Interactive effects of elevated CO2 and ozone on leaf thermotolerance in field-grown Glycine max

Is Tempranillo Blanco Grapevine Different from Tempranillo Tinto Only in the Color of the Grapes? An Updated Review

Tempranillo Blanco is a somatic variant of Tempranillo Tinto that appeared as a natural, spontaneous mutation in 1988 in a single shoot of a single plant in an old vineyard. It was vegetatively propagated, and currently wines from Tempranillo Blanco are commercially available. The mutation that originated Tempranillo Blanco comprised single-nucleotide variations, chromosomal deletions, and reorganizations, losing hundreds of genes and putatively affecting the functioning and regulation of many others. The most evident, visual change in Tempranillo Blanco is the anthocyanin lost, producing this grapevine variety bunches of colorless grapes. This review aims to summarize from the available literature differences found between Tempranillo Blanco and Tinto in addition to the color of the grapes, in a climate change context and using fruit-bearing cuttings grown in temperature-gradient greenhouses as research-oriented greenhouses. The differences found include changes in growth, water use, bunch mass, grape quality (both technological and phenolic maturity), and some aspects of their photosynthetic response when grown in an atmosphere of elevated CO2 concentration and temperature, and low water availability. Under field conditions, Tempranillo Blanco yields less than Tempranillo Tinto, the lower weight of their bunches being related to a lower pollen viability and berry and seed setting.

Effect of elevated ozone and carbon dioxide interaction on growth, yield, nutrient content and wilt disease severity in chickpea grown in Northern India

Wilt caused by Fusarium oxysporum, sp. Ciceris (FOC) is an important disease causing losses up to 10% in chickpea yield. Experiments were conducted growing chickpea in free air ozone and carbon dioxide enrichment rings under four treatments of elevated ozone (O3) (EO:60 ± 10 ppb), elevated carbon dioxide (CO2) (ECO2:550 ± 25 ppm), combination of elevated CO2 and O3 (EO + ECO2) and ambient control for quantifying the effect on growth, yield, biochemical and nutrient content of chickpea. For studying the impact on wilt disease, chickpea was grown additionally in pots with soil containing FOC in these rings. The incidence of Fusarium wilt reduced significantly (p < 0.01) under EO as compared to ambient and ECO2. The activities of pathogenesis-related proteins chitinase and β-1,3- glucanase, involved in plant defense mechanism were enhanced under EO. The aboveground biomass and pod weight declined by 18.7 and 15.8% respectively in uninnoculated soils under EO, whereas, in FOC inoculated soil (diseased plants), the decline under EO was much less at 8.6 and 9.9% as compared to the ambient. Under EO, the activity of super oxide dismutase increased significantly (p < 0.5, 40%) as compared to catalase (12.5%) and peroxidase (17.5%) without any significant increase under EO + ECO2. The proline accumulation was significantly (p < 0.01) higher in EO as compared to EO + ECO2, and ECO2. The seed yield declined under EO due to significant reduction (p < 0.01) in the number of unproductive pods and seed weight. No change in the protein, total soluble sugars, calcium and phosphorus content was observed in any of the treatments, however, a significant decrease in potassium (K) content was observed under EO + ECO2. Elevated CO2 (554ppm) countered the impacts of 21.1 and 14.4 ppm h (AOT 40) O3 exposure on the seed yield and nutrient content (except K) in the EO + CO2 treatment and reduced the severity of wilt disease in the two years' study.

Elevated CO2-induced changes in photosynthesis, antioxidant enzymes and signal transduction enzyme of soybean under drought stress

Rising atmospheric [CO2] influences plant growth, development, productivity and stress responses. Soybean is a major oil crop. At present, it is unclear how elevated [CO2] affects the physiological and biochemical pathways of soybean under drought stress. In this study, changes in the photosynthetic capacity, photosynthetic pigment and antioxidant level were evaluated in soybean at flowering stages under different [CO2] (400 μmol mol-1 and 600 μmol mol-1) and water level (the relative water content of the soil was 75-85% soil capacity, and the relative water content of the soil was 35-45% soil capacity under drought stress). Changes in levels of osmolytes, hormones and signal transduction enzymes were also determined. The results showed that under drought stress, increasing [CO2] significantly reduced leaf transpiration rate (E), net photosynthetic rate (PN) and chlorophyll b content. Elevated [CO2] significantly decreased the content of malondialdehyde (MDA) and proline (PRO), while significantly increased superoxide dismutase (SOD) and abscisic acid (ABA) under drought stress. Elevated [CO2] significantly increased the transcript and protein levels of calcium-dependent protein kinase (CDPK), and Glutathione S- transferase (GST). The content of HSP-70 and the corresponding gene expression level were significantly reduced by elevated [CO2], irrespective of water treatments. Taken together, these results suggest that elevated [CO2] does not alleviate the negative impacts of drought stress on photosynthesis. ABA, CDPK and GST may play an important role in elevated CO2-induced drought stress responses.

