Section 12 — Plasmatic Inheritance 



medium in which killer cells have been grown. 

 The percentage killing depends on the period of 

 incubation of both (1) the killer cells prior to 

 filtration, and (2) the sensitive cells following 

 filtration. So far, up to 39 per cent of the sensitive 

 cells have been killed when incubated for 3 ru- 

 in a filtrate derived from a 48 hr growth of killer 

 cells. A filtrate obtained from homogenized 

 killer cells resuspended in fresh medium also 

 shows killer activity. 



The particular nature of the killing factor is 

 suggested by three types of observation: (1) the 

 retention of activity after dyalasis of the cell-free 

 filtrate for 24 hr in distilled water, (2) the con- 

 centration of activity following its ultracentrifu- 

 gation at 40,000 rev/min for 1 hr, and (3) the 

 appearance of particles approx. 350A in size 

 when a concentrated filtrate is examined under 

 the electron microscope. 



Killer cells have been recovered from an 

 18 hr growth of sensitive cells (nk genotype) in 

 cell-free killer medium. They are presumed to 

 arise by infection since, by appropriate crosses, 

 they have been shown to possess the same nuclear 

 genotype (nk) as the original sensitives. Killer 

 or neutral cells have not yet been recovered 

 following incubation of sensitive cells in cell-free 

 neutral medium. 



12.8. Male Sterility in Castanea. Richard A. Jaynes 

 (New Haven, U.S.A.). 



Male sterility was observed in Castanea sativa 

 Mill., C. mollissima Bl., and several Castanea 

 hybrids. In most cases the event(s) leading to 

 sterility occurred before meiosis. The arrange- 

 ment and early growth of individual flowers on 

 catkins was normal; however, staminate pri- 

 mordia failed to develop anthers. The number and 

 fertility of pistillate flowers of the male sterile 

 trees compared to male fertile trees was not 

 diminished. Sterility observed in these trees may 

 be genie, chromosomal, or the result of a gene- 

 cytoplasm interaction. Somatic chromosome 

 counts of one male sterile tree and progeny 

 (germinating nuts) of six other male sterile trees 

 revealed normal complements, 2«=24, in all but 

 one tree. Neither abnormal chromosome number 

 nor meiotic irregularities appear to be the 

 predominant cause of male sterility among the 

 trees examined. Data obtained indicate that 

 male sterility may be cytoplasmically controlled 

 in a few trees. Final proof will depend on 

 completing enough successive backcrosses to 

 accomplish genome substitution in male steriles 

 by their male fertile parent. 



12.9. Genic-Cytoplasmic Interactions in Peanuts 

 (Arachis hypogaea L.). A. Ashri and E. Gol- 

 din (Rehovot, Israel). 



There are two geotropically distinct growth 

 habits in peanuts — runner (spreading) and 

 bunch (erect). Hitherto their control was 

 attributed to duplicate genes. Reciprocal crosses 

 were made between Virginia Beit-Dagan 4(V.4) 

 and Georgia 2, N.C.2, Dixie Giant, Line 123 

 and Red Virginia, all bunch. In all crosses, when 

 V.4 was female parent, the Fi hybrids were 

 runners. Their F2 progenies segregated (pooled 

 data) 3178 runner: 2511 bunch (fit to 9:7 ratio 

 P=0.70-0.50). When the other varieties were 

 female parents and V.4 male, the Fi plants were 

 bunch. Their F2 progenies segregated (pooled 

 data) 433 runners: 672 bunch (fit to 6 : 10 ratio 

 F = 0.30-0.20). The backcrosses of [(runner 

 Fi hybrids) • (their male parent)] gave 10 

 runners: 15 bunch. Reciprocal crosses between 

 the last mentioned five varieties and also with 

 Virginia Improved (bunch) produced only bunch 

 Fi and F2 plants. Conclusions are: I. There are 

 two types of cytoplasm — one found only in 

 V.4 and another found in all the other tested 

 varieties; II. There are two genes, to be termed 

 Hbi and Hb2, which interact differently with each 

 other in each cytoplasm and with each cytoplasm. 

 It appears thatV.4 isHbiHbihb 2 hb2while all others 

 are hbihbiHb2Hb 2 . In V.4 cytoplasm Hbi-Hb2 

 produce runners, other genotypes give bunch. In 

 the cytoplasm of the others Hbi-Hb 2 andhbihib- 

 Hb 2 Hb 2 produce bunch, other genotypes give 

 runners. Implications of this genic-cytoplasmic 

 interaction and evolutionary aspects will be 

 discussed. 



12.10. Cytoplasmic Effects in Nicotiana. D. R. Came- 

 ron (Berkeley, U.S.A.). 



The observation that there were differences in 

 male-sterility in reciprocal species hybrids and 

 failure to obtain certain hybrids in one direction 

 among species of section Tomentosae, led to a 

 study of various associations of genomes with 

 plasmones of related and unrelated species. 

 Within the Tomentosae, morphological effects 

 ranged from no detectable deviations from nor- 

 mal to those in which flowers had no visible 

 corolla and stamens were absent or vestigial. 

 Some results indicated that failure to obtain 

 certain hybrids was not attributable to the 

 cytoplasm of the ovule parent. When TV. tabacum 

 genomes were incorporated in cytoplasms of 

 several species, the flower morphology was 

 altered depending on the species involved. 



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