Aluminum effect on starch, soluble sugar, and phytohormone in roots of Quercus serrata Thunb. seedlings

Abstract

Key message Glucose was a key substance as an energy source in the root growth promotion by Al, and ABA may relate to metabolism involved with its process. Abstract Generally, excess aluminum (Al) ions in soil solution are toxic to many cultivated plant species, but beneficial effects of Al for plant growth have been reported. Previously, we reported stimulation of root growth and nitrate reductase (NR) activity by Al. In this study, we focused on sugars, such as sucrose, glucose, and fructose, as energy sources and also signaling substances to regulate root growth. To understand the mechanism of root growth stimulation by Al, we investigated the change in concentration of sugars and phytohormones, and the activity of NR in roots using Quercus serrata seedlings. Ten-week-old Q. serrata seedlings were hydroponically cultured with nutrient solution containing 2.5 mM Al (pH 4.0) or 3.25 mM calcium (Ca) (pH 4.0) for 3 and 15 days. The growth of first lateral root and NR activity was stimulated for 3 and 15 days of Al treatment. The concentration of starch and sucrose decreased, while the concentration of glucose increased in the Al-treated roots. The concentration of abscisic acid (ABA) in Al-treated roots increased gradually throughout the experiment. From the present study, the mechanism of root growth promotion by Al involves a complex signaling network. We suggest that glucose is a key substance as an energy source and a signaling substance to promote root growth induced by Al and ABA may relate to nitrogen (N) and carbon (C) metabolism involved with the signaling network to promote root growth induced by Al.

Expression patterns and promoter analyses of aluminum-responsive NAC genes suggest a possible growth regulation of rice mediated by aluminum, hormones and NAC transcription factors

“…Similar results have been reported in other plants like maize [29], Quercus serrata [37] and Camellia sinensis [60]. In Quercus serrata , there was also an increase in the concentration of soluble sugars, especially glucose, as well as abscisic acid (ABA).…”

“…In Quercus serrata , there was also an increase in the concentration of soluble sugars, especially glucose, as well as abscisic acid (ABA). This suggests that growth stimulation by Al involves a complex signaling network where glucose has a key role as an energy source and as a signaling molecule together with ABA, and might be related with carbon (C) and nitrogen (N) metabolism to induce root growth in response to Al [37]. …”

“…Regardless, the present findings suggest consistency in the response of the NAC gene promoters to phytohormones, which suggests that these molecules can act as intermediaries in growth induction promoted by low concentrations of Al (hormetic effect). In fact, ABA might be a key component in the metabolism of C and N, which activates a signal transduction network induced by Al stimulating root growth and development in Quercus serrata [37]. …”

“…To date, no cis -acting elements have been reported in the promoter regions of Al-regulated NAC genes. Al generates complex metabolic responses [36,37], where phytohormones like auxin [38], ethylene [38,39], and jasmonic acid [40] intervene. Together, these signaling molecules may mediate stimulation or inhibition of root growth and development, depending on whether Al is found in beneficial or toxic concentrations, respectively.…”

Editorial note for the special issue “Dynamics and physiological processes of tree roots”

“…or other toxic metal ions, and the decrease in nutrient availability, and these changes may negatively affect tree growth (Hirano et al 2007). Moriyama et al (2016), however, suggested that Al had beneficial effects on root growth of Quercus serrata seedlings. In their experiments, the roots of the seedlings that were treated with Al also showed increased levels of nitrate reductase, soluble sugars such as glucose and abscisic acid, which could be involved in the increase of root growth.…”