Abstract
Potassium (K) is essential for the processes critical for plant performance, including photosynthesis, carbon assimilation, and response to stress. K also influences translocation of sugars in the phloem and regulates sucrose metabolism. Several plant species synthesize polyols and transport these sugar alcohols from source to sink tissues. Limited knowledge exists about the involvement of K in the above processes in polyol-translocating plants. We, therefore, studied K effects in Plantago major, a species that accumulates the polyol sorbitol to high concentrations. We grew P. major plants on soil substrate adjusted to low-, medium-, or high-potassium conditions. We found that biomass, seed yield, and leaf tissue K contents increased in a soil K-dependent manner. K gradually increased the photosynthetic efficiency and decreased the non-photochemical quenching. Concomitantly, sorbitol levels and sorbitol to sucrose ratio in leaves and phloem sap increased in a K-dependent manner. K supply also fostered plant cold acclimation. High soil K levels mitigated loss of water from leaves in the cold and supported cold-dependent sugar and sorbitol accumulation. We hypothesize that with increased K nutrition, P. major preferentially channels photosynthesis-derived electrons into sorbitol biosynthesis and that this increased sorbitol is supportive for sink development and as a protective solute, during abiotic stress.
Highlights
Potassium belongs to the group of major plant nutrients and accumulates to high levels in most plant tissues [1]
A regulated carbohydrate and most importantly sugar accumulation are crucial for acclimation and adaption of plants to changing environmental accumulation are crucial for acclimation and adaption of plants to changing environmental conditions [19], and links K nutrition and the ability of plants to cope with biotic and conditions [19], and links K nutrition and the ability of plants to cope with biotic and abiotic abiotic stresses
In this study an attempt was undertaken to investigate the dose-dependent role of K in P. major as a high accumulator of sorbitol undertaken to investigate the dose-dependent role of K in P. major as a high accumulator of sorbitol under cold stress
Summary
Potassium belongs to the group of major plant nutrients and accumulates to high levels in most plant tissues [1]. In most types of soils, potassium is relatively highly abundant, only about 2% of total soil potassium is available to the plant [2]. This is because most (up to 98%) potassium is tightly bound to minerals like feldspar, feldspathoid (including nepheline and leucite), mica, or clay [2]. While clay-fixed potassium might serve as a reservoir for K when plants grow under K-limiting conditions, only the cationic potassium (K+ form, representing between 1–2 % of total K) is directly available for uptake into roots. In contrast to other highly abundant nutrients like phosphate, sulfate, or nitrogen, K does not become part of a certain cellular structure or molecule. K has crucial functions in enzyme activation, osmotic adjustment, Plants 2020, 9, 1259; doi:10.3390/plants9101259 www.mdpi.com/journal/plants
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