Applying quantitative spatial phenotypes analysis to the investigation of peltate glandular trichomes development pattern in Perilla frutescens

Abstract

Background: Glandular trichomes, often referred to as "phytochemical factories", plays a crucial role in plant growth and metabolism. As the site for secretion and storage, the development of glandular trichomes is related to the dynamic biosynthesis of specialised metabolites. The study aims to explore the relationship between spatial phenotype and dynamic metabolism of glandular trichomes, and establish a novel approach for the exploration and study of the regulatory mechanism governing the development of glandular trichomes.

Results: In this study, we proposed a technical route based on the relative deviation value to distinguish the peltate glandular trichomes (PGTs) from the background tissues and extract their spatial phenotype. By defining glandular trichome developmental stages based on the leaf vein growth axis, we found that young PGTs were densely distributed near the proximal end of growth axis of the leaf veins, where perillaketone, a primary metabolite of PGTs, is predominantly accumulated. Conversely, mature PGTs are typically found near the distal end of the mid-vein growth axis and the lateral end of the secondary vein growth axis, where the accumulation rate of isoegomaketone and egomaketone exceeds that of perillaketone in PGTs. We further identified spatial phenotypic parameters, L_sum and d, as independent variables to construct a linear regression model that illustrates the relationship between the spatial phenotypes and metabolite content of PGTs, including perillaketone (R² = 0.698), egomaketone (R² = 0.593), isoegomaketone (R² = 0.662) and the sum of the amount (R² = 0.773).

Conclusions: This model proved that the development of PGTs was correlated with the growth of the entire leaf, and the development stage of PGTs can be identifined by spatial phenotypes based on the leaf veins. In conclusion, the findings of this study enhance our understanding of correlation between spatial phenotype and development of glandular trichomes and offer a new approach to explore and study the regulatory mechanism of glandular trichome development.

Keywords: Growth axis; Leaf veins; Linear regression equation; Peltate glandular trichomes; Perilla frutescens; Spatial phenotype.

Fig. 1

Technical route of point vector map generation of P. frutescens PGTs distribution. a Photomerge; b Adding a black and white mask; c Generating a map of the mean pixel values (16 × 16 pixels) map; d Calculating and generating a vector graph of RD values; e Setting the threshold to obtain a PGTs distribution raster map; f Converting the PGTs distribution raster map to the point vector map; g Aggregating points; h Artificial modification

Fig. 2

Spatial phenotypic parameters of PGTs. A The zone of the PGTs; B definition of spatial phenotypic parameters

Fig. 3

The morphology of glandular trichomes in P. frutescens. A adaxial surface of P. frutescens leaves; B abaxial surface of P. frutescens leaves; C non-glandular trichome (NGT); D peltate glandular trichome (PGT); E digitiform glandular trichome (DGT); F Capitate glandular trichome (CGT)

Fig. 4

Density heat map of P. frutescens PGTs distribution

Fig. 5

The contents variation of the main compounds in PGTs from different divisions. I The content of perillaketone in single PGT; II The proportion of perillaketone in volatile oils; III The content of egomaketone in single PGT; IV The proportion of egomaketone in volatile oils; V The content of isoegomaketone in single PGT; VI The proportion of isoegomaketone in volatile oils; VII The content of β-caryophyllene in single PGT; VIII The proportion of β-caryophyllene in volatile oils. The leaf shown in the Figure is sample 1

Fig. 6

The predicted and measured contents of compounds in PGTs. XT refers to AT, BT, CT, etc.; X1 refers to A1, B1, C1, etc.; X2 refers to A2, B2, C2, etc.; X3 refers to A3, B3, C3, etc.; X4 refers to A4, B4, C4, etc.; X5 refers to A5, B5, C5, etc.

Fig. 7

Dynamic changes of biosynthesis of perillaketone, isoegomaketone and egomaketone with the maturation of PGTs. Route a is the pathway from egomaketone to perillaketone; b is the pathway from egomaketone to isoegomaketone