Ornithophily in the genus Salvia L. (Lamiaceae)

This dissertation presents for the first time a survey of bird pollinated (ornithophilous) Salvia species. Within the approximately 1000 species of the worldwide distributed genus roughly 20% (186 spp.) are bird pollinated. Excepting four species in the Old World (South Africa and Madagascar), ornithophilous species are restricted to the New World where they represent about one third of the species. They occur mainly in higher altitudes (1500-3000m) and usually grow as shrubs or perennial herbs (97%). The bilabiate to tubular flowers are often red (at least 49%), averaging 35mm (7-130mm) in length and produce a large to medium volume of nectar with rather low sugar concentration. Pollination by sunbirds and white-eyes is documented in a South African species, and that by hummingbirds in 16 species of the New World (USA, Mexico, Guatemala and Bolivia). Beside pollinator observations, the functionality of the staminal levers, the process of pollen transfer and the fitting between flowers and birds are tested by inserting museum skins and metal rods into fresh flowers. The most surprising result is the finding of two different main pollen transfer mechanisms. In at least 54% of the species an active staminal lever mechanism enables pollen deposition on the birds body. This is illustrated in detail in the South African S. lanceolata at which birds were observed to release the lever mechanism and became dusted with pollen. In contrast, the lever mechanism in about 35% of the New World species is reduced in different ways. Pollen transfer by inactive ‘levers’ is demonstrated in detail in S. haenkei in Bolivia, at which four pollinating hummingbird species could be observed. The tubular corolla forced the birds in a specific position, thereby causing pollen transfer from the exserted pollen-sacs to the birds body. With respect to the floral diversity and systematic affiliation of the species, parallel evolution of ornithophily and lever reduction is likely. Considering that bird pollinated species might have derived from bee pollinated species and that the staminal levers have become secondarily inactive, it is concluded that the shift in pollinators induced phenotypic changes even disabling such a sophisticated structure as the staminal lever mechanism.

Pollen-placement and pollen-portioning in diverse Salvia-species

This dissertation addresses the staminal lever mechanism of the genus Salvia. Various hypotheses referring to its purpose and function are tested and elucidated. The first hypothesis maintains that the lever is a mechanical selection mechanism which excludes weak pollinators from the flower. This hypothesis is refuted and the respective results of force measurements and morphological investigations are presented, statistically evaluated and discussed. The force measurements and morphological investigations were conducted on the staminal levers and flowers of 8 bee pollinated (melittophilous) and 6 bird pollinated (ornithophilous) species. For comparison a ninth melittophilous species that lacks the staminal lever was investigated. In this species the force measurements were conducted on floral structures that were suspected to hinder a flower visitor. The hypotheses, which state that the staminal lever is a tool for pollen portioning and reduces the risk of pollen loss as well as hybridisation due to its ability to perform a repeatable, accurate and species-specific pollen placement on a wide range of diverse pollinators, are confirmed. Investigations with respect to pollen portioning were carried out on 13 sages. The lever mechanism can be released several times in a row, while the pollen sacs leave a dosed pollen portion on a well defined spot on the pollinator‘s body. Pollen placement was investigated for 12 sages. In sympatric sages, lever length and the area of pollen placement are of particular interest. A shared pollinator bears species-specific areas of pollen placement for different sages. The accurate pollen placement ensures an efficient pollination. However, the question of the functionality of the lever mechanism can not be answered with absolute certainty. The lever‘s backswing is not caused by the adaxial lever arm; the adaxial lever arm is too light and too short to be an adequate counterweight to the abaxial lever arm. Therefore, the adaxial lever arm can not pull the abaxial lever arm to return it to its neutral position. But there are indications of a cellular mainspring in the filament. According to the current state of knowledge, this is the most plausible explanation for the lever's backswing, but further histological investigations on the joint of the lever mechanism are necessary to confirm this assumption.

In vitro synthesis of the light-harvesting complex into artificial membrane systems

In green plants, the function of collecting solar energy for photosynthesis is fulfilled by a series of light-harvesting complexes (LHC). The light-harvesting chlorophyll a/b protein (LHCP) is synthesized in the cytosol as a precursor (pLHCP), then imported into chloroplasts and assembled into photosynthetic thylakoid membranes. Knowledge about the regulation of the transport processes of LHCP is rather limited. Closely mimicking the in vivo situation, cell-free protein expression system is employed in this dissertation to study the reconstitution of LHCP into artificial membranes. The approach starts merely from the genetic information of the protein, so the difficult and time-consuming procedures of protein expression and purification can be avoided. The LHCP encoding gene from Pisum sativum was cloned into a cell-free compatible vector system and the protein was expressed in wheat germ extracts. Vesicles or pigment-containing vesicles were prepared with either synthetic lipid or purified plant leaf lipid to mimic cell membranes. LHCP was synthesized in wheat germ extract systems with or without supplemented lipids. The addition of either synthetic or purified plant leaf lipid was found to be beneficial to the general productivity of the expression system. The lipid membrane insertion of the LHCP was investigated by radioactive labelling, protease digestion, and centrifugation assays. The LHCP is partially protected against protease digestion; however the protection is independent from the supplemented lipids.