Plants growing in temperate regions are often exposed to stress conditions caused by high temperatures. Photosynthesis is one of the metabolic processes most sensitive to high temperature stress, and it is often inhibited before other cellular functions. Using peach leaf disks, we studied the transient chlorophyll a fluorescence along with the gas exchanges at temperatures of 25 (control) 30, 35, 40 and 45°C in the dark for a period of 30 minutes. Temperatures above 35°C caused significant changes in the transient fluorescence of chlorophyll a, including an increase in the initial fluorescence (F0), a decrease in maximum fluorescence values (FM) and the appearance of K and L bands. The values of the net assimilation rate decreased as the temperature increased and reached negative values at 45°C.
This study aimed to characterize the alarm and resistance phases of stress of Caesalpinia echinata under intense irradiance in order to better define its position on forest succession. The alarm phase was identified by rapid reduction in the maximum quantum yield of PSII primary photochemical reactions (ΦP0 = FV/FM) and Performance Index (PIABS) followed by total leaf abscission in the first week of exposure to direct sunlight. The new leaves grown showed recovery of chlorophyll a parameters, increase in blade thickness, elongation of the palisade and spongy parenchymas, higher water content, and reduction of specific leaf area. These changes were associated with the osmoprotector of sucrose and antioxidative of raffinose effects, which indicate an efficient adjustment system to intense irradiance in the resistance phase of stress. However, the continuous decrease in photosynthetic pigments in the resistance phase combined with the photodamage in the fluorescence of Chl a and total abscission of leaves in the alarm phase are strong indications that C. echinata is a shade and late or climax species in forest succession.
A full-length cDNA clone encoding cyclophilin gene of 848 bp, including a 519 bp open reading frame, has been isolated from the cDNA library constructed from etiolated seedlings of Vigna mungo (GenBank FN668732). The cDNA sequence showed 97% identity with Vigna radiata cyclophilin mRNA. The sequence was GC rich and lacked introns. The open reading frame encoded 172 amino acid polypeptide with molecular weight 18.3 kDa and theoretical pI 8.61. BlastP analysis indicated that its putative amino acid sequence shared 100% identity with several plant cyclophilins particularly legumes. The conserved seven amino acid residues region in V. mungo cyclophilin was RSGKPLH (present in legumes) instead of KSGKPLH, indicating its similarity to the cyclophilins of other legumes. This novel V. mungo cyclophilin gene will broaden the pool of plant cyclophilin genes for further studies.
Zinc deficiency is a global problem of considerable importance for agriculture and human health. Under zinc deficiency conditions, many essential zinc-dependent physiological functions are unable to operate normally, and the cellular homeostasis is adversely affected. This paper described the potential damages that low-zinc bioavailability in soil can have for plants, humans, and animals. In addition, current knowledge on physiological and molecular aspects of zinc homeostasis in plants and strategies used to increase zinc deficiency tolerance were discussed.
The growth and nutrient assimilation was evaluated in CaCl2- and CaSO4-supplemented cowpea plants subjected to salt stress (75 mM NaCl). The salinity significantly reduced the cowpea vegetative growth. The addition of CaCl2 in the growth medium did not significantly affect plant growth, while for the CaSO4, the beneficial effects of Ca2+ were moderate. Salinity increased the Na+, K+, Cl-, N and P content in the plants, however it decreased the content of Ca2+ and Mg2+. Increases in Ca2+ concentration in the nutrient solution caused decreases in the Na+ and Mg2+ contents and increases in Ca2+, K+, P, and Cl- contents. The supplemental Ca2+ may alleviate the Na+ toxicity and may improve nutritional and ionic balance in cowpea, but it cannot overcome the osmotic effects associated with the increased total salt concentration.
