Pollination-induced inhibition of maize silk elongation
Open Access
- Author:
- Sella Kapu, Nuwan Umantha
- Graduate Program:
- Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 05, 2006
- Committee Members:
- Daniel J Cosgrove, Committee Chair/Co-Chair
Teh Hui Kao, Committee Member
Andrew George Stephenson, Committee Member
David M Braun, Committee Member - Keywords:
- maize silk
pollination
expansin
cell wall - Abstract:
- In response to pollination maize silks undergo an accelerated process of senescence that includes an inhibition of elongation. The inhibition of silk elongation became apparent beyond 12 h after pollination. However, the possibility that the reduction in elongation begins earlier than this can not be ruled out. Treatment with dead pollen indicated that the silk growth response requires interaction with viable pollen. Moreover, pollination of some silks on an ear did not have a long distance systemic effect on the elongation of un-pollinated silks on the same ear at 32 h post-pollination. Endogenous expansin activity, as evaluated by acid-induced extension and wall stress relaxation was not significantly reduced after pollination. Immunoblot analyses indicated that the abundance of either α- or β-expansin protein was not considerably decreased in response to pollination. In addition, extractable α-expansin activity was similar in control and pollinated silk walls. These findings suggest that the mechanism of pollination-induced inhibition of silk elongation is largely independent of changes in expansin abundance or activity. On the other hand, pollinated silk walls were less susceptible to extension by pollen β-expansin. Additionally, stress/strain analysis indicated a significant reduction in the wall plastic extensibility 6 h post-pollination. This reduction in the plastic extensibility only occurred after pollen tubes have traversed through a given region of silk. Numerous pollen tubes were initiated at the silk tip. This number gradually declined along the length of the silk and only 1-2 reached the ovary even after 24 h. Based on the timing of the reduction in wall extensibility and the slowing of silk elongation, these two phenomena may be causally related. In addition, it is possible that reduced wall extensibility is a mechanism to control the number of pollen tubes reaching the ovary. Finally, compared to controls, pollinated silk walls had more carboxylic acid groups and phenolic substances. Wall polymer cross-linking by the coupling of feruloyl groups attached to glucuronoarabinoxylan or the ionic bridging of carboxylic acid groups in pectin may be the basis of the reduction in wall extensibility.