The Effect of Low Light Intensity on the Early Development of Radish Hypocotyl

Abstract

The effect of low light intensity on the growth and endogenous components (Cytokinin, auxin and sugar) of radish (Raphanus sativusL. radicula group) was investigated. In addition, Kinetin and naphthaleneacetic acid (NAA) was directly supplied to the intact hypocotyl to examine whether the inhibition of thickening growth of hypocotyl under a low light intensity could be overcome by them.
Under a low light intensity, abnormal hypocotyl elongation was observed and the thickening of hypocotyl was markedly inhibited, so the T/R ratio became high. The cytokinin, auxin and sugar content of the hypocotyl rapidly increased with the thickneing growth under a high light intensity, but did not increase under a low light intensity.
When intact hypocotyl was treated with kinetin or NAA under a low light intensity, NAA did not affect the thickening growth, but kinetin significantly increased the hypocotyl diameter. At the same time, hypocotyl elongation was inhibited by kinetin treatment.
These results suggested that a decrease in cytokinin activity is one of the main factors inhibiting thickning growth of hypocotyl under a low light intensity and the inhibited growth can be overcome by a direct application of cytokinin to the intact hypocotyl.