Halman9000
Well-Known Member
Calcium
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3243358/"
Root Hair Tip Growth.(A) Diagram summarizing the mechanism of tip growth in Arabidopsis root hairs. The tip is packed with membrane-bound vesicles delivering new cell wall material. These vesicles are made in the endoplasmic reticulum (ER) and dictyosomes which are abundant behind the tip. Rop protein is localized to the tip along with F-actin, and a tip-focused calcium gradient. This calcium gradient is thought to be generated by hyperpolarization-activated calcium channels, which are localized to the plasma membrane at the hair tip. Other channels import osmotically active K+ and Cl- ions, which help to sustain turgor pressure as the hair grows. The direction of growth is controlled by microtubules, which run along the length of the hair.(B) Cytoarchitecture at the tip of an elongating root hair. Transmission electron micrographs of sections of an elongating hair showing the cell wall (w), vesicles (v), and endoplasmic reticulum (e). Top – The hair apex is packed with vesicles. Bottom – A section from just behind the apex shows dense endoplasmic reticulum surrounded by vesicles.(C) Tip-growing root hairs have a tip-focused calcium gradient. Time course showing the establishment and maintenance of a calcium gradient in an elongating root hair, and its disappearance when growth ceases. The concentration of cytoplasmic free calcium ([Ca2+]c) was imaged using indo-1 and pseudo-color coded according to the inset scale. [Ca2+]c is shown in the first and third rows with corresponding transmitted light images of the same cell in the second and fourth rows (see Wymer et al. 1997).
Potassium
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6843428/"
1. Introduction
Potassium is a macronutrient that may constitute up to 10% of plant dry weight [1]. It is a major inorganic cation in the plant cytoplasm, essential for activity of various enzymes, including those participating in primary metabolism [2]. It contributes significantly to turgor regulation, which is important for many plant processes, such as stomatal function [3,4], cell volume growth [5,6,7], existence of cytoplasm-plasma membrane-cell wall continuum [8], and plant movements [9]. To fulfil the diverse developmental and physiological functions of K+ in plants, broad spectrum of K+ transporters and channels evolved to orchestrate K+ transport [10,11,12,13].
Root system growth and development relies on K+ at various levels. Protein synthesis and enzyme activity of root cells need adequate cytoplasmic K+ levels to maintain the cytoplasmic pH [14] and the anionic charge of proteins [15]. Cell expansion in the elongation zone requires turgor pressure, which builds up via osmotically active substances, including K+ [16,17]. In the root maturation zone, root hairs grow apically via the action of K+ fluxes [18,19,20]. K+ affects R:S ratio (root to shoot biomass partitioning) via phloem transport [21,22]. Moreover, adaptive changes of root system architecture (RSA) and root hair coverage evolved in plants to enhance K+ uptake in potassium limiting conditions [10,23].
Soil K+ bioavailability is often low (especially in acidic soils) and limited mostly to the topsoil as most of soil potassium is incorporated in minerals [24,25]. K+ limitation is thus a common problem affecting agricultural production [25,26]. Plants engage high-affinity K+ transporters, modulate K+ channel transport properties [27,28,29,30], and change root system architecture (RSA) to cope with K+ deficiency [31]. Some growth responses to low K+ provide functional adjustments of the root system to enhance K+ acquisition efficiency. Sensing local K+ availability in rhizosphere triggers local root growth [32], but preferential branching to K+ rich patches seems to be mild compared to N or P local response [33,34]. K+ limitation negatively impacts root elongation and the number of first order lateral roots [35,36,37], but the response varies among species, cultivars, ecotypes, and even root types [35,38]. Suppressed cell volume growth or limited phloem delivery of assimilates to belowground organs may participate in root growth inhibition [21,22]. K+ scarcity also increases plant susceptibility to biotic and abiotic stresses [26,39].
In this review, we focused on K+ involvement in root growth and root system architecture establishment at various levels, from cell growth up to root system response to stress factors. The root system responses to low K+ stress are highlighted.
