Francisco M. del Amor

Time course of solute accumulation and water relations in muskmelon plants exposed to salt during different growth stages

Abstract A greenhouse experiment was carried out to determine the effect of salinity on the water relations, osmotic adjustment and growth of melon plants (Cucumis melo, L.). Three saline treatments (20, 40 and 60 mM NaCl corresponding to 4, 6 and 8 dS m−1, respectively) were applied at four different phenological stages (seedling, flowering, fruit set and fruit growth) to compare the effect of the time of application on the parameters studied. A reduction in stomatal conductance, water potential and osmotic potential was observed with all treatments. The degree of osmotic adjustment observed indicated that no changes in leaf turgor occurred after any of the saline treatments applied at the different stages. Total sugar concentration increased in the leaves immediately after all treatment applications but later reverted to control values. No changes were observed in the total amino acid concentration. Similar and significant increases were observed in leaf Cl− and Na+ concentrations, which were greater at higher NaCl concentrations. Analysis of the contribution by the different solutes showed that inorganic compounds were increased to a greater extent than organic compounds after treatment application. Measurements of shoot height and leaf elongation rate showed that only salt applications during fruit set produce slight reductions in these two parameters while greater alterations were observed with the rest of the treatments.

Plant growth-promoting bacteria as a tool to improve salinity tolerance in sweet pepper

To characterise the effect of bacterial inoculants (Azospirillum brasilense and Pantoea dispersa) on the response of sweet pepper (Capsicum annuum L.) to saline stress, plants were exposed to 0, 40, 80 and 120mM NaCl in solution. The effect on plant growth; leaf gas exchange; NO3-, Cl-, K+ and Na+ accumulation; and chlorophyll fluorescence and content were investigated. Total plant DW was reduced significantly by salinity but when inoculants were applied, DW was increased. Inoculated plants showed higher DW accumulation in the roots. Salinity levels up to 80mM NaCl did not affect the net assimilation rate in inoculated plants but 40mM NaCl was enough to reduce this parameter in non-inoculated plants. The leaf area ratio was not modified substantially by inoculation. The leaf Cl- concentration of inoculated plants was reduced at the highest salinity, compared with control plants, and NO3- concentration increased markedly. A higher K+:Na+ ratio was found in inoculated plants. Leaf photosynthesis and stomatal conductance were impaired significantly at moderate, but not low, salinity, the effect of inoculation being enough to maintain higher stomatal conductance under higher stress. The photochemical efficiency of PSII and the relative chlorophyll content were not affected by the inoculants. Thus, the effects of the inoculants on the response to salinity were due mainly to stomatal regulation of photosynthesis rather than effects on biochemical limitations on photosynthesis. These results indicate the benefits of these bacterial inoculants in ameliorating the deleterious effect of NaCl in a salt-sensitive crop like sweet pepper.

Effect of foliar application of antitranspirant on photosynthesis and water relations of pepper plants under different levels of CO2 and water stress.

Strategies such as foliar application of antitranspirants have the potential to regulate transpiration, but often, the limitation of CO(2) exchange as a result of reduced stomatal conductance can impair this beneficial effect. Elevated ambient [CO(2)] could significantly improve CO(2) diffusion while effectively reducing transpiration. In this experiment, we examined the response of sweet pepper (Capsicum annuum L.) to the foliar application of antitranspirant (AT) under two [CO(2)] (380 and 2000 micromol mol(-1)) and two drought intensities (4 or 8d without irrigation). The results showed that stomatal conductance and transpiration were reduced, while AT impaired photosynthesis at standard, but not at elevated [CO(2)] of fully irrigated plants. This effect was already apparent after 4d of drought. Drought had a minor impact on chlorophyll fluorescence (F(v)/F(m)). Additionally, root respiration was increased at elevated [CO(2)] but, after 8d of drought, it was higher for plants treated with AT than for non-sprayed plants. Leaf water potential was affected more by drought at ambient compared to elevated [CO(2)], and, especially after 8d of drought, AT minimized the reductions in leaf water potential. Leaf concentrations of proline and starch were affected by both [CO(2)] and AT, especially after 8d of drought. Moreover, increasing [CO(2)] promoted the accumulation of starch, but led to decreases in the tissue concentrations of the soluble organic osmolytes, and hence diminished osmotic adjustment after 8d of water withholding, relative to ambient [CO(2)]. This study indicates that, in addition to the reported beneficial effect of elevated [CO(2)] on drought stress, AT could significantly improve drought tolerance in sweet pepper plants.

Regulation of hormonal responses of sweet pepper as affected by salinity and elevated CO2 concentration.

