Effects of Magnesium Deficiency on the Photosynthesis and Respiration of Leaves of Sugar Beet

Abstract

ABSTRACI'The effects of Mg deficiency on the photosynthesis and respiration of sugar beets (Beta vulgaris L. cv. F58-554H1) were studied by withholding Mg from the culture solution and by following changes in C02 and water vapor exchange of attached leaves. Leaf blade Mg concentration decreased from about 1200 to less than 200 meq kg-' dry matter without change in the rate of photosynthetic C02 uptake per unit leaf area, while from 200 to 50 meq kg-' the rate decreased to onethird. Rates of photorespiratory evolution of CO2 into C02-free air responded to Mg like those of photosynthetic C02 uptake, the rates decreasing to one-half, below 200 meq kg-'. Respiratory C02 evolution in the dark increased almost 2-fold in low Mg leaves. Magnesium deficiency had less effect on leaf (mainly stomatal) diffusion resistance (ri) than oni mesophyli resistance (rm); in Mg-deficient plants rm increased from 2.9 to 7.1 sec cm-', whereas ri became significantly greater than the control value only in the most severe instances of Mg deficiency.Magnesium is required by a large number of enzymes involved in energy transfer, particularly those utilizing ATP (2). It is a constituent of the Chl molecule and is required for the normal structural development of the chloroplast (4, 11), as well as other organelles such as the mitochondrion (5). Thus, it is to be expected that Mg deficiency would have damaging effects on photosynthesis and respiration. This has been shown for both processes in spinach (1), and for photosynthesis in maize (6). Magnesium deficiency has a pronounced effect on sugar beet plants, causing chlorosis, yellowing, scorching of the interveinal tissues of the leaf blade, and eventually, necrosis (13). In the present investigation, our objective was to assess the effects of Mg deficiency on the photosynthetic and respiratory CO2 exchange of sugar beet leaves and to determine whether Mg has any effect on leaf CO2 uptake attributable to changes in stomatal diffusion resistance. attached leaves, and in the estimation of the contents of leaf minerals, are as described in earlier papers (8 to 10). The culture solution employed to obtain Mg deficient plants contained, in mmole/l, 2.5 Ca(NO3)2*4 H20, 0.5 KH2PO4, 2.5 KNO3, 1.0 K2SO4, and 0.5 NaCl, and, in mg/l, 0.25 B, 0.25 Mn, 0.025 Zn, 0.01 Cu, and 0.005 Mo. Iron was added as ferric-sodium ethylene diamine tetraacetate complex to give 2.5 mg of Fe/l. The culture solution for the control plants was the same except for 1 mmole of MgSO/l which was added in place of the K2S04. MATERIALS AND METHODS DetailsThe gas-exchange measurements were begun at Mg cutoff, 28 days from planting, at which time three control plants were supplied with the complete culture solution and eight plants with the culture solution containing no added Mg. Measurements were made on control plants at the beginning and end of each period of deficiency.In addition to the information concerning gas-diffusion resistances, provided in earlier work (8, 9), we wish to make the following points. Assuming a cuticula...

Magnesium deficiency decreases biomass water-use efficiency and increases leaf water-use efficiency and oxidative stress in barley plants

“…Increased dark respiration under progressing Mg deficiency was reported in sugar beet (Terry and Ulrich 1974), and in Phaseolus vulgaris (Fischer and Bremer 1993). In the latter study, dark respiration rates of Mg deficient plants were 50 % higher than in control plants 6 days after onset of Mg deficiency.…”

“…Similarly, Terry and Ulrich (1974) reported a rapid decline in A N due to Mg deficiency in sugar beet already 7 DAO. Similar results were obtained in studies on Pinus (Laing et al 2000;Sun et al 2001), citrus (Tang et al 2012;Yang et al 2012), sugar beet (Terry and Ulrich 1974) and maize (Jezek et al 2015). Tang et al (2012) proposed nonstomatal reasons for a decrease in A N in citrus, as the internal CO 2 concentration did not differ from that of plants supplied with adequate amounts of Mg.…”

“…This decrease in photosynthetic efficiency, which was most prominent in the Mg low -treated plants, might also explain why excessive H 2 O 2 formation was highest in the Mg low treatment: it is very likely that an incomplete or blocked photosynthesis causally triggered the formation of oxygen radicals due to higher light intensities than sufficient to saturate photosynthetic processes under the experimental conditions. Mg deficiency induced decreases in A N are commonly attributed to i) a decrease in chlorophyll content (Peaslee and Moss 1966), and ii) an accumulation of carbohydrates in leaves suffering Mg deficiency causing feedback inhibition of RubisCo activity, and higher mesophyll resistance towards CO 2 diffusion (Terry and Ulrich 1974). Furthermore, Mg deficiency leads to changes in the ultrastructure of chloroplasts as thylakoid stacks are disrupted (Hall et al 1972).…”

Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems�I and II

“…Different substitutions have been applied in previous studies, resulting in variation in the concentrations of major elements (Terry and Ulrich 1974;Fischer and Bremer 1993;Dannehl et al 1996;Fischer et al 1998;Sun et al 2001). In order not to alter the anion/cation balance, equimolecular amounts of sodium sulfate were used, as in Cakmak et al (1994aCakmak et al ( , 1994b.…”

Magnesium Deficiency and High Light Intensity Enhance Activities of Superoxide Dismutase, Ascorbate Peroxidase, and Glutathione Reductase in Bean Leaves

“…In Mg-deficient leaves, CO2 uptake is depressed with corresponding decreases in CO2 fixation (35). CO2 fixation may also be impaired by Mg deficiency as a result of inhibited sucrose export from leaves (10, I. Cakmak, H. Marschner, unpublished) or the Mg dependency of ribulose-1,5-bisphosphate carboxylase (31).…”