Exogenously applied growth regulators protect the cotton crop from heat-induced injury by modulating plant defense mechanism

Episodes of extremely high temperature during reproductive stages of cotton crops are common in many parts of the world. Heat stress negatively influences plant growth, physiology and ultimately lint yield. This study attempts to modulate heat-induced damage to cotton crops via application of growth regulators e.g. hydrogen peroxide (H₂O₂ 30ppm), salicylic acid (SA 50ppm), moringa leaf extract (MLE 30 times diluted) and ascorbic acid (ASA 70ppm). Cotton plants were exposed to different thermal regimes by staggering sowing time (field) or exposing to elevated temperatures (38/24 °C and 45/30 °C) for one week during reproductive growth stages (glasshouse). Elevated temperatures significantly induced lipid membrane damage, which was evident from an increased malondialdehyde (MDA) level in cotton leaves. Heat-stressed plants also experienced a significant reduction in leaf chlorophyll contents, net photosynthetic rate and lint yield. Hydrogen peroxide outclassed all the other regulators in increasing leaf SOD, CAT activity, chlorophyll contents, net photosynthetic rate, number of sympodial branches, boll weight and fiber quality components. For example, hydrogen peroxide improved boll weight of heat stressed plants by 32% (supra), 12% (sub) under glasshouse and 18% (supra) under field conditions compared with water treated plants under the same temperatures. Growth regulators, specifically, H₂O₂ protected physiological processes of cotton from heat-induced injury by capturing reactive oxygen species and modulating antioxidant enzymes. Thus, cotton performance in the future warmer climates may be improved through regulation (endogenous) or application (exogenous) hormones during reproductive phases.

Growth, photosynthetic acclimation and yield quality in legumes under climate change simulations: an updated survey

Continued emissions of CO2, derived from human activities, increase atmospheric CO2 concentration. The CO2 rise stimulates plant growth and affects yield quality. Effects of elevated CO2 on legume quality depend on interactions with N2-fixing bacteria and mycorrhizal fungi. Growth at elevated CO2 increases photosynthesis under short-term exposures in C3 species. Under long-term exposures, however, plants generally acclimate to elevated CO2 decreasing their photosynthetic capacity. An updated survey of the literature indicates that a key factor, perhaps the most important, that characteristically influences this phenomenon, its occurrence and extent, is the plant source-sink balance. In legumes, the ability of exchanging C for N at nodule level with the N2-fixing symbionts creates an extra C sink that avoids the occurrence of photosynthetic acclimation. Arbuscular mycorrhizal fungi colonizing roots may also result in increased C sink, preventing photosynthetic acclimation. Defoliation (Anthyllis vulneraria, simulated grazing) or shoot cutting (alfalfa, usual management as forage) largely increases root/shoot ratio. During re-growth at elevated CO2, new shoots growth and nodule respiration function as strong C sinks that counteracts photosynthetic acclimation. In the presence of some limiting factor, the legumes response to elevated CO2 is weakened showing photosynthetic acclimation. This survey has identified limiting factors that include an insufficient N supply from bacterial strains, nutrient-poor soils, low P supply, excess temperature affecting photosynthesis and/or nodule activity, a genetically determined low nodulation capacity, an inability of species or varieties to increase growth (and therefore C sink) at elevated CO2 and a plant phenological state or season when plant growth is stopped.

Photosynthetic and molecular markers of CO₂-mediated photosynthetic downregulation in nodulated alfalfa

Elevated CO₂ leads to a decrease in potential net photosynthesis in long-term experiments and thus to a reduction in potential growth. This process is known as photosynthetic downregulation. There is no agreement on the definition of which parameters are the most sensitive for detecting CO₂ acclimation. In order to investigate the most sensitive photosynthetic and molecular markers of CO₂ acclimation, the effects of elevated CO₂, and associated elevated temperature were analyzed in alfalfa plants inoculated with different Sinorhizobium meliloti strains. Plants (Medicago sativa L. cv. Aragón) were grown in summer or autumn in temperature gradient greenhouses (TGG). At the end of the experiment, all plants showed acclimation in both seasons, especially under elevated summer temperatures. This was probably due to the lower nitrogen (N) availability caused by decreased N₂-fixation under higher temperatures. Photosynthesis measured at growth CO₂ concentration, rubisco in vitro activity and maximum rate of carboxylation were the most sensitive parameters for detecting downregulation. Severe acclimation was also related with decreases in leaf nitrogen content associated with declines in rubisco content (large and small subunits) and activity that resulted in a drop in photosynthesis. Despite the sensitivity of rubisco content as a marker of acclimation, it was not coordinated with gene expression, possibly due to a lag between gene transcription and protein translation.

