Electrical Charge of Basidiospores of Hymenomycetes (Fungi) and Its Biological Significance
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ELECTRICAL CHARGE OF BASIDIOSPORES OF HYMENOMYCETES (FUNGI) AND ITS BIOLOGICAL SIGNIFICANCE EOSLAVASEENTE KANDEOSTE ELEKTRILAENG JA SELLE BIOLOOGILINE TÄHENDUS MARET SAAR A thesis for applying for the degree of DoCtor of Philosophy in Applied Biology 9lLWHNLULÀORVRRÀDGRNWRULNUDDGLWDRWOHPLVHNVUDNHQGXVELRORRJLDHULDODO 7DUWX Eesti Maaülikooli doktoritööd Doctoral Theses of the Estonian University of Life Sciences ELECTRICAL CHARGE OF BASIDIOSPORES OF HYMENOMYCETES (FUNGI) AND ITS BIOLOGICAL SIGNIFICANCE EOSLAVASEENTE KANDEOSTE ELEKTRILAENG JA SELLE BIOLOOGILINE TÄHENDUS MARET SAAR A thesis for applying for the degree of Doctor of Philosophy in Applied Biology Väitekiri fi losoofi adoktori kraadi taotlemiseks rakendusbioloogia erialal Tartu 2015 Institute of Agricultural and Environmental Sciences Estonian University of Life Sciences According to the verdict No 6-14/14-7 of July 9, 2015 the Doctoral Committee of Agricultural and Natural Sciences of the Estonian University of Life Sciences has accepted the thesis for the defence of the degree of Doctor of Philosophy in Applied Biology. Opponent: Prof. Roy Kennedy Institute of Science and the Environment, University of Worcester, UK Supervisors: D. Sc. Erast Parmasto Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences Prof. Tiiu Kull Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences Defence of the thesis: Estonian University of Life Sciences, room 2A1, Kreutzwaldi 5, Tartu, on September 17, 2015, at 11:15 a.m. The English language was edited by Roger Evans, and the Estonian by Piret Kruuspere. Publication of this thesis is supported by the Estonian University of Life Sciences and by the Doctoral School of Earth Sciences and Ecology created under the auspices of European Social Fund. © Maret Saar, 2015 ISSN 2382-7076 ISBN 978-9949-536-94-8 (trükis) ISBN 978-9949-536-95-5 (pdf) CONTENTS 1. LIST OF ORIGINAL PUBLICATIONS ............................................7 2. INTRODUCTION ...................................................................................8 2.1. Background ........................................................................................8 2.2. Review of the literature ..................................................................14 2.3. Research aims ..................................................................................21 3. MATERIALS AND METHODS .......................................................23 3.1. Sampling, samples, charge type, mean charge-to-mass quotient, mean charge ....................................................................23 3.2. Hymenial emission rate, territorial emission rate ......................26 3.3. Data analysis ....................................................................................27 3.4. Relaxation time, washout of spores .............................................29 4. RESULTS .................................................................................................30 4.1. Charge type of a spore sample ......................................................30 4.2. Spore charge-to-mass quotient and spore charge ......................32 4.3. Intraspecimen and intraspecifi c variabilities of spore charge- to-mass quotient ..............................................................................33 4.4. Hymenial emission rate of charged spores .................................33 4.5. Upper limit of the territorial emission rate of spores and their charges ..............................................................................................34 4.6. Charge relaxation time ...................................................................34 4.7. Role of charges in washout of spores ..........................................35 5. DISCUSSION ..........................................................................................37 5.1. Factors infl uencing the charge type of a spore population .....37 5.2. Mean absolute value of the spore charge-to-mass quotient and the spore charge, their variability .................................................38 5.3. Hymenial emission rate of charged spores, upper limit of the territorial emission rate of charged spores and charges ...........39 5.4. Relaxation time of spore charges in the atmosphere ................40 5.5. Role of charges in washout of spores from the atmosphere....40 6. CONCLUSIONS .....................................................................................42 7. REFERENCES ......................................................................................44 8. GLOSSARY .............................................................................................50 5 9. SUMMARY