IS TRIGONELLINE A PLANT HORMONE?

Experimental results are presented so that trigonelline may be evaluated as a plant hormone. Trigonelline promotes preferential cell arrest in G2 of the cell cycle for about 40% of the cell population in root meristems of Pisum sativum . Trigonelline is present in ungerminated seeds and is transported from cotyledons to other tissues during early seedling development. These experimental results show that trigonelline satisfies all six criteria that have been used to establish whether a substance is a hormone. As the seedlings age from day 3 to 10, the concentration of trigonelline in meristems decreases and so does the proportion of cells arrested in G2. Trigonelline may be isolated from excised cotyledons and can be added back to decotyledonized seedlings or excised root meristems to have the same effect as found in intact organisms. Predominant cell arrest in G2 occurs in roots of some plant species, although other species show preponderant cell arrest in G1. Many members of the Preiss‐Handler metabolic pathway show some ability to promote cell arrest in G2 but only at concentrations 100 (10 ‐5 m ) or 1,000 (10 ‐4 m ) times the concentration of trigonelline (10 ‐7 m ) necessary for function. The proportion of cells arrested in G2 is highly correlated with the concentration of trigonelline within the root meristem.