Air pollution as a possible cause for the decline of some phanerogamic species in The Netherlands

In The Netherlands the decline of some phanerogamic species cannot be readily explained from obvious factors such as lowering of the groundwater table, eutrophication or land reclamation. For a number of species the hypothesis was tested that the decline is partly due to air pollution. A two-factor model was made in which decline is accounted for by (a) habitat destruction assessed from topographic maps and (b) air pollution measured as the SO₂ 95-percentile over the winter period 1978/1979. Effects of both factors were assumed to follow a sigmoid dose-effect curve. For a number of species decline proved to be significantly correlated with air pollution. These are notably species from the syntaxon Violion caninae. A comparison was made with results obtained for epiphytic lichens. It appears that for some phanerogamic species sensitivity is about the same as for moderately sensitive lichens.Nomenclature follows Heukels & van der Meijden (1983).Thanks are due to the Rijksherbarium, for providing some of their unpublished data; and to Ada Groeneveld, for technical assistance.     

Dolichodorus miradvulvus n. sp. (Nematoda: Tylenchida) with a Key to Species

Dolichodorus miradvulvus n. sp. from Anubias nana Engler in Florida is described and illustrated. The female is characterized by deep grooves in the cuticle on the ventral surface just anterior and posterior to the vulva, and by transversely elongate pouches anterior and posterior to the vulva. Both sexes have a constricted area of the stylet shaft just anterior to the knobs, and on the male the intersection of the lateral field and bursa appear sclerotized.     

Antarctic nemerteans: Heteronemertea– descriptions of new taxa, reappraisals of the systematic status of existing species and a key to the heteronemerteans recorded south of latitude 50oS

Twenty-three species representative of 15 heteronemertean genera are recorded from Antarctic and Subantarctic waters south oflatitude 50^oS. Five new genera are established and seven new species are fully described and illustrated. These are Cephalurichus antarcticus gen. et sp. nov., Dokonemertes magellanensis gen. et sp. nov., Dokonemertes macquariensis sp. nov., Micrellides multiperula gen. et sp. nov., Paramicrurinella falklandica gen. et sp. nov., Parborlasia landrumae sp. nov. and Zodionemertes chilensis gen. et sp. nov. Baseodiscus antarcticus Baylis, Antarctolineus scotti (Baylis), Lineus longifissus (Hubrecht) and Parborlasia fueguina Serna de Esteban & Moretto are redescribed and illustrated and the nature of rhynchodaeal pouches protruding into the cephalic blood lacunae of Parborlasia corrugatus (Mcintosh) is reexamined and discussed. The main anatomical characters of the remaining 11 species are recorded and it is concluded that of these only Parapolia grytvikenensis Wheeler, Cerebratulus malvini Wheeler, Chilineus glandulosa (Burger), Huilkia ushuaiensis Serna de Esteban & Moretto, Micrura pacifica Friedrich and Wiolkenia friedrichi Serna de Esteban & Moretto can at present be accepted as valid, although incompletely described, taxa. Cerebratulus larseni Wheeler, Cerebratulus validus Bürger, Lineus autrani Joubin and Lineus turqueli Joubin are so poorly and inadequately described that their taxonomic status cannot be verified, and the recorded occurrence of Lineus nigricans Burger in southern latitudes cannot be substantiated on the available evidence. Maps showing the recorded distribution of all the species are included and a key to the 18 validated species is provided.     

Parapsylla, a Gondwanan element in the psyllid fauna of southern Africa (Homoptera)

The genus Parapsylla (Homoptera: Psylloidea) is redescribed and placed in the Diaphorininae of the Family Aphalaridae. Its relationships within this subfamily are discussed. The genus Agmapsylla syn. nov. is placed into the synonymy of Parapsylla , and Pennavena syn. nov. and Eudiaphorina syn. nov. are placed into the synonymy of Diaphorina. The eight known species of Parapsylla are distributed in southern Africa and upland areas of East Africa. Host plant relationships are not clearly established but the genus appears to be associated with species of Maytenus (Celastraceae), Olinia (Oliniaceae) and possibly Olea (Oleaceae) and Syzygium (Myrtaceae). Parapsylla relicta syn. nov, and A. aureus syn. nov. are placed into the synonymy of Arytaina capensis. Parapsylla capensis comb. nov. is transferred from Arytaina, Parapsylla valens comb. nov. is transferred from Diaphorina , and the following new species are described: P. angolensis sp. nov., P. eafra sp. nov., P. huila sp. nov., P. marginipennis sp. nov., P. rufa sp. nov. and P. theroni sp. nov.     

