Stomatal and mesophyll conductances to CO2 are the main limitations to photosynthesis in sugar beet (Beta vulgaris) plants grown with excess zinc.
*The effects of zinc (Zn) toxicity on photosynthesis and respiration were investigated in sugar beet (Beta vulgaris) plants grown hydroponically with 1.2, 100 and 300 microM Zn. *A photosynthesis limitation analysis was used to assess the stomatal, mesophyll, photochemical and biochemical contributions to the reduced photosynthesis observed under Zn toxicity. *The main limitation to photosynthesis was attributable to stomata, with stomatal conductances decreasing by 76% under Zn excess and stomata being unable to respond to physiological and chemical stimuli. The effects of excess Zn on photochemistry were minor. Scanning electron microscopy showed morphological changes in stomata and mesophyll tissue. Stomatal size and density were smaller, and stomatal slits were sealed in plants grown under high Zn. Moreover, the mesophyll conductance to CO(2) decreased by 48% under Zn excess, despite a marked increase in carbonic anhydrase activity. Respiration, including that through both cytochrome and alternative pathways, was doubled by high Zn. *It can be concluded that, in sugar beet plants grown in the presence of excess Zn, photosynthesis is impaired due to a depletion of CO(2) at the Rubisco carboxylation site, as a consequence of major decreases in stomatal and mesophyll conductances to CO(2).
Sagardoy
R
R
Department of Plant Nutrition, Aula Dei Experimental Station, CSIC, PO Box 13034, 50080 Zaragoza, Spain.
Vázquez
S
S
Department of Plant Nutrition, Aula Dei Experimental Station, CSIC, PO Box 13034, 50080 Zaragoza, Spain.
Florez-Sarasa
I D
ID
Laboratori de Fisiologia Vegetal, Departament de Biologia, Universitat de les Illes Balears, Carretera de Valldemossa, km 7.5, 07071, Palma de Mallorca, Balears, Spain.
Albacete
A
A
Department of Plant Nutrition, CEBAS, CSIC, PO Box 164, 30100 Murcia, Spain.
Ribas-Carbó
M
M
Laboratori de Fisiologia Vegetal, Departament de Biologia, Universitat de les Illes Balears, Carretera de Valldemossa, km 7.5, 07071, Palma de Mallorca, Balears, Spain.
Flexas
J
J
Laboratori de Fisiologia Vegetal, Departament de Biologia, Universitat de les Illes Balears, Carretera de Valldemossa, km 7.5, 07071, Palma de Mallorca, Balears, Spain.
Abadía
J
J
Department of Plant Nutrition, Aula Dei Experimental Station, CSIC, PO Box 13034, 50080 Zaragoza, Spain.
Morales
F
F
Department of Plant Nutrition, Aula Dei Experimental Station, CSIC, PO Box 13034, 50080 Zaragoza, Spain.
D027461:Beta vulgaris / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development*; D002245:Carbon Dioxide / Q000378:metabolism*; D019069:Cell Respiration / Q000187:drug effects; D003576:Electron Transport Complex IV / Q000378:metabolism; D018527:Hydroponics; D024101:Mitochondrial Proteins; D008954:Models, Biological; D010088:Oxidoreductases / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects*; D018515:Plant Leaves / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D010940:Plant Proteins; D054046:Plant Stomata / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D014867:Water / Q000378:metabolism; D015032:Zinc / Q000378:metabolism / Q000633:toxicity*; D000099188:Alternative Oxidase
D002245:Carbon Dioxide; D003576:Electron Transport Complex IV; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D014867:Water; D015032:Zinc; D000099188:Alternative Oxidase