The effects of moisture and temperature on the ageing kinetics of pollen: interpretation based on cytoplasmic mobility

This study shows that characterization of the molecular mobility in the cyt oplasm of pollen provides a new understanding of the effects of moisture an d temperature on ageing rates. Using EPR spectroscopy, we determined the ro tational motion of the polar spin probe, 3-carboxy-proxyl, in the cytoplasm of Typha latifolia pollen, under different temperature and moisture conten t conditions. Increasing the temperature resulted in faster rotational moti on, analogous to faster ageing rates. With decreasing moisture content, rot ational motion first decreased until a minimum was reached, after which rot ational motion slightly increased again. The moisture content at which this minimal rotational motion was observed increased with decreasing temperatu re, comparable to the pattern of ageing rate. A significant linear relation ship was found between ageing rates and rotational motion in the cytoplasm, suggesting that these parameters are causally linked. Upon melting of the intracellular glass, a twofold increase in activation energy of rotational motion and ageing rate was observed. In contrast, melting of the sucrose gl ass resulted in an increase in rotational motion of five orders of magnitud e. The difference in rotational motion upon melting glasses of pollen or su crose suggests that other molecules beside sugars play a role in intracellu lar glass formation in pollen.