Reduction In Net Photosynthetic Rate Research Articles

Severe Preharvest Drought Elevates Respiration and Storage Rot in Postharvest Sugarbeet Roots

ABSTRACTSugarbeets are largely produced without irrigation, making drought stress inevitable when rainfall is insufficient. Whether drought stress impacts root storage, however, is currently unknown. Research was conducted to determine the effect of preharvest water stress on postharvest sugarbeet root respiration rate and susceptibility to storage rots as these traits are the primary determinants for sucrose loss and quality deterioration. Greenhouse‐grown plants were subjected to four levels of water deficit by discontinuing watering for 0, 7, 14 or 21 days prior to harvest. Plants receiving water‐restrictive treatments displayed physiological stress by leaf epinasty, reductions in net photosynthetic rate and leaf relative water content and increases in leaf temperature, whereas the water content of roots harvested from these plants progressively decreased with the severity of the preharvest water‐deficit treatment. Harvested roots from all watering treatments were stored at 10°C and 95% relative humidity for up to 12 weeks and evaluated for respiration rate and susceptibility to storage rot. Root respiration rate during storage was inversely related to root water content at harvest by second‐order equations, such that respiration was not significantly affected by minor reductions in root water content but increased exponentially for roots obtained from severely drought‐stressed plants with water contents at harvest of ≤75%. Similarly, roots with water contents ≤75% had elevated levels of electrolyte leakage, a measure of cellular membrane damage, and were more susceptible to dehydration and fungal infection during storage. In separate experiments, roots harvested from water‐stressed plants were inoculated with Botrytis cinerea or Penicillium vulpinum, two causal agents for storage rots. In these experiments, preharvest water stress quantitatively increased root rot and qualitatively altered symptoms of their infection. Overall, these results demonstrate that severe preharvest drought stress is likely to significantly increase sugarbeet root storage losses caused by root respiration and storage rots and that storage losses are likely to accelerate with time in storage. However, mild‐to‐moderate drought conditions prior to harvest are expected to have no or minimal effect on storage losses from root respiration or storage rots.

Heat Stress Effects on Leaf Physiological Performances, Vegetative Growth and Grain Yield of Grain Corn (Zea mays L.)

The impact of climate change on agricultural production will be most pronounced in tropical and subtropical regions, with numerous climate modeling studies predicting more occurrences of heat waves in the future. Elevated temperatures resulting from global warming pose a significant threat to the agricultural sector, as warmer conditions can hinder plant growth and development, leading to reduced crop yields or even crop failure under extreme circumstances. Therefore, this study aimed to determine the effects of ambient, non-heated (30 °C) and heat stress conditions (38 °C) on the plant physiological responses, growth and yield of grain corn during both the vegetative and reproductive stages. The results demonstrated that exposure to heat stress for 7 days significantly impacted the physiological performance of the plants, resulting in a substantial 46.9% reduction in net photosynthetic rate. However, prolonged exposure to heat for 28 days caused even more severe effects, with a 72.5% reduction in net photosynthetic rate. Although the effects of heat stress on vegetative growth were not apparent after 7 days, the plants exhibited severe damage after 28 days of heat stress treatment. During the flowering stage, heat stress led to significant reduction in kernel set, total kernel number, and grain weight of grain corn by 45%, 41%, and 46%, respectively. Poor and scattered kernel set on cobs during the heat stress treatment at the anthesis period indicated damage to pollen grains, failed pollination, and fertilization. These findings highlight the vulnerability of grain corn varieties cultivated in Malaysia to the negative impacts of heat stress, leading to potential losses in production yield.

Improving photosynthesis and drought tolerance in Nicotiana tabacum L. by foliar application of salicylic acid

Drought causes a decrease in tobacco yield and quality as well as a reduction in net photosynthetic rate. Salicylic acid (SA) is involved in the regulation of many physiological processes and has been widely used to improve plant drought tolerance. The hydroponic experiment was carried out on flue-cured tobacco variety K326. SA solutions (0.3 mM) were sprayed on the leaves every day for three days, after which 15% PEG-6000 was used to simulate moderate drought. The results showed that drought stress reduced the photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate (Tr), while it enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), proline and protein content. Compared with PEG drought stress, SA improved the Pn, Gs and Tr by 45.74%, 26.82%, and 52.22% respectively. Besides, the activities of SOD, POD, CAT, protein and proline content increased by 44.27%, 50.18%, 25%, 34.69% and 24.88%, respectively, while the MDA content decreased by 23.89%. Furthermore, SA spraying increased the drought tolerance of tobacco by modulating the expression level of the genes associated with photosynthesis, carbon metabolism, and photosynthesis-antenna proteins. Hence, SA spraying reduced the inhibition of drought on photosynthesis and stimulated the antioxidant system, thus improving the drought resistance in tobacco.

