Calcium supply alters aquaporin transcription and enhances water deficit resilience in a Eucalyptus hybrid

Calcium plays a role in modulating aquaporin expression, reducing oxidative stress, preserving chlorophyll content, and maintaining membrane integrity, suggesting it may enhance eucalypt resilience to water restriction. Drought is a significant abiotic stress that severely impacts the growth and productivity of forests worldwide. This study investigates the role of calcium (Ca2+) supply in modulating aquaporin (AQP) gene expression and mitigating oxidative stress in eucalypt (Eucalyptus urophylla × Eucalyptus camaldulensis) under water restriction. Three-month-old eucalypt seedlings were subjected to water restriction, with or without Ca2+ supplementation. We measured mRNA expression levels of five aquaporin isoforms (PIP1;2, PIP1;3, PIP2;1, PIP2;2, and PIP2;7), chlorophyll content, and markers of oxidative stress [e.g., hydrogen peroxide (H2O2), malondialdehyde (MDA), and the activities of catalase (CAT) and superoxide dismutase (SOD)]. Our findings reveal that initial water restriction upregulated the expression of PIP1;2, PIP2;1, PIP2;2, and PIP2;7 in roots, which likely facilitated water uptake and maintained cellular hydration. However, under prolonged water limitation, plants supplemented with Ca2+ showed downregulation of these PIPs, possibly as a protective mechanism to reduce water loss. In contrast, plants without Ca2+ exhibited an upregulation of PIP1;2, PIP1;3, and PIP2;7 under prolonged water deficit. Ca2+ supplementation also played a crucial role in preserving chlorophyll content and reducing oxidative damage under water limitation. Plants supplemented with Ca2+ had lower levels of H2O2 and MDA, reduced oxidative damage and membrane permeability, alongside increased CAT activity, which suggests an enhanced oxidative response. Our results provide new insights into how Ca2+ enhances eucalypt responses to water deprivation, enhancing our understanding of the function of Ca2+ in drought responses.