This study examines the extent to which the predicted CO2 -protective effects on the inhibition of growth, impairment of photosynthesis and nutrient imbalance caused by saline stress are mediated by an effective adaptation of the endogenous plant hormonal balance. Therefore, sweet pepper plants (Capsicum annuum, cv. Ciclón) were grown at ambient or elevated [CO2] (400 or 800 µmol mol(-1)) with a nutrient solution containing 0 or 80 mM NaCl. The results show that, under saline conditions, elevated [CO2] increased plant dry weight, leaf area, leaf relative water content and net photosynthesis compared with ambient [CO2], whilst the maximum potential quantum efficiency of photosystem II was not modified. In salt-stressed plants, elevated [CO2 ] increased leaf NO3(-) concentration and reduced Cl(-) concentration. Salinity stress induced ABA accumulation in the leaves but it was reduced in the roots at high [CO2], being correlated with the stomatal response. Under non-stressed conditions, IAA was dramatically reduced in the roots when high [CO2] was applied, which resulted in greater root DW and root respiration. Additionally, the observed high CK concentration in the roots (especially tZR) could prevent downregulation of photosynthesis at high [CO2], as the N level in the leaves was increased compared with the ambient [CO2], under salt-stress conditions. These results demonstrate that the hormonal balance was altered by the [CO2], which resulted in significant changes at the growth, gas exchange and nutritional levels.

Effects of antitranspirant spray and potassium:calcium:magnesium ratio on photosynthesis, nutrient and water uptake, growth, and yield of sweet pepper.

ABSTRACT Sweet pepper plants (Capsicum annuum L.) were cultivated hydroponically under different nutrient cation ratios at both high potassium (K)/calcium (Ca) (12:2) or magnesium (Mg)/Ca (4:2) ratios, compared with half strength Hoaglands solution (K:Ca:Mg; 3.5:2:0.5). Additionally, antitranspirant (Pinolene) was sprayed every fortnight to the aerial part of the plant at 1% (v/v). The antitranspirant (AT) did not affect dry weight accumulation in the leaves, stems, roots, total plant leaf area, or leaf dry weight percentage. Net carbon dioxide (CO2) assimilation was not impaired by the AT but the water uptake was reduced significantly independent of the nutrient solution used. The AT did not affect the cation uptake but high Mg significantly reduced Ca concentration in leaves, stems, and fruits, whilst high K had an effect only in old leaves and fruits. The AT reduced fructose and glucose concentration in the leaves but no effect was found in the fruits. Fruit yield was not affected by AT, but it was increased when plants were grown with high Mg/Ca. The percentage of blossom-end rot was reduced with the AT, whilst it was increased with the solutions having high K/Ca or high Mg/Ca. The AT significantly reduced fruit firmness in high Mg/Ca and control solution but no effect was found for fruit color, shape index, total soluble solids, or pericarp thickness.

Gas exchange, water relations, and Ion concentrations of salt‐stressed tomato and melon plants

Abstract Tomato and melon plants were grown in a greenhouse and irrigated with nutrient solution having an EC of 2 dS m−1 (control treatment) and 4, 6, and 8 dS m−1, produced by adding NaCl to the control nutrient solution. After 84 days, leaf water relations, gas exchange parameters, and ion concentrations, as well as plant growth, were measured. Melon plants showed a greater reduction in shoot weight and leaf area than tomato at the two highest salinity levels used (6 and 8 dS m−1). Net photosynthesis (Pn) in melon plants tended to be lower than in tomato, for all saline treatments tested. Pn was reduced by 32% in melon plants grown in nutrient solution having an EC of 4 dS m−1, relative to control plants, and no further decline occurred at higher EC levels. In tomato plants, the Pn decline occurred at EC of 6 dS m−1, and no further reduction was detected at EC of 8 dS m−1. The significant reductions in Pn corresponded to similar leaf Cl− concentrations (around 409 mmol kg−1 dry weight) in both plant species. Net Pn and stomatal conductance were linearly correlated in both tomato and melon plants, Pn being more sensitive to changes in stomatal conductance (gs) in melon than in tomato leaves. The decline in the growth parameters caused by salinity in melon and tomato plants was influenced by other factors in addition to reduction in Pn rates. Melon leaves accumulated larger amounts of Cl− than tomato, which caused a greater reduction in growth and a reduction in Pn at lower salinity levels than in tomato plants. These facts indicate that tomato is more salt‐tolerant than melon.

Effects of postharvest treatments on fruit quality of sweet pepper at low temperature

BACKGROUND Postharvest storage of sweet pepper fruits (Capsicum annuum L.) at low temperatures could impair their physical and chemical composition. Therefore, maintenance of essential nutrition support or altered gas exchange could preserve fruit quality, minimizing chilling injury. Thus our aim was to determine the response to postharvest application of a low concentration of nitrogen (urea) or antitranspirant (pinolene) during a period of 21 days at 5 °C. RESULTS The results indicate that storage at 5 °C was effective with respect to maintaining firmness of sweet pepper fruits for 21 days, while application of antitranspirant increased firmness compared with non-sprayed fruits. Additionally, urea maintained color while increasing total phenolics and the activity of catalase and ascorbate peroxidase, lowering lipid peroxidation. Composition of free amino acids was affected to a minor extent. CONCLUSION Maintaining quality is of paramount importance in the postharvest period. This study shows the effect of both temperature and spraying treatments with regard to maintaining fruit quality during this period, and provides new insights into the physiological role of enzymes of the antioxidant system during pepper storage at low temperature.

