Diurnal changes in sucrose, nucleotides, starch synthesis and AGPS transcript in growing potato tubers that are suppressed by decreased expression of sucrose phosphate synthase
Diurnal changes in sucrose, nucleotides, starch synthesis and AGPS transcript in growing potato tubers that are suppressed by decreased expression of sucrose phosphate synthase
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DOI：
10.1046/j.1365-313x.2000.00848.x
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发表时间：
2000-09-01
期刊：
影响因子：
7.2
通讯作者：
Stitt, M
中科院分区：
文献类型：
--
作者：
Geigenberger, P;Stitt, M
叶片的蔗糖输出在白天较高，而在夜间较低，这取决于淀粉的再动员。研究了马铃薯块茎光合产物供应日变化对淀粉合成和其它代谢过程的影响。蔗糖、SUS和AGPS的转录物水平、关键代谢物水平以及淀粉和其他主要终产物（包括蛋白质和细胞壁多糖）的合成速率在光照期开始和结束之间增加两倍或更多。淀粉合成的刺激伴随着UDP葡萄糖和ADP葡萄糖的增加，而糖酵解中间体保持不变，揭示了蔗糖合成酶和ADP-葡萄糖焦磷酸化酶正在协调调节。蔗糖合成酶通过其底物UDP和蔗糖的增加而被刺激。UDP增加是由于整体尿苷核苷酸库的增加，以及当生物合成通量在一天结束时高时，与ATP/ADP比率和腺苷酸能量电荷的降低平行发生的UTP/UDP比率的降低。在昼夜变化的时间范围内，SUS和AGPS转录水平的变化不会导致编码酶的显著变化。蔗糖磷酸合成酶表达的逐步减少，其中叶糖水平的昼夜变化被阻尼的转化体，表现出逐步衰减的蔗糖，核苷酸糖和核苷酸的昼夜变化，并在他们的块茎通量。可以得出结论，块茎中的代谢过程与蔗糖的瞬时供应紧密相关。
Sucrose export from leaves is high during the day and lower at night, when it depends on starch remobilisation. We have investigated the consequences of diurnal changes of photoassimilate supply for starch synthesis and other metabolic processes in growing potato tubers. Sucrose, the levels of the transcripts for SUS and AGPS, the levels of key metabolites, and the rate of synthesis of starch and other major end products, including protein and cell wall polysaccharides, increased twofold or more between the start and end of the light period. The stimulation of starch synthesis was accompanied by an increase of UDPglucose and ADPglucose, whereas glycolytic intermediates remained unaltered, revealing that sucrose synthase and ADP-glucose pyrophosphorylase are being co-ordinately regulated. Sucrose synthase is stimulated via an increase of its substrates, UDP and sucrose. UDP increases due to an increase of the overall uridine nucleotide pool, and a decrease of the UTP/UDP ratio that occurs in parallel with a decrease of the ATP/ADP ratio and adenylate energy charge when biosynthetic fluxes are high at the end of the day. Within the time frame of the diurnal changes, the changes in the SUS and AGPS transcript levels do not lead to significant changes in the encoded enzymes. Transformants with a progressive decrease of sucrose phosphate synthase expression, where diurnal changes in leaf sugar levels were damped, exhibited a progressive attenuation of the diurnal changes of sucrose, nucleotide sugars and nucleotides, and fluxes in their tubers. it is concluded that metabolic processes in tubers are tightly linked to the momentary supply of sucrose.