Devlin P F, Halliday K J, Harberd N P, Whitelam G C
Department of Botany, University of Leicester, UK.
Plant J. 1996 Dec;10(6):1127-34. doi: 10.1046/j.1365-313x.1996.10061127.x.
A major function of phytochromes in light-grown plants involves the perception of changes in the relative amounts of red and far-red light (R:FR ratio) and the initiation of the shade-avoidance response. In Arabidopsis thaliana, this response is typified by increased elongation growth of petioles and accelerated flowering and can be fully induced by end-of-day far-red light (EOD FR) treatments. Phytochrome B-deficient (phyB) mutants, which have a constitutive elongated-petiole and early-flowering pheno-type, do not display a petiole elongation growth response to EOD FR, but they do respond to EOD FR by earlier flowering. Seedlings deficient in both phytochrome A and phytochrome B (phyA phyB), have a greatly reduced stature compared with wild-type or either monogenic mutant. The phyA phyB double null mutants also respond to EOD FR treatments by flowering early, suggesting the operation of novel phytochromes. Contrary to the behaviour of wild-type or monogenic phyA or phyB seedlings, petiole elongation in phyA phyB seedlings is reduced in response to EOD FR treatments. This reduction in petiole elongation is accompanied by the appearance of elongated internodes such that under these conditions the plants no longer display a rosette habit.
光敏色素在光照下生长的植物中的一个主要功能涉及感知红光和远红光相对量的变化（R:FR 比值）以及启动避荫反应。在拟南芥中，这种反应的典型表现是叶柄伸长生长增加和开花加速，并且可以通过日终远红光（EOD FR）处理完全诱导。缺乏光敏色素 B（phyB）的突变体具有叶柄伸长和早花的组成型表型，对 EOD FR 不表现出叶柄伸长生长反应，但它们确实通过更早开花对 EOD FR 做出反应。与野生型或任何一种单基因突变体相比，同时缺乏光敏色素 A 和光敏色素 B（phyA phyB）的幼苗高度大大降低。phyA phyB 双缺失突变体也通过早花对 EOD FR 处理做出反应，这表明存在新的光敏色素在起作用。与野生型或单基因 phyA 或 phyB 幼苗的行为相反，phyA phyB 幼苗的叶柄伸长在 EOD FR 处理下会减少。叶柄伸长的这种减少伴随着节间伸长的出现，使得在这些条件下植物不再呈现莲座状习性。
