Figure 1.

Schematic representation of the inferred correlation of circadian rhythms and metabolism involved in the fast-growing pollen tube in pistil. (I) Key transcription factors of circadian clock may be adjusted and highly enriched and specifically present in the in vivo–grown pollen tubes, such as: ATCCA1 (AT2G46830), LHY (AT1G01060), ATTOC12 (AT1G80920), circadian clock-associated PAS protein ZTL (AT5G57360), LACCASE8 (AT5G01040) REVEILLE4 (AT5G02840). (II) Circadian rhythms triggers a rapid activation of the cooperating enzymes and consecutive steps for the ethanol degradation II, TCA cycle variation and fatty acid β-oxidation II of pollen tube, production of the pollen tube's TCA cycle, leading to enhanced ATP production. (III) Four ubiquitin-specific proteases, UBP18 (AT4G31670), UBP23 (AT5G57990), ATUBP5 (AT2G40930) , UBP26 (AT3G49600) had relations with the central components of the circadian clock ATCCA1 (AT2G46830) and LHY (AT1G01060). UBP26 (AT3G49600) had significant relations with the AT1G64190 which encodes phosphogluconate dehydrogenase (NADP+-dependent, decarboxylating) (_EC 1.1.1.44) involved in the pentose phosphate pathway (oxidative branch), which maximize their ability to produce NADPH to reduce ROS level. (IV) Circadian rhythms may have a greater probability of the direct or indirect functional relationship with the cooperation of consecutive steps for production of PA biosynthesis. Intracellular Ca²⁺ dynamics were induced by the 2 messengers, Ins(1,4,5)P₃ and DAG.