Identification and cloning of early senescence leaf mutant esl13 in rice (Oryza sativa L.)

AbstractSenescence in plants is a complex and highly regulated process. However, the early senescence of leaf directly affects crop yield and quality. Identifying early senescence mutants and understanding its mechanism are critical to crop genetic improvement. In this study, we isolated an early senescence mutant esl13 (early senescence leaf 13) by ethyl methane sulfonate mutagenesis of Xinong 1B. Under paddy field conditions, the leaves of esl13 are normal green at the tillering stage, yellow at the booting stage, and gradually extended to the base of the leaves, and the senescence was most severe at the mature stage. At the booting stage, the leaves of mutant showed significantly lower photosynthetic pigment content, weaker chloroplast autofluorescence, and a highly significant reduction in net photosynthetic rate, resulting in shorter plants heights, shorter spike length, and lower seed yield at the mature stage. Similarly, the activity of antioxidant enzymes catalase, superoxide dismutase, and peroxidase decreased continuously, and malondialdehyde and superoxide anion (O2−) accumulated in the mutant esl13. Genetic analysis showed that the leaf senescence phenotype of esl13 is controlled by a single recessive nuclear gene, which was fine mapped between two molecular markers insertion‐deletion 4‐4 and SNP220 on chromosome 4. Gene sequencing showed that the 1230th base starting from ATG of the candidate gene LOC_Os04g48530 changed from T to A, causing the encoded amino acid change. Genetic complementation experiments confirmed the gene LOC_Os04g48530 controlled the mutant phe notype. This research provides new clues for further elucidating the regulation mechanism of rice senescence.

The influence of ABA on the photosynthesis of the rare and endangered Emmenopterys henryi under salt stress

Emmenopterys henryi Oliv., a monotypic genus in family Rubiaceae with high scientific and application value, is currently endangered. Adaptability of E. henryi to environment is important for its cultivation, management, and application. In this paper, the effect of abscisic acid (ABA) on the photosynthesis of E. henryi under salt stress was discussed. Results showed that 0.3 % (m/v) NaCl led to reduction of net photosynthetic rate (PN), instantaneous carboxylation efficiency (ICE), and Rubisco activity but the increase of intercellular CO2 concentration (ci), which were remarkable relieved by ABA pretreatment. NaCl also induced reduction of the maximal efficiency of PS II photochemistry (Fv/Fm), the photochemical quenching (qP), the non-photochemical quenching (NPQ), the actual PS II efficiency [Y(II)], the regulated-energy dissipation [Y(NPQ)], whereas the increase of the unregulated energy dissipation [Y(NO)]. ABA application remarkably mitigated the depression of Fv/Fm, qP, Y(II) and the increase of Y(NO), but further promoted NPQ and Y(NPQ) in E. henryi due to high salinity. In addition, decrease of chlorophyll content, accumulation of MDA, and ion leakage in E. henryi due to high salinity were significantly alleviated by ABA pretreatment. Fluridone, an inhibitor of endogenous ABA synthesis, partially or completely reversed ABA mediated effects. These results suggested that ABA might improve the photosynthesis of E. henryi under salt stress via allocating more energy to photochemical reactions, or/and mitigating the decrease of Rubisco activity, or/and protecting photosynthetic apparatus by reinforcement of heat dissipation and alleviating oxidative damage.

