Effect of sucrose on phase behavior of membranes in intact pollen of Typha latifolia L., as measured with fourier transform infrared spectroscopy

Abstract

In previous studies, we have shown that the temperature dependent vibrational frequency of the CH2 stretch in hydrocarbons in intact pollen grains can be recorded with Fourier transform infrared spectroscopy and used to measure phase transition temperatures (Tm) in these hydrocarbons. Circumstantial evidence was provided that the major contribution to the signal seen in these samples was from membrane phospholipids, and that sucrose in the dry pollen grains reduced Tm of those phospholipids. In the current study, we clarify why a major constituent of the pollen grains, neutral lipids contained in discrete lipid droplets, does not contribute significantly to the signal. Further, we have isolated membranes from the pollen and show that Tm in the isolated membranes rises from -6°C in the hydrated membranes to 58°C when the membranes are dried without the addition of sucrose. However, when the isolated membranes are dried in the presence of increasing amounts of sucrose, Tm fell steadily, reaching a minimal value of 31°C, a figure in good agreement with that seen in the intact pollen grains. The amount of sucrose required to depress Tm maximally in these membranes is also apparently in agreement with that found in the intact pollen, suggesting that sucrose depresses Tm in the pollen.