Structural and Biochemical Properties of Duckweed Surface Cuticle

Abstract

The plant cuticle, which consists of cutin and waxes, forms a hydrophobic coating covering the aerial surfaces of all plants. It acts as an interface between plants and their surrounding environment whilst also protecting them against biotic and abiotic stresses. In this research, we have investigated the biodiversity and cuticle properties of aquatic plant duckweed, using samples isolated from four different locations around Hongze lake in Jiangsu province, China. The samples were genotyped using two chloroplast markers and nuclear ribosomal DNA markers, which revealed them as ecotypes of the larger duckweed, Spirodela polyrhiza. Duckweed cuticle properties were investigated by compositional analysis using Gas Chromatography coupled with Mass Spectroscopy (GC-MS) Flame Ionization Detector (GC-FID), and ultrastructural observation by cryo-Scanning Electron Microscopy (cryo-SEM). Cuticle compositional analysis indicated that fatty acids and primary alcohols, the two typical constituents found in many land plant cuticle, are the major duckweed wax components. A large portion of the duckweed wax fraction is composed of phytosterols, represented by campesterol, stigmasterol, sitosterol and their common precursor squalene. The cryo-SEM observation uncovered significant differences between the surface structures of the top air-facing and bottom water-facing sides of the plant fronds. The top side of the fronds, containing multiple stomata complexes, appeared to be represented by a rather flat waxy film sporadically covered with wax crystals. Underneath the waxy film was detected a barely distinguished nanoridge net, which became distinctly noticeable after chloroform treatment. On the bottom side of the fronds, the large epidermal cells were covered by the well-structured net, whose sections became narrower and sharper under cryo-SEM following chloroform treatment. These structural differences between the abaxial and adaxial sides of the fronds evidently relate to their distinct physiological roles in interacting with the contrasting environments of sunlight/air and nutrients/water. The unique structural and biochemical features of Spirodela frond surfaces with their rapid reproductive cycle and readily availability genome sequence, make duckweed an attractive monocot model for studying the fundamental processes related to plant protection against ultraviolet irradiation, pathogens and other environmental stresses.

Mosaic Arrangement of the 5S rDNA in the Aquatic Plant Landoltia punctata (Lemnaceae)

“…4 However, there were significant differences between the arrangements of the 5S rDNA locus in the two Spirodela species and L. punctata . First, almost no intragenomic or intergenomic variation was observed within each NTS type in Spirodela, which is in agreement with our own analysis of a smaller NTS variant in four S. polyrhiza ecotypes ( Borisjuk et al, 2018 ). By contrast, we identified extensive variation in class I NTS in L. punctata , as illustrated in Figure 3 .…”

Genome of the world’s smallest flowering plant, Wolffia australiana, helps explain its specialized physiology and unique morphology

“…The wax and cuticle components of aquatic plants may act as protective layers against damaging UV irradiation 30 . Supporting this idea, a high percentage of phytosterol has been reported in S. polyrhiza 30 .…”

“…The wax and cuticle components of aquatic plants may act as protective layers against damaging UV irradiation 30 . Supporting this idea, a high percentage of phytosterol has been reported in S. polyrhiza 30 . Moreover, of the total lipids in Wolffia 31 , phytosterols constitute a significant proportion, suggesting essential roles in the floating lifestyle.…”

Chromosome-scale genome assembly for the duckweed Spirodela intermedia, integrating cytogenetic maps, PacBio and Oxford Nanopore libraries

“…This was confirmed by sequencing of the 5S rDNA repeats, amplified from genomic DNA of clones 8410 and 7747. Analysis of individual 5S rDNA clones of Si8410 and Si7747 identified the 119 bp long 5S rRNA genes with 100% identity to the previously sequenced 5S rRNA gene of S. polyrhiza 43 , and two variants of the NTS for each ecotype (Fig. S4), with variant 8410-1 corresponding to 5S rDNA locus on chromosome ChrSi15 and the variant 8410-2 corresponding to the locus on chromosome ChrSi14 (Fig.…”