The effect of calcium on auxin depletion-induced tomato (<i>Lycopersicon esculentum</i> Mill.) pedicel abscission

Abstract

Indole-3-acetic acid (IAA) and calcium are the most important factors that instigate plant organ abscission. This study aimed to elucidate the mechanisms that underlie the effects of IAA and calcium on delayed abscission in tomato. The results showed a clear trend towards reduced abscission rates with increased concentrations of IAA, and the applications on pedicel proximal or distal side also resulted in a different abscission. IAA combined with calcium significantly improved inhibition in contrast to IAA only, while IAA combined with magnesium exhibited little increased inhibition. 1-NNaphthylphthalamic acid (NPA), a polar auxin transport inhibitor, accelerated the abscission. IAA transported basipetally through an assay with 4 mm long pedicel sections indicated that the average transport intensity of [³H]-IAA applied to the distal pedicel end was 65 Bq h^–1 and the average velocity was 5.29 mm h^-1. When the proximal side was incubated in [³H]-IAA, its average transport intensity reduced to 19.53 Bq h^–1 and the average velocity was only 1.92 mm h^-1. Calcium treatment enhanced IAA transportation, as shown by significantly enhancing the transport intensity, but it had no effect on velocity.

Keywords: Indole-3-acetic acid (IAA), calcium, abscission, tomato