Effect of phloridzin and phloroglucinol on apple shoots

Abstract

PHENOLIC compounds and their glycosides are widespread in plants. They have uncertain metabolic roles, although they are regarded as metabolic by-products conferring resistance to pathogens^1,2. Phloridzin, the 2′-glucoside of phloretic acid, for example, is unique to species of Malus and is the major phenolic compound of commercial apple trees (Malus pumila Mill), representing 3–7% of the dry weight of leaves as well as occurring in bark and roots³. It is not involved in resistance to apple scab as formerly supposed⁴, but affects the metabolism of many organisms. It inhibits growth of wheat coleoptiles⁵ and tomato roots⁶ but more than doubles photosynthetic rates in Elodea^7,8. In animals it inhibits the utilisation of carbohydrates⁹, and one of the degradation products^4,10 of phloridzin, phloroglucinol, acts synergistically with auxin to promote growth of oat mesocotyls¹¹. There have been indications that phloridzin, and phloroglucinol, promote the expansion of apple leaves¹² and the rooting of apple shoots¹³, respectively. This suggests that phloridzin may have important effects on Malus. I have now shown that phloridzin promotes the growth of cultured apple shoots. The effect is pronounced and has practical application.