Publisher Summary This chapter focuses on the structural organization of compound eyes, which are the principal photoreceptors of adult insects. They are composed of structural units called ommatidia. Compound eyes can be divided into two groups: photopic eyes and scotopic eyes. The former are characteristic of diurnal insects active in bright light, while the latter are found in nocturnal or crepuscular species and have short, fat rhabdoms that are separated from the crystalline cones by a relatively large distance. The chapter further illustrates examples of insect ommatidia. Many insects, particularly males, have eyes divided into two regions that are characterized by markedly different sizes and pigmentation of ommatidia. In some dragonflies, the dorsal facets are nearly twice the diameter of the ventral.

The visual system of insects

The conditions for luxuriant axenic cultivation of the trypanosomid flagellate Crithidia fasciculata in chemically-defined media were determined. Improvements over the hitherto published media include higher concentrations of amino acids, folic acid (where this is the sole source of pteridine) and purines and the inclusion of threonine and Tween 80. Increased oxygenation was obtained by incubating liquid cultures in tubes in a sloped position. Under these conditions consistently excellent growth (up to 2 × 108 organisms/ml.) was obtained and the useful incubation period could be decreased to 4 days. Using the improved medium, qualitative and quantitative studies on the nutritional requirements of the organism were carried out. Growth failed when any one of the following amino acids was omitted from the basal medium: histidine, phenylalanine, isoleucine, leucine, valine, lysine, arginine, tyrosine, methionine, tryptophan. The omission of threonine caused drastically decreased growth rates and lower yields. It was found that phenylpyruvic acid could replace phenylalanine; cysteine, cystathionine or homocysteine could replace methionine; and citrulline, but not ornithine, could replace arginine for C. fasciculata. In addition to the amino acid requirements a nutritional need for the following was demonstrated: a carbohydrate, haemin, a purine, thiamine, riboflavin, pantothenic acid, nicotinic acid or its amide, pyridoxal or pyridoxamine, biotin, folic acid and an unconjugated pteridine (biopterin). The natural purines, their nucleosides and nucleotides are nearly equivalent, on a molar basis, in growth promotion. Numerous substituted purines were also tested for their ability to supply the purine requirement. No exogenous source of pyrimidine for nucleic acid synthesis is necessary provided folic acid is present. Folic acid can be omitted from the growth medium provided thymine and methionine are present. The absolute requirement for biotin could not be demonstrated in the present medium without the use of avidin.

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The growth and nutrition of Crithidia fasciculata.

Publisher Summary This chapter discusses the genetic aspects of pterins and ommochromes that are complementary to one another. The ommochromes and pterins represent interesting groups of naturally occurring compounds, whose structure, biosynthesis, and physiological interrelationships are elucidated by the study of mutants affecting them. The action of genes results in the specific pattern of phenes, comprising the phenotype of the organism. Gene-dependent formation of ommochromes and pterin pigments presents models in which morphological phenes are relatively closely connected with gene-controlled chemical processes. The chapter focuses on the mutations that block ommochrome synthesis. Biochemical assays for the presence of enzymes involved in ommochrome synthesis from the gene groups in Drosophila melanogaster and D. pseudoobscura offer a promising opportunity to gain information about homologous genes and evolution of genic complexes in Drosophila. Pterins are found in the eyes, the Malpighian tubules, and in the testis. In many cases, the patterns of pterins or of compounds connected with ommochrome metabolism as “phenes” of a certain genotype are reflections of the degree of relationship. The present state of knowledge offers two possibilities for the pathway of synthesis of “eye pterins.”

Genetic Aspects of Ommochrome and Pterin Pigments

The phenylalanine hydroxylating system from mammalian liver.

Durch chromatographische Trennung an phosphorylierter Cellulose wurden Biopterin und 7-Biopterin erstmals in reiner Form erhalten. Im Gegensatz zum Biopterin ist 7-Biopterin im Wachstumstest bei Crithidia fasciculata inaktiv. Die Ausbeute ist bei der Biopterinsynthese stark von den Reaktionsbedingungen abhangig und liefert unter optimalen Bedingungen 7% Biopterin und 26% 7-Biopterin, bezogen auf eingesetztes 2.4.5-Triamino-6-hydroxy-pyrimidin. Die Radiosynthese der beiden pterine, ausgehend von K14CN, wird beschrieben. Ferner werden die Eigenschaften des 2-Amino-4-hydroxy-6-bzw. 7-[L-erythro-1.2.3-trihydroxy-propyl]-pteridins mitgeteilt.

Synthese und chromatographische Trennung von [8a-14C]Biopterin und [8a-14C]7-Biopterin

Es werden die Isolierung von vier fluoreszierenden Stoffen aus Drosophila melanogaster und deren Eigenschaften kurz beschrieben

Isolierung fluoreszierender Stoffe aus Drosophila melanogaster. Vorläufige Mitteilung

Das aus Drosophila melanogaster isolierte, stark fluoreszierende Pterin HB2 besitzt nicht die fruher zur Diskussion gestellte Formel, was durch den oxydativen Abbau der Substanz zu Acetaldehyd bewiesen wird. Eine Strukturformel kann auf Grund der bisherigen Versuchsergebnisse noch nicht vorgeschlagen werden.

Fluoreszierende Stoffe aus Drosophila melanogaster. 3. Mitteilung

Es werden die Konstitutionsaufklarung von zwei fluoreszierenden Stoffen und die Isolierung von 2-Amino-6-oxy-pterin-8-carbonsaure aus Drosophila melanogaster beschrieben.

Fluoreszierende Stoffe aus Drosophila melanogaster. 2. Mitteilung

Die Isolierung des reinen Pteridins HB2 aus Drosophila melanogaster wird beschrieben und seine chemischen und physikalisch-chemischen Eigenschaften werden mit denjenigen des Biopterins verglichen.

E. Loeser

Papers

Isolierung fluoreszierender Stoffe aus Drosophila melanogaster. Vorläufige Mitteilung

Fluoreszierende Stoffe aus Drosophila melanogaster. 3. Mitteilung

Fluoreszierende Stoffe aus Drosophila melanogaster. 2. Mitteilung

Fluoreszierende Stoffe aus Drosophila melanogaster. 8. Mitteilung. Isolierung und Eigenschaften des Pteridins HB2