Anatomical and Biochemical Traits Related to Blue Leaf Coloration of Selaginella uncinata.

Lin Li,Limei Chen,Rongyan Deng,Aihua Qin,Fangyi Jiang,Lulu Yang,Kalidoss Rajakani

doi:10.1155/2022/1005449

Abstract

Selaginella uncinata shows particularly rare blue leaves. Previous research has shown that structural interference by the cell wall of adaxial epidermal cells imparts blue coloration in leaves of S. uncinata; the objective of this study was to see whether anthocyanins might additionally contribute to this color, as changes in pH, and conjugation with metals and other flavonoids is also known to result in blue coloration in plants. We compared anatomical and biochemical traits of shade-grown (blue) S. uncinata leaves to high light (red) leaves of the same species and also to a non-blue (green) leaves of a congeneric S. kraussiana. By examining the anatomical structure, we found that the shape of adaxial epidermis of S. uncinata leaves was convex or lens-shaped on the lateral view and irregular circles with smooth embossment on the top view. These features were different from those of the abaxial and adaxial epidermis of S. kraussiana. We suspect that these structures increase the proportion of incident light entering the cell, deepening the leaf color, and therefore may be related to blue leaf color in S. uncinata. By examining biochemical traits, we found little difference in leaf pH value among the leaf types; all leaves contained several metal ions such as Mg, Fe, Mn, and copigments such as flavones. However, because there was no anthocyanin in blue S. uncinata leaves, we concluded that blue coloration in S. uncinata leaves is not caused by the three hypotheses of blue coloration: alkalization of the vacuole pH, metal chelation, or copigmentation with anthocyanins, but it may be related to the shape of the leaf adaxial epidermis.

Highlights

Colorful leaves are attractive features that characterize ornamental plants
We conducted tests on three leaf types: blue S. uncinata leaves grown under a sunshade net, green S. kraussiana leaves grown under the same conditions, and red S. uncinata leaves grown in full exposure [14]. ere were 6 POTS for each leaf type and 3 replicates for a total of 54 POTS
We found that the shapes of leaf adaxial and abaxial epidermal cells in blue S. uncinata were different: the adaxial epidermis was irregular circles, with smooth embossment, and by contrast, the abaxial epidermis was a long, wavy, irregular strip, with elongated embossment on the top view (Figure 3(e)). e shape of leaf adaxial and abaxial epidermal cells in red leaves was similar to that of blue leaves (Figure 3(f )). e leaf adaxial and abaxial epidermal cells in S. kraussiana were both shaped as irregular long strips, with elongated embossment on the top view (Figure 3(g))

Summary

Introduction

Colorful leaves are attractive features that characterize ornamental plants. Red, purple, yellow, and variegated leaves are common, whereas blue leaves are rare. Selaginella uncinata, a fern species that is adapted to the shaded conditions, is such a blue leaf plant. It has a blue upper and green lower surface. Our previous research showed that the leaf color of S. uncinata appears normally blue in the shade, while it changes to red under full light exposure [14], and this color change under high light corresponded with a reduction in chlorophyll and anthocyanin and an increase in carotenoids, resulting in a dominant orange color. According to the research of leaf coloration mechanism, leaf coloration in plants can be due to either pigments or structural coloration. According to the research of leaf coloration mechanism, leaf coloration in plants can be due to either pigments or structural coloration. ese two groups differ in their appearance—pigmented colors look the same from all angles, while structural colors appear with different hues when viewed from different angles, a unique attribute of structural color called iridescence [16]

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