Effect of insulin on the cell cycle of germinating maize seeds (Zea maysL.)

Abstract

During seed germination, metabolism is reactivated, DNA is repaired and cell division is restarted in the meristems. The mechanisms that co-ordinate cell growth and division in maize embryonic axes during germination are not well understood. However, the presence of a factor similar to IGF (insulin-like growth factor) that accelerates germination has been reported. In the present work, the regulation of the cell-cycle restart by bovine insulin [which has been demonstrated to produce similar effects as insulin-like growth factor of maize (ZmIGF) in maize seeds] was studied in germinating embryonic axes. Our results showed that bovine insulin differentially stimulates growth, S6K phosphorylation, S6rp transcript accumulation on the polysomal fraction, as well as de novo DNA synthesis in the radicles and the coleoptiles of the embryonic axis. A stronger and earlier effect was observed in radicles compared to coleoptiles; therefore, the effect of insulin on the cell cycle of the root meristem was studied by flow cytometry. The G1–S transition was stimulated and cell proliferation was induced. Furthermore, it was determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) that bovine insulin increased E2F and PCNA (proliferating cell nuclear antigen) transcription after 15 h of germination and PCNA de novo synthesis at 15 h of germination. These results show that bovine insulin preferentially stimulates growth in the radicles of germinating embryonic axes and suggest that its effect on the G1–S transition and the activation of cell proliferation is mediated by the induction of E2F and PCNA transcription.

Insights into the TOR-S6K Signaling Pathway in Maize (Zea mays L.). Pathway Activation by Effector–Receptor Interaction

“…Previous results from our research group have already proven that cell division in calli tissues occurs by stimulation with ZmIGF or insulin, 39 and recent evidence also showed that this also happens in maize seedlings, through the promotion of the G1− S1 phase transition during the cell cycle. 40 These data indicate a phenomenon similar to that documented for animal cells in response to insulin. 3,46 To determine the endogenous growth factor content of these calli, Western blot analysis were performed using an antibody raised against human insulin that was previously demonstrated to recognize the purified ZmIGF.…”

“…This phenomenon has also been demonstrated on insulin-stimulated maize seedlings, 37 as well as in ribosome biogenesis, observed in the same system. 38 Furthermore, insulin and ZmIGF have previously been shown to increase the rate of maize seedling and callus mitosis, 16,39 processes that were recently confirmed to occur by the activation of S phase genes promoting cell cycle progression in maize 40 and Arabidopsis 15 tissues. The identity of IGF-like growth factors in plants is scarce; even though few reports indicate their existence on leguminose, 30,31 maize, 16,36 potato, 34 and Arabidopsis, 35 although most of them have not been shown to regulate plant growth through the TOR pathway.…”

“…Indeed, either insulin or ZmIGF induces maize seedling growth and ribosomal protein synthesis, , as well as ribosome biogenesis . Furthermore, ZmIGF has been shown to regulate cell growth by cell proliferation in maize tissues, , suggesting that the biochemical and functional properties are quite similar between plant (ZmIGF) and animal (insulin or IGFs) growth factors. This work provides further evidence of a highly conserved TOR-S6K pathway in maize that regulates growth along with cell division and reveals a putative cell membrane receptor that interacts with either ZmIGF or insulin.…”

Efecto de la insulina en la biogénesis de ribosomas en maíz (Zea mays L.)

“…5A). This is in accordance with previous reports for maize indicating that re-initiation of cell division occurs around 18 h of imbibition [56] and it should be accompanied by intense protein synthesis activity. Hence, new ribosome biogenesis should also occur at high rate.…”

“…Cells in maize dessicated seeds during maturation are arrested in the transition G1/S and when seeds are imbibed the cell cycle is reactivated [57]. Also, our research group has previously shown that insulin stimulates the aforementioned transition and reactivates the cell cycle after 15 h of imbibition in presence of this effector [56]; therefore, we decided to look for the presence of the rRNA precursors in maize seeds imbibed in presence of insulin for periods shorter than 15 h (3 and 6 h) by using labeled probes against the mature rRNA and against the pre-rRNA (including ITS1, 5.8S and ITS2) according to the methodology described by Cevallos et al [58]. Results show that insulin induces rRNA precursors as well as 5.8 rRNA accumulation in maize seeds imbibed for 3 and 6 h (Fig.…”