Abstract
Two α-amino acids were isolated from a mushroom, Koshiro-onitake (Amanita castanopsidis Hongo). Spectroscopic analyses revealed that one was a novel α-amino acid, 2-amino-3-cyclopropyl-butanoic acid (compound 1) and the other a known α-amino acid, 2-amino-5-chloro-4-pentenoic acid (compound 2). Both compounds at concentrations higher than 10^-4 m substantially inhibited root growth in light-grown lettuce seedlings, while they had no effects on hypocotyl growth. Compounds 1 and 2 at 10^-4 M decreased the mechanical extensibility of the cell walls of roots, when they inhibited the growth. On the other hand, these compounds did not affect the osmotic concentration of cell sap of root tissue. The determination of number of cortical cells along the root showed that compound 2 slightly decreased the cell number, but compound 1 did not affect it. These results indicate that compounds 1 and 2 inhibit growth of lettuce roots by decreasing the mechanical extensibility of the cell walls. In addition, suppression of cell division may be also involved in the inhibition of root growth by compound 2.
