Researchers from the SILS Plant Development and (Epi)Genetics group have discovered that species all throughout the plant kingdom use what is described as a super proton pump to ensure a strong pH gradient. This suggests that hyper-acidification functions as a universal mechanism in plant physiology and development. These findings are published together with researchers from the Universities of Turin and Bielefeld in New Phytologist.
Plant vacuoles are a bit more acidic than the surrounding cytoplasm. This pH gradient energises different types of transporters in the membrane of the vacuole. In some cells, like petal epidermal cells, the vacuole is hyper-acidified due to the activity of a ‘super proton pump’ recently discovered through the analysis of petunia mutants with blue flowers. Because the pigments stored in the vacuole of petal cells assume a bluish colour at high pH and a reddish one at low pH, vacuolar hyper-acidification contributes to the attraction of animals for pollination and plant reproduction.
Yanbang Li, Tijs Bliek, Kees Spelt, Ronald Koes and Francesca Quattrocchio (Plant Development and (Epi)Genetics) show that the genes encoding for the two components of the ‘super proton pump’ (PH1 and PH5) are widely spread in the plant kingdom and appeared long before flowers during plant evolution. PH1 and PH5 evolved from ancient pumps: PH1 was acquired by plants from bacteria through horizontal gene transfer and it still resembles prokaryotic magnesium transporters, PH5 originated from plasma membrane ATPases via the acquisition of vacuolar localisation. Altogether, this indicates that vacuolar hyper-acidification is older than petal pigmentation and suggests its involvement in other, yet unknown, mechanisms of plant physiology and development.
Li, Y. et al. Evolution of tonoplast P-ATPase transporters involved in vacuolar acidification New Phytologist, doi:10.1111/nph.14008 (2016).