The development of structure and function in chloroplasts of greening mutants of Scenedesmus II. Development of the photosynthetic apparatus

Mutant C-2A' of Scenedesmus obliquus formed only traces of chlorophylland showed no detectable photosynthesis when grown heterotrophically.When transferred to light this mutant developed chlorophylland its photosynthetic capacity was established. Following ashort initial lag phase, both photosynthetic capacity and totallight absorption of the cells reached saturation more rapidlythan did the rate of chlorophyll synthesis. Consequently, thequantum requirement of photosynthesis showed a rapid declineduring the initial 6 hr of greening, to a best value of 8. Subsequently,a slow increase occurred as additional chlorophyll was synthesized.Behavior parallel to that of the quantum requirement was alsonoted for the relative fluorescence yield and for the onsetof the 520 nm light-induced absorbance change. Of the two photosystems,PS-I seemed to develop more rapidly than did PS-II. The appearanceof PS-II activity appeared to accompany linkage of the two photosystems,as revealed by analysis of the variable-yield fluorescence andthe kinetics of the 520 nm light-induced absorbance change.During the phase of greening at which photosynthetic capacitydeveloped its maximum quantum efficiency, no significant changesin type or content of the various chloroplast cytochromes weredetected. Analysis of the ratio of chlorophyll/plastoquinone,however, showed that changes in this value followed more closelythe observed increase in the quantum efficiency of photosynthesisand the other parameters of photosynthesis examined. (Received May 19, 1972; )     

Temperature dependent reduction of protochlorophyllide in darkness followed by the assembly of active photosystems in pigment mutant C-2A' of Scenedesmus obliquus

In the wild type of Scenedesmus obliquus strain D3 grown heterotrophically, the chlorophyll biosynthesis and thus the reduction of protochlorophyllide to chlorophyllide takes place in darkness. However, in pigment mutant C-2A' of Scenedesmus obliquus only traces of protochlorophyllide are reduced under optimal growth conditions in darkness. By lowering the growth temperature from 33° to 15–25°C, protochlorophyllide can be reduced in darkness. At 20°C this process is about 10 times more active than at 33°C, but reaches only about 13% of the light-dependent chlorophyll biosynthesis. The chlorophylls synthesized at the lower temperatures are inserted into the pigment-protein complexes and photosystem I as well as photosys-tem II capacities are developed. The rate of light-independent protochlorophyllide reduction at lower temperatures is not limited by the enzyme PChlide-oxidoreductase itself, but rather by its substrate, being in turn limited by the amount of 5-amino levulinic acid (ALA) available.     

Biosynthesis and secretion of insect lipoprotein.

Biosynthesis of high density lipophorin (HDLp) was studied in larvae and adults of the migratory locust, Locusta migratoria. In an in vitro system, fat bodies were incubated in a medium containing a mixture of tritiated amino acids. Using SDS-PAGE and immunoblotting, it was shown that larval and adult fat bodies secreted both HDLp apoproteins, apolipophorin I (apoLp-I) and apolipophorin II (apoLp-II). Radiolabel was recovered in both apoproteins, indicative of de novo synthesis. The density of the fractions containing the apoproteins synthesized and secreted by larval and adult fat bodies was determined by density gradient ultracentrifugation. A radiolabeled protein fraction was found at density 1.12 g/ml. Using an enzyme-linked immunosorbent assay for detecting apoLp-I and apoLp-II, it was demonstrated that both apoproteins were present in this fraction, which had a density identical to that of circulating HDLp in hemolymph. Lipid analysis revealed that it contained phospholipid, diacylglycerol, sterol, and hydrocarbons. From these results it is concluded that the fat body of the locust synthesizes both apoLp-I and apoLp-II, which are combined with lipids to a lipoprotein particle that is released into the medium as HDLp.     

Further amides from Echinacea purpurea

The aerial parts of Echinacea purpurea afforded, in addition to known compounds, five further highly unsaturated amides and a derivative of linolen     

Interlocked circle formation by group I introns: structural requirements and mechanism.

Precursor RNA transcribed from the yeast mitochondrial gene coding for the large ribosomal RNA contains a group I intron that can excise itself in vitro. Apart from group I specific sequence elements the intron also contains a gene encoding a DNA endonuclease involved in intron dispersal. A precursor RNA derivative from which this gene has been removed self-splices efficiently, but due to activation of cryptic opening sites located in the 5' exon, the 3' part of this exon is sometimes co-excised with the intron. Upon further reaction, this enlarged intron molecules give rise to interlocked circles, comprising small circles derived from 5' exon parts and large circles of the intron. Sequence comparison between cryptic opening sites and authentic splice sites reveals in most cases homology with the 3' exon part that is capable of interacting with the Internal Guide Sequence. The role of the IGS was further substantiated by replacing the cryptic opening sites with well defined sequences of authentic splice sites: one corresponding to the 3' splice site and its mutant derivatives, the other to a fragment containing the natural 5'-3' exon junction. Precursor RNAs derived from these constructs give rise to interlocked circles, and mutation studies confirm that the 3' exon nucleotides flanking a 3' splice site are essential for their formation. The results underline the crucial role of the IGS in interlocked circle formation which behaves similarly as in the normal self-splicing reactions. It has been proposed that the two short helices formed by basepairing of the IGS with the 5' and 3' exon can co-axially stack on top of each other forming a quasi continuous RNA double helix or pseudoknot. We present a model explaining how transesterification reactions of a mutant precursor RNA in such a pseudoknot can lead to interlocked circles. The experiments support the notion that a similar structure is also operative in splicing of wild type precursor RNA.     

FFU complex: an analysis of 491 cases

A study of 491 patients with femur-fibula-ulna (FFU) complex is presented. The term FFU complex has been proposed for cases in which the femur, fibula and/or ulna show defects, which tend to be associated. These cases are usually sporadic. Some rare anomalies of the arms which are present are particularly frequent in FFU complex. These are amelia, peromelia of humerus, humeroradial synostosis and defect of ulna. In our study, 491 patients were investigated for involvement of limb malformations. Our results, showing nearly equal proportions of the most common malformations in four analysed groups (with one, two, three and four limbs affected) supports the hypothesis that even if one arm or one leg only is affected, the cases may still be classifiable as FFU complex. There is a striking asymmetry in presence and in degree. All malformations are more often unilateral than bilateral. Upper limbs are affected more often than lower limbs. The right side and the male sex are preferentially affected. The limb malformations present in the FFU complex are different from those seen in most other types of limb defects, so there is virtually no overlap between FFU and other limb malformations. Some arguments in favour of early somatic mutation as a cause are discussed.