Effects of photo-selective nets and air humidity coupling on tomato resistance to Botrytis cinerea

Light quality and air humidity play a vital role in plant-pathogen interactions, which profoundly affect the occurrence of crop disease. However, the effect of light quality and air humidity coupling on the interactions between tomato and Botrytis cinerea remains unclear. In this study, 2 humidity levels and 3 colors of photo-selective nets were used to determine the infection process of B. cinerea and the response of plants to pathogen infection. Results showed that low air humidity inhibited the mycelial growth of B. cinerea, and red and blue nets could effectively delay the formation time of pathogen infection structure and reduce the disease incidence. Under high humidity, the reduction of net photosynthetic rate of infected plants was caused by non-stomatal restriction, whereas the changes in light quality by red net reduced the damage of pathogen to tomato photosynthetic structure and improved the photosynthetic capacity of tomatoes. Low air humidity and red net coupling (LR) treatment slowed down the decline of Fv/Fm, ΦPSⅡ and qP; inhibited the increase of malonaldehyde and reactive oxygen contents; increased the activities of antioxidant enzymes in tomato plants; and promoted the quality and yield of fruits. The LR treatment inhibited the infection process of B. cinerea, alleviated the disease severity, improved the photosynthetic and antioxidant capacities, and maintained the fruit quality and yield of tomatoes.

Impact of heat stress on agro-morphological, physio-chemical and fiber related paramters in upland cotton (Gossypium hirsutum L.) genotypes

The unpredictably changing climatic conditions, especially high temperatures, are putting a continuous threat to sustainable cotton production. The current study was designed to investigate the impact of heat stress on several morpho-physiological, biochemical, and fibre quality-related traits. The results revealed the presence of significant variations in agro-morphological, physio-chemical and staple length-related parameters for upland cotton genotypes and stress treatments. Further analysis of pooled data unveiled that heat stress had a detrimental impact on all studied plant traits. Severe reduction in plant height, nodes per plant, sympodial branches per plant, number of bolls per plant, ginning out-turn, and staple length were recorded under heat stress. A significant reduction in net photosynthetic rate (Pn) up to 28.6 % was observed in cotton genotype BH-200 (24.7 to 19.2 µmole m−2 s−1). The accumulation of hydrogen peroxide (H2O2) was increased from 7.1 % in BH-306 to 28.7 % in BH-200 under heat stress due to the incidence of oxidative stress. A substantial increase in the accumulation of antioxidants i.e., catalase (65 %–74 %), peroxidase (54 %–169 %), and superoxide dismutase (52 %–98 %) was seen under high-temperature stress conditions. The correlation coefficient analysis unveiled a significantly positive correlation of seed cotton yield with nodes per plant (r = 0.432*), net photosynthetic rate (r = 0.829**), peroxidase (r = 0.974**), and superoxide dismutase (r = 0.868**), under heat stress conditions. However, a negative but statistically significant correlation of seed cotton yield with ginning out turn (r = −0.466*), staple length (r = −0.898**), hydrogen peroxide (r = −0.955**) and catalase (r = −0.904**) was also observed. The overall results unveiled that cotton genotype BH-232 has a comparatively higher heat tolerance than other contesting genotypes while BH-306 showed the highest susceptibility to heat stress. Hence, BH-232 could be recommended after its approval for general cultivation in heat-prone areas of Pakistan.

Glycolate catabolic bypass pathway integration in rice could be effective in lowering photorespiratory rate with modulating starch content and grain quality

Photorespiration, which is prevalent under higher temperature and arid conditions, significantly affects crop productivity by reducing yields up to 50% in C3 crops like rice under severe stress conditions. This is primarily attributed to a reduction in net photosynthetic rate (PN). Rice flag leaf photosynthesis is the primary supplier of sugar to the maturing spikelets after anthesis. This study evaluated the grain quality traits and starch content of the wild type (WT) and transgenic rice generated by introducing Escherichia coli (E. coli) glycolate catabolic pathway bypassed (GCPB) through agrobacterium mediated transformation. Leaf soluble protein, photosynthetic CO2 assimilation rate, leaf non-structural carbohydrate content, grain quality traits such as hulling and milling percentages, head rice recovery, water uptake, volume expansion, alkali spreading value, gel consistency, grain breadth, grain starch content and amylose content were affected to a great extent in GCPB transgenic plants (T4). This study indicates the possible role of photorespiratory bypass mechanism in the regulation of source-sink communication, starch biosynthesis and grain quality in rice.

