Kurepin Leonid V, Emery R J Neil, Pharis Richard P, Reid David M
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4.
J Exp Bot. 2007;58(8):2145-57. doi: 10.1093/jxb/erm068. Epub 2007 May 8.
An attempt has been made to uncouple the effects of the two primary components of shade light, a reduced red to far-red (R/FR) ratio and low photosynthetically active radiation (PAR), on the elongation of the youngest internode of sunflower (Helianthus annuus) seedlings. Maximal internode growth (length and biomass) was induced by a shade light having a reduced R/FR ratio (0.85) under the low PAR of 157 micromol m(-2) s(-1). Reducing the R/FR ratio under normal PAR (421 micromol m(-2) s(-1)) gave similar growth trends, albeit with a reduced magnitude of the response. Leaf area growth showed a rather different pattern, with maximal growth occurring at the higher (normal) PAR of 421 micromol m(-2) s(-1)), but with variable effects being seen with changes in light quality. Reducing the R/FR ratio (by enrichment with FR) gave significant increases in gibberellin A(1) (GA(1)) and indole-3-acetic acid (IAA) contents in both internodes and leaves. By contrast, a lower PAR irradiance had no significant effect on GA(1) and IAA levels in internodes or leaves, but did increase the levels of other GAs, including two precursors of GA(1). Interestingly, both leaf and internode hormone content (GAs, IAA) are positively and significantly correlated with growth of the internode, as are leaf levels of abscisic acid (ABA). However, changes in these three hormones bear little relationship to leaf growth. By implication, then, the leaf may be the major source of GAs and IAA, at least, for the rapidly elongating internode. Several other hormones were also assessed in leaves for plants grown under varying R/FR ratios and PARs. Leaf ethylene production was not influenced by changes in R/FR ratio, but was significantly reduced under the normal (higher) PAR, the irradiance treatment which increased leaf growth. Levels of the growth-active free base and riboside cytokinins were significantly increased in leaves under a reduced R/FR ratio, but only at the higher (normal) PAR irradiance; other light quality treatments evoked no significant changes. Taken in toto, these results indicate that both components of shade light can influence the levels of a wide range of endogenous hormones in internodes and leaves while evoking increased internode elongation and biomass accumulation. However, it is light quality changes (FR enrichment) which are most closely tied to increased hormone content, and especially with increased GA and IAA levels. Finally, the increases seen in internode and leaf GA content with a reduced R/FR ratio are consistent with FR enrichment inducing an overall increase in sunflower seedling GA biosynthesis.
人们试图将遮荫光的两个主要成分，即降低的红/远红（R/FR）比值和低光合有效辐射（PAR）对向日葵（Helianthus annuus）幼苗最幼嫩节间伸长的影响分离开来。在157微摩尔·米⁻²·秒⁻¹的低PAR条件下，具有降低的R/FR比值（0.85）的遮荫光诱导节间生长达到最大值（长度和生物量）。在正常PAR（421微摩尔·米⁻²·秒⁻¹）下降低R/FR比值也呈现出类似的生长趋势，尽管响应幅度有所减小。叶面积生长呈现出相当不同的模式，最大生长发生在较高（正常）的PAR为421微摩尔·米⁻²·秒⁻¹时，但光质变化会产生不同的影响。通过用远红光富集来降低R/FR比值，节间和叶片中的赤霉素A₁（GA₁）和吲哚 - 3 - 乙酸（IAA）含量显著增加。相比之下，较低的PAR辐照度对节间或叶片中的GA₁和IAA水平没有显著影响，但确实增加了其他赤霉素的水平，包括GA₁的两种前体。有趣的是，叶片和节间的激素含量（GA、IAA）与节间生长呈正相关且显著相关，脱落酸（ABA）的叶片水平也是如此。然而，这三种激素的变化与叶片生长关系不大。由此推断，至少对于快速伸长的节间来说，叶片可能是GA和IAA的主要来源。还对在不同R/FR比值和PAR条件下生长的植物叶片中的其他几种激素进行了评估。叶片乙烯生成不受R/FR比值变化的影响，但在正常（较高）PAR下显著降低，而该辐照度处理会增加叶片生长。在降低的R/FR比值下，叶片中生长活性游离碱和核糖苷细胞分裂素的水平显著增加，但仅在较高（正常）PAR辐照度下；其他光质处理未引起显著变化。总体而言，这些结果表明遮荫光的两个成分都可以影响节间和叶片中多种内源激素的水平，同时引起节间伸长和生物量积累增加。然而，与激素含量增加最密切相关的是光质变化（远红光富集），尤其是GA和IAA水平的增加。最后，随着R/FR比值降低，节间和叶片中GA含量的增加与远红光富集诱导向日葵幼苗GA生物合成总体增加是一致的。
