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Archibald, R. E. M. (1983): The Diatoms of the Sundays and Great Fish Rivers in the Eastern Cape Province of South Africa. - Carmichael, W. W. (ed. ) (1981): The water environment. Algal toxins and health. - Environmental Science Research, Vol 20 - Gorlenko, V. M.; Dubinina, G. A. & Kuznetsov, S. I. (1983) : The ecology of aquatic micro-organisms. - Die Binnengewässer, Vol. XXVID - Rai, H. & Marker, A. F. H. (eds.) (1982): The measurement of photosynthetic pigments in freshwaters and standardization of methods. - Arch. Hydrobiol. Beih., Ergebnisse der Limnologie 16 - Rivera, R. P. (1983): A guide for references and distribution for the class Bacillariophyceae in Chile between 180 28' S and 580 S. - Bibliotheca Diatomologica (Hrsg. J. Cramer), Bd. 3 - Rivera, P.; Parra, O. O.; Gonzalez, M.; Dellarossa, V. & Orellana, M. (1982): Manual taxonomico dei fitoplancton de aguas continentales con especial referencia al fitoplancton de Chile . IV. - Bacillariophyceae - Tell, G. & Mosto, P. (1982) : Chlorophyceae, Chlorococcales . - In: Guarrera, S. A. et al. (eds.): Flora criptogamica de Tierra dei Fuego, 6/2 - van der Heide, J. (1982): Lake Brokopondo. Filling phase limnology of a manmade lake in the humid tropics.

Electrophoretic separation of seed alcohol dehydrogenase (ADH) fromNicotiana tabacumon 12% starch gels at pH 7.8 produced only one band with an apparent Rfof 0.65, which confirmed earlier reports. The same was found with pollen ADH. However, in polyacrylamide gel isoelectric focusing, seed ADH separated into three distinct bands with apparent pI of 5.33, 5.42 and 5.50. The pI 5.33 isoenzyme was found to be the essential form inN. sylvestrisseeds. The analysis of charge properties ofN. tomentosiformisseed ADH showed only one isoenzyme with pI of 5.56. These results present further evidence thatN. tabacumhas arisen from a cross between aN. sylvestrispredecessor and an ancestral type ofN. tomentosiformis. The presence of the pI 5.42 form inN. tabacumis consistent with the reported formation of heterodimeric ADH in tobacco hybrids.

Haploid tobacco plants (cv. Samsun) form inflorescences with a larger number of flowers than diploid plants. Leaves of haploid plants were shown to have lower free IAA level (by 40 %), higher peroxidase (by 160 %) and IAA-oxidase (by 70 %) activities and produce less ethylene (by 25 %) than leaves of corresponding diploid plants. The increase of peroxidase activity in haploids was due to the increase in the activity of the cathodic isozyme which is known to have high IAA-oxidase activity. It is proposed that higher peroxidase/IAA-oxidase activity in haploid plants may take part in IAA catabolism, at least duringin vitroculture of haploid explants. Lowered IAA level and ethylene production may then be directly correlated with a larger number of flower buds; as a higher IAA level is generally considered to act as a background inhibitor of flowering.

Microspectrophotometry following Feulgen staining and autoradiography following (3H)-thymidine labelling were used to study cell-cycle events during pollen development in tobacco (Nicotiana tabacum L.). During normal gametophytic pollen development in the anther and in vitro the generative nucleus passes through the S phase to the G2 phase soon after microspore mitosis, while the vegetative nucleus remains arrested in G1 (=G0). During embryogenie induction by an in vitro starvation treatment of immature pollen ongoing DNA replication in the generative nucleus is completed and followed by DNA replication in the vegetative cell in a large fraction of the pollen grains. Addition of the DNA replication inhibitor hydroxyurea to the starvation medium postpones S phase entry until the pollen is transferred to a rich medium and does not affect embryo formation. These results demonstrate that one of the crucial events of embryogenic induction is the derepression of the G1 arrest in the cell cycle of the vegetative cell.

A simple procedure is described for the in vitro production of tobacco (Nicotiana tabacum L.) pollen from microspores isolated just before entering mitosis. During a 3-day culture period in a liquid medium containing pyrimidine nucleosides these microspores develop into young pollen grains to the stage of starch deposition. Pollen maturation and transition to dormancy is achieved during a further 2- to 3-day culture period in the same medium stepwise supplemented by a concentrated solution of sucrose and l-proline. Upon transfer of the pollen to a simple germination medium containing sucrose and boric acid, up to 40% of the grains were observed to produce relatively long tubes. The in vitro-matured pollen grains can be stored at-20° C either suspended in 1.17 M sucrose and 100 mMl-proline or separated from the medium on filter paper discs. The stored pollen germinated both in vitro and on the stigma, the pollen tubes grew through the style into the ovary and pollination produced up to 300 viable seeds per pod. The procedure is of interest for pollen developmental studies and various fields of pollen manipulation, such as in vitro pollen selection.

Water and osmotic potentials were measured in young and mature styles of selfcompatible (SC) and selfincompatible (SI) species ofSolanaceae. For mature flowers, the stylar water and osmotic potentials were considerably lower in SI speciesNicotiana alataandPetunia hybridathan in SC speciesN. sylvestrisandN. tabacum. Stylar water content (in % fresh mass) was also significantly lower in SI species (N. alata, P. hybrida, diploid clones of potato) than in SC species (N. acuminata, N. glauca, N. paniculata, N. sylvestris, N. tabacum). For flower buds younger than 2 d before anthesis, no differences in stylar water potential betweenN. alata(SI) andN. tabacum(SC) were observed. During further flower bud development the stylar water potential inN. alatadecreased more expressively than inN. tabacum. Pollen culture in media with various concentrations of sucrose or polyethylene glycol revealed that optimal water potential for pollen tube growth was lower inN. alatathan inN. tabacum. The differences were similar as for differences in stylar water potential. The results are considered in relation to possible involvement of stylar water potential in unilateral interspecific incompatibility inSolanaceae.