Photodegradation of Myrigalone A, an Allelochemical from Myrica gale: Photoproducts and Effect of Terpenes

The Chemical Landscape of Leaf Surfaces and Its Interaction with the Atmosphere

Atmospheric chemists have historically treated leaves as inert surfaces that merely emit volatile hydrocarbons. However, a growing body of evidence suggests that leaves are ubiquitous substrates for multiphase reactions-implying the presence of chemicals on their surfaces. This Review provides an overview of the chemistry and reactivity of the leaf surface's "chemical landscape", the dynamic ensemble of compounds covering plant leaves. We classified chemicals as endogenous (originating from the plant and its biome) or exogenous (delivered from the environment), highlighting the biological, geographical, and meteorological factors driving their contributions. Based on available data, we predicted ≫2 μg cm-2 of organics on a typical leaf, leading to a global estimate of ≫3 Tg for multiphase reactions. Our work also highlighted three major knowledge gaps: (i) the overlooked role of ambient water in enabling the leaching of endogenous substances and mediating aqueous chemistry; (ii) the importance of phyllosphere biofilms in shaping leaf surface chemistry and reactivity; (iii) the paucity of studies on the multiphase reactivity of atmospheric oxidants with leaf-adsorbed chemicals. Although biased toward available data, we hope this Review will spark a renewed interest in the leaf surface's chemical landscape and encourage multidisciplinary collaborations to move the field forward.

A review of pesticide phototransformation on the leaf surface: Models, mechanism, and influencing factors

Phototransformation is an important environmental fate of pesticides on plant leaves. This review found that the photodegradation rates of pesticides on leaves might be faster or slower than those in organic solvents or on glass because of the different spectral patterns and light fluxes on the model surface. Wax was found to play an important role in pesticide phototransformation because it has photosensitizing properties, which might be stimulated under light irradiation to produce reactive species, such as hydroxyl radicals, singlet oxygen, methyl radicals, alkyl radicals, and superoxide radicals. These reactive species could accelerate pesticide photodegradation by several times. Wax can also decrease the photodegradation rate of pesticides by quenching reactive species or light-shielding effects. The environmental conditions and phytochemical properties of leaves play important roles in pesticide phototransformation primarily because the composition of wax varies with plant species and environmental factors. The phototransformation of pesticides on leaves was promoted by a low dosage of adjuvant because they act as photosensitizers and improve the dispersity of pesticides, while it was inhibited at a high concentration of adjuvant because of their light shielding effect. Finally, recommendations for future research were discussed, including (1) distinguishing the direct and indirect photodegradation of pesticides; (2) developing model, molecular level visualization and analysis techniques; (3) conducting more field research; and (4) considering the effect of climate change, especially the interaction of climatic factors. This review gives a comprehensive overview of the current knowledge of pesticide phototransformation on leaves and provides suggestions for future studies.

Environmental photochemistry on plants: recent advances and new opportunities for interdisciplinary research

Plants play a central role in the photochemistry of chemicals in the environment. They represent a major atmospheric source of volatile organic compounds (VOCs) but also an important environmental surface for the deposition and photochemical reactions of pesticides, gaseous and particulate pollutants. In this review, we point out the role of plant leaves in these processes, as a support affecting the reactions physically and chemically and as a partner through the release of natural constituents (water, secondary metabolites). We discuss the influence of the chosen support (leaves, needle surfaces or fruit cuticles, extracted cuticular waxes and model surfaces) and other factors (additives, pesticides mixture, and secondary metabolites) on the photochemical degradation kinetics and mechanisms. We also show how plants can be a source of photochemically reactive species which can act as photosensitizers promoting the photodegradation of pesticides or the formation and aging of secondary organic aerosols (SOA) and secondary organic materials (SOM). Understanding the fate of chemicals on plants is a research area located at the interface between photochemistry, analytical chemistry, atmospheric chemistry, microbiology and vegetal physiology. Pluridisciplinary approaches are needed to deeply understand these complex phenomena in a comprehensive way. To overcome this challenge, we summarize future research directions which have been clearly overlooked until now.

Allelopathy: The Chemical Language of Plants

In Nature, the oldest method of communication between living systems is the chemical language. Plants, due to their lack of mobility, have developed the most sophisticated way of chemical communication. Despite that many examples involve this chemical communication process-allelopathy, there is still a lack of information about specific allelochemicals released into the environment, their purpose, as well as in-depth studies on the chemistry underground. These findings are critical to gain a better understanding of the role of these compounds and open up a wide range of possibilities and applications, especially in agriculture and phytomedicine. The most relevant aspects regarding the chemical language of plants, namely kind of allelochemicals, have been investigated, as well as their releasing mechanisms and their purpose will be described in this chapter.