Limits...
The mechanism of pollination drop withdrawal in Ginkgo biloba L.

Jin B, Zhang L, Lu Y, Wang D, Jiang XX, Zhang M, Wang L - BMC Plant Biol. (2012)

Bottom Line: In contrast, nonviable pollen and acetone-treated pollen did not cause PD withdrawal.In contrast, pollen of the angiosperms P. suffruticosa, Salix babylonica, and O. violaceus did not submerge, instead remaining clustered at the edge without entering the PD.We conclude that PD withdrawal is primarily determined by the dynamic balance between evaporation and ovule secretion, of which pollen is a critical stimulator.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, Jiangsu 225009, China.

ABSTRACT

Background: The pollination drop (PD) is a characteristic feature of many wind-pollinated gymnosperms. Although accumulating evidence shows that the PD plays a critical role in the pollination process, the mechanism of PD withdrawal is still unclear. Here, we carefully observed the PD withdrawal process and investigated the underlying mechanism of PD withdrawal, which will aid the understanding of wind-pollination efficiency in gymnosperms.

Results: In Ginkgo biloba, PDs were secreted on the micropyle during the pollination period and persisted for about 240 h when not pollinated under laboratory conditions. The withdrawal of an isolated PD required only 1 h for evaporation, much less than a PD on the living ovule, which required 100 h. When pollinated with viable pollen, PDs withdrew rapidly within 4 h. In contrast, nonviable pollen and acetone-treated pollen did not cause PD withdrawal. Although 100% relative humidity significantly inhibited PD withdrawal, pollinated PDs still could withdraw completely within 48 h. Pollen grains of Cycas revoluta, which are similar to those of G. biloba, could induce PD withdrawal more rapidly than those of two distantly related gymnosperms (Pinus thunbergii and Abies firma) or two angiosperms (Paeonia suffruticosa and Orychophragmus violaceus). Furthermore, pollen of G. biloba and C. revoluta submerged immediately when encountering the PD, then sank to the bottom and entered the micropyle. The saccate pollen of P. thunbergii and A. firma submerged into the PD, but remained floating at the top and finally accumulated on the micropyle after PD withdrawal. In contrast, pollen of the angiosperms P. suffruticosa, Salix babylonica, and O. violaceus did not submerge, instead remaining clustered at the edge without entering the PD.

Conclusions: We conclude that PD withdrawal is primarily determined by the dynamic balance between evaporation and ovule secretion, of which pollen is a critical stimulator. When conspecific pollen grains were submerged in the PD, ovule secretion was subsequently terminated and active absorption occurred. These processes cooperated to influence PD withdrawal. In addition, pollen grain behavior within PDs varied dramatically among taxa, and PDs played a role in distinguishing and transporting pollen in G. biloba.

Show MeSH
Diagrammatic illustration of PD withdrawal. (A) PD is produced constantly by nucellar tip cells and reaches its maximum volume at pollination. (B)Ginkgo biloba pollen grains entered the PD, and the nucellar tip cells terminated secretion. (C) Pollen grains entered the pollen chamber along with PD withdrawal. I, integument; Mc, micropyle canal; Mi, micropyle; Nu, nucellus; P, pollen grains; Pc, pollen chamber; PD, pollination drop.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3403970&req=5

Figure 10: Diagrammatic illustration of PD withdrawal. (A) PD is produced constantly by nucellar tip cells and reaches its maximum volume at pollination. (B)Ginkgo biloba pollen grains entered the PD, and the nucellar tip cells terminated secretion. (C) Pollen grains entered the pollen chamber along with PD withdrawal. I, integument; Mc, micropyle canal; Mi, micropyle; Nu, nucellus; P, pollen grains; Pc, pollen chamber; PD, pollination drop.

Mentions: Withdrawal of the PD is affected by several factors, including RH, the quantity of viable pollen on the ovule, the state of ovule secretion, and the position of ovules [18-20]. Möller et al. [3] considered PD withdrawal to be an active process and that pollen can activate PD withdrawal and terminate PD secretion. Another explanation for PD withdrawal interprets it as a physical process attributed to passive evaporation rather than active withdrawal, i.e., independent of the presence of pollen [8,9,21]. In this study, we found that PDs withdrew quickly either at low humidity or when pollinated with a large quantity of viable conspecific pollen. In addition, when PDs were isolated from ovules, nonpollinated PDs took 1 h to withdraw completely, whereas the disappearance of nonpollinated PDs on the living ovule required over 100 h, which suggested that the ovule could secrete the PD continuously during pollination. These results indicate that PD withdrawal was determined by the balance between evaporation and ovule secretion, in which pollen was an important stimulus (Figure 10).


The mechanism of pollination drop withdrawal in Ginkgo biloba L.

