Stage of Pollen Development - The optimum stage of pollen varies with the species. For many species, including Datura, tobacco, etc., the optimum stage is just before or just after the first pollen mitosis, while the early binucleate stage is the most suitable for species like Atropa belladona and Nicotiana sylvestris, and is absolutely essential for Nicotiana knightiana. In cereals, the best stage appears to be the early or mid uninucleate stage, i.e., before the first pollen mitosis. In contrast, in species like tomato and Arabidopsis thaliana, the optimum stage is when the PMC's are in meiosis I, while in Brassica trinucleate pollen grains (at the time of pollen shedding) are the best.
Pollen grains of Brassica remain responsive throughout the maturation phase, but their auxin requirement increases with the pollen age.In tobacco, the beginning of starch accumulation in pollen grains marks the end of their embryogenic potential. Further, the presence of starch in early binucleate pollen is indicative of a lack of androgenic potential of the species, while in species having the potential starch is absent.