A novel system for in situ determination of heat tolerance of plants: first results on alpine dwarf shrubs

BACKGROUND

Heat stress and heat damage to plants gain globally increasing importance for crop production and plant survival in endangered habitats. Therefore the knowledge of heat tolerance of plants is of great interest. As many heat tolerance measurement procedures require detachment of plants and protocols expose samples to various heat temperatures in darkness, the ecological relevance of such results may be doubted. To overcome these constraints we designed a novel field compatible Heat Tolerance Testing System (HTTS) that opens the opportunity to induce controlled heat stress on plants in situ under full natural solar irradiation. Subsequently, heat tolerance can be evaluated by a variety of standard viability assays like the electrolyte leakage test, chlorophyll fluorescence measurements and visual assessment methods. Furthermore, recuperation can be studied under natural environmental conditions which is impossible when detached plant material is used. First results obtained on three alpine dwarf - shrubs are presented.

RESULTS

When heat tolerance of Vaccinium gaultherioides Bigelow was tested with the HTTS in situ, the visual assessment of leaves showed 50% heat injury (LT50) at 48.3°C, while on detached leaves where heat exposure took place in small heat chambers this already happened at 45.8°C. Natural solar irradiation being applied during heat exposure in the HTTS had significantly protective effects: In Loiseleuria procumbens L. (Desv.), if heat exposure (in situ) took place in darkness, leaf heat tolerance was 50.6°C. In contrast, when heat exposure was conducted under full natural solar irradiation heat tolerance was increased to 53.1°C. In Rhododendron ferrugineum L. heat tolerance of leaves was 42.5°C if the exposure took place ex situ and in darkness, while it was significantly increased to 45.8°C when this happened in situ under natural solar irradiation.

CONCLUSIONS

The results obtained with the HTTS tested in the field indicate a mitigating effect of natural solar irradiation during heat exposure. Commonly used laboratory based measurement procedures expose samples in darkness and seem to underestimate leaf heat tolerance. Avoidance of detachment by the use of the HTTS allows studying heat tolerance and recuperation processes in the presence of interacting external abiotic, biotic and genetic factors under field conditions. The investigation of combined effects of heat exposure under full solar irradiation, of recuperation and repair processes but also of possible damage amplification into the results with the HTTS appears to be particularly useful as it allows determining heat tolerance of plants with a considerably high ecological significance.

Impact of elevated levels of atmospheric CO2 and herbivory on flavonoids of soybean (Glycine max Linnaeus)

Atmospheric levels of carbon dioxide (CO2) have been increasing steadily over the last century. Plants grown under elevated CO2 conditions experience physiological changes, particularly in phytochemical content, that can influence their suitability as food for insects. Flavonoids are important plant defense compounds and antioxidants that can have a large effect on leaf palatability and herbivore longevity. In this study, flavonoid content was examined in foliage of soybean (Glycine max Linnaeus) grown under ambient and elevated levels of CO2 and subjected to damage by herbivores in three feeding guilds: leaf skeletonizer (Popillia japonica Newman), leaf chewer (Vanessa cardui Linnaeus), and phloem feeder (Aphis glycines Matsumura). Flavonoid content also was examined in foliage of soybean grown under ambient and elevated levels of O3 and subjected to damage by the leaf skeletonizer P. japonica. The presence of the isoflavones genistein and daidzein and the flavonols quercetin and kaempferol was confirmed in all plants examined, as were their glycosides. All compounds significantly increased in concentration as the growing season progressed. Concentrations of quercetin glycosides were higher in plants grown under elevated levels of CO2. The majority of compounds in foliage were induced in response to leaf skeletonization damage but remained unchanged in response to non-skeletonizing feeding or phloem-feeding. Most compounds increased in concentration in plants grown under elevated levels of O3. Insects feeding on G. max foliage growing under elevated levels of CO2 may derive additional antioxidant benefits from their host plants as a consequence of the change in ratios of flavonoid classes. This nutritional benefit could lead to increased herbivore longevity and increased damage to soybean (and perhaps other crop plants) in the future.