Biologisches Institut II der Universität, Schänzlestrasse 1, D-7800, Freiburg i. Br., Federal Republic of Germany.
Planta. 1987 Mar;170(3):400-7. doi: 10.1007/BF00395033.
The phytochrome-controlled expression of genes coding for plastidic proteins was studied in mustard (Sinapis alba L.) seedling cotyledons in continuous red (R) and far-red (FR) light, i.e. under steady-state conditions with regard to phytochrome, and in darkness over a time span of 8 d after sowing (25° C). (i) The time courses of the levels of the Calvin-cycle enzymes ribulose-1,5-bisphosphate carboxylase (RuBPCase) and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (NADP-GPD) were found to be optimum curves. The time at which the optimum (peak) occurred was - independent of fluence rate - the same in R (strong phytochrome action, chlorophyll accumulation and photosynthesis) and FR (strong phytochrome action but no significant chlorophyll accumulation and no photosynthesis). The starting point (first detectable inccrease of enzyme level) was also endogenously fixed and not affected by light. However, the two enzymes differed insofar as the peak was at 4 d after sowing for RuBPCase activity and 4.5 d for GPD. Western blots of the small (SSU) and large (LSU) subunits of RuBPCase showed that enzyme activity and protein levels were correlated. It was concluded that a dramatic change of competence towards phytochrome had occurred and that this change was endogenous. This conclusion was confirmed by short-term induction experiments. In constant darkness (D) the low enzyme levels were saturation rather than optimum curves, presumably because enzyme turnover was lacking. (ii) The time course of accumulation of membrane components showed that chlorophyll and LHCP (light-harvesting chlorophyll a/b-binding protein of photosystem II) levels were closely correlated in R until 6 d after sowing. Thereafter the levels remained constant. The accumulation of membrane components was not related to the accumulation of Calvin-cycle enzymes. (iii) Time courses of the levels of translatable mRNAs, particularly SSU mRNA and LHCP mRNA were determined. In the case of SSU the maximum mRNA-level was found in R, FR and D around 3 d. This was compatible with the in-situ protein accumulation rate. Induction experiments with FR showed that accumulation of SSU mRNA followed the same rise and fall (peak at 3 d) as would be expected from the time course of mRNA levels and from enzyme-induction experiments. In the case of LHCP mRNA the peak was between 3 and 4 d in R, and was not well correlated with in-situ protein accumulation. Translatable LHCP mRNA was also formed in FR and in D-with a peak between 3 and 4 d-although LHCP protein was not detectable under these circumstances (because of the lack of chlorophyll). The data indicate that competence of gene expression towards phytochrome is determined endogenously. However, in the case of LHCP its appearance is not only limited by mRNA but also depends on the availability of chlorophyll.
在持续的红光（R）和远红光（FR）下（即对于光敏色素处于稳态条件下），以及播种后 8 天的黑暗中（25°C），研究了拟南芥（Sinapis alba L.）幼苗子叶中质体蛋白编码基因的光敏素控制表达。（i）发现核酮糖-1,5-二磷酸羧化酶（RuBPCase）和 NADP-依赖性甘油醛-3-磷酸脱氢酶（NADP-GPD）的卡尔文循环酶的水平时间过程是最佳曲线。出现最佳（峰值）的时间 - 与通量率无关 - 在 R（强光敏色素作用，叶绿素积累和光合作用）和 FR（强光敏色素作用但没有明显的叶绿素积累和没有光合作用）中是相同的。起点（首次检测到酶水平的增加）也是内源性固定的，不受光的影响。然而，这两种酶的不同之处在于 RuBPCase 活性的峰值出现在播种后 4 天，而 GPD 的峰值出现在 4.5 天。RuBPCase 的小（SSU）和大（LSU）亚基的 Western blot 显示酶活性和蛋白质水平相关。得出的结论是，对光敏色素的能力发生了巨大变化，并且这种变化是内源性的。这一结论通过短期诱导实验得到了证实。在持续的黑暗中（D），低酶水平是饱和而不是最佳曲线，可能是因为缺乏酶的周转率。（ii）膜成分积累的时间过程表明，在播种后 6 天之前，叶绿素和 LHCP（光系统 II 的光捕获叶绿素 a/b 结合蛋白）水平在 R 中密切相关。此后，水平保持不变。膜成分的积累与卡尔文循环酶的积累无关。（iii）确定了可翻译的 mRNA，特别是 SSU mRNA 和 LHCP mRNA 的水平时间过程。就 SSU 而言，在 R、FR 和 D 中大约在 3 天左右发现最大的 mRNA 水平。这与原位蛋白积累率相匹配。用 FR 进行的诱导实验表明，SSU mRNA 的积累遵循相同的上升和下降（3 天的峰值），这与 mRNA 水平的时间过程和酶诱导实验相符。在 LHCP mRNA 的情况下，R 中的峰值在 3 到 4 天之间，并且与原位蛋白积累没有很好的相关性。在 FR 和 D 中也形成了可翻译的 LHCP mRNA-峰值在 3 到 4 天之间-尽管在这些情况下无法检测到 LHCP 蛋白（由于缺乏叶绿素）。数据表明，对光敏色素的基因表达能力是由内源性决定的。然而，在 LHCP 的情况下，它的出现不仅受到 mRNA 的限制，还取决于叶绿素的可用性。
