Direct Involvement of Benzoxazinoids in the Growth Suppression Induced by Phototropic Stimulation in Maize Coleoptiles

Abstract

The process of growth suppression observed in the illuminated sides in response to phototropic stimulation was investigated in maize coleoptiles. In our previous studies, the increased level of benzoxazinoids, 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 6-methoxybenzoxazolinone (MBOA), and the up-regulation of β-glucosidase (DIMBOA-glucosidase) activity have been observed in the illuminated halves. In this report, significant accumulation of hydrogen peroxide (H 2 O 2 ) was observed in the phototropically stimulated sides. Moreover, exogenously applied DIMBOA and MBOA induced a significant up-regulation of H 2 O 2 in the applied sides, respectively. In addition, lignin level was also slightly increased in the illuminated sides within 60 min. These results suggest that phototropic stimulation induced the production of benzoxazinoids, resulting to the up-regulation of H 2 O 2 in the illuminated halves. Consequently, the up-regulated H 2 O 2 promoted the cell-wall stiffness, leading to the growth suppression in the illuminated sides. This is the first indication that blue-light induced benzoxazinoids play the role of directional effecter in the growth suppression in the illuminated sides in maize coleoptiles.