Magnesium-Deficiency Effects on Pigments, Photosynthesis and Photosynthetic Electron Transport of Leaves, and Nutrients of Leaf Blades and Veins in Citrus sinensis Seedlings

Abstract

Citrus sinensis seedlings were irrigated with nutrient solution at a concentration of 0 (Mg-deficiency) or 2 (Mg-sufficiency) mM Mg (NO3)2 for 16 weeks. Mg-deficiency-induced interveinal chlorosis, vein enlargement and corkiness, and alterations of gas exchange, pigments, chlorophyll a fluorescence (OJIP) transients and related parameters were observed in middle and lower leaves, especially in the latter, but not in upper leaves. Mg-deficiency might impair the whole photosynthetic electron transport, including structural damage to thylakoids, ungrouping of photosystem II (PSII), inactivation of oxygen-evolving complex (OEC) and reaction centers (RCs), increased reduction of primary quinone electron acceptor (QA) and plastoquinone pool at PSII acceptor side and oxidation of PSI end-electron acceptors, thus lowering energy transfer and absorption efficiency and the transfer of electrons to the dark reactions, hence, the rate of CO2 assimilation in Mg-deficiency middle and lower leaves. Although potassium, Mg, manganese and zinc concentration in blades displayed a significant and positive relationship with the corresponding element concentration in veins, respectively, great differences existed in Mg-deficiency-induced alterations of nutrient concentrations between leaf blades and veins. For example, Mg-deficiency increased boron level in the blades of upper leaves, decreased boron level in the blades of lower leaves, but did not affect boron level in the blades of middle leaves and veins of upper, middle and lower leaves. To conclude, Mg-deficiency-induced interveinal chlorosis, vein enlargement, and corkiness, and alterations to photosynthesis and related parameters increased with increasing leaf age. Mg-deficiency-induced enlargement and corkiness of veins were not caused by Mg-deficiency-induced boron-starvation.

Photosynthetic Responses of Canola to Exogenous Application or Endogenous Overproduction of 5-Aminolevulinic Acid (ALA) under Various Nitrogen Levels

“…We observed that ALA-treated plants had more active PS II reaction centers (estimated as an increase in RC/ABS) than untreated plants at all N levels. The higher RC/ABS implies that either the active PS II reaction centers were more numerous or the apparent antenna size was smaller [38,50]. In this study, the increase in active PS II reaction centers in ALA-treated plants was supported by an increase in the active reaction centers per excited cross-section (RC/CSo) and a decrease in the closure rate of reaction centers (Mo).…”

“…ALA-treated plants exhibited N-dosage-specific effects on PS II activity, as indicated by the appearance of three feature peaks at all N levels ( Figure 3 d–f). The ΔK peak is an important feature of serious nutrient deficiency, as reported in radishes [ 38 ], citrus [ 50 ], maize and tomatoes [ 52 ], and beans [ 53 ]. The appearance of a positive ΔK peak suggests that the oxygen-evolving complex (especially the Mn complex on the PS II donor side) was inactivated and the antenna complexes were more connected, possibly due to improper membrane organisms.…”

“…The appearance of a positive ΔK peak suggests that the oxygen-evolving complex (especially the Mn complex on the PS II donor side) was inactivated and the antenna complexes were more connected, possibly due to improper membrane organisms. Thus, there was lower energy transfer and absorption efficiency in those leaves, especially the N-deficient ones [ 50 ]. On the contrary, a negative ΔK peak occurred in both treatment groups under the low-N condition ( Figure 3 d), confirming earlier observations that ALA promotes activity on the donor side of PS II reaction centers [ 24 ].…”

Application of Trichoderma harzianum, 6-Pentyl-α-pyrone and Plant Biopolymer Formulations Modulate Plant Metabolism and Fruit Quality of Plum Tomatoes

“…In fact, carboxymethyl cellulose hydrogel is known to facilitate nutrient availability in the rhizosphere, enhancing not only nitrogen uptake, but in particular the absorption of important bivalent ions by the plant [ 43 ]. For example, magnesium (Mg 2+ ) is the central atom in the tetrapyrrole ring of chlorophyll molecules and can act as an activator of more than 300 enzymes, thus playing a key role in various physiological and biochemical processes, including chlorophyll biosynthesis and photosynthesis [ 44 ]. In addition, manganese (Mn 2+ ) is necessary for chlorophyll synthesis, but above all, it plays a key role in the oxygen evolving complex (OEC) of photosystem II, since four atoms of Mn 2+ are required to split water [ 45 ].…”

Excess Copper-Induced Alterations of Protein Profiles and Related Physiological Parameters in Citrus Leaves

“…Gas exchange was measured with a CIARS-2 portable photosynthesis system (PP systems, Herts, UK) at a controlled light intensity of~1000 µmol m −2 s −1 and a controlled CO 2 concentration of 380 µmol mol −1 between 9:30 and 12:30 a.m. on a sunny day [79].…”