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 ZnNO3 (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 ZnNO3 (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-NO3 are good options to carry out foliar Zn fertilization in pecan trees.

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.

Tomato is one of the most important vegetables cultivated in Mexico. Nitrogen-based fertilizers have greatly contributed to the increase in tomato production; however, the excessive application of this fertilizer may affect yield and fruit quality. A greenhouse experiment was conducted to evaluate the effect of increasing in rates of nitrogen from deficiency to toxic levels. Five N-treatments (0, 15, 30, 45 and 60 mM of N) were applied in two tomato varieties, Caballero and Victoria The optimum N doses for leaf growth in both varieties was 30 mM reaching 13.0 and 13.5 cm in Caballero and Victoria respectively. At low toxic levels leaf growth was recovered more easily in Caballero than Victoria. Nitrate concentration for the low toxicity treatment was greater in leaf and stems for Caballero than Victoria; conversely nitrate in fruits was higher in Victoria. Final yield per plant was not statistically different between varieties except at the low toxic treatment where Caballero had a yield of 780 g per plant compared to that of 330 g per plant of Victoria. Tomato quality was also affected by the applied N-doses, where treatment 30 mM reached the maximum fruit firmness in both varieties while high toxic N-levels decreased significantly this parameter. Soluble solids and titratable acidity increased with increased N-Doses. Caballero variety seems to be more tolerant than Victoria at low levels of N-toxicity.

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 ZnSO4 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 ZnSO4 or an aqueous suspension of ZnO NPs (both 150 mg · L−1). The application of ZnO NPs significantly increased concentrations of Zn2+ 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 Zn2+ applications, but no differences were found in total phenols (TP), total flavonoids (TFl) or antioxidant capacity (AC). In the pods and seeds, Zn2+ 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 ZnSO4 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’.

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