Phytochrome-mediated phototropism in maize seedling shoots
Phytochrome-mediated phototropism in maize seedling shoots
复制标题
光敏色素介导的玉米幼苗的向光性
作者：
M. Iino;W. Briggs;E. Schäfer
用红光 (R) 或蓝光 (BL) 进行单侧照射，可引起玉米 (Zea mays L.) 幼苗中胚轴的正曲率，在 R 下培养 2 天，然后在曲率诱导前在黑暗中保存 1 天。通过在向光诱导后 100 分钟测量曲率获得 R 诱导的中胚轴曲率的注量响应曲线，显示两个注量范围内的峰值，指定为第一个正范围（从阈值到波谷）和第二个正范围（波谷上方）。 BL 的注量响应曲线与 R 的相似，但向更高的注量移动了两个数量级。蓝光引起胚芽鞘的经典第一正曲率，而 R 则没有发现这种反应。由 R 或 BL 引起的正中胚轴曲率在单侧照射之前被上面给出的 R 消除，而 BL 诱导的胚芽鞘曲率则未被消除。上述结果共同证明中胚轴的向光性曲率是由 R 敏感光系统引起的。第二个正范围内的中胚轴曲率因 R 向光性诱导后施加的垂直远红光 (FR) 而减小，但不受 R 之前施加的 FR 的影响。在高 R 通量垂直照射后用 FR 进行单侧照射会导致中胚轴的负曲率。结论是，第二正范围内的中胚轴曲率是由跨植物轴建立的 FR 吸收形式光敏色素 (Pfr) 的量梯度造成的。第一个正范围内的中胚轴曲率受到在用 R 向光诱导之前或之后给予的垂直 FR 的抑制。由于此处使用的 FR 可能比 R 的非常低的通量产生更多的 Pfr，从而引起第一个正范围内的中胚轴曲率，因此假设 FR 通过在植物轴两侧添加 Pfr 来减少这种情况下的响应。通过在轴水平的回转器上旋转幼苗，可以在没有抵消重力响应的情况下研究中胚轴曲率的动力学。在回转器上，R诱导的中胚轴曲率在滞后后发展，通过具有不同曲率率的两个连续阶段，晚期阶段比早期阶段慢。胚芽鞘的负曲率可以由 R 或 BL 引起； BL 引起的负曲率的注量高于正曲率的注量。回转器实验表明，由 R 或 BL 引起的负胚芽鞘曲率是对正中胚轴曲率的向地性补偿。
Unilateral irradiation with red light (R) or blue light (BL) elicits positive curvature of the mesocotyl of maize (Zea mays L.) seedlings raised under R for 2 d from sowing and kept in the dark for 1 d prior to curvature induction. The fluenceresponse curve for R-induced mesocotyl curvature, obtained by measuring curvature 100 min after phototropic induction, shows peaks in two fluence ranges, designated first positive range (from the threshold to the trough), and second positive range (above the trough). The fluence-response curve for BL is similar to that for R but shifted two orders of magnitude to higher fluences. Blue light elicits the classical first positive curvature of the coleoptile, whereas this response is not found with R. Positive mesocotyl curvature induced by either R or BL is eliminated by R given from above just before the unilateral irradiation, whereas BL-induced coleoptile curvature is not eliminated. The above results collectively offer evidence that phototropic curvature of the mesocotyl is induced by R-sensitive photosystem(s). Mesocotyl curvature in the second positive range is reduced by vertical far-red light (FR) applied after phototropic induction with R, but is not affected by FR applied before R. Unilateral irradiation with FR following vertical irradiation with a high R fluence leads to negative curvature of the mesocotyl. It is concluded that mesocotyl curvature in the second positive range results from a gradient in the amount of the FR-absorbing form of phytochrome (Pfr) established across the plant axis. Mesocotyl curvature in the first positive range is inhibited by vertical FR given either before or after phototropic induction with R. Since the FR used here is likely to produce more Pfr than the very low fluences of R eliciting the mesocotyl curvature in the first positive range, it is assumed that FR reduces the response in this case by adding Pfr at both sides of the plant axis. By rotating seedlings on a clinostat with its axis horizontal, the kinetics of mesocotyl curvature can be studied in the absence of a counteracting gravitropic response. On the clinostat, the R-induced mesocotyl curvature develops after a lag, through two successive phases having different curvature rates, the late phase is slower than the early phase. Negative curvature of the coleoptile can be induced by either R or BL; the BL-induced negative curvature is found at fluences higher than those giving positive curvature. The clinostat experiments show that the negative coleoptile curvature induced by either R or BL is a gravitropic compensation for positive mesocotyl curvature.