Diurnal changes in the regulatory metabolite, fructose-2,6-bisphosphate (F26BP), and key metabolic intermediates of sucrose biosynthesis were studied in maize (Zea mays L. cv Pioneer 3184) during a day-night cycle. Whole leaf concentrations of dihydroxyacetonephosphate (DHAP) and fructose 1,6-bisphosphate changed markedly during the photoperiod. DHAP concentration was correlated positively with the rate of sucrose formation in vivo (assimilate export plus sucrose accumulation) and extractable activity of sucrose phosphate synthase (SPS). The changes closely followed net photosynthetic rate, which tracked irradiance. The other metabolic intermediates measured (glucose 6-phosphate, fructose 6-phosphate, and UDP-glucose) were either relatively constant over the 24 hour period or changed in a different pattern. Diurnal changes in leaf F26BP concentrations were pronounced, and fundamentally different than the pattern reported with other species. F26BP concentration decreased at the beginning of the day and remained low and constant; a 3- to 4-fold increase occurred with darkness, and slowly declined thereafter. In general, leaf F26BP concentration was negatively correlated with net photosynthetic rate, and also leaf DHAP concentration. Consequently, co-ordination of the regulation of cytosolic fructose 1,6-bisphosphatase and SPS was apparent. The results support the postulate that in maize leaves the activation state of SPS may be dependent on availability of DHAP and possibly other metabolites.
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机译:在昼夜循环中,研究了玉米(Zea mays L. cv Pioneer 3184)中调节代谢产物果糖-2,6-二磷酸(F26BP)和蔗糖生物合成关键代谢中间体的日变化。在光周期中,全叶磷酸二羟基丙酮磷酸酯(DHAP)和果糖1,6-双磷酸酯的浓度发生了显着变化。 DHAP浓度与体内蔗糖形成速率(同化出口加蔗糖积累)和蔗糖磷酸合酶(SPS)的可提取活性呈正相关。这些变化紧随净光合速率,并跟踪辐照度。测得的其他代谢中间体(6-磷酸葡萄糖,6-磷酸果糖和UDP-葡萄糖)在24小时内相对恒定或以不同方式变化。叶片F26BP浓度的昼夜变化明显,与其他物种报道的模式根本不同。 F26BP浓度在一天开始时下降,并保持较低且恒定;在黑暗中增加了3到4倍,此后缓慢下降。通常,叶片F26BP浓度与净光合速率以及叶片DHAP浓度呈负相关。因此,显而易见的是胞质果糖1,6-双磷酸酶和SPS的协调作用。结果支持以下假设:玉米叶片中SPS的激活状态可能取决于DHAP的可用性以及其他代谢物。
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