IN ESTONIAN ..............................................................51 10. ACKNOWLEDGEMENTS ...............................................................58 PUBLICATIONS .........................................................................................59 CURRICULUM VITAE...........................................................................113 6 1. LIST OF ORIGINAL PUBLICATIONS This thesis is based on the following publications, which are referred in the further text by their Roman numeral. I. Saar, Maret (2013). Investigation of the electrostatic charge of basidiospores of the Phellinus igniarius group. Central European Journal of Biology, 8 (5), 410 - 422. II. Saar, Maret & Salm, Jaan (2014). Emission rate of charged spores in basidiomycetous fungi and the relaxation time of their electric charges. Aerobiologia, 30 (1), 71 - 89. III. Saar, Maret & Parmasto, Erast (2014). Primary basidiospore charge and taxonomy of Agaricomycetes. Central European Journal of Biology, 9 (9), 874-887. Table 1. Authors’s contribution to each paper (%) IIIIII Concept 100 100 60 Design 100 90 100 Data collection 100 100 100 Data analyses 100 85 50 Manuscript preparation 100 80 80 7 2. INTRODUCTION 2.1. Background Fungi spread mostly by windborne spores (Ingold 1971). Wind-dispersed spores are violently or passively discharged into the atmosphere (Ingold 1971). When spores liberate from spore-bearing structures, both the violently ejected spores and the passively released spores can carry electric charges (Buller 1909, Gregory 1957, Swinbank et al. 1964, Garrett 1972, Webster et al. 1988, McCartney et al. 1982). Charges are present also on freshly discharged pollen grains of anemophilous plants (Bowker & Crenshaw 2003, 2007). The knowledge of primary charges of wind-dispersed pollen grains is precise. The investigation by Bowker & Crenshaw (2007) of seven species covered deciduous, coniferous and herbaceous plants. This showed that nearly all pollen grains are electrically charged. Each species had a bipolar distribution of pollen charges. Often the distribution of spore charges was roughly centered about zero. In some species, the distributions were tightly centered, while in others there was a wide spread of charges. Seldom the distributions were skewed toward the positive. The magnitude of charge (the average of the absolute value) carried by a typical pollen grain was 5,250 e (referred to as 0.84 fC in Bowker & Crenshaw 2007). Some pollen grains carried charges up to 250,000 e (40 fC). Little appears to be known about primary electric charges carried by fungal spores. Primary charges of passively released conidia were investigated in Blumeria graminis (DC.) Speer. McCartney et al. (1982) sought to determine whether barley mildew spores carry electric charges as large as the minimum charge (3 × 104 e per spore) that, by a theory, would be needed to infl uence spore deposition to a crop. Field measurements showed a bipolar distribution of spore charges and the charge magnitude smaller than 104 e per spore. The conclusion that conidia of Setosphaeria turcica (Luttr.) K.J. Leonard & Suggs carry electric charges when liberating from conidiophores was made by Leach from his experiments with sporulating maize leaf lesions (1976). This conclusion should be revised because Leach had omitted alternative interpretations of his experimental results (Aylor & Paw U 1980). Primary charges of 8 ascospores were examined only in the fungal component of lichens. To determine the existence and nature of charges on freshly ejected ascospores, Garrett (1972) performed tests in four lichen species, using fi ve different ascocarps for each. Spores of three species generally bear positive electric charges whereas spores of one species bear negative. Fifteen fungal species were involved in the works on the primary charges of violently ejected basidiospores (Buller 1909, Gregory 1957, Swinbank et al. 1964, Webster et al. 1988). However, these works provide fragmentary information insuffi cient for understanding the phenomenon. Therefore, the opinion of Gregory (1973) has remained valid up to now: little is known about the phenomenon of the electrostatic charges on freshly liberated basidiospores. These works show us that electrically charged spores are emitted by various ballistospore-bearing structures: fruitbodies with basidia entirely exposed to the air, fruitbodies exposing only outgrowths of basidia, and single-celled fungi producing aerial ballistoconidia. Basidiomata of the Agaricomycetes (Buller 1909, Gregory 1957, Swinbank et al. 1964, Webster et al. 1988) and Tremellomycetes (Webster et al. 1988), and yeast-like anamorphic stages of the Tremellomycetes (Webster et al. 1988) were involved in these works. Few species, which were studied and in which the primary charges were