Synthesis of protein and RNA in pollen tubes stimulated with 2-thiouracil

Protein synthesis in pollen tubes of Nicotiana alata Link et Otto estimated by the incorporation of leucine- 14 C is linear over six hours of artificial cultivation after a short lag phase. 2-Thiouracil and other growth-stimulating antimetabolites of natural pyrimidines and purines, such as 6-azauracil, 5-nitrouracil, 8-azaguanine and 8-azaadenine, stimulate the incorporation of leucine- 14 C into protein. The intensity of stimulation of protein synthesis is associated with the intensity of growth stimulation by antimetabolite. Synthesis of RNA is inhibited by 2-thiouracil (according to the incorporation of uracil- 14 C, orotic acid- 14 C and 32 PO 3− 4 ). Chloramphenicol (25 and 250 ppm) decreases during a one-hour treatment of pollen tubes the incorporation of leucine- 14 C by 12 and 24%, respectively. The same inhibition is found in pollen tubes stimulated with 2-thiouracil. Pollen tubes incorporated 2-thiouracil into RNA. Stimulation of growth by 2-thiouracil can be reversed with uracil or uridylic acid. These findings are related to the present views on protein synthesis and the mechanism of the chloramphenicol effect especially with respect to the possible explanation of the stimulation of protein synthesis during a simultaneous inhibition of RNA formation. Physiological resistance of pollen tubes toward RNA antimetabolites, the relatively low sensitivity toward chloramphenicol, the contradictory change in RNA and protein synthesis due to 2-thiouracil and, further, resistance toward actinomycin D ( Tupý, Süss 1965) point to the stability of the complex of messenger RNA with ribosomes in pollen tubes.