Nitrogen modulates strontium uptake and toxicity in Hypericum perforatum plants

Area of Science:

• Plant Physiology
• Environmental Science
• Medicinal Botany

Background:

• Strontium (Sr) is an abundant soil element due to its chemical similarity to calcium, leading to its uptake by plants.
• Medicinal plants like Hypericum perforatum L. can accumulate strontium, necessitating an understanding of its physiological impacts.
• Nitrogen (N) availability is crucial for plant growth and metabolism, potentially influencing responses to heavy metal stress.

Purpose of the Study:

• To investigate the effects of different nitrogen sources (inorganic nitrate, organic urea, allantoin) and nitrogen deficit on strontium-induced changes in Hypericum perforatum L.
• To assess how nitrogen forms modulate strontium accumulation and its impact on primary and secondary metabolites, and mineral content.
• To explore the role of nitrogen in mitigating strontium's toxic effects and influencing oxidative stress markers.

Main Methods:

• Cultivation of Hypericum perforatum L. with 100 µM strontium (Sr) under varying nitrogen conditions (nitrate, urea, allantoin, or N deficit).
• Analysis of primary metabolites (amino acids, Krebs acids, ascorbic acid, thiols), secondary metabolites (phenols, pseudo/hypericin), and mineral elements (Ca).
• Measurement of reactive oxygen species (ROS) and nitric oxide (NO) formation in root tissues; germination experiments were also conducted.

Main Results:

• Strontium exposure altered primary and secondary metabolism and reduced calcium content, but organic nitrogen forms (urea, allantoin) mitigated these negative effects.
• Organic nitrogen forms increased strontium accumulation in shoots, while nitrogen deficit reduced it; these forms also influenced ROS and NO formation.
• Germination trials showed no strontium toxicity up to 1 mM, with even stimulation of amino acids and phenols, indicating ontogenetic resilience.

Conclusions:

• Organic nitrogen sources can effectively mitigate strontium's adverse effects in Hypericum perforatum L. and influence its accumulation.
• Nitrogen availability, particularly organic forms, plays a key role in modulating plant responses to strontium stress and associated metabolic changes.
• Hypericum perforatum L. exhibits resilience to strontium toxicity during germination, with potential metabolic benefits observed under specific conditions.