Integrated Multiscale Imaging and Noninvasive Micro-Sensing Decipher Spatiotemporal Calcium Dynamics in Thermogenic Tissue of Magnolia Flower.

Abstract

Magnolia denudata is characterized by floral thermogenesis and blooms in the cold early spring. However, the specific thermogenic tissues and molecular signals that modulate thermogenesis remain elusive. Here, we categorized the developmental process of M. denudata into five stages with stage 2 being the thermogenic peak stage, and identified the thermogenic region as the lateral tissue of gynoecium by integrating infrared (IR) imaging and multispectral imaging (MSI). The optimized integration of these imaging techniques not only distinguished the gynoecium of the non-thermogenic and thermogenic stages but also revealed compound differences between the lateral and central tissues at the thermogenic stage. Moreover, we unveiled the in situ distribution of calcium in thermogenic organs using micro X-ray fluorescence imaging (μ-XRF), and its distribution pattern closely matched the heat distribution. The increased rate of Ca²⁺ influx both into the cytosol and mitochondria aligns with the upregulation of genes related to mitochondrial Ca²⁺ transport at the thermogenic stage. Additionally, changes in respiratory capacity caused by altering cytosolic Ca²⁺ concentration further demonstrated that Ca²⁺ regulates mitochondrial respiratory metabolism. This study comprehensively utilized multiscale imaging to distinguish the thermogenic tissue within the complex-structured thermogenic organ of M. denudata, revealing the close relationship between Ca²⁺ and thermogenesis.