Effects of drought and rewatering on growth, physiology and flavonoid metabolism of Ginkgo biloba seedlings
To clarify the effects of drought stress and rewatering on growth, physiology and flavonoid metabolism of Ginkgo biloba seedlings, and improve the theory of drought resistance and quality regulation for leaf-used Ginkgo biloba, 3-year-old ginkgo seedlings were used as materials, and different gradients of drought and rewatering treatments were set by pot water control method. Growth traits, leaf ultrastructure, photosynthetic fluorescence, osmotic regulation, antioxidant system, hormones, non-structural carbohydrates and total flavonoids were systematically determined, and the molecular response mechanism was analyzed by transcriptome and metabolome. The main results are as follows:(1) Drought stress significantly inhibited the aboveground growth of ginkgo seedlings, and the inhibition effect increased with stress intensity. Ginkgo adapted to water deficit by increasing root-shoot ratio and underground biomass distribution. Growth could recover significantly in moderate and mild drought after rewatering, while severe drought caused irreversible damage.(2) Drought stress led to the transformation of leaves from physiological wilting to structural damage. The degree of stomatal closure and epidermal cell shrinkage was positively correlated with stress intensity. Rewatering could only repair the cell structure damage caused by moderate and mild stress, while severe drought still remained structural damage.(3) Drought stress significantly reduced photosynthetic efficiency and PSII activity, increased instantaneous water use efficiency, activated antioxidant and osmotic adjustment systems, changed hormone balance and non-structural carbohydrate metabolism. Physiological indexes recovered gradually after rewatering, but severe drought showed obvious recovery lag.(4) There were significant correlations between growth indexes and physiological metabolism indexes. Photosynthetic capacity drove aboveground growth, and stress-resistant substance accumulation was positively coordinated with root expansion, reflecting the resource trade-off between growth and stress resistance of ginkgo seedlings.(5) Transcriptome and metabolome analysis showed that flavonoid biosynthesis was the core pathway of ginkgo response to drought. Key genes such as PAL, CHS, FLS and transcription factors such as AP2/ERF, bHLH jointly regulated flavonoid metabolism. Drought significantly promoted flavonoid accumulation, and severe drought showed stress memory effect after rewatering.This study clarified the comprehensive response of ginkgo seedlings to drought and rewatering, revealed the regulation mechanism of flavonoid metabolism, and provided a scientific basis for drought-resistant cultivation, precise water management and medicinal quality improvement of leaf-used Ginkgo biloba.Keywords: Ginkgo biloba seedlings; drought stress; rewatering; growth and physiology; flavonoid metabolism; transcriptome; metabolome