<![CDATA[Carbonic anhydrase (CA) (EC: 2.4.1.1) catalyzes the rapid conversion of carbon dioxide plus water into a proton and the bicarbonate ion (HCO3-) that can be found in prokaryotes and higher organisms; it is represented by four different families. Carbonic anhydrase is a metalloenzyme that requires Zn as a cofactor and is involved in diverse biological processes including pH regulation, CO2 transfer, ionic exchange, respiration, CO2 photosynthetic fixation, and stomatal closure. Therefore, the review includes relevant aspects about CA morphology, oligomerization, and structural differences in the active site. On the other hand, we consider the general characteristics of Zn, its geometry, reactions, and physiology. We then consider the CA catalysis mechanism that is carried out by the metal ion and where Zn acts as a cofactor. Zinc deficiency can inhibit growth and protein synthesis, and there is evidence that it reduces the CA content in some plants, which is a relationship addressed in this review. In leaves, CA represents 20.1% of total soluble protein, while it is the second most abundant in the chloroplast after ribulose 1,5-disphosphate carboxylase/oxygenase (RuBisCO). This facilitates the supply of CO2 to the phosphoenolpyruvate carboxylase in C4 and CAM plants and RuBisCO in C3 plants.]]>

The objective of this study was to assess the changes in leaflet zinc (Zn), leaf nutritional state, vegetative and physiological parameters, and yield quality in pecan trees sprayed with different Zn compounds. Eight-year-old ‘Western Schley’ pecan trees grafted to native seedlings were treated with ZnNO ₃ (100 mg·L ⁻¹ Zn), Zn-EDTA (50, 100, and 150 mg·L ⁻¹ Zn), and Zn-DTPA (100 mg·L ⁻¹ Zn) and compared with the Zn-untreated control. After 3 years of evaluation, the trees with the best appearance were those treated with ZnNO ₃ (100 mg·L ⁻¹ Zn) and Zn-DTPA (100 mg·L ⁻¹ Zn), which showed leaf Zn concentration increases of 73% and 69%, respectively, when compared with the controls. The chlorophyll values of the Zn-treated trees reached 46 SPAD units, equivalent to 43 mg·kg ⁻¹ dry weight (DW) of chlorophyll compared with values of 22 mg·kg ⁻¹ DW in Zn-deficient leaves. On a leaf area basis, chlorophyll value was 37% lower under Zn deficiency conditions than that of Zn-treated trees. Nut quality was unaffected by the Zn treatments. Data suggest that Zn-DTPA and Zn-NO ₃ are good options to carry out foliar Zn fertilization in pecan trees.

The green bean ( Phaseolus vulgaris L.) is a very widely grown food crop that contributes significantly to human dietary needs in many countries due to its high content of protein. This study evaluates foliar applications of ZnSO ₄ versus that of zinc oxide nanoparticles (ZnO NPs) to leaves of the green bean cv. ‘Strike’ and records the plant responses in terms of Zn uptake and concentrations of photosynthetic pigments and bioactive compounds. The experiment was conducted under greenhouse conditions in Chihuahua, Mexico, with a completely randomised experimental design with 10 replicates. The two treatments were foliar applications of either an aqueous solution of ZnSO ₄ or an aqueous suspension of ZnO NPs (both 150 mg · L ⁻¹ ). The application of ZnO NPs significantly increased concentrations of Zn ²⁺ in the leaflets, roots, stems and pods of chlorophylls a and b (values 15.40 μg · g ⁻¹ and 11.64 μg · g ⁻¹ , respectively). Sucrose concentration was also increased by Zn ²⁺ applications, but no differences were found in total phenols (TP), total flavonoids (TFl) or antioxidant capacity (AC). In the pods and seeds, Zn ²⁺ application left sucrose and TFl concentrations unchanged, but the TP increase was significant. The AC was affected by both zinc sources and only in the pods. The applications of ZnSO ₄ or ZnO NPs significantly increased the biomass accumulation (79.10 g · p ⁻¹ and 84.70 g · p ⁻¹ DW) and yield (55.64 g · p ⁻¹ and 53.80 g · p ⁻¹ FW). These results suggest that the application of ZnO NPs could represent a worthwhile biofortification strategy in the commercial production of green bean cv. ‘Strike’.

Several studies indicate that nitrogen fertilization is one of the main constraints in obtaining higher yields and better nut quality in pecan (Carya illinoensis [Wangenh] K. Koch). Therefore, the aim of this research was to evaluate a single and split application of nitrogen in 'Western Schley' variety pecan, as well as its effect on leaf nutrient concentration, yield and nut quality. A randomized complete block design with six replicates was established. N doses were 100, 150 and 200 kg·ha-1; the single application was made in March and the split one in March and June. The leaf concentration of total N, P, K+, Ca2+, Mg2+, Fe2+, Mn2+, Zn2+ and Cu2+, yield (kg·tree-1), quality (nuts per kilogram and kernel percentage) and nitrogen use efficiency (NUE) were determined. Significant interaction between factors was detected for the Zn2+ concentration and the single applied dose of 200 kg·ha-1. With the single application of 100 kg·ha-1, the highest yield (44.60 kg·tree-1) and nuts per kilogram (194.83) values were recorded, where the kernel percentage remained constant. The maximum NUE was obtained with 100 kg·ha-1 applied in a single and split application (31.10 and 30.10 kg of nuts produced per kg of N applied, respectively). Increased yield and nut quality is the main objective in applying optimal N doses; however, ways of reducing the economic and environmental impact caused by its excessive application should also be sought.

This research aimed to compare two levels (medium and high) and three types of fertilization (organic, chemical, and integrated) in both foliar nutritional content and fruit quality of Golden Delicious apple variety. The foliar concentration of macro and micronutrients was affected neither by fertilization level nor fertilization type, with the exception of potassium which reached their highest concentration in the high level of chemical fertilization (T1-HC). Regarding the fruit quality attributes, results showed no statistical differences in weight, size, firmness, pH, and starch content between the level and type of fertilization. With the high level of organic fertilization, the best apple color was found, while the medium level of organic fertilization showed the highest concentration of both soluble solid content and total phenolic compounds. Thus, fertilization level had greater influence than the fertilization type. Results also showed that under organic fertilization management is possible obtaining a foliar nutritional content and fruits quality attributes similar to those treated with chemical fertilizers. Future studies must be carried out for elucidating the impact of long-term organic fertilization on the fruit quality and foliar nutritional content of other crops.