The positive effects of exogenous sodium nitroprusside on the plant growth, photosystem II efficiency and Calvin cycle of tomato seedlings under salt stress

Although some studies have shown that exogenous sodium nitroprusside (SNP, an NO donor) participates in the tolerance of plants to stress, the protective role of the level of SNP-mediated endogenous nitrous oxide (NO) on the salt-induced inhibition of photosynthesis in salt-stressed tomato seedlings merits understanding. Thus, in this study, with the exception of tomato seedlings treated with 0 or 100 mmol· L−1 NaCl alone or together with 0.1 mmol· L−1 SNP, 100 μmol· L−1 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO, an NO scavenger) and 100 μmol· L−1 N-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthase) was applied jointly to saline-stressed tomato seedlings by a foliage spray of 0.1 mmol· L−1 SNP, respectively. The application of SNP counteracted the saline-induced growth inhibition and the reduction in net photosynthetic rate of tomato seedlings by enhancing their stomatal conductance, intercellular CO2 concentration, apparent photosynthetic quantum efficiency, PSII maximum photochemical efficiency, actual photochemical efficiency of PSII, non-photochemical quenching coefficient, and a decrease in the dark respiration rate, which is coupled with an increase in the endogenous levels of NO. In addition, treatment with SNP increases the maximum carboxylation rate of ribulose-1,5-bisphosphate carboxylase (Rubisco), the maximum regeneration rate of ribulose-1,5-bisphosphate (RuBP) and the upregulated total and initial activity of Rubisco; the activity in Rubisco activase and fructose-1,6-bisphosphate phosphatase; and the transcriptions of genes that encode Rubisco activase, the Rubisco large subunit, and the Rubisco small subunit, and sedoheptulose-1,7-bisphosphatase, 3-phosphogiyceric acid kinase, transketolase and ribulose-5-phosphate kinase, which are the key enzymes involved in the Calvin-Benson cycle. However, the positive effect of SNP was impaired by the application of PTIO and L-NAME to eliminate the generation of endogenous NO, respectively. Our findings conclusively revealed that SNP triggers the upregulation of endogenous NO signal, which, in turn, conferred tolerance to salinity in tomato seedlings and positively regulated photosynthesis by overcoming stomatal limitations, enhancing the efficiency of photosystem II and maintaining the activation states of the Calvin-Benson cycle through the regulation of gene expressions and activities of key CO2 assimilation enzymes.

Combined influence of low temperature and drought on different varieties of rapeseed (Brassica napus L.)

In recent years, due to the change of farming system, delayed the sowing time of rapeseed, and low temperature and drought would affect the sowing quality, seedling growth, and rapeseed yield.Thirty-one rapeseed materials were screened for low-temperature drought resistance; Zayou15 (ZY15) was selected as low temperature and drought resistance, Huiyou48 (HY48) was established as moderate low temperature and drought resistance, and Huiyou49 (HY49) was identified as low temperature and drought-sensitive.Low temperature and drought stress significantly decreased the germination potential (GP), germination rate (GR), germination index (GI), seed vigor index (SVI) of rapeseed during the germination period and increased the average germination time. Drought intensified the influence of low temperature on germination traits. ZY15 exposed 74-98% germination in 4-5.5 days under 10, 15, and 20°C at all water potentials. HY48 revealed 44-98% germination in 4.5-7 days under 10, 15, and 20°C at all water potentials. Likewise, HY49 disclosed 41-97% germination in 5-8 days under 10, 15, and 20°C at all water potentials. The relative water content of leaves decreased considerably due to drought and low temperature. These also considerably affected the chlorophyll content(Chl). Low-temperature and drought resulted in significant increase of intercellular carbon dioxide (CO2) concentration(Ci), significant reduction in net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), and a decrease in Fv/Fm. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbic peroxidase (APX) increased in rapeseed seedlings by low temperature and drought. The contents of auxin (IAA), gibberellin (GA), and abscisic acid (ABA) in rape leaves were increased under low temperature and drought, while the content of cytokinin (CTK) was decreased. The average performance of ZY15 was better than HY48 and HY49, while HY48 performance was better than HY49 under combine stresses. This study found that antioxidant enzymes and hormones are beneficial for plants to cope with adverse conditions. The current study confirmed that in rapeseed seedlings, the combined effect of low temperature and drought stress negatively impacts seedling growth and development, but this impact varies with varieties and surrounding conditions.

Effect of Cotton Leafroll Dwarf Virus on Physiological Processes and Yield of Individual Cotton Plants.