Halman9000
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3243358/"
Root Hair Tip Growth.(A) Diagram summarizing the mechanism of tip growth in Arabidopsis root hairs. The tip is packed with membrane-bound vesicles delivering new cell wall material. These vesicles are made in the endoplasmic reticulum (ER) and dictyosomes which are abundant behind the tip. Rop protein is localized to the tip along with F-actin, and a tip-focused calcium gradient. This calcium gradient is thought to be generated by hyperpolarization-activated calcium channels, which are localized to the plasma membrane at the hair tip. Other channels import osmotically active K+ and Cl- ions, which help to sustain turgor pressure as the hair grows. The direction of growth is controlled by microtubules, which run along the length of the hair.(B) Cytoarchitecture at the tip of an elongating root hair. Transmission electron micrographs of sections of an elongating hair showing the cell wall (w), vesicles (v), and endoplasmic reticulum (e). Top – The hair apex is packed with vesicles. Bottom – A section from just behind the apex shows dense endoplasmic reticulum surrounded by vesicles.(C) Tip-growing root hairs have a tip-focused calcium gradient. Time course showing the establishment and maintenance of a calcium gradient in an elongating root hair, and its disappearance when growth ceases. The concentration of cytoplasmic free calcium ([Ca2+]c) was imaged using indo-1 and pseudo-color coded according to the inset scale. [Ca2+]c is shown in the first and third rows with corresponding transmitted light images of the same cell in the second and fourth rows (see Wymer et al. 1997).
Potassium
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6843428/"
1. Introduction
Potassium is a macronutrient that may constitute up to 10% of plant dry weight [1]. It is a major inorganic cation in the plant cytoplasm, essential for activity of various enzymes, including those participating in primary metabolism [2]. It contributes significantly to turgor regulation, which is important for many plant processes, such as stomatal function [3,4], cell volume growth [5,6,7], existence of cytoplasm-plasma membrane-cell wall continuum [8], and plant movements [9]. To fulfil the diverse developmental and physiological functions of K+ in plants, broad spectrum of K+ transporters and channels evolved to orchestrate K+ transport [10,11,12,13].
Root system growth and development relies on K+ at various levels. Protein synthesis and enzyme activity of root cells need adequate cytoplasmic K+ levels to maintain the cytoplasmic pH [14] and the anionic charge of proteins [15]. Cell expansion in the elongation zone requires turgor pressure, which builds up via osmotically active substances, including K+ [16,17]. In the root maturation zone, root hairs grow apically via the action of K+ fluxes [18,19,20]. K+ affects R:S ratio (root to shoot biomass partitioning) via phloem transport [21,22]. Moreover, adaptive changes of root system architecture (RSA) and root hair coverage evolved in plants to enhance K+ uptake in potassium limiting conditions [10,23].
Soil K+ bioavailability is often low (especially in acidic soils) and limited mostly to the topsoil as most of soil potassium is incorporated in minerals [24,25]. K+ limitation is thus a common problem affecting agricultural production [25,26]. Plants engage high-affinity K+ transporters, modulate K+ channel transport properties [27,28,29,30], and change root system architecture (RSA) to cope with K+ deficiency [31]. Some growth responses to low K+ provide functional adjustments of the root system to enhance K+ acquisition efficiency. Sensing local K+ availability in rhizosphere triggers local root growth [32], but preferential branching to K+ rich patches seems to be mild compared to N or P local response [33,34]. K+ limitation negatively impacts root elongation and the number of first order lateral roots [35,36,37], but the response varies among species, cultivars, ecotypes, and even root types [35,38]. Suppressed cell volume growth or limited phloem delivery of assimilates to belowground organs may participate in root growth inhibition [21,22]. K+ scarcity also increases plant susceptibility to biotic and abiotic stresses [26,39].
In this review, we focused on K+ involvement in root growth and root system architecture establishment at various levels, from cell growth up to root system response to stress factors. The root system responses to low K+ stress are highlighted.
Halman9000
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