In vitro pollen germination and tube development study of Pisum sativum L.

Studies on in vitro pollen germination at different time intervals after anthesis indicated that 60% germinating pollen along with a mean of 505 µm long pollen tube developments was observed in 20% sucrose solution (Table 1). Individually 200 ppm boric acid showed 50% germination along with 303 µm long pollen tube (Table- 2). The maximum 75% pollen germination along with 656 µm long pollen tube developed after 6 hours in 20% sucrose solution supplemented with 100 ppm boric acid (Table -3 Fig.-3). Among the salts, maximum 50% pollen germination along with 452 µm pollen tube development in 50 ppm calcium nitrate solution following 45% pollen germination along with 302 µm long pollen tube in 100 ppm potassium nitrate solution and 35% pollen germination along with 292 µm pollen tube was observed in 100 ppm magnesium sulphate solution  (Table-4). Both calcium and potassium  showed good results, however maximum pollen germination as well as tube development was observed in calcium nitrate solution.   The combination with boric acid promotes pollen germination and tube development. This is because boron forms a complex with the sugar, and this sugar-borate complex is known to have a superior migration capacity than non-borate and non-ionized sugar molecules (Gauch and Dugger, 1953; Sidhu and Malik, 1986). The pronounced effect of sucrose and boric acid on increasing trend of germinating pollen might be reflected with the views of Johri and Vasil (1961), Shivanna and Johri (1989) who stated that the externally supplied sucrose maintains the osmotic pressure and acts as a substrate for pollen metabolism. The role of boron has been confirmed in germinating pollen and growing pollen tubes in vascular plants (Lewis, 1980; Sidhu and Malik, 1986).The studies of Stanley and Loewus (1964) indicated that boron is directly involved in pectin synthesis and thus indirectly involved in development of pollen tube membrane. Scott (1960) suggested that boron may have a protective effect by preventing excessive sugar polymerization at sites of sugar metabolism. In nature, water, sugar and amino acids are provided by the body to nourish growing pollen tubes. Boron is also provided by stigmas and styles, facilitates sugar uptake and has a role in pectin production in the pollen tube (Richards, 1986).   Salts like calcium, potassium and magnesium were used to study the effect of Ca, K and Mg ions on in vitro pollen germination. The results show that calcium ions most effectively affect pollen germination. Calcium is one of the most important cations involved in cellular metabolism. It is also known for its important role in maintaining membrane integrity and permeability (Jones and Lunt, 1967 and Brewbaker and Kwack, 1964). According to Kwak (1967), calcium probably strengthens the pollen tube wall by binding to pectin carboxyl groups and also induces pollen germination. Picton and Steer (1983) and Miller et al. (1992) demonstrated that calcium concentration plays an important role in maintaining oviduct growth. Pollen germination and pollen tube growth are primarily regulated by the transport of inorganic ions, such as Ca++ and K+, across the plasma membrane of pollen and/or pollen tubes (Feijo et al., 1995 and Taylor and Hepler, 1997). According to Huang et al. (2001), external supply of K + ions increased pollen germination rate and pollen tube growth in Arabidopsis. Moore and Young (1974) pointed out that NO3- and Mg++ promoted tube growth during sugarcane pollen germination in vitro. The stimulatory role of magnesium in pollen germination and tube development has been established in tobacco (Loguercio, 2002) and gossypium (Burke et al., 2004). Prajapati and Jain (2010) showed that calcium, magnesium, and nitrate play important roles in pollen tube growth of Aedes aegypti. According to Brewbaker and Kwak (1963), magnesium ions enhance the effect of calcium ions, which leads to vigorous growth of the pollen tube. Mondal et al. (1997); Chowdhury et al. (2013); Ganta and Mondal (2013) studied the role of sucrose, boric acid and various salts such as calcium nitrate, potassium nitrate and magnesium sulfate on pollen germination in vitro.    

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