Effects of Histidine on Root Systems
Chelation of Metal Ions and Nutrient Uptake

Histidine chelates metal ions such as iron (Fe²⁺/Fe³⁺) and zinc (Zn²⁺) via its imidazole group, enhancing plant uptake of trace elements. These elements act as cofactors for enzymes involved in root cell division and elongation (e.g., iron is essential for peroxidase activity). Iron deficiency can lead to stunted root tip growth.

Studies show that under iron-deficient conditions, plants synthesize histidine derivatives (e.g., nicotianamine) to improve iron transport in roots.

Antioxidant Activity and Stress Response

Histidine is a precursor for glutathione (GSH) synthesis, which scavenges reactive oxygen species (ROS), reducing oxidative damage to root apical meristems under stress (e.g., salinity, heavy metals).

Under aluminum toxicity, histidine secreted into the rhizosphere binds Al³⁺, mitigating toxicity and maintaining root growth.

Hormonal Regulation and Signaling

Histidine may regulate lateral root formation by influencing the synthesis of ethylene or auxin (IAA). For example, histamine (generated from histidine decarboxylation) inhibits primary root elongation but promotes lateral root development in Arabidopsis thaliana.

II. Effects of Leucine on Root Systems

Energy Metabolism and Cell Proliferation

As a branched-chain amino acid, leucine is catabolized into acetyl-CoA, fueling the TCA cycle to provide energy for root cell division. Leucine deficiency reduces meristematic activity in root tips.

Leucine activates the TOR (Target of Rapamycin) signaling pathway, stimulating ribosomal biogenesis and protein synthesis to support root development.