Unveiling the mechanism of melatonin impacts on maize seedling growth: sugar metabolism as a case

Abstract

Melatonin regulates growth in many plants; however, the mechanism remains unclear. In this study, exogenous melatonin feeding resulted in both promotional (≤10 μm) and inhibitory (≥100 μm) effects on maize seedling growth. Initial analyses suggested positive correlations between the amount of melatonin and sucrose synthesis and hydrolysis-related gene expression, enzyme activities, and sucrose metabolites. However, assays of photosynthetic rate, hexokinase (HxK) activity, expression of photosynthetic marker genes, and HxK-related genes showed opposite effects under 10 μm (positive) and 100 μm (negative) melatonin treatments. Similarly, 10 μm melatonin accelerated starch catabolism at night, whereas 100 μm melatonin significantly decreased this process and led to starch accumulation in photosynthetic tissues. Furthermore, expression analysis of genes related to sucrose phloem loading resulted in a slight upregulation of sucrose transporters (SUT1 and SUT2) when seedlings were induced with 10 μm melatonin, while treatment with 100 μm melatonin resulted in significant downregulation of these sucrose transporter genes (SUT1 and SUT2), as well as tie-dyed2 (Tdy2) and sucrose export defective 1. Taken together, these results suggest that low doses of melatonin benefit maize seedling growth by promoting sugar metabolism, photosynthesis, and sucrose phloem loading. Conversely, high doses of melatonin inhibit seedling growth by inducing the excessive accumulation of sucrose, hexose and starch, suppressing photosynthesis and sucrose phloem loading.

A new balancing act: The many roles of melatonin and serotonin in plant growth and development

“…The interaction with the cytokinin or 5HT responses may also be a causal factor. A recent study on Zea mays has also suggested a direct interaction with sugar metabolism 101 . This publication reported that at low levels (10 µM) MEL acted to enhance gene expression of photosynthesis, sucrose biosynthesis and hydrolysis-related genes, to increase starch catabolism during the night, to elevate sucrose-related enzyme activity and to promote photosynthetic rates.…”

“…This publication reported that at low levels (10 µM) MEL acted to enhance gene expression of photosynthesis, sucrose biosynthesis and hydrolysis-related genes, to increase starch catabolism during the night, to elevate sucrose-related enzyme activity and to promote photosynthetic rates. This was coupled to a rise in the expression of sugar transporters SUT1 and SUT2 as well as higher levels of hexokinase activity and sugar metabolites which resulted in elevated levels of available sugars for plant growth 101 . Interestingly, when the authors increased exogenously applied MEL concentrations to 100 µM, the reverse effect was seen with reduced sucrose metabolism, transport and gene expression, increased starch accumulation in photosynthesizing tissues and lower photosynthetic rates 101 .…”

“…This was coupled to a rise in the expression of sugar transporters SUT1 and SUT2 as well as higher levels of hexokinase activity and sugar metabolites which resulted in elevated levels of available sugars for plant growth 101 . Interestingly, when the authors increased exogenously applied MEL concentrations to 100 µM, the reverse effect was seen with reduced sucrose metabolism, transport and gene expression, increased starch accumulation in photosynthesizing tissues and lower photosynthetic rates 101 . Somatic embryogenesis is induced by MEL in coffee plants in culture (Coffea canephora) though whether this effect is a result of a balance between 5HT and MEL concentrations, or is due to an interaction with other signaling cascades is not reported 102 .…”

Distinct Carbon and Nitrogen Metabolism of Two Contrasting Poplar Species in Response to Different N Supply Levels

“…Sucrose influences and reflects photosynthesis, C export, and nutrient mobilization (Figure 1). Sucrose is the primary product of photosynthesis, the form in which carbohydrates are transported from the photosynthetic tissues (i.e., the source) to non-photosynthetic tissues (i.e., the sink) and the initial building block of most natural organic matter [10]. In the photosynthetic tissues, sucrose is synthesized by the enzyme sucrose phosphate synthase (SPS) via the consumption of uridine diphosphate glucose (UDP-G) from the Calvin cycle and fructose-6-phosphate.…”

Melatonin in Edible and Non-Edible Plants

“…80 Reports, which investigated effect of exogenous melatonin on both tomato's and maize's seeds, have confirmed this case too. 78,81 Melatonin plays an important role to maintain the vitality of the plants. 82 KOCA ÇALIŞKAN et al Plant's Melatonin …”