Variation Of Pollen Morphology Under Different Observing Methods

Pollen is the male gametophyte of seed plant.The study of pollen morphology is the basic element of palynology.At present,optical and electron microscopes are the main instruments for observing pollen morphology.However,traditional observation methods need the pollens to be processed with various reagents,which will distort the recorded pollen morphology.Such circumstance highlights the academic value of observation and recording of original pollen shapes.With the innovation of microscope technology,cryo-SEM can observe the samples under ultra-low temperature treatment.This kind of treatment has minimal morphological variation effect on biological samples with high moisture.In this study,cryo-SEM was used as the main method to record the original shapes of various pollens.Combining historical observation data,the morphological variation of pollen under different observation methods were investigated.A total of 99 species of angiosperms were observed under cryo-SEM,and supplemented the experiments with alcohol treatment,water absorption,drying and rehydration to discuss the morphological variation of pollens.The results are as follows:1.Pollens treated with different methods will produce different degrees of morphological variation.This variation is affected by experimental conditions and also related to the type of aperture.Based on the data from cryo-SEM,it was found that under the acetolysis method,air-dried method,and fresh pollen method,the morphological variation of pollens mostly showed a decrease in polar axis and P/E value.The above three methods and alcohol treatment have basically the same effect on the variation trend of the same kind of pollen,but with significant difference in the amplitude of variation.Simultaneously,the amplitude of morphological variation is affected by the moisture of pollens.From the respect of aperture type,the most stable pollens are those of panporate(inaperturate).2.From the point of systematic taxonomy,given the variation of pollen morphology in cryo-SEM as reference scale,pollens of Rosids is usually reduced by polar and equatorial axis,pollens of Asterids usually decrease in polar axis and increase in equatorial axis,and pollens of Magnoliids and Monocots usually increases in polar axis and decreases in equatorial axis.3.The pollen morphology recorded in the traditional literature deviated significantly from its original shape,which may affect the value in taxonomy.The natural pollen morphology observed under cryo-SEM was used to rebuild the dendrogram of 8 species of Yulania.It was found to be inconsistent with the previous clustering results derived from air-dried method(SEM),but supported the recent concept of Xia(2007)that these species should be treated as members of sect.Yulania and sect.Tulipastrum.This case confirmed that the original shape of pollens has great value in taxonomic researches.4.Different pollen observation methods have their advantages and disadvantages.We should give full play to the respective advantages of related methods in palynology.One or more optimal methods should be selected according to different research objects,purposes,and conditions for extracting valuable information from pollen morphology.