Leonardo Lombardini

ECOPHYSIOLOGY OF PLANTS IN DRY ENVIRONMENTS

Drought is a meteorological term which indicates a long period when there is not enough rain for the successful growth of crops or replenishment of water supplies (see also Chap. 1). The expression water stress is frequently used to indicate the complex series of effects that are triggered in plants by drought. The term drought stress is more appropriate to specify when the stress status occurs only over a long period of time. However, because it is often difficult to separate the two phenomena, the definitions of water stress, drought stress, and water deficit are often used interchangeably. Drought leads to water deficit in the soil and plant tissues, which in turn alters physiological processes and can have ultimate consequences for growth, development, and survival of plants. Among the many biochemical and developmental processes that are affected by water stress, decrease of photosynthesis (Cornic and Massacci 1996; Flexas et al. 2002; Sperlich et al. 2016), changes in water relations (Gorai et al. 2015; Reinhardt et al. 2015; Yousfi et al. 2016), reduction of both cell division and expansion (Avramova et al. 2016; Clauw et al. 2015, 2016), abscisic acid (ABA) synthesis (Du et al. 2018; Linster et al. 2015; Teng et al. 2014), and accumulation of sugars (Srivastava et al. 2018; Zandalinas et al. 2018) play a fundamental role in reducing productivity. The concept of stress cannot be separated from that of stress tolerance (sometimes indicated with the less appropriate term of stress resistance), which is the plant’s ability to survive in an unfavorable environment. Such an ability can derive either from adaptation or acclimation to the stress condition. Both terms indicate an increase in tolerance and are sometimes erroneously used interchangeably. The difference is in the cause of the increased tolerance: in acclimated plants, it is the result of a previous stress condition, while in adapted plants, the tolerance is fixed in the genome and derives from selection processes that have occurred over many generations.

Electron-Beam Irradiation Effects on Phytochemical Constituents and Antioxidant Capacity of Pecan Kernels [Carya illinoinensis (Wangenh.) K. Koch] During Storage

Pecans kernels (Kanza and Desirable cultivars) were irradiated with 0, 1.5, and 3.0 kGy using electron-beam (E-beam) irradiation and stored under accelerated conditions [40 degrees C and 55-60% relative humidity (RH)] for 134 days. Antioxidant capacity (AC) using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC) assays, phenolic (TP) and condensed tannin (CT) content, high-performance liquid chromatography (HPLC) phenolic profile, tocopherol content, peroxide value (PV), and fatty acid profiles were determined during storage. Irradiation decreased TP and CT with no major detrimental effects in AC. Phenolic profiles after hydrolysis were similar among treatments (e.g., gallic and ellagic acid, catechin, and epicatechin). Tocopherol content decreased with irradiation (>21 days), and PV increased at later stages (>55 days), with no change in fatty acid composition among treatments. Color lightness decreased, and a reddish brown hue developed during storage. A proposed mechanism of kernel oxidation is presented, describing the events taking place. In general, E-beam irradiation had slight effects on phytochemical constituents and could be considered a potential tool for pecan kernel decontamination.

Physiological effects of cerium oxide nanoparticles on the photosynthesis and water use efficiency of soybean (Glycine max (L.) Merr.)

Widespread industrial uses of cerium oxide nanoparticles (CeO2 NPs) and their unregulated disposal have raised concerns about their environmental consequences. While studies are abundant on the phyto-effects of CeO2 NPs, detailed understanding of the impact of CeO2 NPs on plant photosynthesis is still lacking. In addition, no studies have evaluated the effects of CeO2 NPs on plant water use efficiency (WUE), a key parameter for crop yield. The goal of this study was to determine the impact of CeO2 NPs with two different surface properties (uncoated and polyvinylpyrrolidone (PVP)-coated) on the photosynthesis and WUE of soybean at four different concentrations (0, 10, 100 and 500 mg kg−1 dry soil). At the concentration of 100 mg kg−1, both types of CeO2 NPs stimulated plant growth and enhanced the photosynthesis rate by 54% for bare CeO2 NPs and 36% for PVP-CeO2 NPs. The maximum rate of Rubisco carboxylase activity represented by Vcmax also increased by 32% and 27%, respectively, for bare and PVP-coated CeO2 NPs at this concentration during the 3 week treatment. Conversely, the net photosynthesis rate was reduced by about 36% for both nanoparticles at 500 mg kg−1 CeO2 NPs. In addition, CeO2 NPs at concentrations >500 mg kg−1 also inhibited Rubisco activity and interfered with CO2 diffusion pathways. The results also confirmed that the physiological effects of CeO2 NPs on soybean depend on both the concentration and surface coating properties of the nanoparticles.