Jin B, Zhang L, Lu Y, Wang D, Jiang XX, Zhang M, Wang L - BMC Plant Biol. (2012)

Diagrammatic illustration of PD withdrawal. (A) PD is produced constantly by nucellar tip cells and reaches its maximum volume at pollination. (B)Ginkgo biloba pollen grains entered the PD, and the nucellar tip cells terminated secretion. (C) Pollen grains entered the pollen chamber along with PD withdrawal. I, integument; Mc, micropyle canal; Mi, micropyle; Nu, nucellus; P, pollen grains; Pc, pollen chamber; PD, pollination drop.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3403970&req=5

Figure 10: Diagrammatic illustration of PD withdrawal. (A) PD is produced constantly by nucellar tip cells and reaches its maximum volume at pollination. (B)Ginkgo biloba pollen grains entered the PD, and the nucellar tip cells terminated secretion. (C) Pollen grains entered the pollen chamber along with PD withdrawal. I, integument; Mc, micropyle canal; Mi, micropyle; Nu, nucellus; P, pollen grains; Pc, pollen chamber; PD, pollination drop.
Mentions: Withdrawal of the PD is affected by several factors, including RH, the quantity of viable pollen on the ovule, the state of ovule secretion, and the position of ovules [18-20]. Möller et al. [3] considered PD withdrawal to be an active process and that pollen can activate PD withdrawal and terminate PD secretion. Another explanation for PD withdrawal interprets it as a physical process attributed to passive evaporation rather than active withdrawal, i.e., independent of the presence of pollen [8,9,21]. In this study, we found that PDs withdrew quickly either at low humidity or when pollinated with a large quantity of viable conspecific pollen. In addition, when PDs were isolated from ovules, nonpollinated PDs took 1 h to withdraw completely, whereas the disappearance of nonpollinated PDs on the living ovule required over 100 h, which suggested that the ovule could secrete the PD continuously during pollination. These results indicate that PD withdrawal was determined by the balance between evaporation and ovule secretion, in which pollen was an important stimulus (Figure 10).

Bottom Line: In contrast, nonviable pollen and acetone-treated pollen did not cause PD withdrawal.In contrast, pollen of the angiosperms P. suffruticosa, Salix babylonica, and O. violaceus did not submerge, instead remaining clustered at the edge without entering the PD.We conclude that PD withdrawal is primarily determined by the dynamic balance between evaporation and ovule secretion, of which pollen is a critical stimulator.

View Article: PubMed Central - HTML - PubMed

Affiliation: College of Horticulture and Plant Protection, Yangzhou University, Yangzhou, Jiangsu 225009, China.

ABSTRACT

Background: The pollination drop (PD) is a characteristic feature of many wind-pollinated gymnosperms. Although accumulating evidence shows that the PD plays a critical role in the pollination process, the mechanism of PD withdrawal is still unclear. Here, we carefully observed the PD withdrawal process and investigated the underlying mechanism of PD withdrawal, which will aid the understanding of wind-pollination efficiency in gymnosperms.

Results: In Ginkgo biloba, PDs were secreted on the micropyle during the pollination period and persisted for about 240 h when not pollinated under laboratory conditions. The withdrawal of an isolated PD required only 1 h for evaporation, much less than a PD on the living ovule, which required 100 h. When pollinated with viable pollen, PDs withdrew rapidly within 4 h. In contrast, nonviable pollen and acetone-treated pollen did not cause PD withdrawal. Although 100% relative humidity significantly inhibited PD withdrawal, pollinated PDs still could withdraw completely within 48 h. Pollen grains of Cycas revoluta, which are similar to those of G. biloba, could induce PD withdrawal more rapidly than those of two distantly related gymnosperms (Pinus thunbergii and Abies firma) or two angiosperms (Paeonia suffruticosa and Orychophragmus violaceus). Furthermore, pollen of G. biloba and C. revoluta submerged immediately when encountering the PD, then sank to the bottom and entered the micropyle. The saccate pollen of P. thunbergii and A. firma submerged into the PD, but remained floating at the top and finally accumulated on the micropyle after PD withdrawal. In contrast, pollen of the angiosperms P. suffruticosa, Salix babylonica, and O. violaceus did not submerge, instead remaining clustered at the edge without entering the PD.

Conclusions: We conclude that PD withdrawal is primarily determined by the dynamic balance between evaporation and ovule secretion, of which pollen is a critical stimulator. When conspecific pollen grains were submerged in the PD, ovule secretion was subsequently terminated and active absorption occurred. These processes cooperated to influence PD withdrawal. In addition, pollen grain behavior within PDs varied dramatically among taxa, and PDs played a role in distinguishing and transporting pollen in G. biloba.

Show MeSH