RECIPROCAL TRANSLOCATION IN PEA

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19 79

Kaul, M. L. H. Institute of Cienetics, Bonn, West Germany

Interaction of recessive mutant genes has led to some new and bizarre

genotypes in the garden pea. During one such synthesis of digenic and trigenic

pea mutants, translocation heterozygosity was detected in the progeny of a plant

homozygous for acacia, afila, and cochleata (tl^w, af, coch). Such translocations

were not detected either in the single gene mutants or in the two gene recom-

binants viz. acacia/afila, acacia/cochleata, afila/ cochleata. Since such

translocations appeared only when these three mutant genes were present together

in a homozygous state, it was thought that the translocations are not only

gene-dependent but also genome-dependent (1). But further studies have not

revealed that the translocation is simply due to a gene mutation in the trigenic

pea mutant and its genetic status is being investigated.

Plants with the translocation heterozygote were partially sterile, had

much reduced pollen fertility, and reduced seed production. At MI, a ring of

4 chromosomes and 5 bivalents were present in the majority of the pollen mother

cells (Pig. 1). At advanced MI stages, in a few PMCs, associations of 4 chromo-

somes and a free univalent along with 5 bivalents were also observed. The

elimination of the 4th chromosome in these associations may be due to the avail-

ability of an extremely short chromosomal segment that is insufficient for

chiasma formation and, therefore, one of the translocated chromosomes is unable

to remain in this association. This inference is supported by the presence

of many IV configurations occurring as open rings, chains, or zizags. Whereas

the disjunction in the bivalents was normal at AI, the quadrivalent exhibited

an anomalous disjunction. This led to misdistributions and fragmentations and

laggard and bridge formations. However, a distribution of 6 + 8 was observed

in nearly 40% AI cells during male meiosis. Besides, monocentric and dicentric

bridges were also common at AI (Fig. 3, 4, 5). Second division stages were

abnormal and the microspores with micronuclei were abundant. While the genetic

tests indicated that these translocations were gene controlled, plants with

a ring of 6 chromosomes were detected (Fig. 2) from the progeny of the trans-

location heterozygote hybrids. This points to the possibility that some other

chromosome may be involved in the translocation as well. The translocation

homozygotes are weak, inviable, and with small flowers and abortive seeds.

(1) Kaul, M. L. 11. 1978. Proc. XIV Int. Cong. Genet. Moscow. (Abstr.).

Pt. 1, 29b p.



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		Fig. 1. 5 bivalents and a ring of IV chromosomes at MI. Fig. 2. 4 bivalents and an open VI configuration at MI. Fig. 3-4. Anaphase I - the very long arms represent the crossover chromatids of one of the chromosomes. Fig. 5. Anaphase I bridge and misdistri- bution of chromosomes.