Melanins are dark-brown to black pigments found in animals, plants, and microorganisms. These pigments are not essential for growth and develop­ ment, but rather they enhance the survival and competitive abilities of species in certain environments. The association of melanins with immune responses has been noted for plants (13) and invertebrates (180, 227, 239, 250). Melanin biosynthesis and function have been studied most extensively in animals, primarily because of the association of melanins with skin disorders (25,53, 188) and malignant melanomas (119). Melanins in the eye and inner ear have also received considerable attention because of their interactions with drugs (84). The synthesis of animal melanin from tyrosine by the action of tyrosinase is proven (52, 175, 270). Tyrosinase, the key enzyme in animal melanin synthesis, also occurs and is best characterized in the common mushroom (Agaricus bisporus) and Neurospora crassa (136). Consequently, some researchers have been hasty to conclude that fungal melanins also are derived from tyrosine. The importance of melanins for survival and longevity of fungal propagules has been recognized for many years (126, 235). During the past ten years three additional discoveries have increased interest among plant pathologists in fungal melanins. First, unique pathways for melanin biosynthesis were discovered in both Ascomycotina (16) and Basidiomycotina (234). Second, investigators discovered a new class of fungicides that prevent direct penetra­ tion of plant tissue by inhibiting melanin biosynthesis in appressorial cells (221, 223). Third, phytotoxins were discovered that are shunt products of

Biosynthesis and Functions of Fungal Melanins

A PECULIAR sterol has been found in recent sedimentary environments which we eventually found was identical with the Black Sea sterol. This sterol was first mentioned among the extractable sterols from the Black Sea sapropel layer as the dominant component1. The concentration of this sterol in these rare sediments seemed high enough for us to isolate and purify the object to determine its molecular structure and evaluate its significance. We have isolated and analysed the sterol fractions from the Black Sea sapropel (by techniques to be described elsewhere), but here only elucidate the molecular structure of the Black Sea sterol and discuss its significance.

Black Sea sterol—a molecular fossil for dinoflagellate blooms

Publisher Summary This chapter deals with humic substances and discusses its chemistry and reactions. Humic substances, major organic constituents of soils and sediments, are widely distributed over Earth's surface, occurring in almost all terrestrial and aquatic environments. Humic substances arise from the chemical and biological degradation of plant and animal residues and from synthetic activities of microorganisms. The products so formed tend to associate into complex chemical structures that are more stable than starting materials. Important characteristics of humic substances are their ability to form water-soluble and water-insoluble complexes with metal ions and hydrous oxides and to interact with clay minerals and organic compounds such as alkanes, fatty acids, dialkyl phthalates, and pesticides. The capacity of humic substances to adsorb water and plant nutrients was one of the first observations. Humic substances were thought to arise from the prolonged rotting of animal and plant bodies. The chapter also describes the synthesis of humic substances.

Chapter 1 Humic Substances: Chemistry and Reactions

Curie-point pyrolysis and field ionization mass spectrometry of polysaccharides

Analytical pyrolysis - an overview

Curie point pyrolysis in combination with low voltage mass spectrometry has shown that humic acids extracted from three typical Indian soils have similar structures which resemble that of a fungal ‘humic acid’ rather than that of a lignin.

H. L. C. Meuzelaar

Papers

Studies on the structure and origin of soil humic acids by curie point pyrolysis in direct combination with low-voltage mass spectrometry