Genetics of salt tolerance in higher plants: theoretical and practical considerations

Summary An interdisciplinary approach to breeding for stress tolerance in plants has gained considerable recognition in the past few years. Accordingly, this article presents a synthesis of the genetic, physiological, and ecological aspects of salt tolerance in plants. An understanding of these aspects and the interrelationships between them is essential for an efficient breeding program.A significant part of the presentation concentrates on the basic problems associated with the genetics of tolerance to stresses and of quantitative characters in general, since many of the unsolved problems relevant to the genetics of salt tolerance are still general. Significant progress in the breeding of quantitative as well as qualitative traits in multicellular organisms depends on an understanding of the genetic and epigenetic dimensions of gene action. The discussion therefore includes an overview of (1) the limited existing knowledge on the genetic control of salt tolerance and (2) the physiological mechanisms and molecular targets central to the control of salt resistance as expressed by the amount and stability of yield.An additional subject emphasized here concerns the main strategies of adaptation of wild species to their natural habitats. An understanding of them is essential to (1) enable distinction between traits that can increase agricultural yield and traits that are favorable only for survival under natural conditions (such a distinction is essential, especially when wild species are used as a gene source), and (2) predict the best combinations of characters for efficient agricultural production in stressful environments.     

Export of species to islands from sources of differing maturity

Export of species from sources (epicenters) of differing ages and complexities was examined using laboratory microcosms. Polyurethane foam (PF) artificial substrates were colonized by protozoans for different time periods in a small pond. Substrates were returned to the laboratory and used as epicenters for protozoan colonization of barren PF islands in initially sterile microcosms. Islands were exposed to epicenters for either 24 h or continuously for 28 d. Islands from pairs of microcosms exposed to epicenters of identical ages were sampled on 1, 3, 7, 14, 21, 28 and 46 d after initial epicenter exposure. Colonization parameters were estimated by fitting numbers of colonizing species to the MacArthur-Wilson equilibrium model. Islands exposed continuously to epicenters were colonized by significantly more species than those exposed for only 24 h. Islands exposed to immature, species poor epicenters were colonized by a greater proportion of the source community than those exposed to more mature, species rich epicenters. All islands were depauperate compared to epicenters except those exposed to the most immature (1 d old) epicenter. Colonization continued at a reduced rate in spite of the absence of the epicenter. Results from communities with rapid species turnover and rapidly reproducing species suggest that the continuous presence of a species source is less important for colonization of a new habitat. Dispersal of potential colonists occurs rapidly in these communities. Less mature communities dominated by pioneer forms are more effective at producing colonists than more mature communities.     

Comparison of the mitochondrial genome of Nicotiana tabacum with its progenitor species

Summary Mitochondrial DNAs from Nicotiana tabacum, an amphiploid, and its putative progenitor species, N. sylvestris and N. tomentosiformis were compared in structure and organization. By using DNA transfer techniques and cloned fragments of known genes from maize and N. sylvestris as labeled probes, the positions of homologous sequences in restriction digests of the Nicotiana species were analyzed. Results indicate that the mitochondrial DNA of N. tabacum was inherited from N. sylvestris. Conservation in organization and sequence homology between mtDNAs of N. tabacum and the maternal progenitor, N. sylvestris, provide evidence that the mitochondrial genome in these species is evolutionarily stable. Approximately one-third of the probed restriction fragments of N. tomentosiformis mtDNA showed conservation of position with the other two species. Pattern variations indicate that extensive rearrangement of mtDNA has occurred in the evolution of these Nicotiana species.     

Micropropagation of the rare species Stylidium coroniforme and other Stylidium species

The number of plants in the gazetted rare species Stylidium coroniforme was increased through micropropagation. A method was first developed using the common species S. brunonianum. It was found that for both species, rapid propagation could be obtained by excising shoots from sterile seedlings and inducing shoot proliferation on Murashige and Skoog medium supplemented with 1 M BAP. Rooting was achieved using 1 M IBA and over 100 plants of each species were successfully established in soil. Leaf pieces could also be used to initiate cultures. In media with 20–25 M BAP and 1–5 M IBA, leaf pieces of S. brunonianum, S. piliferum, S. caricifolium and S. crassifolium produced adventitious buds, thus providing another method of micropropagation.     

Diversity in the immune system: “Preconceived ideas” or ideas preconceived?

Two concepts of the evolution and regulation of expression of the combining site repertoire of the immune system, are compared. One view is based on the Associative Recognition Theory as formulated by the author and the other is based on the Idiotype Network Idea as conceived by Jerne. The two concepts are analyzed from the point of view of their logic, internal consistency and factual support.