We report the occurrence of cytomixis in wild populations of Himalayan poppy (Meconopsis aculeata Royle),which is considered to be an important and threatened medicinal plant growing in the high hills of the Himalayas. The impact of cytomixis on meiotic behaviour, reduced pollen viability and heterogeneous-sized pollen grains was also studied. Cytological studies in the seven wild populations from the high hills of Himachal Pradesh revealed that all the Himalayan populations exist uniformly at the tetraploid level (2n=56) on x=14. The phenomenon of chromatin transfer among the proximate pollen mother cells (PMCs) in six populations caused various meiotic abnormalities. Chromatin transfer also resulted in the formation of coenocytes, aneuploid, polyploid and anucleated PMCs. Among individuals that showed chromatin transfer, chromosome stickiness and interbivalent connections were frequently observed in some PMCs. The phenomenon of cytomixis in the species seems to be directly under genetic control; it affects the meiotic course considerably and results in reduced pollen viability.

Summary Caltha palustris L. (Ranunculaceae), popularly known as Kingcup or Marsh Marigold is a polymorphic species distributed in the cold temperate regions of western Himalayas. The species exhibits considerable amount of intraspecific morphological and chromosomal diversity involving polyploidy, aneuploidy and hybridization. Besides, some individuals also show the presence of Bchromosomes. Presently three populations from the cold desert region of Kullu and Lahaul-Spiti districts of Himachal Pradesh have been studied for detailed meiotic studies. These populations which uniformly show the presence of 16 bivalents at M-I are tetraploid on xϭ8. Presence of eight large sized and eight small sized bivalents at M-I, suggest these populations to be allotetraploid. Majority of the individuals in one of the populations show normal meiotic course and high pollen fertility. However, in the other two populations, the individuals show inter PMC transfer of chromatin material at various stages of meiosis and associated meiotic irregularities such as chromosome stickiness, pycnotic chromatin, late disjunction of bivalents, micronuclei and chromatin bridges at anaphases and telophases. Besides, the chromatin migration also results in the formation of aneuploid with 8, 11 and 13 bivalents and anucleated PMCs. Although the phenomenon of cytomixis does not affect apparent pollen fertility but it surely resulted into heterogenous sized pollen grains. Although the genetic constitution and fate of such apparently fertile heterogenous sized pollen grains is yet to be ascertained, but their possible role in the development of individuals with varied chromosome number could not be ruled out. The phenomenon of chromatin transfer in the species seems to be under direct genetic control as the individuals with and without cytomixis found to grow in the same environmental conditions.

Present cytological investigations from the cold desert regions of Lahaul-Spiti and Kinnaur (India) record the first ever tetraploid (2n=32) chromosome count and cytomixis in Clematis orientalis L. var. acutifolia Hook. f. et Thoms. The phenomenon of cytomixis (9.33 -29.80 %) involving chromatin transfer among 2 -3 proximate pollen mother cells (PMCs) during male meiosis occurs through narrow and broad cytoplasmic channels from early prophase to tetrad stage. However, frequency of its occurrence during the later meiotic stages is rather low. Chromatin transfer results into the formation of hypo-, hyperploid and enucleated PMCs. Various meiotic abnormalities associated with cytomixis such as chromatin stickiness, pycnotic chromatin, interbivalent connections, out of plate bivalents, late disjunction of bivalents, and laggards and bridges resulted into some pollen sterility (16.33 -49.30 %) and heterogeneous pollen grains size.

Lindelofia longiflora (Royle ex Benth.) Baill. var. falconeri (Cl.) Brand (Family: Boraginaceae) is investigated cytologically (n= 12) for the first time from the cold deserts of Pangi Valley, Chamba District (Himachal Pradesh) in India. We report the formation of syncytes and 2n pollen grains in the species. During meiosis, the majority of the pollen mother cells (PMCs) exhibited 12 bivalents, equal segregation of chromosomes during anaphases, regular tetrads, and normal‐sized pollen grain formation. Occasionally, two proximate PMCs fused during the early stages of prophase‐I and resulted in the formation of syncytes. The frequency of syncytes in the accession is rather low, at 25 out of 1866 (1.33%). Such syncyte PMCs are detectable during meiosis due to their larger size compared to typical PMCs. The syncytes or polyploid cells showed normal 24 bivalents and depicted perfectly regular meiotic course. But the products of such PMCs yield 2n or larger sized pollen grains that are almost double the size of typical normal or n pollen grains. The origin of syncytes as a consequence of the fusion of meiocytes during the early stages of meiosis‐I could be attributed to low temperature stress conditions prevailing in the Pangi Valley, where temperature during May and June dip to below freezing, the time the plants enters the reproductive/flowering bud stage. It is possible that such apparently fertile 2n pollen grains originating from syncytes might play a role in the origin of intraspecific polyploids in the species.

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