TIGHE NEIRA, RICARDO MARCELO
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Response of sink manipulation in Lapins sweet cherry (Prunus avium L.) branches to late-deficit irrigation
Photosynthetic traits, leaf soluble sugars and fruit yield and size were evaluated in order to identify the role of early sink manipulation (girdling and fruiting spur thinning applied in winter) in modulating the effect of late-deficit irrigation (recovering 60% of crop evapotranspiration during 36 days pre-harvest) in Lapins sweet cherry branches. Photosynthesis (PN), stomatal conductance (gs), and fruit weight were affected by both treatments, whereas intercellular CO2 concentration of leaves (Ci), mesophyll conductance (gm), Rubisco carboxylase activity (Vcmax), electron transport rate (Jmax), leaf soluble sugars and branch yield were exclusively affected by sink manipulation. The effect of sink manipulation on PN was mainly observed in the girdling treatment as it was not altered by thinning. In girdled branches, PN dropped by 34%, accompanied by a two-fold increase in leaf soluble sugars, indicating that sink feedback regulation of carbon assimilation occurred. Irrespective of the irrigation, the higher PN observed in the controls were not sufficient to achieve the fruit weight and yield of the girdled branches, indicating that fruit carbon demand in control branches was source-limited. The depressed PN by girdling was associated with significant reductions in gs, gm, Vcmax and Jmax. Since lowered PN by deficit irrigation was neither attributable to a gs-associated decrease in Ci nor to changes in any other photosynthetic variable, further research is needed to clarify this point. Results showed that irrigation deficit was sufficient to reduce PN in girdled branches, whereas it had no effect in control and thinned branches. Thus, the depressive effect of deficit irrigation on PN appeared to be exacerbated by the sink effect. © 2022 Elsevier B.V., All rights reserved.
Physiological and molecular effects of TiO2 nanoparticle application on UV-A radiation stress responses in Solanum lycopersicum L.
Nanoparticles (NPs) of titanium dioxide (TiO2) alter photosynthetic and biochemical parameters in Solanum lycopersicum L., possibly due to their photocatalytic properties given by energy absorption in the UV-A range; however, the joint effects TiO2 NPs and UV-A radiation are not well understood. This work evaluates the combined responses of TiO2 NPs and UV-A radiation at the physiological and molecular levels in S. lycopersicum. In a split growth chamber, the presence (UV-A +) and absence (UV-A ?) of UV-A were combined with 0 (water as a control), and 1000 and 2000 mg L?1 of TiO2 NPs applied at sowing. At the end of exposure (day 30 after sowing), the photosynthetic performance was determined, and biochemical and molecular parameters were evaluated in leaf tissues. Better photochemical performance in UV-A + than UV-A ? in control plants was observed, but these effects decreased in 1000 and 2000 mg TiO2 L?1, similar to net CO2 assimilation. A clear increase in photosynthetic pigment levels was recorded under UV-A + compared to UV-A ? that was positively correlated with photosynthetic parameters. A concomitant increase in total phenols was observed on adding TiO2 in UV-A ? conditions, while a decreasing trend in lipid peroxidation was observed for the same treatments. There was an increase in psbB gene expression under TiO2/UV-A + treatments, and a reduced expression of rbcS and rbcL under UV-A ?. These results suggest that the reduction in photosynthetic performance on applying high doses of TiO2 NPs is probably due to biochemical limitation, while UV-A achieves the same result via the photochemical component. © 2023 Elsevier B.V., All rights reserved.