Spatial and temporal pattern of light-regulated gene expression during tobacco seedling development: the photosystem II-related genes Lhcb (Cab) and PsbP (Oee2)

The white mustard ( Sinapis alba L.) Lhcb1*1 and PsbP*1 genes that code for proteins related to photosystem II (PSII) in chloroplasts were examined by analysis of promoter fragment β-glucuronidase (GUS) reporter constructs in transgenic tobacco ( Nicotiana tabacum L.) seedlings. The endogenous tobacco genes and the introduced mustard genes follow the same kinetics during seedling development and they show the same expression characteristics for light regulation and for the influence of a 'plastidic signal'. Hence, the cellular environment of the host plant always dominates the regulation of Lhcb1*1 and PsbP*1 gene expression; as with the mustard system clear differences in the temporal pattern and the physiological responses could be seen. The spatio-temporal pattern of gene expression was analysed in the different organs of the transgenic tobacco seedlings. In the cotyledons, expression at the PsbP*1 promoter starts in advance, and both genes show a rather uniform distribution of expression during seedling development. In the hypocotyl, a sequential basipetal pattern could be detected and a coordinated expression for the two promoters was analysed. The hypocotyl base is only included in this expression pattern if the seedlings receive light at early stages of development, whereas in later stages gene expression is repressed. A model is proposed that divides tobacco seedling development into three main phases.     

叶绿体发育和光对小麦叶谷氨酰胺合成酶基因表达的影响

利用电镜、ＤＥＡＥ－纤维素柱层析技术和小麦叶谷氨酰胺合成酶（ＧＳ）酶活性测定,研究了小麦叶片不同发育梯度的叶绿体超微结构和ＧＳ同功酶活性之间的关系。结果表明,从叶基至叶尖,随着叶绿体的成熟,净光合率增加,ＧＳ活性增加。各发育阶段离体叶绿体的３Ｈ－Ｕｒａ,３Ｈ－Ｌｅｕ 掺入试验和ＧＳ的Ｎｏｒｔｈｅｒｎ ｂｌｏｔ表明,基部是基因表达活性最高的部位。ＧＳｍ ＲＮＡ 在叶绿体发育阶段最多,而ＧＳ酶活性则在成熟叶绿体的部位最高。对黄化苗进行光照,ＧＳｍ ＲＮＡ 和ＧＳ活性明显增加,７２小时达到正常绿苗同等水平。由此说明核编码的叶绿体ＧＳ基因为光调控基因,明显促进了叶绿体ＧＳ基因的转录,而后叶绿体ＧＳ合成量增加     

Regulation of 5-aminolevulinic Acid synthesis in developing chloroplasts : I. Effect of light/dark treatments in vivo and in organello

Intact chloroplasts isolated from greening cucumber (Cucumis sativus L. var Beit Alpha) cotyledons regenerated protochlorophyllide (Pchlide) in the dark with added cofactors from either exogenous glutamate or endogenous substrates. No other intermediates of the chlorophyll biosynthetic pathway accumulated. When inhibitors of 5-aminolevulinic acid (ALA) dehydratase were added, the Pchlide that failed to form was replaced by an excessive amount of ALA. When greening seedlings were returned to the dark, ALA-synthesizing activity in the isolated chloroplasts decreased dramatically and recovered if the dark-treated seedlings were again exposed to continuous white light prior to chloroplast isolation. Both the decline and the recovery of ALA-synthesizing activity were complete in approximately 50 minutes. Changes in chloroplast structure during in vivo light to dark and dark to light transitions (as evidenced by electron microscopy) were much slower. Exposing isolated chloroplasts from dark-treated seedlings to short white flashes before incubation transformed nearly all the endogenous Pchlide, but hardly stimulated ALA synthesis, suggesting that Pchlide does not act as a feed-back inhibitor on ALA synthesis. Chloroplasts isolated from dark-treated tissue did not form Pchlide from glutamate when incubated in the dark with added cofactors; moreover, the endogenous Pchlide did not turn over in organello. However, these chloroplasts did synthesize Pchlide from added ALA at the normal rate and synthesized ALA from glutamate at a reduced, but still significant, rate. Mg chelation was not affected by in vivo dark treatment.