Initial Moisture Content and Temperature of Imbibition Determine Extent of Imbibitional Injury in Pollen

Abstract

Summary Imbibitional chilling damage was frequently observed in air-dry pollen from different plant species, although partial resistance did occur. Damage included excessive leakage of endogenous soluble components into the in vitro medium and loss of vitality. Prehydration in humid air largely prevented the leakage of K + and NAD + . Similarly, imbibition of air-dry pollen in media at 29°C prevented most of the leakage and conserved germinative capacity. However, further reduction of pollen moisture levels increasingly induced imbibitional damage, even at 29°C. A strong negative correlation was established between leakage of NAD+ and fluorescence score in tests with the vital stain, fluorescein diacetate. Since initial pollen moisture content and temperature of imbibition evoke similar patterns of reduced vitality and membrane leakage, we conclude that both imbibitional damage and cold hydration-induced injury are not essentially different. On the basis of literature data on phase behaviour of pure phospholipids in relation to water content, we suggest that the injury in pollen originates from the presence of gel phase lipid during the uptake of liquid medium. No correlation was found between sensitivity to imbibitional stress in several pollen species and composition of fatty acids in the phospholipids.