The premeiotic DNA replication of euchromatin and heterochromatin in Lilium longiflorum (Thunb.)

Abstract

The presynaptic stages of Lilium longiflorum have been analyzed in the light microscope. Seven substages can be defined on the basis of changes in morphology of the heterochromatin and the nucleoli. The duration of the presynaptic interval and the substages has been calculated from bud length measurements and cell stage gradients in the anthers. The premeiotic and somatic DNA replication has been investigated using 3H-thymidine autoradiography. The premeiotic S phase lasts 50 hours whereas the somatic S phase in root tip nuclei is six times shorter. Moreover, premeiotic S phase nuclei house 2-3 times more heterochromatin than somatic nuclei. The premeiotic DNA replication can be divided into three periods: In early S phase the DNA of euchromatin is replicated; in mid S phase synthesis is arrested for a minimum of 9 hours; and in late S phase the DNA of heterochromatin is replicated. DNA synthesis in heterochromatin is correlated with a dispersal of these chromatin regions. Determinations of volume and staining characteristics of heterochromatin after the application of C and Q banding procedures indicate that the premeiotic heterochromatin comprises C bands, Q bands and interbands. The premeiotic DNA replication is discussed in relation to the observed chromatin dynamics, and a proposal is made for the significance of the replication sequence to the formation of the leptotene chromosome and the control of crossing-over.

The Relation of Chromosome Compaction to DNA Synthesis During Meiosis in <I>Lilium</I>

“…Regardless of the precise duration of the exclusion, the behavior is impressive because glutaraldehyde appears to act principally on the transient heterochromatin that is so prominent cytologically in premeiotic nuclei. If true, the evidence presented is in line with the radioautographic observations of Holm (8), who noted in Lilium that heterochromatic DNA granules were being labelled almost as late as leptotene.…”

Effect of hydroxyurea on mitotic and meiotic divisions in explanted lily microsporocytes.

“…The transition between the S and G2 phase shows no distinctive change in chromatin morphology, but through both stages many small, similarly shaped chromatin masses are found scattered in the nucleus. Euchromatin threads are extremely faint and discontinuous (2,16). This appearance is seen in cells from buds 10-11 mm long for Georgia and from buds 9-10 mm long for Enchantment lilies.…”

Meiotic roles of Mec1, a budding yeast homolog of mammalian ATR/ATM

“…In budding yeast (SK1 background), mitotic-and meiotic-S phases are about 20 min and 60Y80 min, respectively (Williamson et al 1983, Cha et al 2000. The lengthening of S-phase during meiosis is proposed to reflect the extra time needed for developing additional chromosomal features that are later utilized for meiosis-specific chromosomal metabolism (Holm 1977). Consistent with this notion, the lengthening of meiotic S-phase is dependent on the establishment of DSB-independent homolog pairing mediated by Spo11 (Cha et al 2000).…”