| Karyotypical observations The established karyotype of A. striatulum (the procedure was described by COUCOLI & SYMEONIDIS 1980) was found to be a symmetrical one, with chromosomes varying in length between 7 and 9 microm approximately (Fig. 1). In spite of this symmetry, according to the data presented in Table 1, all chromosome members could be identified, due to the following reasons:1) The two longest pairs, though not significantly differing in chromosome length, can be easily distinguished from each other by arm ratio. The one (No. 1) was constantly recognized as submetacentric, the second (No. 2) represents a typically metacentric chromosome. 2) The two SAT pairs are fairly distinguishable by their morphology, chromosome No. 3 being strongly heterobrachial (A.R.=0.44), with a small satellite ranging in length around the one fourth of the total short arm. This chromosome (Fig. 1) corresponding to the typical form A2 (HENEEN & RUNEMARK 1972) was found in all populations, covering the majority of the cells analysed, whereas a variant of the same chromosome, identified as A1 (with a larger satellite) was sporadically observed and confined exclusively in one population (the most abundant one). The two homologues of SAT pair No. 5 (SM in centromere class) coincide with B1 morphological type, being easily recognized by their size and arm ratio, though they do not always show prominently their large satellites, especially the one chromosome of the pair, probably due to heteromorphic conditions. This feature was in particular observed in plants exclusively found in one population. Chromosomes No. 6 and 7, though overlapping in size can be clearly separated by arm ratio. Finally, chromosome No. 4 is fairly distinguished by its intermediate size. The cytological analysis of the present material gave evidence rather in favour of karyotypic constancy than of chromosomal polymorphism, as it was formerly shown for the small isolated island populations of A. striatulum studied by HENEEN & RUNEMARK (1972). The observed variant A1 proved limited (a few individuals of one population) and, besides, no other SAT chromosome polymorphism was detected. The observed karyotype is likely to represent a J1J1 genome formula. The original J genome, as referred by OSTERGREN (1940), HENEEN (1962), CAUDERON (1966) and summarized by CAUDERON (1979) and DEWEY (1981) occurs broadly in A. junceum (L.) Beauv. complex, having been used for variant genome designations (J1-J6) in other closely related species (HENEEN 1977). |
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