Chromosome Instabilities and Programmed Cell Death in Tapetal Cells of Maize With B Chromosomes and Effects on Pollen Viability

Abstract

B chromosomes (B's), knobbed chromosomes, and chromosome 6 (NOR) of maize undergo nondisjunction and micronucleus formation in binucleate tapetal cells. These chromosome instabilities are regular events in the program of tapetal cell death, but the B's strongly increase A chromosome instability. We studied 1B and 0B plants belonging to selected lines for high or low B transmission rate and their F 1 hybrids. These lines are characterized by meiotic conservation or loss of B chromosomes, respectively. The female B transmission ( fBt l ) allele(s) for low B transmission is dominant, inducing micronucleus formation and B nondisjunction. We hypothesize that the fBt l allele(s) induces knob instability. This instability would be sufficient to produce B loss in both meiocytes and binucleate tapetal cells. B instability could, in turn, produce instabilities in all chromosomes of maize complement. To establish whether the chromosomal instabilities are related to the tapetal programmed cell death (PCD) process, we applied the TUNEL technique. PCD, estimated as the frequency of binucleate tapetal cells with TUNEL label, was significantly correlated with the formation of micronuclei and the frequency of pollen abortion. It can be concluded that the observed chromosome instabilities are important to the PCD process and to the development of microspores to form viable pollen grains.

Centromere Function and Nondisjunction Are Independent Components of the Maize B Chromosome Accumulation Mechanism

“…In the presence of the B chromosome, increased rates of nondisjunction and chromosome breakage have been observed for A chromosomes in tapetal cells and other terminal tissues where B chromosome nondisjunction can be observed (Chiavarino et al, 2000;Gonzalez-Sanchez et al, 2004). Chromosomes containing knobs are especially susceptible to B chromosome-induced instability.…”

Nondisjunction in Favor of a Chromosome: The Mechanism of Rye B Chromosome Drive during Pollen Mitosis

“…In maize, B nondisjunction also occurs during tapetal programmed cell death (Chiavarino et al, 2000;González-Sánchez et al, 2004), and in the endosperm (Alfenito and Birchler, 1990) and in plants containing multiple Bs, the nondisjunction rate in root meristems is increased (Masonbrink and Birchler, 2010). By contrast, in a number of species, nondisjunction of Bs occurs regularly in somatic tissue (listed in Jones and Rees, 1982).…”

Cytological evidences of pollen abortion in Ornithogalum caudatum Ait

“…This phenomenon is similar to that described earlier in the B chromosomes of rye (Wiegas, 1980;Houben et al, 2001). In maize, B chromosomes also affect the pollen viability; they could make A chromosomes, which show more complex genetic behavior, the frequency of univalent in PMCs is increased significantly in meiosis metaphase I (Rusche et al, 1997;González-Sánchez et al, 2004;Masonbrink and Birchler, 2010). Such behavior of B chromosomes may cause pollen abortion.…”

“…Phenomenon of pollen abortion in O. caudatum is very common, and it could be related to abnormality of euchromosome pairing in meiosis; further, B chromosomes may affect the pollen fertility (Wiegas, 1980;Parker et al, 1990;González-Sánchez et al, 2004;Kumar and Srivastava, 2010). The B chromosomes are accessory genomic elements to the so-called A or standard genome.…”