Decrease of phosphoribulokinase activity by antisense RNA in transgenic tobacco: definition of the light environment under which phosphoribulokinase is not in large excess
Decrease of phosphoribulokinase activity by antisense RNA in transgenic tobacco: definition of the light environment under which phosphoribulokinase is not in large excess
复制标题
转基因烟草中反义RNA降低磷酸核糖激酶活性：磷酸核糖激酶不过量过量的光环境的定义
作者：
M. Paul;S. Driscoll;P. J. Andralojc;J. S. Knight;J. Gray;D. Lawlor
抽象的。 为了检验磷酸核糖激酶 (PRK) 对光合作用控制的贡献随植物光环境而变化的假设，测定了用反义 PRK 构建体转化的转基因烟草 (Nicotiana tabacum L.) 对辐照度的响应。在低辐照度 (330μmolm−2s−1) 下生长的植物中，暴露于较高辐照度后 PRK 活性降低的植物稳态光合作用受到限制，在 800μmolm−2s−1 及以上时 PRK 对 CO2 同化的控制系数为 0.25。然而，在 800μmolm−2 s−1 下生长的植物材料和仲夏温室中生长的植物（阴影和阳光交替 300–1600μmol m−2 s−1）下生长的植物中，PRK 稳态 CO2 同化的通量控制系数为零。为了解释在低辐照度和高辐照度下生长的植物之间的这些差异，测定了卡尔文循环酶活性和代谢物含量。 PRK 和其他非平衡卡尔文循环酶果糖-1,6-二磷酸酶、景天庚酮糖-1,7-二磷酸酶和核酮糖-1,5-二磷酸羧化酶-加氧酶的活性在 800μmol m−2 s−1 或温室中生长的植物比在 800μmol m−2 s−1 下生长的植物高两倍330 μmol m−2 s−1。平衡酶转酮醇酶、醛缩酶、5-磷酸核酮糖差向异构酶和异构酶的活性在所有生长辐照度下都非常相似。在 330 μmol m−2 s−1 下生长的植物中通量控制系数为 0.25，这可以解释为低 5-磷酸核酮糖含量与低 PRK 活性相结合限制了 1,5-二磷酸核酮糖的合成。这种限制在高光生长的植物中得到了克服，因为在这些条件下景天庚酮糖-1,7-双磷酸酶和果糖-1,6-双磷酸酶的活性相对大幅增加，这有利于更大量的核酮糖-5-磷酸的合成。这种潜在的限制将维持叶绿体内高浓度 PRK 的进化选择压力。
Abstract. To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate. This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate. This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.