Building a Barrier: The Influence of Different Wax Fractions on the Water Transpiration Barrier of Leaf Cuticles

Evidence for within-species transition between drought response strategies in Nicotiana benthamiana

Nicotiana benthamiana is predominantly distributed in arid habitats across northern Australia. However, none of six geographically isolated accessions shows obvious xerophytic morphological features. To investigate how these tender-looking plants withstand drought, we examined their responses to water deprivation, assessed phenotypic, physiological, and cellular responses, and analysed cuticular wax composition and wax biosynthesis gene expression profiles. Results showed that the Central Australia (CA) accession, globally known as a research tool, has evolved a drought escape strategy with early vigour, short life cycle, and weak, water loss-limiting responses. By contrast, a northern Queensland (NQ) accession responded to drought by slowing growth, inhibiting flowering, increasing leaf cuticle thickness, and altering cuticular wax composition. Under water stress, NQ increased the heat stability and water impermeability of its cuticle by extending the carbon backbone of cuticular long-chain alkanes from c. 25 to 33. This correlated with rapid upregulation of at least five wax biosynthesis genes. In CA, the alkane chain lengths (c. 25) and gene expression profiles remained largely unaltered. This study highlights complex genetic and environmental control over cuticle composition and provides evidence for divergence into at least two fundamentally different drought response strategies within the N. benthamiana species in < 1 million years.

Water-Repellent Spray for Textiles Using Plant Waste from Conifer Trees

A superhydrophobic textile coating, applied by using a home drying machine, was developed as an aqueous dispersion of waxes that were extracted from recycled Christmas trees. Because the bulk extraction of waxes yielded a mixture of hydrophobic and hydrophilic compounds, a purification process was tested to determine if removing noncrystallizing wax components would enhance the performance of the coating. The performances of coatings created from the crude and enriched extracts were compared, and no significant difference in hydrophobicity was found. Moreover, although the enriched coating was slightly more breathable, there was not enough of an improvement to justify the additional purification steps, rendering the crude extract more industrially viable. Overall, Christmas tree waxes are readily sourced and are capable of producing superhydrophobic coatings without the need for a costly purification step.

Water permeability of different aerial tissues of carnations is related to cuticular wax composition

Cuticular wax protects aerial plant tissues against uncontrolled water loss. To compare the differences among tissues, cultivars, and postharvest stages, we characterized the surface morphology, water permeability, and chemical composition of cuticular wax on the leaf, calyx, and petals of two carnation cultivars ('Master' and 'Lady green') at two postharvest stages. Obvious differences in these characteristics were found among tissues but not among cultivars or postharvest stages. The leaf surface was relatively smooth, whereas convex cells were observed on the petals. The mean minimum conductance of leaves was significantly higher than that of the calyx, followed by that of petals. It ranged between 8.8 × 10^-4  m s^-1 for 'Lady green' leaves at Stage II and 3.6 × 10^-5  m s^-1 for 'Master' petals at Stage I. Petal wax contained high concentrations of n-alkanes, whereas primary alcohols dominated in leaf wax. The weighted average chain length (ACL) was higher in petal wax than in leaf wax; it ranged from 19.6 in 'Lady green' leaves to 24.14 in 'Lady green' petals at Stage I. In conclusion, carnation petals are characterized by numerous convex cells on both the adaxial and abaxial surfaces, and their main cuticular wax components, alkanes, have a higher ACL than leaf cuticular wax, which contributes to their higher water barrier property. The results provide further evidence for the association between cuticular chemical composition and the physiological function of the cuticle in blocking water transpiration.

Genome-wide association study and genetic mapping of BhWAX conferring mature fruit cuticular wax in wax gourd

BACKGROUND

Wax gourd [Benincasa hispida (Thunb) Cogn. (2n = 2x = 24)] is an economically important vegetable crop of genus Benincasa in the Cucurbitaceae family. Fruit is the main consumption organ of wax gourd. The mature fruit cuticular wax (MFCW) is an important trait in breeding programs, which is also of evolutionary significance in wax gourd. However, the genetic architecture of this valuable trait remains unrevealed.

