Single‐cell analysis clarifies mosaic color development in purple hydrangea sepal

Abstract

Summary Hydrangea sepals exhibit a wide range of colors, from red, through purple, to blue; the purple color is a color mosaic. However, all of these colors are derived from the same components: simple anthocyanins, 3‐O‐glycosyldelphinidins, three co‐pigment components, acylquinic acids and aluminum ions (Al3+). We show the color mosaic is a result of graded differences in intravacuolar factors. In order to clarify the mechanisms of mosaic color, we performed single‐cell analyses of vacuolar pH, and anthocyanin, co‐pigment and Al3+ content. From the sepals, a protoplast mixture of various colors was obtained. The cell color was evaluated by microspectrophotometry and vacuolar pH then was recorded by using a pH microelectrode. The organic and Al3+ contents were quantified by micro‐HPLC. We found that the bluer the cell, the greater the ratio of 5‐O‐acylquinic acids and Al3+ to anthocyanins. Furthermore, reproducing experiments were conducted by mixing the components under various pH condition; all the colors could be reproduced in the various mixing conditions. Based on the above, we provide experimental evidence for cell color variation in hydrangea. Our study demonstrates the expression of phenotypic differences without any direct genomic control.

Insight into chemical mechanisms of sepal color development and variation in hydrangea

“…7 ). 40 , 41 ) Interestingly, using this method, we reported that the molar equivalent of 5- O -acylquinic acids ( 2 , 3 ) to anthocyanins ( 1 , 5 ) was strongly correlated with blue cell coloration; however, the content of anthocyanin and 3- O -caffeoylquinic acid ( 4 ) did not correlate with cell color. Nonetheless, these results indicated a clear contribution of 5- O -acylquinic acids ( 2 , 3 ) to the blue sepal cell color in hydrangea.…”

“…Nonetheless, these results indicated a clear contribution of 5- O -acylquinic acids ( 2 , 3 ) to the blue sepal cell color in hydrangea. 40 , 41 )…”

“…This strongly suggested that 5- O -acylquinic acids play a very important role in blue cell coloration in hydrangea sepals. 40 , 41 )…”

“…By reducing the reaction system and HPLC analytical condition, we established an Al 3+ analytical method for single cells. 40 , 41 )…”

“…( P < 0.001), indicating that this ratio is another critical condition for blue cell color in hydrangea sepals. 40 , 41 )…”