Cotton leafroll dwarf disease (CLRDD) caused by cotton leafroll dwarf virus (CLRDV) is an emerging threat to cotton production in the United States. The disease was first reported in Alabama in 2017 and subsequently has been reported in 10 other cotton producing states in the United States, including Georgia. A field study was conducted at field sites near Tifton, Georgia in 2019 and 2020 to evaluate leaf gas exchange, chlorophyll fluorescence, and leaf temperature responses for a symptomatic cultivar (diseased plants observed at regular frequency) at multiple stages of disease progression and for asymptomatic cultivars (0% disease incidence observed). Disease-induced reductions in net photosynthetic rate (An, decreased by 63–101%), stomatal conductance (gs, decreased by 65–99%), and efficiency of the thylakoid reactions (32–92% decline in primary photochemistry) were observed, whereas leaf temperature significantly increased by 0.5–3.8°C at advanced stages of the disease. Net photosynthesis was substantially more sensitive to disease-induced declines in gs than the thylakoid reactions. Symptomatic plants with more advanced disease stages remained stunted throughout the growing season, and yield was reduced by 99% by CLRDD due to reductions in boll number per plant and declines in boll mass resulting from fewer seeds per boll. Asymptomatic cultivars exhibited more conservative gas exchange responses than apparently healthy plants of the symptomatic cultivar but were less productive. Overall, it is concluded that CLRDV limits stomatal conductance and photosynthetic activity of individual leaves, causing substantial declines in productivity for individual plants. Future studies should evaluate the physiological contributors to genotypic variation in disease tolerance under controlled conditions.

Evaluation of curcuminoids, physiological adaptation, and growth of Curcuma longa under water deficit and controlled temperature.

Turmeric (Curcuma longa L.; Zingiberaceae), an economically important crop and a major spice in Indian cuisine, produces natural yellow color (curcumin) as well as curcuminoids which are widely utilized in traditional and modern medicinal practices. During the turmeric culture, the fluctuations of precipitation and seasonal changes in the whole life cycle play a major role, especially water shortage and decreasing temperature (in winter season), leading to rhizome dormancy under extreme weather conditions. The objective of this investigation was to understand how the water deficit and reduced temperature affect turmeric growth, physiological adaptation, quantity, and quality of turmeric rhizomes. Four-month-old turmeric plants were subjected to four treatments, namely normal temperature and well-watered (RT-WW), or water-deficit (RT-WD) conditions in the greenhouse, 25°C controlled temperature and well-watered (CT-WW), or water-deficit (CT-WD) conditions in glasshouse. Leaf osmotic potential considerably declined in 30days CT-WD treatment, leading to chlorophyll degradation by 26.04%, diminution of maximum quantum yield of PSII (Fv/Fm) by 23.50%, photon yield of PSII (ΦPSII) by 29.01%, and reduction of net photosynthetic rate (Pn) by 89.39% over CT-WW (control). After 30days water withholding, fresh- and dry-weights of rhizomes of turmeric plants grown under CT-WD declined by 30-50% when compared with RT-WW conditions. Subsequently, curcuminoid content was reduced by 40% over RT-WW plants (control), whereas transcriptional expression levels of curcuminoids-related genes (CURS1, CURS2, CURS3, and DCS) were upregulated in CT-WD conditions. In summary, the water withholding and controlled temperature (constant at 25°Cday/night) negatively affected turmeric plants as abiotic stresses tend to limit overall plant growth performances and curcuminoid yield.

CO2 exchange, dry matter accumulation and growth response of sorghum (Sorghum bicolor L. Moench) to terminal drought as affected by potassium and blended‐NPSBZn fertilization

AbstractSorghum production is constrained by terminal drought stress in semi‐arid areas of north‐eastern Ethiopia. Data from field experiments conducted in the region for two consecutive years (2015 – 2016) were used to investigate the effect of potassium (K) and NPSBZn‐blended fertilizer (BF) inputs on the drought response of sorghum through analysis of gas exchange, dry matter accumulation and growth parameters. Leaf gas exchange properties varied strongly with K and BF application both under normal rainfall and drought conditions. Data taken at anthesis in drought‐exposed sorghum indicated reduction of net photosynthetic rate (AN) with BF supply. AN declined from 15.7 µmol CO2/m2/s in the control to 13.4 µmol CO2/m2/s with application of 164 kg/ha BF. However, higher total dry matter yield was recorded at maturity in response to blended fertilizer and K inputs. Increasing supply of NPSBZn‐blended fertilizer was associated with declining leaf K content, increasing intercellular CO2 concentration and water use efficiency (WUE) during anthesis. Significant variations in crop growth rates were also observed in response to K and BF inputs. At physiological maturity, net assimilation rate (NAR) increased with K and BF inputs both under drought and normal rainfall conditions. In general, K application modulated the response of sorghum to BF input under both normal rainfall and drought conditions. Therefore, grain sorghum could benefit from early supply of K and BF fertilizer in drought prone areas of Northeastern Ethiopia.

