Abstract
BackgroundIn this study, we aimed to test the hypothesis that magnesium (Mg) remobilization in citrus plants is regulated by Mg supply and contributes to differences in the growth of the parent and branch organs. Citrus seedlings were grown in sand under Mg deficient (0 mmol Mg2+ L−1, -Mg) and Mg sufficient (2 mmol Mg2+ L−1, + Mg) conditions. The effects on biomass, Mg uptake and transport, gas exchange and chlorophyll fluorescence, as well as related morphological and physiological parameters were evaluated in different organs.ResultsMg deficiency significantly decreased plant biomass, with a decrease in total plant biomass of 39.6%, and a greater than twofold decrease in the branch organs compared with that of the parent organs. Reduced photosynthesis capacity was caused by a decreased in pigment levels and photosynthetic electron transport chain disruption, thus affecting non-structural carbohydrate accumulation and plant growth. However, the adaptive responses of branch leaves to Mg deficiency were greater than those in parent leaves. Mg deficiency inhibited plant Mg uptake but enhanced Mg remobilization from parent to branch organs, thus changing related growth variables and physiological parameters, including protein synthesis and antioxidant enzyme activity. Moreover, in the principal components analysis, these variations were highly clustered in both the upper and lower parent leaves, but highly separated in branch leaves under the different Mg conditions.ConclusionsMg deficiency inhibits the growth of the parent and branch organs of citrus plants, with high Mg mobility contributing to differences in physiological metabolism. These findings suggest that Mg management should be optimized for sustainable citrus production.
Highlights
In this study, we aimed to test the hypothesis that magnesium (Mg) remobilization in citrus plants is regulated by Mg supply and contributes to differences in the growth of the parent and branch organs
Principal component analysis (PCA) was performed to evaluate differences in the growth and physiological characteristics of the branch, upper and lower leaves between the Mg treatment groups using SPSS 22 (IBM, Armonk, NY, USA). Mg deficiency inhibited both parent and lateral plant growth Compared with Mg sufficiency, Mg deficiency markedly inhibited citrus plant growth, with typical symptoms of chlorosis between veins in the LL (Fig. 1; Additional file 1: Fig. S1)
The leaf water content under Mg deficiency was higher than that under Mg sufficiency in the parent, while there was no effect on the branch (Fig. 2). These findings indicate that Mg deficiency modulates the water cycle properties in citrus plants, which accounts for the lower Photosynthetic water-use efficiency (PWUE) (Fig. 5e)
Summary
We aimed to test the hypothesis that magnesium (Mg) remobilization in citrus plants is regulated by Mg supply and contributes to differences in the growth of the parent and branch organs. Magnesium (Mg) is an essential element required for plant growth and development, playing important roles in many physiological and biochemical processes, including chlorophyll and protein synthesis, assimilate production and transport, and enzyme activities [1, 2]. The effects of Mg deficiency on plant growth and nutritional function have been widely studied, the results have not always been consistent. Compared to other plants such as sugar beet [10, 12], wheat [13], and rice [14, 15], the effects of Mg deficiency on Mg mobility from parent to branch organs of woody plants, especially citrus plants, are not clear [5, 16]
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