**Abstract**

Numerous genes in flowering plants, including onion (*Allium cepa* L.) govern morphological character differences in structure, shape, orientation, weight and number, etc. arising from their assortment and recombination due to pollination. Pollination in onion flower occurs mainly by insects (91%) and wind (9%), with gravity also contributing to the pollination process. The hybrid vigour seeds through cross pollination as an essential input in enhancing crop productivity. The present study reveals that an onion plant generally takes around 63 days to attain flowering position, and complete flowering condition in 70–72 days, which include 15–18 days for sprouting of the green hollow fleshy shoots along with about 45 days to complete the peduncle formation on the top small part of the bud. *A. cepa* L. takes around 160 days to produce mature seeds with life cycle completion. The onion bulb roots are used for the last 50 years to study chromosomal behaviour as an indicator of environmental water pollution. The presence of different impurities and heavy metals in the polluted water causes reduction in reproductive capacity of cells due to the occurrence of peculiarity from the normal mitotic cell division in onion . Cytotoxicity influences all morphological characters, including root growth retardation, mitotic index, chromosomal aberration, etc. Thus, the present investigation explores the effect of pollutant water on pollination biology, cytotoxicity, root apical meristem cells in onion. We report a significant (p < 0.05) in the mitotic index in polluted water as compared to normal water.

**Keywords:** cross pollination, heavy metals, chromosomal aberration, cytotoxicity and environmental indicator, water pollution, pollination biology

### **1. Introduction**

The *Allium* (family:Amaryllidaceae) is a large genus of onion or garlic fragrant perennial bulbous herbs and globally represents about 700 species, but only seven species are cultivated. Members of the family are the world's oldest cultivated plants after potatoes, yams, and tomatoes, comprising an important group of vegetables, except the tropics, New Zealand and Australia. *Allium* is a native to southern western Asia with cultivation throughout the world, predominantly in the temperate regions [1].

There are different species of *Allium* which are grown in the field for the next generation in the form of flowers instead of bulbous structures. Generally, the seedlings are used for bulb production as vegetable. Two development phases occur to complete the life cycle of onions. One phase is entirely responsible for the production of seeds only whereas the other herbaceous annual phase is for the production of bulb from the seedling. Pollination in onion takes by an array of insects [2, 3]. The hermaphrodite onion flowers cannot fertilise themselves since the anthers exhibit protandry, releasing sticky and wet pollens before the stigma becomes receptive [4]. Thus, a crosspollination between two flowers of the same plant (Geitonogamy) or two flowers from different plants (Allogamy) accomplishes seed production in the onion. The cross-pollinated seeds are used for the production of the onion bulb. FAO [5] reported that the production of onion in India is 12.5 ton/ha only whereas it is much lower than the production 41.12 ton/ha in the USA. Different sources of Municipal, Industrial, Agricultural, and advanced technological waste components ingredients can increase significant amounts of impurities in surface water and later on slowly deposited at a lower base as a consequence water pollution contributed a serious problem for the health of the biological organism along with human, those interact with this aquatic ecosystem in developed and developing countries. Those waste materials released from the different sources are mainly toxic metals and metalloids which are not converted into harmless nontoxic forms by the biological process but engaged in the environmental system which react the suppression activity of metabolism and translocation of reserve food materials into low concentration and impose to damage of the growing regions cells of the living organism [6]. Living organisms encounter nasty toxic heavy materials responsible for damage/modification of the genetic materials happening in the cell cycle. Meristematic root tips of *A. cepa* L. are used all over the world for testing the level of environmental water pollution [7–10]. To evaluate water quality being used for cytological studies of *A. cepa* L. root tips squash technique offers one of the best and quick methods, which also provides a reliable estimate for the genotoxic effect of heavy metal and chloride interaction on the environment. The water samples from three locations, Preonagar, Mathpara and Harishnagar 24 Parganas (N), West Bengal, India have been assessed on the basis of mitotic cell activity (Mitotic Index) and different chromosomal abnormalities (CAs) in the meristematic root tips cells of *A. cepa* L. (**Table 1**). The effect was compared with distilled water. The wastewater from the above locations enters, in different ways, either the agriculture fields for irrigation or river flow which makes a hazard to the ecosystem of that environment. With this background, the hazardous elements in the water samples assumingly react with the chromosome of the meristematic part of root tip cells of *A. cepa* L. that acts as an indicator for natural water pollution.