Changes in the salinity tolerance of sweet pepper plants as affected by nitrogen form and high CO2 concentration.

The assimilation and availability of nitrogen in its different forms can significantly affect the response of primary productivity under the current atmospheric alteration and soil degradation. An elevated CO2 concentration (e[CO2]) triggers changes in the efficiency and efficacy of photosynthetic processes, water use and product yield, the plant response to stress being altered with respect to ambient CO2 conditions (a[CO2]). Additionally, NH4(+) has been related to improved plant responses to stress, considering both energy efficiency in N-assimilation and the overcoming of the inhibition of photorespiration at e[CO2]. Therefore, the aim of this work was to determine the response of sweet pepper plants (Capsicum annuum L.) receiving an additional supply of NH4(+) (90/10 NO3(-)/NH4(+)) to salinity stress (60mM NaCl) under a[CO2] (400μmolmol(-1)) or e[CO2] (800μmolmol(-1)). Salt-stressed plants grown at e[CO2] showed DW accumulation similar to that of the non-stressed plants at a[CO2]. The supply of NH4(+) reduced growth at e[CO2] when salinity was imposed. Moreover, NH4(+) differentially affected the stomatal conductance and water use efficiency and the leaf Cl(-), K(+), and Na(+) concentrations, but the extent of the effects was influenced by the [CO2]. An antioxidant-related response was prompted by salinity, the total phenolics and proline concentrations being reduced by NH4(+) at e[CO2]. Our results show that the effect of NH4(+) on plant salinity tolerance should be globally re-evaluated as e[CO2] can significantly alter the response, when compared with previous studies at a[CO2].

Variation in the leaf δ13C is correlated with salinity tolerance under elevated CO2 concentration

Increasing atmospheric CO(2) concentration is expected to impact agricultural systems through a direct effect on leaf gas exchange and also due to effects on the global availability of good-quality water as a result of climate warming. Thus, the planning of land use for agriculture requires new tools to identify the capability of current cultivars to adapt to growth restrictions under new ambient conditions. We hypothesized that salinity stress may produce a specific pattern of carbon isotopic composition (δ(13)C) in tomato (Solanum lycopersicum L.) at elevated CO(2) concentration ([CO(2)]) that could be used in the breeding of salinity tolerance in a near-future climate scenario. Five commercial tomato cultivars were evaluated at elevated (800 μmol mol(-1)) or standard (400 μmol mol(-1)) [CO(2)], being irrigated with a nutrient solution containing 0, 60 or 120 mM NaCl. The biomass enhanced ratio, leaf net CO(2) assimilation and stomatal conductance, leaf NO(3)(-) and Cl(-) concentrations and leaf free amino acid profile were analyzed in relation to the pattern of δ(13)C, under different saline stress conditions. The results indicate that at high [CO(2)]: (i) salinity tolerance was enhanced, but the response was strongly cultivar dependent, (ii) leaf NO(3)(-) concentration was increased whilst Cl(-) and proline concentrations decreased, and (iii) leaf δ(13)C was highly correlated with plant dry matter accumulation and with leaf proline concentration, leaf gas exchange and ion concentrations. This study shows that δ(13)C is a useful tool for the determination of the salinity tolerance of tomato at high [CO(2)], as an integrative parameter of the stress period, and was validated by traditional physiological plant stress traits.

Regulation of the drought response of sweet pepper (Capsicum annuum L.) by foliar-applied hormones, in Mediterranean-climate greenhouse conditions

Plant hormones play an important role in regulating stress responses and signaling in plants; many of them act to alleviate environmental stresses. However, the specific effects and physiological changes could be significantly altered according to the crop species, application concentration and frequency, and cultivation conditions. In this study, we investigated the effect of leaf-applied abscisic acid (ABA), gibberellic acid (GA3), and indole-3-acetic acid (IAA) on plant growth before, during, and after water stress. The objective was to determine their effects on pepper plants (Capsicum annuum L.) in commercial greenhouse conditions, specifically their ability to mitigate water stress, through the study of different stress traits—such as plant growth, gas exchange parameters, chlorophyll content and fluorescence, ascorbate peroxidase activity, total phenolic compounds, and lipid peroxidation. While ABA and IAA heightened the water shortage in the leaves along the experiment, GA3 diminished it. The effects of ABA involved short-term responses, such as stomatal closure and decreased transpiration, and long-term changes, affecting the ratios and concentrations of chlorophylls. Moreover, GA3 complicated the crop management since the plants suffered high stress when treated with this hormone. The results obtained represent a first approach to studying the effect of foliar hormone application in sweet pepper and its ability to regulate (mitigate or amplify) the water stress suffered by the plant under greenhouse conditions.