The effects of NaCl salinity on seed germination, growth, physiology, and biochemistry of two bambara groundnut landraces (Vigna subterranea (L.) Verdc), Kakamega (white seed coat) and Mumias (red seed coat), were investigated with the aim of establishing traits, which can provide a basis for breeding to salt tolerance in groundnuts. A study was conducted under laboratorial and greenhouse conditions. Bambara groundnut seeds and plants were subjected to five concentrations of NaCl solutions with several electrical conductivities: 0 (control), 6.96, 12.93, 19.89, and 25.86 dS m-1. Germination percentage, growth, chlorophyll fluorescence, and leaf chlorophyll content were determined. Sodium chloride salinity (p 0.05) differences in the Fv/Fm values for Mumias' landrace, as compared to the Control. Overall, Mumias' landrace seeds seemed to be more salt-tolerant at higher salinity levels compared to Kakamega. A greater reduction in growth in Mumias than in Kakamega is a possible indicator for salt tolerance. The chlorophyll fluorescence parameters may not be used to identify salt sensitivity between the two landraces. The results indicated that leaf area and seed germination were suitable parameters for screening the two bambara landraces for salt tolerance.
The effects of aminooxyacetic acid, benzyladenine, and 1-methylcyclopropene treatments on the post-production flower quality of potted carnation plants (Dianthus caryophyllus L. Clove Pink) were investigated considering ethylene production and antioxidant metabolism. Maximum plant longevity (17 days) was obtained using 70 ppb of 1-methylcyclopropene. As compared to control plants, ethylene production was significantly decreased by aminooxyacetic acid at concentrations over 100 mg L-1, benzyladenine at 20 or 30 mg L-1, and 1-methylcyclopropene at 70 and 140 ppb. A significant increase in 1-aminocyclopropane-1-carboxylic-acid concentration was observed in 1-methylcyclopropene treated plants compared with the control ones. On the other hand, decline in 1-aminocyclopropane-1-carboxylic-acid concentration was observed after using 100 or 150 mg L-1 of aminooxyacetic acid. Use of 1-methylcyclopropene (70 or 140 ppb), aminooxyacetic acid (100 or 150 mg L-1), and benzyladenine (20 or 30 mg L-1) significantly decreased H2O2 concentration and superoxide radical when compared with the untreated control. Significant increases in activities of superoxide dismutase, catalase, and peroxidase were noticed when plants were treated with 70 ppb 1-methylcyclopropene. In conclusion, aminooxyacetic acid, benzyladenine (at high concentrations), and 1-methylcyclopropene treatments can be suitable candidates for extending plant longevity, maintaining the visual quality, and reducing the loss of flower anthocyanin.
The present study was conducted to evaluate salt tolerance in seven different pure-line cultivars of tomato (Solanum lycopersicum L.) viz. K-21, Pusa Ruby, Pusa Gorav, Hera research, Selection N5, PKM-1 and S-22 based on several physiological and biochemical traits. Seedlings were transplanted to the pots, being exposed to different salinity levels in the form of NaCl (0, 50, 100, or 150 mM) at a 35-day stage of growth for six days. The plants exposed to salt stress presented a significant decline in growth, photosynthetic parameters, maximum quantum yield of PSII and leaf water relations, which were drastically reduced in variety S-22, while variety K-21 was the least affected. Electrolyte leakage was superior in proportion to an increase in salinity levels. Proline content and activity of antioxidant enzymes catalase, peroxidase, and superoxide dismutase were found maximum in variety K-21. Almost all the growth and physiological and biochemical traits had a significant genotypic variation, indicating that these parameters could be used as novel screening criteria for selecting the tolerant and sensitive cultivars exposed to salt stress.
