Variation in Petal and Leaf Wax Deposition Affects Cuticular Transpiration in Cut Lily Flowers

Evidence of combined flower thermal and drought vulnerabilities portends reproductive failure under hotter-drought conditions

Despite the abundant evidence of impairments to plant performance and survival under hotter-drought conditions, little is known about the vulnerability of reproductive organs to climate extremes. Here, by conducting a comparative analysis between flowers and leaves, we investigated how variations in key morphophysiological traits related to carbon and water economics can explain the differential vulnerabilities to heat and drought among these functionally diverse organs. Due to their lower construction costs, despite having a higher water storage capacity, flowers were more prone to turgor loss (higher turgor loss point; ΨTLP) than leaves, thus evidencing a trade-off between carbon investment and drought tolerance in reproductive organs. Importantly, the higher ΨTLP of flowers also resulted in narrow turgor safety margins (TSM). Moreover, compared to leaves, the cuticle of flowers had an overall higher thermal vulnerability, which also resulted in low leakage safety margins (LSM). As a result, the combination of low TSMs and LSMs may have negative impacts on reproduction success since they strongly influenced the time to turgor loss under simulated hotter-drought conditions. Overall, our results improve the knowledge of unexplored aspects of flower structure and function and highlight likely threats to successful plant reproduction in a warmer and drier world.

The cuticular wax composition and crystal coverage of leaves and petals differ in a consistent manner between plant species

Both leaves and petals are covered in a cuticle, which itself contains and is covered by cuticular waxes. The waxes perform various roles in plants' lives, and the cuticular composition of leaves has received much attention. To date, the cuticular composition of petals has been largely ignored. Being the outermost boundary between the plant and the environment, the cuticle is the first point of contact between a flower and a pollinator, yet we know little about how plant-pollinator interactions shape its chemical composition. Here, we investigate the general structure and composition of floral cuticular waxes by analysing the cuticular composition of leaves and petals of 49 plant species, representing 19 orders and 27 families. We show that the flowers of plants from across the phylogenetic range are nearly devoid of wax crystals and that the total wax load of leaves in 90% of the species is higher than that of petals. The proportion of alkanes is higher, and the chain lengths of the aliphatic compounds are shorter in petals than in leaves. We argue these differences are a result of adaptation to the different roles leaves and petals play in plant biology.

The dynamic changes of mango (Mangifera indica L.) epicuticular wax during fruit development and effect of epicuticular wax on Colletotrichum gloeosporioides invasion

Mango fruits are susceptible to diseases, such as anthracnose, during fruit development, leading to yield reduction. Epicuticular wax is closely related to resistance of plants to pathogenic bacterial invasion. In this study, the effect of mango fruit epicuticular wax on the invasion of Colletotrichum gloeosporioides was investigated, followed by to understand the changes of wax chemical composition and crystal morphology during mango fruit development using GC-MS and SEM. Results showed that the epicuticular wax of mango fruits can prevent the invasion of C. gloeosporioides, and 'Renong' showed the strongest resistance to C. gloeosporioides. The wax content of four mango varieties first increased and then decreased from 40 days after full bloom (DAFB) to 120 DAFB. In addition, 95 compounds were detected in the epicuticular wax of the four mango varieties at five developmental periods, in which primary alcohols, terpenoids and esters were the main wax chemical composition. Furthermore, the surface wax structure of mango fruit changed dynamically during fruit development, and irregular platelet-like crystals were the main wax structure. The present study showed the changes of wax content, chemical composition and crystal morphology during mango fruit development, and the special terpenoids (squalene, farnesyl acetate and farnesol) and dense crystal structure in the epicuticular wax of 'Renong' fruit may be the main reason for its stronger resistance to C. gloeosporioides than other varieties. Therefore, these results provide a reference for the follow-up study of mango fruit epicuticular wax synthesis mechanism and breeding.

Combined heat and water stress leads to local xylem failure and tissue damage in pyrethrum flowers

Flowers are critical for angiosperm reproduction and the production of food, fiber, and pharmaceuticals, yet for unknown reasons, they appear particularly sensitive to combined heat and drought stress. A possible explanation for this may be the co-occurrence of leaky cuticles in flower petals and a vascular system that has a low capacity to supply water and is prone to failure under water stress. These characteristics may render reproductive structures more susceptible than leaves to runaway cavitation-an uncontrolled feedback cycle between rising water stress and declining water transport efficiency that can rapidly lead to lethal tissue desiccation. We provide modeling and empirical evidence to demonstrate that flower damage in the perennial crop pyrethrum (Tanacetum cinerariifolium), in the form of irreversible desiccation, corresponds with runaway cavitation in the flowering stem after a combination of heat and water stress. We show that tissue damage is linked to greater evaporative demand during high temperatures rather than direct thermal stress. High floral transpiration dramatically reduced the soil water deficit at which runaway cavitation was triggered in pyrethrum flowering stems. Identifying runaway cavitation as a mechanism leading to heat damage and reproductive losses in pyrethrum provides different avenues for process-based modeling to understand the impact of climate change on cultivated and natural plant systems. This framework allows future investigation of the relative susceptibility of diverse plant species to reproductive failure under hot and dry conditions.

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.

Exploring Thrips Preference and Resistance in Flowers, Leaves, and Whole Plants of Ten Capsicum Accessions

Capsicum species grown for pepper production suffer severely from thrips damage, urging the identification of natural resistance. Resistance levels are commonly assessed on leaves. However, Capsicum plants are flower-bearing during most of the production season, and thrips also feed on pollen and flower tissues. In order to obtain a comprehensive estimate of elements contributing to thrips resistance, flower tissues should be considered as well. Therefore, we assessed resistance to Frankliniella occidentalis in flowers, leaves, and whole plants of ten Capsicum accessions. Using choice assays, we found that thrips prefer flowers of certain accessions over others. The preference of adult thrips for flowers was positively correlated to trehalose and fructose concentration in anthers as well as to pollen quantity. Resistance measured on leaf discs and thrips population development on whole plants was significantly and positively correlated. Leaf-based resistance thus translates to reduced thrips population development. Results of the flower assays were not significantly correlated with resistance in leaves or on whole plants. This suggests that both leaves and flowers represent a different part of the resistance spectrum and should both be considered for understanding whole plant resistance and the identification of resistant Capsicum varieties.

The full-length genome sequence of a novel amalgavirus in Lilium spp. in China

We report for the first time the complete genome sequence of a novel amalgavirus, tentatively designated as 'lily amalgavirus 1' (LAV-1), isolated from Lilium spp. in China. LAV-1 is a 3448-nt double-stranded RNA virus that encodes two putative proteins. Open reading frame 1 (ORF1) encodes a 394-aa protein with unknown function. ORF2 encodes a putative RNA-dependent RNA polymerase (RdRp) of 895 aa. The two ORFs putatively encode a '1 + 2' fusion protein generated by a '+1' programmed ribosomal frameshift (PRF). BLASTp analysis revealed that the complete genome sequence of LAV-1 shares 48.23-59.80% sequence identity (query sequence coverage > 77%) with those of members of the genus Amalgavirus, with the highest nucleotide sequence identity of 59.80% with that of Allium cepa amalgavirus 1 (query sequence coverage, 87%). The genome structure, phylogenetic relationships, and sequence similarities to other plant amalgaviruses suggest that LAV-1 is a new member of the genus Amalgavirus.