Effect of co-inoculation with arbuscular mycorrhizal fungi and phosphate solubilizing fungi on nutrient uptake and photosynthesis of beach palm under salt stress environment

Beach plum (Prunus maritima) is an ornamental plant, famous for its strong salt and drought stress tolerance. However, the poor growth rate of transplanted seedlings has seriously restricted its application in salinized soil. This study investigated the effects of inoculation with arbuscular mycorrhizal fungus (AMF), Funneliformis mosseae, and phosphate-solubilizing fungus (PSF), Apophysomyces spartima, on the growth, nutrient (N, P, and K) uptake, and photosynthesis of beach plum under saline (170 mM NaCl) and non-saline (0 mM NaCl) conditions. We aimed to find measures to increase the growth rate of beach plum in saline-alkali land and to understand the reasons for this increase. The results showed that salinization adversely affected colonization by AMF but positively increased PSF populations (increased by 33.9–93.3% over non-NaCl treatment). The dual application of AMF and PSF mitigated the effects of salt stress on all growth parameters and nutrient uptake, significantly for roots (dry weight and P and N contents increased by 91.0%, 68.9%, and 40%, respectively, over non-NaCl treatment). Salinization caused significant reductions in net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), and intercellular CO2 concentration (Ci) value, while inoculation with AMF and PSF inoculations significantly abated such reductions. The maximum efficiency of photosystem II (PSII) (Fv/Fm), the photochemical quenching coefficient (qP), and the nonphotochemical quenching (NPQ) values were affected little by inoculation with AMF, PSF, or both under non-NaCl treatments. However, plants inoculated with AMF and/or PSF had higher Fv/Fm, qP, and ФPSII values (increased by 72.5–188.1%) than the control under NaCl treatment, but not a higher NPQ value. We concluded that inoculation with AMF or PSF increased nutrient uptake and improved the gas-exchange and Chl fluorescence parameters of beach plum under salt stress environment. These effects could be strengthened by the combination of AMF and PSF, especially for nutrient uptake, root growth, and Pn, thereby alleviating the deleterious effects of NaCl stress on beach plum growth.

English

Canola is a moderately salt tolerant plant, high salinity inhibits germination of seeds, vegetative growth of young plantlets, and reduces biomass production. This study investigated the effects of priming with 1 mM S-methylmethionine (SMM) on germination, leaf gas exchange, induced chlorophyll fluorescence, photosynthetic pigment content and membrane damage through lipid peroxidation by exposing canola (Brassica napus L. cv. Cindi) plants to moderate and severe salt stress (induced by 60 mM and 120 mM NaCl) for different periods. Priming with SMM alleviated the reduction of net photosynthetic rate, the effective quantum efficiency and efficiency of excitation energy capture by open photosystem II reaction centers, chlorophylls to carotenoids ratio, enhanced water use efficiency and contributed to reduction of oxidative membrane damage in fully developed young leaves. Delay and inhibition of seed germination by salt stress were significantly reduced by SMM, as well as the non-photochemical quenching of the singlet excited state of chlorophyll a, suggesting a more efficient protection against hyperosmotic stress, ionic toxicity and associated oxidative stress in primed plants exposed to high salinity. This first assay of SMM as a priming agent for canola plants under high salinity contributes to a better understanding of the mode of action of this natural, plant-derived bioactive compound and the optimization of canola cultivation under the adverse growth conditions caused by salt stress. © 2021 Friends Science Publishers

Exogenous calcium mitigates heat stress effects in common bean: a coordinated impact of photoprotection of PSII, up-regulating antioxidants, and carbohydrate metabolism

