title: Boron excess affects photosynthesis and antioxidant apparatus of greenhouse Cucurbita pepo and Cucumis sativus.
abstract: This study aimed to evaluate the behavior of zucchini (Cucurbita pepo L.) and cucumber (Cucumis sativus L.) under boron (B) excess. Plants were grown under greenhouse conditions in a sandy soil-peat mixture using a nutrient solution containing 0.2 (control), 10 and 20 mg L(-1) B. Visible symptoms were quantified and leaf B accumulation, gas exchanges, chlorophyll (Chl) a fluorescence, malondialdehyde by-products and antioxidants were investigated 20 days after the beginning of the treatments. Boron toxicity induced oxidative load and leaf necrotic burns coupled with the reduction of leaf growth and biomass accumulation in both species. Boron excess resulted in a decrease of Chl a/b ratio, potential (Fv/Fm) and actual (ΦPSII) PSII quantum efficiency, photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) as well. A general stimulation of the antioxidant enzymes ascorbate peroxidase, catalase and superoxide dismutase was observed, and a significant increase in the oxidized form of ascorbate and glutathione was evidenced for treated plants of both species. A difference between the two species was observed: C. pepo appeared to be more sensitive to B stress being damaged at all B concentration. C. sativus grown at 10 mg L(-1) B in nutrient solution showed some down-regulated mechanisms, i.e. increase in Chl b content and a good photochemical PSII efficiency as well as a higher amount of constitutive antioxidant molecules, that, however, are not sufficient to contrast the negative effects of B.
authors.affiliation: Department of Agriculture, Food and Environment, University of Pisa, Via del Borghetto, 80, 56124, Pisa, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Landi
authors.forename: Damiano
authors.initials: D
authors.lastname: Remorini
authors.forename: Alberto
authors.initials: A
authors.lastname: Pardossi
authors.forename: Lucia
authors.initials: L
authors.lastname: Guidi
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D018533:Biomass; D001895:Boron / Q000633:toxicity*; D002338:Carotenoids / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D018553:Cucumis sativus / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D028464:Cucurbita / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D015536:Down-Regulation; D018506:Gene Expression Regulation, Plant; D015227:Lipid Peroxidation / Q000187:drug effects; D018384:Oxidative Stress; D010788:Photosynthesis / Q000187:drug effects*; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects*; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000502:physiology
chemical_list: D000975:Antioxidants; D002734:Chlorophyll; D002338:Carotenoids; D001895:Boron; D000077194:Chlorophyll A