Phytochrome-mediated phototropism in maize mesocotyls. Relation between light and Pfr gradients, light growth response and phototropism
✍ Scribed by P. Kunzelmann; E. Schäfer
- Publisher
- Springer-Verlag
- Year
- 1985
- Tongue
- English
- Weight
- 615 KB
- Volume
- 165
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
Unilateral irradiation of maize (Zea mays L.) seedlings results in a fluence-rate gradient, and hence below saturation, a gradient of the far-redabsorbing form of phytochrome (Pfr). The Pfr-gradients established by blue, red and far-red light were spectrophotometrically measured in the mesocotyl. Based on these Pfr-gradients and the fluence-response curves of phytochrome photoconversion the fluence-rate gradients were calculated. The fluence-rate gradient in the blue (460 nm) was steeper than that in the red (665 nm), which in turn was steeper than that in the far-red light (725 nm). The fluence-rate ratios front to rear were 1:0.06 (460nm), 1:0.2 (665nm), and 1:0.33 (725 nm). The assumption that phytochrome-mediated phototropism of maize mesocotyls is caused by local phytochrome-mediated growth inhibition was tested in the following manner. Firstly, the Pfr response curve for growth inhibition was calculated; these calculations were based on measurements of Pfr-gradients and data from red-lightinduced phototropism. Secondly, the Pfr response curve for growth inhibition was used as a basis for calculating fluence-response curves for blueand far-red-light-induced phototropism. Finally, these calculated results were compared with experimental data. It was concluded that the threshold for phytochrome-mediated phototropism of maize mesocotyls reflects the apparent photoconversion cross section of phytochrome whereas the maximal inducable curvature depends on the steepness of the light (Pfr) gradient across the mesocotyl.