Low temperature inhibits pollen viability by alteration of actin cytoskeleton and regulation of pollen plasma membrane ion channels in Pyrus pyrifolia

Abstract Low temperature (LT) generally inhibits pollen germination and pollen tube growth, but the cellular mechanism(s) of this response are still largely unknown. Here we report that LT induced alterations in pear (Pyrus pyrifolia) pollen in the actin cytoskeleton and increased cytosolic free calcium ([Ca2+]cyt). The increased [Ca2+]cyt came from extracellular Ca2+ influx and intracellular Ca2+ release. Extracellular Ca2+ influx occurred within a short time of sensing LT. Intracellular Ca2+ release was followed by, but independent of, the extracellular Ca2+ influx. Outward K+ current was also activated during LT in the mediation of increased [Ca2+]cyt. Moreover, the LT-induced Ca2+ conductance was regulated by cytoskeleton depolymerization. Our data provide evidence of a signal transduction pathway for the early stage of LT stress in pear pollen. Thus, LT induced depolymerization of the actin cytoskeleton, which induced the extracellular Ca2+ influx, and the increased [Ca2+]cyt promoted a K+ outward flux; these reactions finally inhibited pear pollen germination and tube growth.