Calcium (Ca2+) is involved in mediating anti-stress responses in plants through one or combination of biochemical processes. Thus, the major objective of present study was to assess the protective effect of exogenous Ca2+ (0, 2.5, 5.0, and 7.5 mM) on photosynthetic machinery of cv. Jaguar and SER-16 under heat stress (HS 25–45 °C for 48 h). The applied HS (45 °C) caused substantial reduction in net photosynthetic rate (Pn 73%), photosystem II quantum yield (ΦII 24%), linear electron flow (LEF 13%), and SPAD values (27%) with imbalancing of sugars metabolism and redox potential. At heat stress (40 °C), plants of both cultivars tried to acclimate by regulating leaf temperature through increased stomatal conductance (gs 36%), transpiration rate (E 60%) and by increase in non-photochemical quenching (NPQ 19%). In addition, Ca2+ pre-treatment protected the membrane from oxidative damage by up-regulating the enzymatic activities and down-regulation of malondialdehyde (MDA) accumulation and electrolyte leakage in plant leaf tissues. Pre-treatment with Ca2+ enhanced the accumulation of sugars (glucose, fructose, inositol, and raffinose) in both heat stressed bean plants (45 °C). In conclusion, cv. Jaguar had greater tolerance to HS than SER-16, which is associated with Ca2+-induced photo-protective effect on PSII, the balance between LEF and reactive oxygen species (ROS) generation with concomitant up-regulation of antioxidant enzymes, and increase in compatible solutes. Based on changes in physiological attributes, it is speculated that Ca2+ application might have mediated thermo-tolerance in plants via Ca2+-sensing and signaling pathway, which needs to be verified through molecular studies.

Variability in physiological responses of Venezuelan cacao to drought

AbstractIn order to assess the response of cocoa trees to drought, changes in water status, gas exchange, leaf carbon isotopic ratio (δ13C), photochemical activity, and leaf N and chlorophyll content during the rainy and dry season were measured in 31 Venezuelan cocoa clones (17 Trinitarios, 6 Criollos, and 8 Modern Criollos) grown in a common garden. Drought caused a 40% decrease in water potential (ψ) in all but the Modern Criollos, and a reduction in net photosynthetic rate (A) and stomatal conductance (gs) without an increase in instantaneous water use efficiency (WUE) in 93% of clones, and an increase inδ13C (long-term WUE) in 74% of clones; these responses suggest differences in tolerance to drought among clones. A positive correlation betweenAand bothgsand leaf N content was found for all genotypes. Leaf N content, chlorophyll content, and photochemical activity were reduced during drought, suggesting that metabolism was also inhibited. The best performance during drought was shown by Modern Criollos with the highest WUE, while five Trinitario clones seemed to be less sensitive to drought, since neither chlorophyll, N, total soluble protein concentration, norgschanged with drought, indicating that those Trinitario clones, with lowerA, have a conservative water use. Modern Criollos showed no reductions in eitherψorgs;Aremained unchanged, as did WUE, which was the highest, suggesting that these clones would be more successful in environments with low water availability. Our results indicate large variation in physiological response to drought over a range of parameters, suggesting possible differences in tolerance among clones.

Photosynthetic Cost Associated With Induced Defense to Plasmopara viticola in Grapevine.

Downy mildew caused by Plasmopara viticola is one of the most destructive diseases of Vitis vinifera worldwide. Grapevine breeding programs have introgressed P. viticola-resistant traits into cultivated V. vinifera genotypes and launched interspecific hybrids with resistance against downy mildew. In general, pathogen infection affects primary metabolism, reduces plant growth and development and modifies the secondary metabolism toward defense responses, which are costly in terms of carbon production and utilization. The objective of this work was to evaluate the photosynthesis impairment by inducible defenses at the leaf level in V. vinifera cultivars resistant to P. viticola. Photosynthetic limitations imposed by P. viticola in susceptible and resistant grapevine cultivars were evaluated. Histochemical localization of hydrogen peroxide and superoxide and the activity of ascorbate peroxidase were assessed. Measurements of leaf gas exchange, chlorophyll fluorescence and the response of leaf CO2 assimilation to increasing air CO2 concentrations were taken, and photosynthetic limitations determined in cultivars Solaris (resistant) and Riesling (susceptible). The net photosynthetic rates were reduced (−25%) in inoculated Solaris plants even before the appearance of cell death-like hypersensitive reactions (“HR”). One day after “HR” visualization, the net photosynthetic rate of Solaris was reduced by 57% compared with healthy plants. A similar pattern was noticed in resistant Cabernet Blanc and Phoenix plants. While the susceptible cultivars did not show any variation in leaf gas exchange before the appearance of visual symptoms, drastic reductions in net photosynthetic rate and stomatal conductance were found in diseased plants 12 days after inoculation. Decreases in the maximum Rubisco carboxylation rate and photochemical impairment were noticed in Riesling after inoculation with P. viticola, which were not found in Solaris. Damage to the photochemical reactions of photosynthesis was likely associated with the oxidative burst found in resistant cultivars within the first 24 h after inoculation. Both chlorophyll degradation and stomatal closure were also noticed in the incompatible interaction. Taken together, our data clearly revealed that the defense response against P. viticola causes a photosynthetic cost to grapevines, which is not reversible even 12 days after the pathogen infection.