Glutamate metabolism and amino acid translocation were investigated in the control and cadmium stressed shoots of tomato (Solanum lycopersicum - 63/5 F1), using (15N) ammonium and (15N) glutamate tracers. Regardless of organ type, [15N] ammonium assimilation occurred via glutamine synthetase (EC 6.3.1.2), in the control and stressed plants, and it did not depend on glutamate dehydrogenase (EC 1.4.1.2). The [15N] ammonium and ammonium accumulation patterns support the role of glutamate dehydrogenase in the deamination of [15N] glutamate to provide 2-oxoglutarate and [15N] ammonium. In the presence of cadmium, excess [15N] ammonium was incorporated into asparagine, which served as an additional detoxification molecule. In the presence both of methionine sulfoximine and cadmium, glutamate, alanine, and γ-amino butyrate of leaf tissue continued to become labelled with 15N. The labelling kinetics of amino acids in leaves of tomato plants in the presence of cadmium show that continued assimilation of [15N] ammonium can occur when the glutamine synthetase-glutamate synthase cycle is inhibited. The data provided evidence that the glutamine synthetase pathway and glutamate dehydrogenase play distinct roles in the source-sink nitrogen cycle of tomato leaves under cadmium stress conditions.
The role of seed reserves on the ability to resprout and on the responses of resprouting in Araucaria angustifoliawas investigated. Seedlings were separated into three groups: plants which had their shoot damaged, a similar group in which damaged plants had their connection to the supporting seed removed, and a control group. All damaged seedlings resprouted, but those which remained connected to their seeds had a greater mass of resprouted shoots than the ones disconnected from their seeds. A greater accumulation of seed mass in the underground hypocotyl was a very distinct initial response to damage, but, on the long run, damaged plants were able to reestablish a biomass allocation pattern, which was very similar to the control plants. These results indicate that seed and underground reserves are important for the quantitative resprouting response of seedlings of Aangustifolia and for its ability to reestablish the functional balance when severely damaged.
Two maize varieties, viz. Sartaj and Deccan, have been evaluated according to their responses to chromium (Cr) in terms of specific physiological and biochemical attributes. During the exposure to Cr concentration (0, 50, 100, 200 and 300 µM) of potassium dichromate (K2Cr2O7) for seven days, significant changes of oxidative stress in terms of lipid peroxidation and protein oxidation were recorded along with other antioxidative pathways. It is revealed that irrespective of varieties, Sartaj was more prone to oxidative stress since the amount of superoxide due to Cr exposure was found to be significant, unlike the second variety, Deccan. In addition, for Sartaj the activity of NAD(P)H oxidase recorded a significant linear increase in a dose response manner.The changes of antioxidative enzymes recorded significant variation in both varieties under stress compared to control. However, Deccan maintains a consistent up regulation in SOD and GPX activities. Contrarily, APX activity was less sensitive to both varieties. The activation of antioxidative mechanisms due to the impact of Cr-induced oxidative stress has been described subsequently. The results deriving from this investigation might be effective for the selection of tolerant plant types under chromium contamination.
We studied the effects of n-propyl gallate, which is a plastid terminal oxidase inhibitor involved in chlororespiration, on photosynthesis and physiological parameters in Dunaliella salina grown under different salinities and under low or high irradiance using chlorophyll a fluorescence transient measurements and pigment analysis. The inhibitor up to 1 mM had an additive significant effect on the photosynthetic efficiency in the cell suspensions grown under low salinity and irradiance. However, in the presence of high n-propyl gallate concentration (4 mM), there was a negative effect on all physiological aspects. In contrast, this high concentration of the inhibitor could enhance efficiency of electron transport and growth parameters under high irradiance. On the other hand, with salinity increase, the unfavorable effects of high inhibitor concentration on the efficiency of photosystem II were less evident than of low salinity. Interestingly, n-propyl gallate high concentration had a positive effect on fluorescence and on physiological parameters when high salinities-grown cells were exposed to high irradiance. The results suggest that there is a rational correlation between increase of salinity and algae ability to bypass n-propyl gallate inhibited plastid terminal oxidase function and also direct influence of its lethal concentration on photosystem II compartment. The ability is especially substantial when the increase of salinity is accompanying high irradiance. Furthermore, these data show that algal responses to inhibitor concentrations are different under various environmental conditions.
