Pollen tube development and competitive ability are impaired by disruption of a Shaker K⁺ channel in Arabidopsis

Abstract

Sexual reproduction in plants requires elongation of the pollen tube through the transmitting tissues toward the ovary. Tube growth rate is a major determinant of pollen competitive ability. We report that a K + channel of the Shaker family in Arabidopsis, SPIK, plays an important role in pollen tube development. SPIK was found to be specifically expressed in pollen. When SPIK was heterologously expressed in COS cells, its product formed hyperpolarization-activated K + channels. Disruption (T-DNA insertion) of the SPIK coding sequence strongly affected inwardly rectifying K + -channel activity in the pollen-grain plasma membrane. Measurements of membrane potential in growing pollen tubes yielded data compatible with a contribution of SPIK to K + influx. In vitro pollen germination assays were performed, revealing that the disruption results in impaired pollen tube growth. Analysis of the transmission rate of the disrupted allele in the progeny of heterozygous plants revealed a decrease in pollen competitive ability, the probability of fertilization by mutant pollen being ∼1.6 times lower than that by wild-type pollen. The whole set of data supports the hypothesis that functional expression of SPIK plays a role in K + uptake in the growing pollen tube, and thereby in tube development and pollen competitive ability.

Ca2+-Dependent Protein Kinase11 and 24 Modulate the Activity of the Inward Rectifying K+ Channels inArabidopsisPollen Tubes

“…One component was defined as the hyperpolarization-activated, time-, and voltagedependent inward rectifier. This component is contributed by SPIK in Arabidopsis (Mouline et al, 2002) and is responsible for 90% of pollen tube K + in currents ( Figure 6A). The other was defined as instantaneously activated, voltage-independent conductance that is mediated by TPK4 in Arabidopsis .…”

“…It has been reported that disruption of the Shaker potassium channel SPIK (AKT6) impaired K + channel activity in pollen (Mouline et al, 2002). In this study, pollen tube protoplasts were (D) Real-time PCR analysis of CPK24 expression in the wild type (Col), cpk24 mutant, and two complementation lines (24COM1 and 24COM2).…”

“…Considering that CPK11 and CPK24 are involved in the Ca 2+ -dependent regulation of K + in channels in pollen tubes, we further hypothesized that SPIK may be the downstream target of CPK11 and CPK24. Since the K + channel activity of SPIK had been identified in COS cells (Mouline et al, 2002), we also used COS cells for patch clamping to test if CPK11 and CPK24 could regulate SPIK in vitro. As shown in Figure 6B, the currents recorded from COS cells expressing SPIK alone were approximately 3 times larger than those in cells coexpressing SPIK, CPK11, and CPK24 when the membrane potential was clamped to 2180 mV.…”

“…Shaker pollen inward K + channel (SPIK; also named AKT6) is expressed specifically in pollen and pollen tubes. Disruption of SPIK strongly reduces the inward rectifying K + channel activity and results in impaired pollen tube growth (Mouline et al, 2002). Arabidopsis TPK4, a member of tandem-pore K + channel (TPK/ KCO) family, was reported to be responsible for a marginal proportion of pollen tube K + conductance and function in the control of membrane potential .…”

“…Potassium is required for both pollen germination and tube growth (Weisenseel and Jaffe, 1976;Feijó et al, 1995;Fan et al, 2001;Mouline et al, 2002). K + is present in relatively large amounts and regulates several basic cellular parameters, such as turgor and membrane potential during pollen tube growth (Holdaway-Clarke and Hepler, 2003).…”