Zinc deficiency in field-grown pecan trees: changes in leaf nutrient concentrations and structure

BACKGROUND Zinc (Zn) deficiency is a typical nutritional disorder in pecan trees [Carya illinoinensis (Wangenh.) C. Koch] grown under field conditions in calcareous soils in North America, including northern Mexico and south-western United States. The aim of this study was to assess the morphological and nutritional changes in pecan leaves affected by Zn deficiency as well as the Zn distribution within leaves. RESULTS Zinc deficiency led to decreases in leaf chlorophyll concentrations, leaf area and trunk cross-sectional area. Zinc deficiency increased significantly the leaf concentrations of K and Ca, and decreased the leaf concentrations of Zn, Fe, Mn and Cu. All nutrient values found in Zn-deficient leaves were within the sufficiency ranges, with the only exception of Zn, which was approximately 44, 11 and 9 µg g(-1) dry weight in Zn-sufficient, moderately and markedly Zn-deficient leaves, respectively. Zinc deficiency led to decreases in leaf thickness, mainly due to a reduction in the thickness of the palisade parenchyma, as well as to increases in stomatal density and size. The localisation of Zn was determined using the fluorophore Zinpyr-1 and ratio-imaging technique. Zinc was mainly localised in the palisade mesophyll area in Zn-sufficient leaves, whereas no signal could be obtained in Zn-deficient leaves. CONCLUSION The effects of Zn deficiency on the leaf characteristics of pecan trees include not only decreases in leaf chlorophyll and Zn concentrations, but also a reduction in the thickness of the palisade parenchyma, an increase in stomatal density and pore size and the practical disappearance of Zn leaf pools. These characteristics must be taken into account to design strategies to correct Zn deficiency in pecan tree in the field.

Ethylene-inhibiting compound 1-MCP delays leaf senescence in cotton plants under abiotic stress conditions

Cotton (Gossypium hirsutum L.) plants produce more ethylene when subjected to abiotic stresses, such as high temperatures and drought, which result in premature leaf senescence, reduced photosynthetic efficiency, and thus decreased yield. This study was conducted to test the hypothesis that the ethylene-inhibiting compound 1-methylcyclopropene (1-MCP) treatment of cotton plants can delay leaf senescence under high temperature, drought, and the aging process in controlled environmental conditions. Potted cotton plants were exposed to 1-MCP treatment at the early square stage of development. The protective effect of 1-MCP against membrane damage was found on older compared to younger leaves, indicating 1-MCP could lower the stress level caused by aging. Application of 1-MCP resulted in reduction of lipid peroxidation, membrane leakage, soluble sugar content, and increased chlorophyll content, in contrast to the untreated plants under heat stress, suggesting that 1-MCP treatment of cotton plants may also have the potential to reduce the effect of heat stress in terms of delayed senescence. Application of 1-MCP caused reductions of lipid peroxidation, membrane leakage, and soluble sugar content, together with increases in water use efficiency (WUE), water potential, chlorophyll content, and fluorescence quantum efficiency, compared to the untreated plants under drought, suggesting that 1-MCP treatment of cotton plants may also have the ability to reduce the level of stress under drought conditions. In conclusion, 1-MCP treatment of cotton should have the potential to delay senescence under heat and drought stress, and the aging process. Additionally, 1-MCP is more effective under stress than under non-stress conditions.

The impact of cerium oxide nanoparticles on the physiology of soybean (Glycine max (L.) Merr.) under different soil moisture conditions

AbstractThe ongoing global climate change raises concerns over the decreasing moisture content in agricultural soils. Our research investigated the physiological impact of two types of cerium oxide nanoparticles (CeO2NPs) on soybean at different moisture content levels. One CeO2NP was positively charged on the surface and the other negatively charged due to the polyvinylpyrrolidone (PVP) coating. The results suggest that the effect of CeO2NPs on plant photosynthesis and water use efficiency (WUE) was dependent upon the soil moisture content. Both types of CeO2NPs exhibited consistently positive impacts on plant photosynthesis at the moisture content above 70% of field capacity (θfc). Similar positive impact of CeO2NPs was not observed at 55% θfc, suggesting that the physiological impact of CeO2NPs was dependent upon the soil moisture content. The results also revealed that VCmax (maximum carboxylation rate) was affected by CeO2NPs, indicating that CeO2NPs affected the Rubisco activity which governs carbon assimilation in photosynthesis. In conclusion, CeO2NPs demonstrated significant impacts on the photosynthesis and WUE of soybeans and such impacts were affected by the soil moisture content. Graphical abstractSoil moisture content affects plant cerium oxide nanoparticle interactions

Antioxidants in Pecan Nut Cultivars [Carya illinoinensis (Wangenh.) K. Koch]

Publisher Summary This chapter provides an insight into the potential of using pecan nuts to promote health and prevent diseases. Pecan kernels are sources of protein, dietary fiber, vitamins, minerals, and many other bioactive substances, also called phytochemicals, which are known to provide health benefits. Regarding the vitamins and minerals, pecan kernels are a good source of vitamins A and E, the B vitamins, folic acid, calcium, magnesium, potassium, and zinc. The phytochemical constituents in defatted pecan kernels were investigated in six cultivars chosen for their commercial relevance. The main fatty acids found in the lipid fraction of pecan kernels were oleic (over 60%), linoleic, palmitic, stearic, and linolenic. The presence of high contents of phenolic compounds, tocopherol, and monounsaturated fatty acid suggest several health benefits. Phenolic compounds have been reported to protect against atherosclerosis, hypertension, cardiovascular diseases, cancer, and viral infections and to act as general antioxidants. The prevention of several chronic diseases, including cancer, cardiovascular and neurological diseases, and inflammation, have been associated with the intake of tannins. In general, tannins are known to have certain health benefits, such as antioxidant, anti-allergy, antihypertensive, and antitumor, as well as antimicrobial activities. However, pecans can become toxic when they get moldy.