The early increase of S-adenosylmethionine decarboxylase activity is essential for the normal germination and tube growth in tomato ( Lycopersicon esculentum Mill.) pollen

Abstract

The effect of polyamine biosynthesis inhibitors on pollen germination and tube growth and putrescine (Put), spermidine (Spd) and spermine (Spm) levels in germinating tomato ( Lycopersicon esculentum Mill.) pollen was investigated. Pollen germination was initiated 20 min after incubation at 25 °C and completed within 2 h. The activity of arginine decarboxylase (ADC), an enzyme catalyzing Put synthesis, exhibited a marked increase during the initial 2 h and remained high thereafter. The activity of S-adenosylmethionine decarboxylase (SAMDC), an essential enzyme in the synthesis of Spd and Spm, increased transiently during the first hour of incubation. Consequently, the germinating pollen showed elevated ratios of Spd+Spm to Put during the first hour in all of the free, conjugated and bound forms. The addition to the germination medium of either methylglyoxal-bis(guanylhydrazone) (MGBG) or cyclohexylamine, inhibitors of SAMDC and spermidine synthase, respectively, caused a marked decrease of Spd and Spm contents, together with ratios of Spd+Spm to Put, and resulted in inhibition of pollen germination and tube growth. Simultaneous addition of Spd or Spm reversed the adverse effect of MGBG. However, Put failed to reverse the inhibitory effect of d-arginine, a competitive inhibitor of ADC. MGBG treatment 2 h after incubation was still inhibitory to tube growth, which was partially reversed by Spd. The results suggest that the increased activity of SAMDC and the resultant elevation of Spd and Spm contents during the early pollen germination phase are essential for the occurrence of normal germination and tube growth in tomato pollen.