Effects of salinity, irradiance, and phytohormones on early development in the red mangrove, Rhizophora mangle L

Propagules of the red mangrove Rhizophora mangle L. were subjected to separate and combination treatments of salinity, irradiance, and phytohormones in an attempt to understand the relationships among these variables with respect to early development. Growth (particularly that of shoots) was suppressed by a photosynthetic inhibitor (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and salinity. The effects of irradiance were variable although it can be reasonably stated that optimal levels fall below full-strength sunlight, thereby characterizing R. mangle as shade-tolerant during this stage of development. Epicotyl elongation and, in some cases, leaf growth, was enhanced by applications of exogenous gibberellic acid (as GA{dollar}{bsol}sb3{dollar}) while root growth was promoted by naphthaleneacetic acid (NAA). Abscisic acid (ABA) also stimulated shoot and root growth to a certain extent. Inhibitions of development under suboptimal salinity and/or irradiance conditions could be fully or partially alleviated by applications of these phytohormones. This information is incorporated into a theoretical model of early development in R. mangle.