Thesis

The role of phenolic compounds in the growth of light and dark grown seedlings

Seedlings of five species of plants were grown in darkness or light for two weeks. Shoots were measured in length and exhaustively extracted. The total phenolic content was determined colorimetrically after addition of Folin-Denis reagent. In all species, the lengths of the dark grown seedlings were longer than the corresponding light grown plants. It was found that the endogenous levels of phenolics were substantially higher in the light grown seedlings. The gallotannin content was also found to be higher in light grown seedlings. Dwarf pea seedlings were grown in continuous darkness and watered with water alone or solutions of tannic acid (0.5g/l and 5.0g/l ). At the lower concentration, there was a stimulatory-effect on growth relative to the water control. At higher concentration, although there was an increase in total length, there was substantial reduction in the length of the first two internodes and development of a fourth internode not present in either the water control or the lower concentration of tannic acid. Lettuce hypocotyl sections were incubated in light or darkness in water or solutions of GA3, tannic acid, dialyzed extracts from light or dark grown peas, or mixtures of GA3 and tannic acid or pea extracts. Tannic acid and pea extracts inhibited growth of hypocotyl sections regardless of lighting conditions. The degree of inhibition was greater in dark incubated sections and extracts from light grown peas were more inhibitory than extracts from dark grown peas. These data suggest that phenolics may be involved and play a regulatory role in the light-mediated inhibition of growth.

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