| Cytological observations The meiotic analysis revealed two separate group of mutants . Group I includes all compactoids and in addition, S1, S2, S7 and S8 speltoids. Group II is represented by three speltoid muntants (S3, S4, S5). All compactoids manifested a polymorphic meiotic spectrum, corresponding with phenotypic grades of compactoidy. Mutant biotypes C2 and C3 showed to be the less compactoid off-types. In contrast, mutants C4 and C6 were found to possess a typical or extreme compactoid ear. The climax of meiotic behaviour can be set in the following sequence, beginning with the most normal situation (Tab. 1). The persisting occurrence of multivalents indicate that the particular compactoid off-types comprise structural mutants. Besides, the fact that the observations have been carried out at the fifth generation after seed irradiation, supports the view that chromosomal interchanges have played an essential role in the maintenance of mutability, by increasing the probability for further meiotic abnormalities. The commonest process by which multiple dose of Q locus is accomplished, might be translocations which involve a segment of 5AL (MAC KEY 1954, HAlR and RIGHT 1968). Four speltoids (all derivatives of m1), were also found to be structural mutants having originated by deficiency-duplication process as shown by the observed deviations from meiotic normality. A high frequency of multivalents, associated more or less with univalency, proved to be a common feature. The climax of meiotic indices corresponds to the following sequence, the most normal meiotic situation being the starting point (Tab.2). Mutant S1, the most unstable speltoid of the group, is clearly distinct morphologically by possessing the most lax spike (D 11, 5) and cytologically by containing a high proportion of univalents (up to 12 per cell). In addition, sporadic aneuploid cells (2.9%) as well as two quadrivalents in one cell (2.7%) have been recorded. Speltoid S7, the less "speltoid" mutant in the series (D 16), showed a high proportion of normal meiocytes, but it was distinct in containing a persisting heteromorphic bivalent, usually rod-bivalent, including a telocentric member. However, as it was never found to participate a quadrivalent, it might not be considered to be involved in the system affecting the speltoid character. The findings were strikingly different with speltoids belonging to the group II. All three manifested normal meiotic behaviour, almost approximating that of the martyrs (Table 2). This is an indication that gross chromosome changes, implicating interchanges within genome do not account for their evident speltoid form. The bearded character of the S4 mutant, the spontaneous derivative of the awnless m2, could be expected among the offspring of a variety like C-38290, resembling in chromosome structure and meiotic attitude with Chinese Spring (COUCOLI and SKORDA 1966). Therefore it would be more likely to suggest that the three speltoids arose due to point mutations. This conclusion has been strongly supported by the electrophoretic analysis of the material. Analysis of the zymograms Taking into consideration the whole sptctrum of zymograms as revealed by both enzyme system studied, in association with all tissues used in the procedure, 7-9 esterase bands and 4-7 peroxidase bands were separated. The two parental forms (m1 and m2, Fig.2) appeared to differ 1) in three bands of shoot esterase zymograms (slow bd. 2 absent in m1, present in m2; slow bd. 4 and fast bd 9 present in m1, absent in m2). 2) in three esterase bands of the coleoptile pattern (weak band 1 present only in m2, intense band 3 present only in m1, fast band 9 being substantially weaker in m2) and 3) in one zone of endosperm peroxidase pattern (band 3 present in m1 and absent in m2). In compactoids, isozymic patterns of both enzymic systems, as revealed by all tissues studied, did not show any intermutant variation or any variation between any mutant and the parental variety m1. For the same organ the enzymic bands were common to all compactoids as regards both number and density. The above mentioned findings concerning the similarity of zymograms, suggest that biosynthesis of the two investigated enzymic systems is presumably controlled by other genetic sites, different from the segment of 5AL which carries the Q and B1 genes (MITRA and BHATIA 1971). Thus, there was found no genic alteration or inactivation interfering with compactoid character. Speltoid mutants showed intermutant variation as well as variation between mutants and varieties in their isoenzymic patterns. The situation was of small degree for the structural mutants S1,S2,S7,S8 (Group I) which differed from their common parental variety m1 only by separating the slow band 1 in shoot esterase spectrum (Fig. 2). |
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