Abstract
This research was conducted to investigate the effects of low magnesium (Mg) with high potassium (K) supply on the Mg concentration, sugar partitioning and root growth of rice (Oryza sativa L. cv. Wuyunjing 7) plants grown in hydroponics under greenhouse conditions, at Nanjing Agricultural University, China. The nutrient solution contained 0.01 and 1.0 mM Mg concentration, with K at 1.0 and 6.0 mM. Compared with the control (1mM Mg and K) treatment, the soluble sugar content at the treatment of low Mg (0.01 mM) with high K (6 mM) decreased by 35.7% in leaves, whereas increased 29.2% in roots at day 15 after treatment initiation. The shoot dry weight (DW) declined 12.9%, but root DW increased 12.1% leading to the significant increase in the root to shoot ratio at day 30. Furthermore, the total root length, total root surface area, root volume, average root diameter, total length of 0 - 0.5 mm and 0.5 - 1.0 mm diameter roots at day 30 significantly increased by 11.8%, 16.4%, 25.3%, 8.1%, 16.6% and 12.5%, respectively. Correlation analysis revealed the root to shoot ratio is closely related to the soluble sugar contents in roots and root morphological parameters of rice at day 15 and day 30. The typical visible symptoms of Mg deficiency in leaves of rice were obtained in the treatment of low Mg with high K at day 35. These findings indicated that low Mg with high K supply altered sugar partitioning and root morphological parameters, resulting in the increased root to shoot ratio prior to visible Mg deficiency symptoms in rice leaves. The increase in root to shoot ratio maybe an important adaptive mecha-nism for rice plants to respond to low-Mg stress during the early growth stage.
Highlights
Magnesium (Mg) is one of the essential mineral nutrients for the growth and development of plants
We found that under Mg stress induced by low Mg with high K supply, rice changes its soluble sugar partitioning and root growth parameters leading to an increase in root to shoot dry weight (DW) ratio before visible Mg deficiency symptoms occur in the leaves of rice plants
Since the rice seedlings had been grown in one fifth of full nutrient solution for two weeks prior to treatment initiation, the initial accumulated Mg and its internal recycling in the seedlings attenuated the visible signs of Mg deficiency
Summary
Magnesium (Mg) is one of the essential mineral nutrients for the growth and development of plants. Apart from being a central atom of the chlorophyll molecule, Mg acts as activator or regulator of many key enzymes in plant physiological processes [1,2]. Both Mg deficiency and oversupply have detrimental effects on plant photosynthesis [3], resulting in abnormal or restricted growth of plants [2]. Many light-textured soils have been shown to exhibit Mg deficiencies, in highly weathered acid soils with high percolation rates and leaching losses. Mg deficiency can be caused by small concentrations of the nutrient in a soil and by ionic antagonism, in acid and K-rich soils. Mg deficiency in plants occurs worldwide influencing productivity and quality in agriculture [4]
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