Pollen tube growth: where does the energy come from?

Abstract

This review focuses on the energy metabolism during pollen maturation and tube growth and updates current knowledge. Pollen tube growth is essential for male reproductive success and extremely fast. Therefore, pollen development and tube growth are high energy-demanding processes. During the last years, various publications (including research papers and reviews) emphasize the importance of mitochondrial respiration and fermentation during male gametogenesis and pollen tube elongation. These pathways obviously contribute to satisfy the high energy demand, and there are many studies which suggest that respiration and fermentation are the only pathways to generate the needed energy. Here, we review data which show for the first time that in addition plastidial glycolysis and the balancing of the ATP/NAD(P)H ratio (by malate valves and NAD C biosynthesis) contribute to satisfy the energy demand during pollen development. Although the importance of energy generation by plastids was discounted during the last years (possibly due to the controversial opinion about their existence in pollen grains and pollen tubes), the available data underline their prime role during pollen maturation and tube growth.

Defects in Peroxisomal 6-Phosphogluconate Dehydrogenase Isoform PGD2 Prevent Gametophytic Interaction in Arabidopsis thaliana

“…These analyses showed that pgd2-1 ovules can be fertilized by wild-type pollen tubes, and vice versa, pgd2-1 pollen tubes successfully compete for the fertilization of wild-type ovules. The latter is consistent with Suc (imported from stylar tissues; Leydon et al, 2014) being the primary energy source for pollen tube growth, mainly involving OPPP reactions in plastids (Selinski and Scheibe, 2014). However, pgd2-1 pollen tubes with (1) and Suc (2) gradients after centrifugation of 34 mL of crude extract, resulting in a band of purified peroxisomes (0.9 mL).…”

Pollen Development at High Temperature: From Acclimation to Collapse

“…Accordingly, a proteomic study detected catalase (CAT3) and glutathione reductase (GR1) in developing pollen (Chaturvedi et al, 2013). Pollen and tapetum cells have also been shown to accumulate large numbers of mitochondria and show high rates of respiration (Lee and Warmke, 1979;Selinski and Scheibe, 2014). Under high temperatures, this might be expected to cause a dramatic increase in ROS.…”

“…Developing pollen and tapetum cells seem to have unusually high energy demands as indicated by their high numbers of mitochondria (Lee and Warmke, 1979;Selinski and Scheibe, 2014); depletion in carbohydrate reserves might thus affect tapetum and pollen more than other cells. However, experimental proof for the carbohydrate deficiency hypothesis is still lacking: Studies have not yet clarified whether reduced carbohydrate levels at elevated temperatures cause pollen abortion or merely reflect the consequence of reduced pollen functioning.…”

S-Adenosylmethionine Synthetase 3 Is Important for Pollen Tube Growth

“…Pollen tubes are the fastest growing plant cells (Selinski and Scheibe, 2014). Pollen tubes grow by transferring chemical energy from stored starch and newly assimilated sugars into ATP (Rounds et al, 2011).…”