Protoplasma (1995) 188: I04- 10 8 PROTOPLASMA © Springe r-Verlag 1995 Printed in Au stria Effects of lead on the nuclear repetitive DNA of the moss Funaria hygrometrica (Bryophyta) P. Bassil. *, A. Basile 2 , A. Stefanini ', C. G. Vosa' , M. Maf'fei 4 , S. Giordano ", and R. Castaldo-Coblanchl ? I Department of Plant Biology, un iversity "La Sap ienza", Rome, 2 Departm ent of Plant Biology, University " Federico II", Nap les, 3 Dep artm ent of Plant Sciences, University of Oxford , Ox ford, and 4 Department of Plant Biology, University of Turin, Turin Rece ived Jul y 18, 1994 Accepted December 2, 1994 Summary. Fum/ria hygrometrica game toph ytes were grown in in vitro controlled systems in the presence and absence of lead, Th eir nuclear genomes were then analyzed directly in situ with ATT and GTe specific f1uorochromcs, image analys is and stat istical data elabora- tion by specifi c softwa re, in order to characterize the different frac- tion s of repetitive DNA . The results reveal qualitative and quantit a- tive differences between the nuclear genomes of lead-stressed and unstres sed individu als. These differences see m to consist of a signifi- cant inc rea se in GTe rich repe titive DNA sequences in nuclei of the stressed individuals. The se sequences form well defined agg lomer- ates, generally situated ad jace nt to the nucleolar regi on, whic h incre ase in both size and number in the presence of lead. Some hypotheses are discussed. Ke ywords : Environmental stress; Fluorochromes; Image ana lysis; Lea d; Funaria hygrometrica; Repetitive DNA. Abbreviations: DAPl 4 ' ,6-d iamid ino-2-ph en ylindo lc; 8 BM bold basal medium. Introduction In recent years various lines of research hav e shown that the repetitive fraction of a plant g enome ca n he susce ptible to the action of some environ me ntal stress es, which cause qualitative and quantitative variation in specific families of DNA (see Bassi 1990 ). This may affect DNA sequence s involved in protein synthesis , for example , ribosomal DNA, but also sequences not involved in transcription. In thi s seco nd c ase the environmental stimul i could exert an indirect effect on transcription by a confor mational , Correspondence and reprints: Dipartimento di Biologia Vege tale, Universita degli Studi "La Sapienza", Piazzale Aida Moro 5. t-OO185 Rom a, Italy. effec t (G uille and Qu etier 1973 ; Zu ck erk andl 1981, see also Nagl 1990). It has been s ugge sted that the repeated fra ction of the genome could act as a med iator between environmental stimuli and gene ex pr ess ion. In other words, the repeated sequence s of DNA would con stitute a target which could re ceive me ssa ges from the env ironment, be modified accord - ing ly and thu s, according to the message, intluenc e the express ion or non-expression of specific genes (Bassi 1991, 1992). Environmental stimuli which are known to cause repetitive DNA variation in plant genome are many and of vari ous types: they may be of a chemi cal (e.g ., Nagl and Ruck er 1976), mechanical (e.g., Natali et a1. 1986), or even biological nature (e .g., Gen se 1980). Envi ronmentally induced genome variation s are gen- erally transit ory ; however, according to some autho rs and und er p arti cul ar condition s, they can be perma- nent and be tran smitted to subsequent generations (Cullis 1981; Cullis and Clearly 1986; Cullis and Charlton 1981). Thu s they co uld have not onl y fun c- tional and eco log ica l co nse que nces, but a lso sys tem- atic and evo lutionary implications. Th e present research is aimed at investigating wh eth- er stress caused by heavy metals may influence repet- itive DNA in plant s. Some publi shed data, obtained from both pl ant s and animals, have shown that this component of the ge no me may be a preferential target of such element s (Sissoeff et al. 1976). Furthermore , it has been ob ser ved th at aluminium may cause amp lifica tion of metabolic ally labile DNA sequences