Acclimatization mechanisms in Populus deltoides roots to zinc excess

Abstract

Zinc excess can interfere with the uptake and distribution of essential nutrients, altering their homeostasis and resulting in stunted plant growth, nutrient deficiency, and chlorosis. However, plants utilize various adjustments to help improve their metabolome, enhance defense mechanisms, and thrive under challenging environmental conditions. Despite advances in understanding mechanisms towards metal tolerance, specific questions remain open, especially regarding environmental cues signaling in woody plants. The study explores the early signaling of zinc uptake and sequestration within tissues, with emphasis on cellular redox-balance and plant functional traits. Nutrient analysis revealed that Zn retention in roots was coupled with adjustments in iron and calcium homeostasis, preventing Zn overaccumulation in leaves. Excess Zn induced a decrease in growth without affecting the carbon allocation, while photosynthesis was primarily affected on the stomatal level, without apparent effects on photosystem efficiency. The study highlights poplar nutrients acquisition strategy under zinc excess conditions, where small molecules sequestration in the roots prevents zinc hyperaccumulation in above-ground parts. With such adjustments, poplar plants were able to keep above-ground biomass allocation patterns stabile, maintaining steady growth increase under adverse conditions. Zinc excess triggered proline accumulation and enhanced antioxidant enzyme activities, mitigating oxidative stress. Further on, we observed transcript-level changes indicating possible zone-specific responses to zinc in roots. This observation opens new frontiers in how environmental sensing in woody species is regulated