Stomatal and mesophyll conductances to CO₂ are the main limitations to photosynthesis in sugar beet (Beta vulgaris) plants grown with excess zinc

Abstract

Summary• 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 lM 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 .Abbreviations: A N , net photosynthesis; AOX, alternative oxidase; APX, ascorbate peroxidase; BL, DL, MCL, NSL and SL, biochemical conductance, diffusional conductance, mesophyll conductance, and nonstomatal and stomatal limitations, respectively; C a , C C and C i, atmospheric, chloroplastic and substomatal CO 2 concentrations, respectively; CA, carbonic anhydrase; Chl, chlorophyll; ETR, electron transport rate; F PSII, actual photosystem II efficiency; FAAS, flame atomic absorption spectroscopy; F o , minimal Chl fluorescence in the dark; F v ⁄ F m , maximum potential photosystem II efficiency; g m and g s , CO 2 mesophyll and stomatal conductances, respectively; J max , in vivo maximum rate of electron transport driving regeneration of RuBP; Mn-SOD, manganese-superoxide dismutase; PPFD, photosynthetic photon flux density; PSII and PSI, photosystems II and I, respectively; V c,max , in vivo maximum rate of Rubisco carboxylation; WC, water content.

Effect of Supplementation of <i>Spirulina platensis</i> to Enhance the Zinc Status in Plants of <i>Amaranthus gangeticus, Phaseolus aureus</i> and Tomato

“…From Figure 1(a) it is evident that both positive and negative percent change has been observed in the zinc status in Amaranthus gangeticus when the setups were compared with their respective controls. In the figure the spray method has shown the positive change which is according to results of the previous study [19] [20]. In Phaseolus aureous the trend is more towards positive percent change in the experimental variations of all setups and as the concentration of Spirulina increased there is an increase in zinc status of the yield.…”

Awaiting better times: A quiescence response and adventitious root primordia formation prolong survival under cadmium stress in Tetradenia riparia (Hochst.) Codd

“…S2b), these results support the view that photosynthesis was initially limited by CO 2 diffusion as a consequence of low leaf stomatal conductance ( Medrano et al, 2002). This result is in accordance with the increasing evidence suggesting that exposure to toxic metal concentrations initially affects plant water relations (Barcelo and Poschenrieder, 1990;Sagardoy et al, 2010;Bazihizina et al, 2014).…”

Zinc stress induces physiological, ultra-structural and biochemical changes in mandarin orange (Citrus reticulata Blanco) seedlings

“…2a). In Beta vulgaris, stomatal size, density were smaller and stomatal slits were sealed in plants grown under high Zn (Sagardoy et al 2010) and citrus plants when grown under 15 mM Zn manifested stress imposition by keeping pores slightly opened. In high Zn plants stomata were smaller and had a more rounded shape than those present in control plants (Sagardoy et al 2009).…”