Unleashing the Potential of Biostimulants in Stimulating Pollen Germination and Tube Growth

The complex processes of pollen germination and pollen tube elongation are important events in the sexual reproduction of flowering plants and are essential to the success of seed formation. However, unfavourable environmental and climatic conditions affect pollen performance negatively. Integrating the application of various biostimulants represents one of the most innovative and promising strategies to improve crop productivity. Biostimulants are known to sustainably improve pollen viability, germination and elongation. However, there is limited information on the effects of biostimulants on pollen grains. The present review investigates the potential of biostimulants (such as seaweed extracts, smoke–water, polyamines, amino acids, melatonin, carbohydrate-based biostimulants and inorganic biostimulants) as signaling molecules that can improve crucial stages of pollen growth in a range of crops, both in optimal and suboptimal environments. Furthermore, this review investigates the stages of pollen development, including uninucleate microspores and different stages of mature pollen, following various biostimulant treatment during the flowering period. Regulation of biostimulant-induced pollen germination and elongation has also been discussed along with recent developments regarding the mechanism of action of biostimulants in various growth aspects of pollen. This review not only summarizes what is known currently, but it also lays the groundwork for future investigations to clarify the complex physiological and molecular processes involved in pollen performance as well as the regulatory systems that are impacted by biostimulants.