Water supply is the main yield-limiting abiotic factor of oil palm in Colombia. To determine the effect of water deficit on the physiology of oil palm and to assess the tolerance degree to this condition, interspecific Elaeis oleifera versus Elaeis guineensis 'U1273', 'U1859', 'U1914', and 'U1937' hybrids were planted for 60 days in soil with different water potentials (-0.042, -0.5, -1.0, and -2.0 MPa) in a complete randomized factorial design with three replications. The water potential, osmotic adjustment molecules (total and reducing sugar content), gas exchange (photosynthesis rate, stomatal conductance, water use efficiency, and leaf respiration), and vegetative growth (height, bulb diameter, leaf area, number of leaves, total dry matter, and assimilate partitioning between roots and aerial parts) were measured. Soil water potential had a significant effect on the ecophysiological response of the hybrids. At -2 MPa, there was practically no carbon dioxide assimilation. Under optimal moisture conditions, the 'U1859' hybrid recorded the highest photosynthetic rate and the lowest respiratory rate, while under moderate and severe water deficits, the 'U1937' hybrid showed the highest photosynthetic rate, the lowest respiratory rate, moved its assimilates mainly towards the roots, and was the only one to adjust its water potential (active accumulation of sugars). Two environment/genotype tolerance relationships were established based on high photosynthetic rate, low leaf respiration rate, water potential adjustment, water use efficiency under adequate moisture conditions ('U1859'>'U1937'='U1914'>'U1273'), and under water deficit ('U1937'>'U1914'>'U1859'>'U1273').
Nicotiana glauca, a shrub native to southern South America, is widely distributed in the Americas, from Patagonia to the USA, from zero up to 3,700 m; it rapidly invades disturbed environments. In Venezuela, it has been reported from zero up to 2,000 m growing in contrasting conditions of relative humidity, temperature, rainfall, and salinity. In order to gain insight into the extent and mode of resistance to drought and salinity in N. glauca, we studied the effect of these factors on water relations and photosynthesis under both natural and greenhouse conditions. In the field, water potential, photosynthetic rate (A) and stomatal conductance (gs), but not relative water content (RWC) decreased because of drought. Manual removal of epicuticular wax increased excess energy dissipation through non-photochemical quenching without altering the capacity of photochemical quenching. In the greenhouse, water deficit as well as salinity resulted in osmotic adjustment; at the end of the experiment, turgor potential and RWC under water deficit were similar to control and higher under salinity. Water deficit and salinity caused marked decreases in A and gs. There were very few or no changes with natural drought, salinity or experimental water deficit in potential quantum efficiency of PSII, which could be explained partly by an increased non-photochemical quenching. We conclude that the partial tolerance to drought and salinity in plants of N. glauca resides in their ability to achieve water conservation through stomatal closure and osmotic adjustment, reduce absorption of excess radiation through the presence of leaf wax and dissipate it through increased non-photochemical quenching. All these characteristics confer plants of N. glauca advantages to invade disturbed areas, subject to salinity and/or seasonal drought under high irradiance.
To evaluate physiological genotypic differences between two Barbados cherry genotypes (13- and 14-CPA) under water deficit, initial growth, water relations, and organic solute accumulation were evaluated in an experiment performed using four-month-old seedlings, which were subjected to four water treatments (100, 75, 50, and 25% of field capacity), with five replications. Severe water deficit (25% of field capacity) negatively affected plant height, stem diameter, leaf area, dry matter of the leaves and stem to both genotypes, and root dry matter to genotype 13-CPA. Predawn (Ywpd) and midday leaf water potentials (Ywmd) were reduced in plants grown under 25% of field capacity, only in the genotype 14-CPA. There was not a change in relative water content, even with the reduction in the leaf water potential. Severe water deficit did not induce organic solutes accumulation, instead it reduced carbohydrate content in leaves of genotypes and aminoacids, proline and proteins, in genotype 13-CPA. In the roots accumulation of all organic solutes studied, it was verified genotype 13-CPA under 25% of field capacity, but only carbohydrates increased in plants under 25% of field capacity to 14-CPA. These results suggest two different mechanisms used by Barbados cherry genotypes to maintain the water status. To the 13-CPA one, the accumulation of soluble organic solutes in the roots is the main mechanism used to maintain the tissue hydration. However, the 14-CPA genotype changed the root to shoot ratio in order to avoid desiccation. Despite the mechanism used by both genotypes, a moderate drought stress does not induce significant morphophysiological changes in Barbados cherry.
