Aluminum toxicity-induced pollen tube growth inhibition in apple (Malus domestica) is mediated by interrupting calcium dynamics and modification of cell wall components

Abstract Aluminum (Al) is known the most abundant metal in the Earth’s crust which is a major problem limiting crop production and yield throughout the world. Al could inhibit pollen tube elongation, however the mechanism is largely unknown. The aim of this study was to investigate the influence of Al toxicity on Malus domestica pollen tube growth and possible cytological mechanism. The results showed that Al inhibited pollen germination and tube growth in a concentration dependent manner. An non-invasive ion-selective electrode technique together with fluorescent labeling indicated that Al toxicity decreased pollen tube apex calcium influx and disrupted [Ca2+]c gradient. Al toxicity also altered actin filament orientation. Results from immuno-localization and fluorescence labeling indicated that Al toxicity affected the accumulation and distribution of callose, acid pectins, esterified pectins and arabinogalactan proteins in pollen tubes, which were supported by Fourier-transform infrared analysis. In a word, Al induced a series of the cellular toxic changes concerning calcium influx, [Ca2+]c gradient, actin and cell wall components. Based on the information provided in this article, it is concluded that Al toxicity inhibits apical growth of pollen tubes by changing calcium influx and [Ca2+]c and cell wall components.