The response of physiological and xylem anatomical traits under cadmium stress in Pinus thunbergii seedlings.

Studying the response of physiological and xylem anatomical traits under cadmium (Cd) stress is helpful to understand plants' response to heavy metal stress. Here, seedlings of Pinus thunbergii were treated with 50, 100 and 150 mg/kg Cd2+ for 28 days. Cd and nonstructural carbohydrate (NSC) content of leaves, stems and roots, root Cd2+ flux, Cd distribution pattern in stem xylem and phloem, stem xylem hydraulic traits, cell wall component fractions of stems and roots, phytohormonal content such as abscisic acid (ABA), gibberellic acid 3 (GA3), molecule -indole-3-acetic acid (IAA) and jasmonic acid (JA) from both leaves and roots, as well as xylem anatomical traits from both stems and roots were measured. Root Cd2+ flux increased from 50 to 100 mmol/L Cd2+ stress, however, decreased at 150 mmol/LCd2+. Cellulose and hemicellulose in leaves, stems and roots did not change significantly under Cd stress, while pectin decreased significantly. The NSC content of both leaves and stems showed significant changes under Cd stress while the root NSC content was not affected. In both leaves and roots, the ABA content significantly increased under Cd stress, while the GA3, IAA and JA-ME content significantly decreased. Both xylem hydraulic conductivity and xylem water potential decreased with Cd stress, however, tracheid diameter and double wall thickness of the stems and roots were not affected. High Cd intensity was found in both the stem xylem and phloem in all Cd stressed treatments. Our study highlighted the in-situ observation of Cd distribution in both the xylem and phloem, and demonstrated the instant response of physiological traits such as xylem water potential, xylem hydraulic conductivity, root Cd2+ flux, NSC content, as well as phytohormonal content under Cd stress, and the less affected traits such as xylem anatomical traits, cellulose and hemicellulose.