Single-cell analysis clarifies mosaic color development in purple hydrangea sepal.

Area of Science:

• Plant biology
• Biochemistry
• Molecular genetics

Background:

• Hydrangea sepals display a spectrum of colors, from red to blue, with purple hues forming a mosaic.
• These diverse colors originate from the same core components: anthocyanins, co-pigments, acylquinic acids, and aluminum ions (Al³⁺).

Purpose of the Study:

• To elucidate the mechanisms behind the mosaic color patterns in Hydrangea sepals.
• To investigate the role of intravacuolar factors in determining petal coloration.

Main Methods:

• Single-cell analysis of vacuolar pH, anthocyanin, co-pigment, and aluminum ion (Al³⁺) content.
• Microspectrophotometry for cell color evaluation and pH microelectrode for vacuolar pH measurement.
• Micro-high-performance liquid chromatography (micro-HPLC) for quantifying organic and Al³⁺ content.

Main Results:

• A mixture of protoplasts with varying colors was obtained from Hydrangea sepals.
• A higher ratio of 5-O-acylquinic acids and Al³⁺ to anthocyanins correlated with bluer cell coloration.
• Reproduction experiments successfully recreated all observed colors by mixing components under different pH conditions.

Conclusions:

• The study provides experimental evidence for cell color variation in Hydrangea, driven by intravacuolar factors.
• Phenotypic differences in Hydrangea coloration can be expressed without direct genomic control, highlighting the role of post-transcriptional or environmental factors.