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 (F M) 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.

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.

Physiological and anatomical features of Cd-tolerance in Pfaffia glomerata were examined by exposing plantlets to nutrient solutions with increasing Cd concentrations (0, 15, 45, and 90 µmol Cd L-1), and possible Cd-tolerance markers were established. Cd contents were found to be higher in roots than in shoots. According to the bio-concentration factor data, this species is effectively a Cd-hyperaccumulator, as previously attested. Cd induced the appearance of xeromorphic characteristics in leaves (decreased water potential, increased numbers and decreased stomata size) and increased root endodermis thickness. The enzymatic antioxidant systems of roots and leaves were differently affected by Cd. The coordinated activities of antioxidant enzymes were effective in reducing Cd-induced reactive oxygen species in plants, mainly in leaves. Root endodermis thickness, stomatal size and numbers, root superoxide dismutase, and guaiacol peroxidase, as well as leaf guaiacol peroxidase and catalase activities can all be considered Cd-tolerance markers in Pfaffia glomerata. Due to its high root Cd accumulation, Pfaffia glomerata may be useful in Cd-phytoextraction programs, however the pharmacological use of plants grown in the presence of Cd must be avoided.

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').

Lulo (Solanum quitoense Lam.) is an exotic fruit from the Andes Mountains with a high export potential. However, the browning that is produced during harvest and the postharvest processes alters the organoleptic and nutritional properties of this fruit, which has made its management as a fresh fruit difficult. The browning processes are regulated by the enzyme family of the polyphenol oxidases (PPOs) located in the thylakoids of the chloroplast. When there is damage at the tissue level, the phenolic compounds found in the vacuoles enter into contact with the polyphenol oxidase. This enzyme produces polymerization among the phenolic compounds, as well as between them and the proteins and cell walls. This study analyzed the polyphenol oxidase in lulo var. Castilla at the genetic level, based on DNA and RNA samples. The results showed a high level of homology with other polyphenol oxidases from plants. The highest degree of homology was found with Solanum melongena L., which belongs to the same clade, Leptostemonum. The tyrosinase and two copper-binding domains, characteristic of the polyphenol oxidase, the conserved residues that maintain the natural environment, the sequence of a signal peptide for targeting chloroplast, and the UTRA domain of transcription regulation for recognizing small molecules were identified. Southern blot was used to analyze the number of gene copies, identifying at least eight ones in the lulo genome.

Annona emarginata (Schldtl.) H. Rainer ("araticum-de-terra-fria") is used as a rootstock for several species of Annonaceae. It is suggested that these seeds should be sown immediately after extraction and, therefore, they could be intolerant to desiccation. There are several mechanisms involved with desiccation tolerance. Soluble sugars, for example, can accumulate and act as osmoprotectants for the membrane system during desiccation. The aim of this study is to assess desiccation tolerance in A. emarginata seeds. In addition, we examined the soluble sugars involved in desiccation tolerance. Finally, we determined the effect of gibberellic acid (GA4+7) and N-(phenylmethyl)-aminopurine in promoting the germination of seeds with different water contents. The experiment consisted of a randomized 4x5 factorial design (desiccation levels x concentration of growth regulators). After drying, seeds containing 31 (control), 19, 12 and 5% water were incubated in different concentrations of GA4+7 N-(phenylmethyl)-aminopurine (0, 250, 500, 750 and 1000 mg L-1) for 60 hours. The experiment was conducted in a germination chamber with alternating temperature and photoperiod of 20ºC for 18 hours of darkness and 30ºC for 6 hours of light. We analyzed electrical conductivity, germination rate, mean germination time, germination speed, frequency and uniformity of germination, percentage of dormant seeds and soluble sugar profile in intact seeds through high-performance liquid chromatography (HPLC). The data were subjected to analysis of variance, and the means were compared using Tukey's test at a threshold of p<0.05. The results showed that seeds of A. emarginata appears to be desiccation tolerant and, also, that sucrose increases when seed water content is reduced to values as low as 12%, exogenous GA4+7+N-(phenylmethyl)-aminopurine improves its germinability.

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.

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.

Zinc deficiency is not only the cause of low productivity of crops, but it also results in low zinc content in seeds, which leads to poor dietary zinc intake. To study the effect of zinc foliar application on improving plant yield and seed zinc content for human consumption, chickpea plants were raised in refined sand culture with deficient (0.2 µM) and sufficient (1µM) supply of zinc under glass-house conditions. Prior to initiation of the reproductive phase, zinc was applied as 0.1% ZnSO4 foliar spray to both zinc sufficient and deficient plants. The plants exposed to different zinc treatments were studied for pollen and stigma structure and their involvement in fertilization and seed yield. Zinc deficiency induces flower abortion, pollen, and ovule infertility leading to low seed set and ultimately its yield. Foliar application of ZnSO4 to zinc deficient plants at the time of initiation of flowering partially reverses the adverse effect of zinc deficiency on pollen-stigma morphology, pollen fertility, and greatly enhanced seed yield of plants. Zinc foliar application improved not only the boldness and vigor of seeds in zinc-deficient plants, but also the seed zinc content in zinc-deficient seeds as well as the sufficient ones.

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.

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.

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) significantly decreased germination and plant growth in both landraces. Mumias had significantly higher total chlorophyll, chlorophyll a and b content compared to Kakamega landrace. Salinity significantly decreased Fv/Fm ratio and electron transport rate in the two landraces, however there were no significant (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.