This study was made to ascertain whether gibberellin influences leaf growth or not, and to study its mode of action on leaf growth. The materials used were
Pisum sativum and
Raphanus sativus. The effect of gibberellin on growth of intact
Pisum plant and excised
Pisum internodes has been examined together.
Gibberellin is effective on leaf disk and excised internodes of
Pisum floated on a medium containing gibberellin. But it has no effect on leaf growth of intact
Pisum plant.
The optimum concentration of gibberellin, for the promotion of leaf growth is 10mg./1. and its effect appears on excised leaf within three hours after treatment.
Remarkable cell enlargement is observed in gibberellin treated leaves without any obvious increase in cell number.
Gibberellin promotes the leaf expansion rather than the increase of fresh weight in contrast with kinetin which accelerates the increase of fresh weight rather than that of leaf area. In the presence of both compounds, increase on leaf area and fresh weight is larger than when only one of the compounds is used. Therefore, gibberellin and kinetin seem to act in different manners on leaf growth.
When the intact
Pisum was treated with gibberellin at lower stipule, the growth promoting effect of gibberellin moves to the upper internodes and petioles.
The authors wish to express their deep gratitude to Prof. M. Monsi and Ass. Prof. T. Yamaki of University of Tokyo and Prof. K. Hogetsu of Tokyo Metropolitan University who gave the authors helpful suggestions.
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