Improving salt tolerance in potato through overexpression of AtHKT1 gene

BackgroundSurvival of plants in response to salinity stress is typically related to Na+ toxicity, but little is known about how heterologous high-affinity potassium transporter (HKT) may help alleviate salt-induced damages in potato (Solanum tuberosum L.).ResultsIn this study, we used the Arabidopsis thaliana high-affinity potassium transporter gene (AtHKT1) to enhance the capacity of potato plants to tolerate salinity stress by decreasing Na+ content and improving K+/Na+ ratio in plant leaves, while maintaining osmotic balance. Seven AtHKT1 transformed potato lines (namely T1, T2, T3, T5, T11, T13 and T15) were compared with non-transgenic control plant at molecule and whole-plant levels. The lines T3 and T13 had the highest AtHKT1 expression with the tolerance index (an quantitative assessment) being 6.8 times that of the control. At 30 days under 100 and 150 mmol L− 1 NaCl stress treatments, the T3 and T13 lines had least reductions in net photosynthetic rate, stomatal conductance and transpiration rate among the seven lines, leading to the increased water use efficiency and decreased yield loss.ConclusionsWe conclude that the constitutive overexpression of AtHKT1 reduces Na+ accumulation in potato leaves and promotes the K+/Na+ homeostasis that minimizes osmotic imbalance, maintains photosynthesis and stomatal conductance, and increases plant productivity.

Biochemical, Physiological and Anatomical Mechanisms of Adaptation of Callistemon citrinus and Viburnum lucidum to NaCl and CaCl2 Salinization.

Callistemon citrinus and Viburnum lucidum are appreciated and widespread ornamental shrubs for their abundant flowering and/or brilliant foliage. The intrinsic tolerance to drought/salinity supports their use in urban areas and in xeriscaping. Despite adaptive responses of these ornamental species to sodium chloride (NaCl) have been extensively explored, little is known on the effects of other salt solution, yet iso-osmotic, on their growth, mineral composition and metabolism. The present research was aimed to assess responses at the biochemical, physiological and anatomical levels to iso-osmotic salt solutions of NaCl and CaCl2 to discriminate the effects of osmotic stress and ion toxicity. The two ornamental species developed different salt-tolerance mechanisms depending on the salinity sources. The growth parameters and biomass production decreased under salinization in both ornamental species, independently of the type of salt, with a detrimental effect of CaCl2 on C. citrinus. The adaptive mechanisms adopted by the two ornamental species to counteract the NaCl salinity were similar, and the decline in growth was mostly related to stomatal limitations of net CO2 assimilation rate, together with the reduction in leaf chlorophyll content (SPAD index). The stronger reduction of C. citrinus growth compared to V. lucidum, was due to an exacerbated reduction in net photosynthetic rate, driven by both stomatal and non stomatal limitations. In similar conditions, V. lucidum exhibited other additional adaptive response, such as modification in leaf functional anatomical traits, mostly related to the reduction in the stomata size allowing plants a better control of stomata opening than in C. citrinus. However, C. citrinus plants displayed an increased ability to retain higher Cl- levels in leaves than in roots under CaCl2 salinity compared to V. lucidum, thus, indicating a further attempt to counteract chloride toxicity through an increased vacuolar compartmentalization and to take advantages of them as chip osmotica.