The sensitivity of photosynthesis to magnesium deficiency differs between rice (Oryza sativa L.) and cucumber (Cucumis sativus L.)

Abstract

Magnesium is an essential macronutrient for plant photosynthesis, and in response to Mg deficiency, dicots appear more sensitive than monocots. Under Mg deficiency, we investigated the causes of differing photosynthetic sensitivities in a dicot and a monocot species. Rice (Oryza sativa L.) and cucumber (Cucumis sativus L.) were grown in hydroponic culture to explore their physiological responses to Mg deficiency stress. Both Mg-deficient rice and cucumber plants exhibited lower biomass, leaf area, Mg concentration, and chlorophyll content (Chl) compared with Mg-sufficient plants. However, a more marked decline in Chl and carotenoid content (Car) occurred in cucumber. A lower CO2 concentration in chloroplasts (Cc) was accompanied by a decrease in the maximum rate of electron transport (Jmax) and the maximum rate of ribulose 1,5-bisphosphate carboxylation (Vcmax), restricting CO2 utilization in Mg-deficient plants. Rice and cucumber photorespiration rate (Pr) increased under Mg deficiency. Additionally, for cucumber, Car and non-photochemical quenching (NPQ) were reduced under lower Mg supply. Meanwhile, cucumber Mg deficiency significantly increased the fraction of absorbed light energy dissipated by an additional quenching mechanism (Φf,D). Under Mg deficiency, suppressed photosynthesis was attributed to comprehensive restrictions of mesophyll conductance (gm), Jmax, and Vcmax. Cucumber was more sensitive to Mg deficiency than rice due to lower NPQ, higher rates of electron transport to alternative pathways, and subsequently, photooxidation damage.

Insights into Key Biometric, Physiological and Biochemical Markers of Magnesium (Mg) Deficiency Stress in the Halophyte Cakile maritima

“…In Eustoma grandiflorum, a native species of alkaline soils in Texas, Mg deficiency was found to reduce root dry weight without affecting shoot dry matter [21]. Besides, low Mg supply impeded the growth of both rice and cucumber cultivars [22]. As described previously in many plant species, Mg deficiency altered the plant organ growth, leading to a significant decrease in the root/shoot ratio [37][38][39][40].…”

“…Likewise, Farhat et al studied the effect of Mg deficiency on the halophyte S. carnosa and found a significant decrease in the photosynthetic performance, especially when plants were subjected to severe Mg shortage [20,44]. Such findings could be explained by the fact that a high fraction of Mg is found in chloroplasts where it ensures an optimal functioning of photosynthesis [21] and that Mg is an important component of the photosynthetic machinery as a cofactor involved in the biosynthesis of various enzymes, including those involved in respiration and photosynthesis [45] and consequently its deficiency underpins the photosynthetic performance of most crop species [20][21][22]. As shown recently by Pang et al and Jamali et al, Mg shortage adversely impacted the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the main enzyme involved in CO 2 fixation resulting in a decrease in photosynthetic performance [46,47].…”

“…As shown recently by Pang et al and Jamali et al, Mg shortage adversely impacted the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the main enzyme involved in CO 2 fixation resulting in a decrease in photosynthetic performance [46,47]. According to Meng et al, the reduction in the photosynthetic activity observed in rice and cucumber upon Mg deprivation could be due to a restriction in mesophyll conductance, maximum rate of electron transport as well as the rate of ribulose 1,5-bisphosphate carboxylation [22].…”

“…As Mg is an important component of the photosynthetic machinery, its deficiency underpins the photosynthetic performance of most crop species [20][21][22]. The impairment of the electron transport chain is a common effect of Mg shortage widely described in a wide range of plant species.…”

Exogenous Easily Extractable Glomalin-Related Soil Protein Stimulates Plant Growth by Regulating Tonoplast Intrinsic Protein Expression in Lemon

“…Interestingly, the exogenous EE-GRSP applications only significantly increased the Mg content in the roots but not in the leaves. It is well known that Mg and Fe are the essential components involved in chlorophyll synthesis [ 32 , 33 ], but chlorophyll contains only Mg but no Fe. In this study, Mg might be more consumed during the chlorophyll synthesis.…”