Abstract
In agriculture, boron is known to play a critical role in healthy plant growth. To dissect the role of boron in maize metabolism, radioactive carbon-11 (t½ 20.4 min) was used to examine the physiological and metabolic responses of 3-week-old B73 maize plants to different levels of boron spanning 0 mM, 0.05 mM, and 0.5 mM boric acid (BA) treatments. Growth behavior, of both shoots and roots, was recorded and correlated to plant physiological responses. 11CO2 fixation, leaf export of [11C]-photosynthates, and their rate of transport increased systematically with increasing BA concentrations, while the fraction of [11C]-photosynthates delivered to the roots under 0 mM and 0.5 mM BA treatments was lower than under 0.05 mM BA treatment, likely due to changes in root growth. Additionally, solid-phase extraction coupled with gamma counting, radio-fluorescence thin layer chromatography, and radio-fluorescence high-performance liquid chromatography techniques applied to tissue extracts provided insight into the effects of BA treatment on ‘new’ carbon (as 11C) metabolism. Most notable was the strong influence reducing boron levels had on raising 11C partitioning into glutamine, aspartic acid, and asparagine. Altogether, the growth of maize under different regimes of boron affected 11CO2 fixation, its metabolism and allocation belowground, and altered root growth. Finally, inductively coupled plasma mass spectrometry provided insight into the effects of BA treatment on plant uptake of other essential nutrients. Here, levels of boron and zinc systematically increased in foliar tissues with increasing BA concentration. However, levels of magnesium, potassium, calcium, manganese, and iron remained unaffected by treatment. The rise in foliar zinc levels with increased BA concentration may contribute to improved 11CO2 fixation under these conditions.
Highlights
Crop yields are negatively impacted by various biotic and abiotic stresses and by nutrient deficiencies
To shed light on the previously unstudied effects of boron exposure on maize photosynthesis, carbohydrate, and amino acid metabolisms, we examined the developmental, physiological, and metabolic responses of 3-week-old B73 maize plants grown under different regimes spanning 0 mM boric acid (BA) treatment to 0.5 mM BA treatment, using
We refer to 0.05 mM BA as normal boron levels, as this is the concentration of BA in Hoaglands solution used to grow the plants, while 0 mM BA refers to no added boron and 0.5 mM
Summary
Crop yields are negatively impacted by various biotic and abiotic stresses and by nutrient deficiencies. The range of soil boron concentrations for optimal plant growth is narrow and has been reported to be the narrowest among the micronutrients [7] Both boron-deficient and boron-toxic soils can be found worldwide, overlapping with major plant growing areas and negatively affecting many agricultural crops [2]. Both deficiency and toxicity of boron lead to impairments of plant growth and yield [8,9], necessitating studying how non-optimal boron conditions affect both plant development and metabolism. This growth behavior is correlated with boron being passively transported via the transpiration stream and accumulating at the end of the transpiration stream (i.e., the leaf tips and edges of the leaf blade) when in excess [23,24,25]
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