Abstract:
The mangrove seedlings Bruguiera and Aviceania develop in
a swamp environment where oxygen may be deficient and carbon dioxide in high concentration. Both of these states may be inimical to respiratory
processes in plants and especially to the early stages of
germination. While vivipary allows the development of the seedlings
to a stage where they may better withstand the unfavourable conditions
of the environment, nevertheless mangrove seedlings are still liberated
when low oxygen concentrations can have severe effects. The developing
Avicennia seedling, while on the parent tree, is surrounded by a tough
pericarp which restricts gaseous diffusion and induces a partially anaerobic
environment around the cotyledon tissues. The detection of high
lactic acid levels in Avicennia seedlings may be linked with the carbon dioxide-rich atmospheres which build up around the tissues. It is
possible that high levels of carbon dioxide induce the production of
lactic acid, a non-toxic product of fermentation, rather than of the more toxic ethanol. Lactic acid is also formed during the initial stages
of anaerobiosis in Bruguiera seedlings.