Analysis of physiological-biochemical index regulation in Chardonnay grape leaf phototaxis and gene hub module mining

Phototropic movement is an evolutionary strategy that increases light capture and photosynthetic efficiency in plants. Despite its importance, the physiological, biochemical, and molecular basis of pulvinus-driven leaf movement in grape species remains poorly understood. To simulate adverse light conditions, Chardonnay grapevine branches were artificially inverted, altering the natural growth orientation of the leaves. In this study, the dynamic characteristics of pulvinus-mediated leaf movement were meticulously documented, and key physiological parameters (gas exchange and water potential) were evaluated. Additionally, the daily fluctuations in H⁺-ATPase activity, electrical conductivity, ions (K⁺, Ca²⁺, Mg²⁺, Cu²⁺, Fe^2+/3+, Zn²⁺, and Mn²⁺), and hormones (IAA, GA₃, ABA, and ZT) in pulvinus were systematically measured. Transcriptomic analysis was employed to identify potential molecular hub regulatory modules involved in the photosynthetic and hormonal pathways. A significant increase in leaf gas exchange and water potential resulted from a change in leaf orientation. During pulvinus movement, H⁺-ATPase activity and extensor conductivity increased significantly, and Fe^2+/3+ exhibited antagonistic and synergistic changes with K⁺ and Mn²⁺, respectively. The IAA content in the flexor decreased gradually, whereas the GA₃ content in the extensor first decreased and then increased. A total of seven hub modules were identified among the differentially expressed genes associated with the photosynthetic and hormonal pathways. Overall, grapevines adjust leaf orientation through strategies that increase leaf gas exchange and water potential and alter the differential distribution of hormones and ions within the pulvinus. This study offers valuable insights into leaf movement's physiological and biochemical mechanisms and provides genetic resources for molecular-level research.