the effects of supra-optimal temperature. Synchronized cultures were grown at optimal (30 °C) and supra-optimal (40 °C) temperatures and incident light intensities of 110 and 500 μmol photons m⁻² s⁻¹. The time course of cell reproduction (DNA replication, cellular division), growth (total RNA, protein, cell dry matter, cell size), and synthesis of energy reserves (net starch, neutral lipid) was studied. At 40 °C, cell reproduction was arrested, but growth and accumulation of energy reserves continued; this led to the production of giant cells enriched in protein, starch, and neutral lipids. Furthermore, we examined whether the increased temperature could alleviate the effects of deuterated water on Parachlorella kessleri growth and division; results show that supra-optimal temperature can be used in algal biotechnology for the production of protein, (deuterated) starch, and neutral lipids. Full article

An increase in temperature can have a profound effect on the cell cycle and cell division in green algae, whereas growth and the synthesis of energy storage compounds are less influenced. In Chlamydomonas reinhardtii, laboratory experiments have shown that exposure to a supraoptimal temperature (39 °C) causes a complete block of nuclear and cellular division accompanied by an increased accumulation of starch. In this work we explore the potential of supraoptimal temperature as a method to promote starch production in C. reinhardtii in a pilot-scale photobioreactor. The method was successfully applied and resulted in an almost 3-fold increase in the starch content of C. reinhardtii dry matter. Moreover, a maximum starch content at the supraoptimal temperature was reached within 1–2 days, compared with 5 days for the control culture at the optimal temperature (30 °C). Therefore, supraoptimal temperature treatment promotes rapid starch accumulation and suggests a viable alternative to other starch-inducing methods, such as nutrient depletion. Nevertheless, technical challenges, such as bioreactor design and light availability within the culture, still need to be dealt with. Full article

Eggplant (Solanum melongena) is the third most important vegetable in Asia and of considerable importance in the Mediterranean belt. Although global eggplant production has been increasing in recent years, productivity is limited due to insects, diseases, and abiotic stresses. Genetic engineering offers new traits to eggplant, such as seedless parthenocarpic fruits, varieties adapted to extreme climatic events (i.e., sub- or supra-optimal temperatures), transcription factor regulation, overexpressing osmolytes, antimicrobial peptides, Bacillusthuringiensis (Bt) endotoxins, etc. Such traits either do not occur naturally in eggplant or are difficult to incorporate by conventional breeding. With controversies, Bt-expressing eggplant varieties resistant to eggplant fruit and shoot borers have already been adopted for commercial cultivation in Bangladesh. However, to maximize the benefits of transgenic technology, future studies should emphasize testing transgenic plants under conditions that mimic field conditions and focus on the plant’s reproductive stage. In addition, the availability of the whole genome sequence, along with an efficient in vitro regeneration system and suitable morphological features, would make the eggplant an alternative model plant in which to study different aspects of plant biology in the near future. Full article

Plants are affected by the features of their surrounding environment, such as climate change and air pollution caused by anthropogenic activities. In particular, agricultural production is highly sensitive to environmental characteristics. Since no environmental factor is independent, the interactive effects of these factors on plants are essential for agricultural production. In this context, the interactive effects of ozone (O₃) and supraoptimal temperatures remain unclear. Here, we investigated the physiological and stomatal characteristics of leaf mustard (Brassica juncea L.) in the presence of charcoal-filtered (target concentration, 10 ppb) and elevated (target concentration, 120 ppb) O₃ concentrations and/or optimal (22/20 °C day/night) and supraoptimal temperatures (27/25 °C). Regarding physiological characteristics, the maximum rate of electron transport and triose phosphate use significantly decreased in the presence of elevated O₃ at a supraoptimal temperature (OT conditions) compared with those in the presence of elevated O₃ at an optimal temperature (O conditions). Total chlorophyll content was also significantly affected by supraoptimal temperature and elevated O₃. The chlorophyll a/b ratio significantly reduced under OT conditions compared to C condition at 7 days after the beginning of exposure (DAE). Regarding stomatal characteristics, there was no significant difference in stomatal pore area between O and OT conditions, but stomatal density under OT conditions was significantly increased compared with that under O conditions. At 14 DAE, the levels of superoxide (O₂^-), which is a reactive oxygen species, were significantly increased under OT conditions compared with those under O conditions. Furthermore, leaf weight was significantly reduced under OT conditions compared with that under O conditions. Collectively, these results indicate that temperature is a key driver of the O₃ response of B. juncea via changes in leaf physiological and stomatal characteristics. Full article