Aluminium Effects on Pollen Germination and Tube Growth of Chamelaucium uncinatum. A Comparison with Other Ca2+Antagonists

An interaction between aluminium (Al) and calcium (Ca) may bea cause of Al toxicity in plants. The pollen tube is a suitablesystem to test the interaction between Al and Ca since Ca ionsplay a pivotal role in pollen germination and tube growth. Weinvestigated how Al and other known blockers of Ca²⁺-permeablechannels (trivalent cations, ruthenium red, verapamil and nifedipine)influence pollen of an Australian native species Geraldton waxflower(Chamelaucium uncinatum). Pollen germination was inhibited bymicromolar concentrations of trivalent cations (La³⁺>Al³⁺>Gd³⁺)and ruthenium red, but it was relatively insensitive to a micromolarconcentration of verapamil. Exposure of the growing pollen tubesto micromolar concentrations of Al³⁺and La³⁺, and a millimolarconcentration of Ca²⁺chelator ethyleneglycol-bis(ß-aminoethylether)-N,N'-tetraacetic acid (EGTA) led to rapid tip bursting.In contrast, exposure to Gd³⁺, nifedipine, ruthenium red, verapamiland the organic trivalent cation tris (ethylenediamine)cobalt(TEC³⁺) caused only inhibition of pollen tube growth. The Al³⁺-relatedpollen tube bursting was reduced significantly by increasingeither solution pH from 4.5 to 6 or activity of Ca²⁺from 0.25to 5 m M. In contrast, La³⁺-related pollen tube bursting wasinsensitive to changes in Ca²⁺activity. The results are discussedin terms of Al interactions with cell wall Ca²⁺and the plasmamembrane Ca²⁺-permeable channels. Copyright 1999 Annals of BotanyCompany Aluminium toxicity, Ca²⁺-channel blockers, cell wall, Chamelaucium uncinatum, pollen germination, pollen tube growth.