The microrelief of plant surfaces, mainly caused by epicuticular wax crystalloids, serves different purposes and often causes effective water repellency. Furthermore, the adhesion of contaminating particles is reduced. Based on experimental data carried out on microscopically smooth (Fagus sylvatica L., Gnetum gnemon L., Heliconia densiflora Verlot, Magnolia grandiflora L.) and rough water-repellent plants (Brassica oleracea L., Colocasia esculenta (L.) Schott., Mutisia decurrens Cav., Nelumbo nucifera Gaertn.), it is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces. The plants were artificially contaminated with various particles and subsequently subjected to artificial rinsing by sprinkler or fog generator. In the case of water-repellent leaves, the particles were removed completely by water droplets that rolled off the surfaces independent of their chemical nature or size. The leaves of N. nucifera afford an impressive demonstration of this effect, which is, therefore, called the “Lotus-Effect” and which may be of great biological and technological importance.

Purity of the sacred lotus, or escape from contamination in biological surfaces

Characterization and Distribution of Water-repellent, Self-cleaning Plant Surfaces

Multifunctional surface structures of plants: An inspiration for biomimetics

Adsorption dynamics of surfactants at the air/water interface: a critical review of mathematical models, data, and mechanisms

Limitation of grain crop productivity by phosphorus (P) is widespread and will probably increase in the future. Enhanced P efficiency can be achieved by improved uptake of phosphate from soil (P-acquisition efficiency) and by improved productivity per unit P taken up (P-use efficiency). This review focuses on improved P-use efficiency, which can be achieved by plants that have overall lower P concentrations, and by optimal distribution and redistribution of P in the plant allowing maximum growth and biomass allocation to harvestable plant parts. Significant decreases in plant P pools may be possible, for example, through reductions of superfluous ribosomal RNA and replacement of phospholipids by sulfolipids and galactolipids. Improvements in P distribution within the plant may be possible by increased remobilization from tissues that no longer need it (e.g. senescing leaves) and reduced partitioning of P to developing grains. Such changes would prolong and enhance the productive use of P in photosynthesis and have nutritional and environmental benefits. Research considering physiological, metabolic, molecular biological, genetic and phylogenetic aspects of P-use efficiency is urgently needed to allow significant progress to be made in our understanding of this complex trait.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.2012.04190.x

Opportunities for improving phosphorus-use efficiency in crop plants.

The absorption, transport and mobility of foliar applied radioactive isotopes of rubidium, sodium, potassium, phosphorus, chlorine, sulfur, zinc, copper, manganese, iron, molybdenum, calcium, strontium, and barium were determined with the bean as the experimental plant. Using as a criterion the percent of the foliar applied radioactive isotope recovered in non-treated plant parts, and autoradiography to portray gross distribution in the plant it was found that rubidium, sodium and potassium were the most readily absorbed and most highly mobile. Calcium, strontium and barium while absorbed by the leaf were not exported from the leaf and were considered immobile. Phosphorus, chlorine, sulfur, zinc, copper, manganese, iron, and molybdenum were intermediate with decreasing mobility in the order given. Since the preparation of this manuscript, preliminary observations with magnesium (Mg/sup 28/) showed that it was immobile and its distribution following foliar application was the same as Ca/sup 45/, Sr/sup 89/ or BaLa/sup 140/. 22 references, 4 figures, 4 tables.

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Absorption and Mobility of Foliar Applied Nutrients.

Wettability of the leaf surface, surface tension of the liquid, and stomatal morphology control penetration of stomata by liquids. The critical surface tension of the lower leaf surface of Zebrina purpusii Bruckn. was estimated to be 25 to 30 dyne cm−1. Liquids having a surface tension less than 30 dyne cm−1 gave zero contact angle on the leaf surface and infiltrated stomata spontaneously while liquids having a surface tension greater than 30 dyne cm−1 did not wet the leaf surface and failed to infiltrate stomata. Considering stomata as conical capillaries, we were able to show that with liquids giving a finite contact angle, infiltration depended solely on the relationship between the magnitude of the contact angle and the wall angle of the aperture. Generally, spontaneous infiltration of stomata will take place when the contact angle is smaller than the wall angle of the aperture wall. The degree of stomatal opening (4, 6, 8, or 10 μm) was of little importance. Cuticular ledges present at the entrance to the outer vestibule and between the inner vestibule and substomatal chamber resulted in very small if not zero wall angles, and thus played a major role in excluding water from the intercellular space of leaves. We show why the degree of stomatal opening cannot be assessed by observing spontaneous infiltration of stomata by organic liquids of low surface tension.

Penetration of stomata by liquids: dependence on surface tension, wettability, and stomatal morphology.

