Abortion Of Microsporocytes Is Possibly Associated With Autophagy In The Male Sterile Line Of Allium Cepa

Autophagy(AP)is a self-degradation process occurring in normal development,senescence or under nutrition,biotic and abiotic stress in eukaryocytes,and plays a pivotal role in keeping nutrient recycle and intracellular homeostasis as well as resisting the invasion of pathogens.AP can be divided into macroautophagy,microautophagy,megaautophagy and chaperone-mediated Autophagy.Rrevious researches on AP were mainly concentrated on yeast,human,and other mammals.Reports in plant are relatively few and most of them are limited in the tissues or cells stressed by C or N deficient.Little work has done for normal development of organs,tissues or cells.Furthermore,these reports were mostly based on somatic cells,little finding is reported in generative cells.A few years ago our research group found large numbers of double membrane-bound inclusions,multiple membrane-bound inclusions and multivesicular body in pollen mother cells(PMCs)of a Brassica napus male sterility(MS)line.According to above results,we suspect that the appearance of these autophagosomes may be in connection with abortion of anther.In order to demonstrate whether this phenomenon is universal,the present research took a MS line of Allium cepa as study object.The results follow as:1.Anatomical lens observation showed that anthers of MF line were mellow and full in size,had smooth surfaces and bright colour.However,the anthers of the MS line were abnormal and wizened,with uneven surfaces and lustre was gray.2.Semi-thin section observation showed that in the MS line,reproductive cells stopped growing at PMCs stage,the structure of cells was abnormal,cell walls(CWs)were thinner and projection or depression in some parts compared with MF line,some cells were degraded and no tetrad or microspore showed up.3.Ultrathin section showed the same results compared with semi-thin section.The secondary walls and callose walls were blocked in PMCs MS line which result in thinner CWs,also the surface of cell dramatically protrude or dent,and adjacent cells were chimeric to each other.In addition,plenty of single membrane-bound inclusions(SMBI)and double membrane-bound inclusions(DMBI)appeared in cytoplasm,some of them contained ribosome,plastid,vesicle,parts of chromatin etc.intracellular substance.Multivesicular body was also found around plasmalemma and convex or concave area of CWs,some of them could fuse mutually,later inclusions in the vesicular dropped off and finally disappear;Nucleus was disintegrated which resulting in a large number of electron density floccule,and apoptosis body like calathiform structures were also found;Adjacent cells were connected by many wide(0.3-o.6?m)channels and you can see parts of cytoplasm and chromatin came into another PMC,namely plasmogamy.Above results were dramaticlly different from MF line.4.Using RT-PCR technology,we tested the transcriptional level of Atg8 gene in root,leaf,and the anthers of MF,MS line.Results showed that Atg8 gene was expressed in different degrees.All the above results showed that autophagy do take an active part in abortion of anther in plant or programmed cell death,also demonstrated that this phenomenon may have a certain generality.