CUTICLE BIOSYNTHESIS IN RAPIDLY GROWING INTERNODES OF DEEP-WATER RICE

Submergence induces rapid elongation of deepwater rice (Oryza sativa L .) internodes. This adaptive feature allows deepwater rice to grow out of the water and to survive flooding. The growth response of submerge d deepwater rice plants is, ultimately, elicited by gibberellin (GA). Little attention has been given to the synthesis and role of the cutic le during plant growth. We investigated two questions regarding the cu ticle in rapidly elongating deepwater rice internodes: (a) how does cu ticle formation keep pace with internodal growth, which can reach rate s of up to 5 mm/h; and (b) does the cuticle contribute to tissue stres s in rice internodes? Treatment with GA for 48 h caused an up to 60-fo ld increase in the incorporation of [C-14]palmitic acid and an up to 6 -foId increase in the incorporation of [C-14]oleic acid into the cutic le of growing internodes. GA also caused a qualitative change in the i ncorporation pattern of palmitic acid into several cutin monomers, the most prominent of which was tentatively identified by thin-layer chro matography as a derivative of dihydroxyhexadecanoic acid. Rapidly grow ing plant organs exhibit longitudinal tissue stress: the epidermal cel l layer is under tension with a tendency to contract, whereas the inte rnal cells are under compression with a tendency to expand. As a resul t of tissue stress, longitudinally sliced sections of elongating inter nodes bend outward upon isolation from the plant. Treating rapidly gro wing rice internodes with cutinase reduced such outward bending, indic ating that the cuticle contributes to tissue stress. Based on these re sults, we propose that rapidly elongating structures such as deepwater rice internodes constitute an excellent system to study cuticle forma tion at the biochemical and cellular level.