Role of hydroxyproline-rich cell wall protein in growth regulation of rice coleoptiles grown on or under water

The elongation of both intact and excised rice coleoptiles waspromoted when they were submerged in water. Amino acid analysisof the cell wall revealed that air-type coleoptiles (grown onthe surface of water) contained more hydroxyproline than water-typeones (grown under water). The suppression of hydroxylation ofpeptidyl proline under water was confirmed with air-type sectionsby examining the imino acid content, ¹⁴C-proline incorporationinto the cell wall and its modification by ,'-dipyridyl. Also,dipyridyl significantly promoted the growth of floated sectionsto the level of submerged sections. Therefore, the lower hydroxyprolinecontent caused by lower oxygen tension in water is concludedto be one of the factors promoting growth of rice coleoptilesunder water. However, the hydroxyproline content in the cellwall decreased with growth of both air-and water-type coleoptiles;thus hydroxyproline-rich cell wall protein can not be regardedas the final growth cessation factor in rice coleoptiles. (Received December 17, 1979; )