Mechanical buckling can pattern the light-diffracting cuticle of Hibiscus trionum.

Many species have cuticular striations that play a range of roles, from pollinator attraction to surface wettability. In Hibiscus trionum, the striations span multiple cells at the base of the petal to form a pattern that produces a type of iridescence. It is postulated, using theoretical models, that the pattern of striations could result from mechanical instabilities. By combining the application of mechanical stress with high-resolution imaging, we demonstrate that the cuticle buckles to create a striated pattern. Through mechanical modeling and cryo-SEM fractures, we show that the cuticle behaves like a bilayer system with a stiff film on a compliant substrate. The pattern of buckling aligns with the direction of the stress to create a larger-scale pattern. Our findings contribute to the understanding of the formation of tissue-wide patterns in living organisms.

Rapid modulation of ultraviolet shielding in plants is influenced by solar ultraviolet radiation and linked to alterations in flavonoids.

The accumulation of ultraviolet (UV)-absorbing compounds (flavonoids and related phenylpropanoids) and the resultant decrease in epidermal UV transmittance (TUV ) are primary protective mechanisms employed by plants against potentially damaging solar UV radiation and are critical components of the overall acclimation response of plants to changing solar UV environments. Whether plants can adjust this UV sunscreen protection in response to rapid changes in UV, as occurs on a diurnal basis, is largely unexplored. Here, we use a combination of approaches to demonstrate that plants can modulate their UV-screening properties within minutes to hours, and these changes are driven, in part, by UV radiation. For the cultivated species Abelmoschus esculentus, large (30-50%) and reversible changes in TUV occurred on a diurnal basis, and these adjustments were associated with changes in the concentrations of whole-leaf UV-absorbing compounds and several quercetin glycosides. Similar results were found for two other species (Vicia faba and Solanum lycopersicum), but no such changes were detected in Zea mays. These findings reveal a much more dynamic UV-protection mechanism than previously recognized, raise important questions concerning the costs and benefits of UV-protection strategies in plants and have practical implications for employing UV to enhance crop vigor and quality in controlled environments.

The flower of Hibiscus trionum is both visibly and measurably iridescent.

Living organisms can use minute structures to manipulate the reflection of light and display colours based on interference. There has been debate in recent literature over whether the diffractive optical effects produced by epoxy replicas of petals with folded cuticles persist and induce iridescence in the original flowers when the effects of petal pigment and illumination are taken into account. We explored the optical properties of the petal of Hibiscus trionum by macro-imaging, scanning and transmission electron microscopy, and visible and ultraviolet (UV) angle-resolved spectroscopy of the petal. The flower of Hibiscus trionum is visibly iridescent, and the iridescence can be captured photographically. The iridescence derives from a diffraction grating generated by folds of the cuticle. The iridescence of the petal can be quantitatively characterized by spectrometric measurements with several square-millimetres of sample area illuminated. The flower of Hibiscus trionum has the potential to interact with its pollinators (honeybees, other bees, butterflies and flies) through iridescent signals produced by its cuticular diffraction grating.

Effect of different drying methods on chlorophyll, ascorbic acid and antioxidant compounds retention of leaves of Hibiscus sabdariffa L.

BACKGROUND: Use of the indigenous, easily accessible leafy vegetable roselle (Hibiscus sabdariffa L.) for value addition is gaining impetus as its nutritive and nutraceutical compounds are exposed by investigations. Being a perishable, storage is challenging, hence different methods of drying have been an attractive alternative for its postharvest usage in foods without much compromising its quality and antioxidant potential. RESULTS: Room- and freeze-dried samples were found to have best quality in terms of colour, total flavonoid content (18.53 ± 2.39 and 18.66 ± 1.06 g kg(-1) respectively), total phenolic content (17.76 ± 1.93 and 18.91 ± 0.48 g kg(-1)), chlorophyll content (1.59 ± 0.001 and 1.55 ± 0.001 g kg(-1)) and ascorbic acid content (11.11 ± 1.04 and 8.92 ± 0.94 g kg(-1)) compared with those subjected to infrared, crossflow, microwave, oven or sun drying. Samples treated by room and freeze drying retained maximum antioxidant potential as shown by the phosphomolybdate method and the 2,2-diphenyl-1-picrylhydrazyl free radical-scavenging activity and ferric-reducing antioxidant power assays. Cold water and hot water extracts showed significantly higher total phenolic content and total antioxidant activity owing to the greater solubility of phenolics and destruction of cellular components in polar solvents than in organic solvents. CONCLUSION: The data obtained show the potential for retaining quality parameters of roselle leaf under suitable drying methods.

Leaf photosynthesis and respiration of three bioenergy crops in relation to temperature and leaf nitrogen: how conserved are biochemical model parameters among crop species?

Given the need for parallel increases in food and energy production from crops in the context of global change, crop simulation models and data sets to feed these models with photosynthesis and respiration parameters are increasingly important. This study provides information on photosynthesis and respiration for three energy crops (sunflower, kenaf, and cynara), reviews relevant information for five other crops (wheat, barley, cotton, tobacco, and grape), and assesses how conserved photosynthesis parameters are among crops. Using large data sets and optimization techniques, the C(3) leaf photosynthesis model of Farquhar, von Caemmerer, and Berry (FvCB) and an empirical night respiration model for tested energy crops accounting for effects of temperature and leaf nitrogen were parameterized. Instead of the common approach of using information on net photosynthesis response to CO(2) at the stomatal cavity (A(n)-C(i)), the model was parameterized by analysing the photosynthesis response to incident light intensity (A(n)-I(inc)). Convincing evidence is provided that the maximum Rubisco carboxylation rate or the maximum electron transport rate was very similar whether derived from A(n)-C(i) or from A(n)-I(inc) data sets. Parameters characterizing Rubisco limitation, electron transport limitation, the degree to which light inhibits leaf respiration, night respiration, and the minimum leaf nitrogen required for photosynthesis were then determined. Model predictions were validated against independent sets. Only a few FvCB parameters were conserved among crop species, thus species-specific FvCB model parameters are needed for crop modelling. Therefore, information from readily available but underexplored A(n)-I(inc) data should be re-analysed, thereby expanding the potential of combining classical photosynthetic data and the biochemical model.

Study of temperature influence on electron transport in higher plants via delayed luminescence method: experiment, theory.

The temperature dependence of steady-state millisecond delayed luminescence (DL) is studied within the temperature range from -23 to 45 degrees C in leaf segments of chinese rose (Hibiscus rosa-sinensis L.) and bean (Ficia faba). To describe the experimental dependence of DL steady-state intensity on temperature theoretically, we suggest the temperature dependences of rate constants in earlier proposed model of photosynthesis. Under these conditions, the temperature dependence of DL steady-state value has the same form as experimental curve.