Tomato (Solanum lycopersicum L.) is a climacteric fruit, i.e., during ripening an increase in ethylene synthesis and high rate of respiration are observed. Low oxygen levels might inhibit or block ethylene biosynthesis and therefore retard the ripening process. Despite commercial applications of low oxygen treatments, the precise mode of action of low oxygen in fruit tissues and ripening is not well understood. In order to delineate the molecular responses to low oxygen stress in fruits, hypoxia-responsive tomato genes encoding heat shock factors, heat shock proteins, and enzymes involved in fermentation and ethylene synthesis pathways were analyzed. In this study, tomato fruit stored under hypoxia conditions showed that HSP17.7 and HSP21 genes were highly induced by low oxygen level, indicating their primary role in maintaining cellular homeostasis after this stress.
Citrus plants were grown under two thermal conditions for evaluating carbon metabolism acclimation to moderate warm temperature (30/20ºC, day/night), and its likely impact on plant growth.As reference, plants were grown at 25/20ºC, in which they were subjected to optimum temperature for photosynthesis during the diurnal period (25ºC).Higher photosynthetic rates were found at 30/20ºC as compared to 25/20ºC in both mature and young leaves, being this response associated with higher stomatal conductance.After 30 days of thermal treatment, plants grown at 30/20ºC presented higher shoot growth as compared to those at 25/20ºC.The carbohydrate concentration decreased in stem and root tissues, while it increased in leaf tissues under moderate warm conditions.Both mature and young leaves showed higher photoassimilate consumption/exportation at 30/20ºC than at 25/20ºC.In this paper, we have proven that citrus plants present a positive balance in carbon metabolism as an acclimation mechanism to temperature changes, with plants presenting increased photosynthesis.Such photosynthetic acclimation was associated with improved vegetative growth, being both mature and young tissues sensitive to changes in thermal regimen.
Vochysia divergens Pohl (commonly known as cambara) is a pioneer tree species that is native to the Amazon Basin but has been invading the seasonally flooded wetlands of the Brazilian Pantanal, forming monospecific communities. The physiological aspects associated with cambara invasion, including the effects of flooding and shading on growth and leaf gas exchange, are unknown but may shed light on why cambara is able to invade this novel habitat so rapidly. Thus, we conducted a manipulative experiment to quantify the effects of shading and flooding on the growth, gas exchange and leaf nutrient content of V. divergens saplings. Based on previous research we hypothesized that (1) experimental flooding would have no effect on the growth and gas exchange of V. divergens,and (2) experimental shading would reduce the growth and gas exchange of V. divergens regardless of the water treatment plants are subjected. Our data indicate that shading significantly increased the height, stomatal conductance (g s), and transpiration (T) of V. divergens saplings, especially for plants exposed to normal irrigation. Experimental flooding significantly reduced rates of leaf production, plant height, and gas exchange; however, shaded plants exposed to flooding had a higher water use efficiency than plants exposed to full sun and flooding, because Twas more depressed than net photosynthesis (A) in flooded plants exposed to full sun. Despite the inhibitory effects of flooding and shading, V. divergenssaplings exhibited positive growth and C gain, regardless of the growth light environment or water level, indicating that the growth and leaf gas exchange of species is tolerant to both flooding and shading. Such tolerance to a wide variety of hydrological and growth light conditions presumably explains the ability of cambara to invade, and ultimately form dense, monospecific stands in the Brazilian Pantanal.
