CHANGES IN POTASSIUM-ION CONCENTRATIONS DURING POLLEN DEHYDRATION AND GERMINATION IN RELATION TO PROTEIN-SYNTHESIS

In the dehydrated T. paludosa pollen grain at the time it is shed from anther most of the ribosomes are present as monosomes. The shift from monosomes to polysomes occurs very rapidly during germination. The K+-content of the pollen grains was analyzed by atomic absorption spectrometry. From the volume of pollen grains measured at different levels of hydration, the internal K+-concentration was calculated. The presence of single ribosomes in the dehydrated grain at anthesis and the initiation of protein synthesis in the germinating grain can be explained on the basis of the K+-concentration. During dehydration the K+-levels and possibly those of other factors become inhibitory to the initiation of protein synthesis and hence the presence of primarily single ribosomes. With hydration of the grain during germination, the K+-ions reach a concentration that is optimal for reinitiation of protein synthesis. During the initial periods of hydration on the stigma when the K+-concentration is high, certain mRNA could be preferentially translated. Changes in ion concentration might also explain similar patterns of protein synthesis in structures such as seeds and spores in which dehydration and hydration occur.