Suppression of S-adenosylmethionine Decarboxylase Activity is a Major Cause for High-Temperature Inhibition of Pollen Germination and Tube Growth in Tomato (Lycopersicon esculentum Mill.)

Possible involvement of impaired polyamine biosynthesis in the poor performance of tomato pollen (Lycopersicon esculentum Mill.) at high temperatures was investigated. Incubation of pollen at 38°C suppressed the increase of S-adenosylmethionine decarboxylase (SAMDC) activity in germinating pollen with little influence on arginine decarboxylase activity. Consequently, spermidine and spermine content in the pollen did not increase at 38°C, while putrescine content increased at both 25°C and 38°C. High-temperature inhibition of pollen germination was alleviated by the addition of spermidine or spermine but not of putrescine to the germination medium. Cycloheximide inhibited SAMDC activity in parallel with pollen germination at 25°C, whereas actinomycin D had no effect on either of them, indicating that enhanced SAMDC activity is associated with de novo protein synthesis. Incubation of crude enzyme extracts at 40°C for 1 h did not affect SAMDC. In addition, high temperatures did not enhance protease activity in germinating pollen. These results indicate that low activity of SAMDC, probably due to impaired protein synthesis or functional enzyme formation, is a major cause for the poor performance of tomato pollen at high temperatures.