Lithium-sensitive calcium activity in the germination of apple(Malus×domesticaBorkh.), tobacco (Nicotiana tabacumL.), and potato (Solanum tuberosumL.) pollen

Abstract

We have investigated Ca 2+ activity during pollen germination and the possibility that it may be responding to a phosphoinositide signal transduction pathway, by employing inhibitors of Ca 2+ channels (verapamil and TMB-8), EGTA as a Ca 2+ scavenger and the inositol 1-phosphatase inhibitor lithium chloride. We have found that at least two Ca 2+ pools are utilized during pollen germination. Influx of extracellular Ca 2+ appears to be necessary for the germination of apple and tobacco pollen, but it does not appear to be required for the germination of potato pollen. Conversely, activation of intracellularly stored Ca 2+ was necessary for optimal germination of all three pollen species. LiCI had strong effects on pollen germination. At 5 mM LiCI, pollen germination was inhibited by 78% for apple, 84% for tobacco, and 74% for potato. Li + inhibition was overcome by the addition of Ca 2+ , which restores germination of all three species to 85-100% of that observed in controls. myo-lnositol also partially overcomes Li + inhibition of pollen germination, thus providing some evidence for a link between Li + inhibition and Ca 2+ rescue. myo-lnositol rescue of Li + inhibition was most effective for potato pollen. Chlorotetracycline (CTC) spectroscopy revealed a higher level of membrane-Ca 2+ in Li + -treated pollen grains than in controls, and the short pollen tubes which did emerge did not accumulate membrane-associated Ca 2+ . The results suggest that Li + inhibition may interfere with the release (activation) or partitioning of membrane-Ca 2+ during pollen germination and that this Ca 2+ activity may be responding, at least in part, with a phosphoinositide signal transduction pathway.