Isolated tomato fruit cuticular membrane, free of extractable materials, was titrated potentiometrically using various bases. Three dissociable groups were observed in the pH ranges 3-6 (0.2 meq g(-1)), 6-9 (0.3 meq g(-1)) and 9-12 (0.55 meq g(-1)). The first group was tentatively assigned to-COOH groups of pectic materials and protein embedded in the membrane, the second to nonesterified-COOH groups of the cutin polymer and the third to phenolic-OH groups, such as non-extractable flavenoids present in the membrane, and to a small amount of-NH 3 (+) groups of proteins. The cuticular membrane exhibited a behavior typical of highly cross-linked, high-capacity ion exchange resins of the weak-acid type. Ion exchange capacity increased with increasing pH and neutral salt concentration. At constant pH and salt concentration, the exchange capacity increased with increasing counter ion valence and decreasing crystal radius, e.g. [tris (ethylenediamine) Co](3+)≥Ca(2+)>Ba(2+)>Li(+)>Na(+)>Rb(+)>N(CH3) 4 (+) . The cutin polymer exhibited a pronounced selectivity for Ca(2+) over Na(+) which increased with increasing neutralization of fixed charges. The large trivalent [Co(en)3](3+) was preferred only at low equivalent ionic fractions in the polymer. These results are discussed in relation to the structure and function of cuticular membranes.

Ion exchange properties of isolated tomato fruit cuticular membrane: Exchange capacity, nature of fixed charges and cation selectivity.

Rheological properties were determined for cuticular membranes (CMs) enzymatically isolated from mature tomato (Lycopersicon esculentum Mill. cv Pik Red) fruit. The cuticle responded as a viscoelastic polymer in stress-strain studies. Both CM and dewaxed CM expanded and became more elastic and susceptible to fracture when hydrated, suggesting that water plasticized the cuticle. Dewaxing of the CM caused similar changes in elasticity and fracturing, indicating that wax may serve as a supporting filler in the cutin matrix. Exposure of the cuticle to the surfactant Triton X-100 did not significantly affect its rheological properties.

Rheological Properties of Enzymatically Isolated Tomato Fruit Cuticle.

1. BENTLEY, J. A. 1961. The states of auxin in the plant. In: Handbuch d. Pflanzenphysiologie. W. Ruhland, ed. Springer-Verlag, Berlin, Germany. vol XIV, pp 609-19. 2. CUMMING, B. G. 1959. The control of growth and development in red clover (Trifolium patense L.). III. Endogenous diffusible auxin. Can. J. Botany 37: 1049-62. 3. MILLER, J. S. AND S. A. GORDON. 1962. Auxin relations in illuminated shoots. Plant Physiol. 37: xvi-xvii. 4. NAKAMURA, T., H. ISHII, AND T. YAMAKI. 1962. Intercellular localization of native auxin in Avena coleoptile. Plant and Cell Physiol. 3: 149-56. 5. RAADTS, E. AND H. S6DING. 1957. Chromatographische Untersuchungen iiber die Wuchsstoffe der Haferkoleoptile. Planta 49: 47-60. 6. SCOTT, T. K. AND W. R. BRIGGS. 1960. Auxin relationships in the Alaska pea (Pisum sativurm). Am. J. Botany 47: 492-99. 7. Scorr, T. K. AND W. P. JACOBS. 1962. The isolation and identification of diffusible auxin. Am. J. Botany 49: 657. 8. SHIBAOKA, H. 1961. Studies on the mechanism of the growth inhibiting effect of light. Plant and Cell Physiol. 2: 175-97. 9. SHIBAOKA, H. AND T. YAMAKI. 1959. A sensitized Avena curvature test and identification of the diffusible auxin Avena coleoptile. Botan. Mag. Tokyo. 72: 152-58. 10. SHIBAOKA, H. AND T. YAMAKI. 1959. Studies on the growth movement of sunflower plant. Sci. Papers Coll. Gen. Educ. Univ. Tokyo 9: 105-26. 11. STOWE, B. B. AND K. V. THIMANN. 1954. The paper chromatography of indole compounds and some indole-containing auxins of plant tissues. Arch. Biochem. Biophys. 51: 499-516. 12. THIMANN, K. V. 1952. Plant growth hormones. In: The Action of Hormones in Plants and Invertebrates. Academic Press. New York. 13. ZENK, M. H. 1961. 1(Indole-3-acetyl)-,/-D-glucose, a new compound in the metabolism of indole3-acetic acid in plants. Nature 191: 493-94.

Martin J. Bukovac

Papers

Absorption and Mobility of Foliar Applied Nutrients.

Penetration of stomata by liquids: dependence on surface tension, wettability, and stomatal morphology.

Ion exchange properties of isolated tomato fruit cuticular membrane: Exchange capacity, nature of fixed charges and cation selectivity.

Rheological Properties of Enzymatically Isolated Tomato Fruit Cuticle.

Penetration of Ions through Isolated Cuticles.