Erratic Male Meiosis Resulting in2nPollen Grain Formation in a 4x Cytotype (2n=28) ofRanunculus laetusWall. ex Royle

Abstract

Two accessions were studied for male meiosis in Ranunculus laetus from the cold regions of Northwest Himalayas. One accession showed the presence of 14 bivalents at diakinesis and regular segregation of bivalents at anaphase I which lead to normal tetrad formation with four n microspores and consequently n pollen grains and 100% pollen fertility. Second accession from the same locality revealed the erratic meiosis characterized by the presence of all the 28 chromosomes as univalents in meiocytes at metaphase I. Univalent chromosomes failed to segregate during anaphases and produced restitution nuclei at meiosis I and II. These restitution nuclei resulted into dyads and triads which subsequently produced two types of apparently fertile pollen grains. On the basis of size, the two types of pollen grains were categorized as n (normal reduced) and 2n (unreduced, 1.5-times larger than the n pollen grains). The estimated frequency of 2n pollen grains from dyads and triads (61.59%) was almost the same as that of the observed one (59.90%), which indicated that 2n pollen grains in R. laetus were the result of dyads and triads. The present paper herein may provide an insight into the mechanisms of the formation of various intraspecific polyploids through sexual polyploidization in R. laetus.

Cytological Studies of Some Dicots from the Hills of Mandi District (Himachal Pradesh) in Northwest Indian Himalayas

“…These spindle abnormalities resulted in some pollen sterility (7%) and heterogeneous sized fer- , 2012a, it showed abnormal meiotic behaviour in the form of asynaptic mutant resulting in 2n pollen grains formation and other meiotic irregularities, causing pollen steriliry. The present tetraploid chromosome count of n=14 in the species (based on x=7) is in agreement with the earlier chromosome records of 2n=28 from India (Mehra and Kaur 1963, Roy and Sharma 1971, Bhat et al 1972, Mehra and Remanandan 1972, Bir and Thakur 1984, Bir et al 1987, Kumar 2011, Kumar and Singhal 2012b) and outside of India (Goepfert 1974, Khatoon 1991. The other Himalayan populations of the species is also known to have intraspecific hexaploids, 2n=42 (Roy and Sharma 1971), and octoploid cytotypes, 2n=56 (Kabu et al 1988).…”

Chromosome Counts through Male Meiosis in Some Dicots from the Hills around Shimla, Himachal Pradesh

“…The phenomenon of cytomixis involving chromatin transfer among neighbouring PMCs along with associated meiotic irregularities has been detected in some individuals of Clematis grata (n=8) and Ranunculus laetus (n=14). The cytomixis in both the species has already been reported in plants from other regions of the Northwest Himalayas and seems to be a natural phenomenon under genetic control as suggested by a majority of researchers (Singhal and Kumar 2008, Kumar et al 2008b, 2012a, b, Singhal and Kaur 2011a, b, Kaur et al 2013, Rana et al 2013. In rest of the species, the study confirms the earlier chromosome counts.…”

“…and have also recorded the presence of cytomixis, associated meiotic irregularities and pollen sterility in the individuals from other parts of Himalayas in India. Kumar and Singhal (2012a) have also detected some asynaptic mutant individuals in the species from Chamba district. Further, the Indian taxa in the Himalayas also showed the presence of intraspecific polyploid cytotypes at two basic numbers, x=7 (2x, 4x, 8x) and x=8 (2x, 4x), indicating that the species is quite active in evolution.…”

High Pollen Sterility and 2<i>n</i> Pollen Grains in an Asynaptic 4<i>x</i> Cytotype (2<i>n</i>=48) of <i>Solanum nigrum</i> L.

“…The occurrence of univalents in the asynaptic mutant during prophase I and M-I, followed by abnormalities in subsequent stages resulted in the formation of different sized microspores at the sporad stage which clearly reflected the impact of asynaptic mutation. Meiotic irregularities resulting in the production of sterile and imbalanced gametes have been reported in several flowering plants by different researchers (Riley and Law 1965, Sjödin 1970, Gottschalk and Kaul 1980, Bennetzen 2002, Bione et al 2002, Pandit and Babu 2003, Gaut et al 2007) and also from this laboratory (Singhal 1982, Kumar and Singhal 2008, b, 2012a, b, Kumar et al 2008a, 2008b, Singhal and Kumar 2008a, 2008b, Singhal et al 2008, 2009a, 2009b, b, Gupta et al 2009, Kaur et al 2010, Kumar 2011. In the present study, the high pollen sterility in one of the accessions of 4x cytotype can be ascribed to asynaptic mutation.…”

“…Generally, the meiotic course in such asynaptic mutants is accompanied by a large number of meiotic anomalies such as scattered distribution of univalents in the cytoplasm, laggards at anaphases, unequal distribution of chromosomes at anaphases and multipolar PMCs. Several reserchers have reported a similar type of irregular behaviour as a result of asynaptic mutations (Koduru and Rao 1981, Kaul and Murthy 1985, Singh 2002, Sharma et al 2010, Kumar and Singhal 2012b, Kumar et al 2012.…”