Photomodulation of mesocotyl elongation in maize seedlings: Is there a correlative relationship between phytochrome,auxin and cell wall extensibility?

Three h white light irradiation of etiolated maize seedlings ( Zea mays L. cv. Jubilee) inhibited mesocotyl elongation and caused a sharp decrease in cell wall plastic extensibility as measured by the Instron technique. The plastic extensibility following white light irradiation (3 h) was photomodulated by phytochrome. Although the photomodulation of the plastic extensibility was correlated with growth during 20 h, no such correlation was observed at shorter times. The addition of indole-3-acetic acid to light-inhibited intact seedlings, or seedlings from which the coleoptile and inner leaves were excised, resulted in a stimulation of growth. However, none of the IAA concentrations could reverse light inhibition. The possibility of a correlative relationship between phytochrome, auxin and cell wall extensibility is discussed.