RESULTS

In this study, genetic analysis revealed that the inheritance of MFCW was controlled by a single gene, with MFCW dominant over non-MFCW, and the gene was primarily named as BhWAX. Genome-wide association study (GWAS) highlighted a 1.1 Mb interval on chromosome 9 associated with MFCW in wax gourd germplasm resources. Traditional fine genetic mapping delimited BhWAX to a 0.5 Mb region containing 12 genes. Based on the gene annotation, expression analysis and co-segregation analysis, Bhi09G001428 that encodes a membrane bound O-acyltransferase (MBOAT) was proposed as the candidate gene for BhWAX. Moreover, it was demonstrated that the efficiency of a cleaved amplified polymorphic sequences (CAPS) marker in the determination of MFCW in wax gourd reached 80%.

CONCLUSIONS

In closing, the study identified the candidate gene controlling MFCW and provided an efficient molecular marker for the trait in wax gourd for the first time, which will not only be beneficial for functional validation of the gene and marker-assisted breeding of wax gourd, but also lay a foundation for analysis of its evolutionary meaning among cucurbits.

Insight into the regulatory networks underlying the high lipid perennial ryegrass growth under different irradiances

Under favourable conditions, perennial ryegrass (Lolium perenne) engineered to accumulated high lipid (HL) carbon sink in their leaves was previously shown to also enhance photosynthesis and growth. The greater aboveground biomass was found to be diminished in a dense canopy compared to spaced pots. Besides, the underlying genetic regulatory network linking between leaf lipid sinks and these physiological changes remains unknown. In this study, we demonstrated that the growth advantage was not displayed in HL Lolium grown in spaced pots under low lights. Under standard lights, analysis of differentiating transcripts in HL Lolium reveals that the plants had elevated transcripts involved in lipid metabolism, light capturing, photosynthesis, and sugar signalling while reduced expression of genes participating in sugar biosynthesis and transportation. The plants also had altered several transcripts involved in mitochondrial oxidative respiration and redox potential. Many of the above upregulated or downregulated transcript levels were found to be complemented by growing the plants under low light. Overall, this study emphasizes the importance of carbon and energy homeostatic regulatory mechanisms to overall productivity of the HL Lolium through photosynthesis, most of which are significantly impacted by low irradiances.

Effect of Seasonal Variation on Leaf Cuticular Waxes’ Composition in the Mediterranean Cork Oak (Quercus suber L.)

Quercus suber L. (cork oak) leaves were analyzed along one annual cycle for cuticular wax content and chemical composition. This species, well adapted to the long dry summer conditions prevailing in the Mediterranean, has a leaf life span of about one year. The cuticular wax revealed a seasonal variation with a coverage increase from the newly expanded leaves (115.7 µg/cm2 in spring) to a maximum value in fully expanded leaves (235.6 µg/cm2 after summer). Triterpenoids dominated the wax composition throughout the leaf life cycle, corresponding in young leaves to 26 µg/cm2 (22.6% of the total wax) and 116.0 µg/cm2 (49% of the total wax) in mature leaves, with lupeol constituting about 70% of this fraction. The total aliphatic compounds increased from 39 µg/cm2 (young leaves) to 71 µg/cm2 (mature leaves) and then decreased to 22 µg/cm2 and slightly increased during the remaining period. The major aliphatic compounds were fatty acids, mostly with C16 (hexadecanoic acid) and C28 (octacosanoic acid) chain lengths. Since pentacyclic triterpenoids are located almost exclusively within the cutin matrix (intracuticular wax), the increase in the cyclic-to-acyclic component ratio after summer shows an extensive deposition of intracuticular waxes in association with the establishment of mechanical and thermal stability and of water barrier properties in the mature leaf cuticle.