? NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY o ? ? L. CORNELL UNIVERSITY AGRICULTURAL EXPERIMENT STATION ITHACA. N. Y. 3 3 DEPARTMENT OF PLANT BREEDING f .- June 27, 1937. Dear Curt: I am returning the paper which you sent to me. since ? you stated you were leaving July I,1 h,-ve had to hurry to get it back to you in time ayid have not given it the amount of 2 5 thought I should like to h;.ve. licjwever, I have some comments. which i shc;?,l.d like to make. ?- 3 j The facts abo;:t the 3x - wx ease of dimorphism of the --Lb pollen ma its staining reaction is common knowledge, to maize geneticists, i.e., when the reaction con be noted. ,' From our experience the starch begins to ai:.jecr shortly after the firat division of the micros-pore (about 5 days after meiosis) but &E staining reaction with iodine is not good until just before the pollen is ready to shed. The wx gene is not s:r:m case since wx is located close to the spindle fiber at-kchment region on the short arm of chromosome 9 and probably is segregated in the first meiotic mitosis. *The tetrads in big--er plants are of two kinds with regard to division of the cytoijlasm. in some (monocots mainly) the first &iQbsis is followed by cell wall formation. In other plats (dicots mainly) the -MO meiotic mitoses t&e place in a common cytoplasIp. `(la11 formation does not occur until after the two nuclear divisions are completed. Datura has this form of tetrad ;,jroduction while maize has the former type. The case Niss Clark is working on, which she has described to you, is quite relevant. At the end of the first me?8tic mitosis 1G chromosones (full set) are in each cell although not all in one nucleus. In the second divisio:i these nuclei form one to several spindles all in one cytoplasmic mass of each dyad. 17all formation takes place~FZucing four or more cells depending u'on the orientation of the spindles in the second division dgads. In each cell the:fae are from one to several nuclei with one or more chrcmosomes in ezch* P,b 0-u t five days elapse between the end of the meio-tic divisions and the first division in the microspore in which growth and differentiation of the spores take pl ce. ;ihat takes pl ce during this -,,eriod is a direct expression of the chromsome content 02 the nuclei. The s?ores with deficient chx-;?omosc;r.le complements do not develo,; normally (cytoplasm degenerates or nuclei ap,:.ear degenerate) although they came from cytoplasm exposed during the sec;):ld mei;jtic mitoses to the full ,-enonic c omplenent on the basis o:- release of genes z.t this period. Zhe s L.! 0 1' e s T,-rith a full genonic CGX: lement , ~~,.'i~;l,ou.~:h in sepc,r:-:.te nuclei, dovelo~, norM.lly. In this cass, 3.0 er^:"oc-I; of the ChrOl:lO SOL!2 co;y):ler:ie.l.t i_:: the rlrestj.-.g nucleus:: is i.:i:otli~.tely e;rl, ;i es s ed. . 12 ;;e:l.e 3 -'.F,::.- c b c 21; rele:isecJ. <.:yi; :j:.`L:'. 17 .- ' o 1." i,,* .^ -- during division all the spores, regardless of their cord~ositiO::~9, s;houM ;?rogess Fr$~~:lly Tntil after the first division in "who s;)ore, unles~~ tlic t:e'--es hLI '.I 6-78 been une qu.~,lly distributed in the cyto3l~,sm. ._ i 9 r:..*,J There are 0th~~ cases in rx2ize th::t c3z Se used, lie h: .ve an interch,me between chromosome G (with the nucleolus or;;sli;:er) 2nd chrom mme 5. In the heteroz ygous following figure: condition it produces the Crossing; over occurs in tile marked region ix from 50 - '75;; of the sporocytes (clepending upon environmental conditions). As a result of such crossing- over, each telophase I nucleus has a full ~enomic comislement (when suc.h crossing-over occurs, segregation of homologous s-indle fiber chro8.0some constitutions regions occu::s alG?ays-at`CI). after such crossing-over are: At TI, the `7 r I - ; ,--a _c.c_x. - -. -*" a .-,* o ? ? ? ?? A Pull genomic corn. lement is present in each nucleus, althol-gh not balanced. If genes are release& during nuclear Siivisions, deficient and nDrmal,,ohromosome oarrying s>ores should develop at similar rztes.. 'his, however, does not 0ccuT. the 12~11 genomic complement develoii ;;lvch faster. Spores with Spores with m deficient chr nosome cor.:;,leneil~~develop much slower. as I hc!ve nGt figure& the r;-,,es ty'e of spore in 'this of differential dxve1o~)men-b of each particulz i;ltercha,_l~e,vr~leile crossin&-over has been m<:asu:,ea,but it is a common practice to look for these types in A&DE' m +X&ZQZEXXXZ~ athers of differnt ages. The first sp-jres to go through divisions are normal chro osji:le-carrying spores, the l.st to go through the first division in the s;:ore are the deficient c.hrontiso::;e carrying s ores. I can look more carefully for timing and let you know. I think the s>ore development cases in maize coul! be used gxi.te effectively if the right set-ups were chosen. I ha-v-e several cases involving inversions and deficiencies whdch could be easily used. I will briefly outtie a deficiency case which can be done easily. ;ie hate plants a deficiency in chromosome 5 which is covered by a ring chrcmas%rle. l?laxtts heterozygous for this deficiency and ring have one normal chromosome 5, one deficient chr,ncsome 5 and a ring ehroxosome. The deficient and the n...rmal chromosome 5 pair ald segregate noxlally at meiosis. 3 The ring chromosome divides at I and gets iizto practically every TI nucleus. In II, the ring chrom!Jso;ie does not hivide again but wonders to one or the other pole, nucleus and sorletines not. so!:etimes being included in the 1~11 the necessary genes a:>e present in the TI nuclei but the TII nuclei are h$@erploid, hygoBloid anr7 normal. The hypoploid -pollen is yracticallg empty of starch. I may be able to find a dimorphism of the spores before the first division anit relate it to the deficient an&'-FiXI-genomBn carrying complements (the hyp!:r&oid complement is klown to h:Lve practically the same divisii;n rate as the normal and need not be a factor). Since at metaphaae II, the full genoaic oompli-ment . resent in all cells, the:L,e should be no s.:-ore dimorphism relateA io" full an& deficient genomio carriers on the basis of release of genes at nuclear divisions. If such is found, the constitution of the Vesting nucleus" is the det.rmininc factor in differentia- tion. I have ssent some time bescribing the possibilities of spores in maize since I think they ctul be decisive cases. 'They oa;n give better evidence than the wx gene. The case of enaosperm constitution in Jane's paper is not p8rticularly g00a in qy estimation since he has not proven the number of nuclei~*:in his enciosperm ctells. (Ijstronglg suspect), aone of his large cells may be mu&tinucleate Is it obvious sister cells3 in Ustilago that the spores 1,2 and 3,4 are In some forms the divisions -?,re not strictly linear but the spindles are &laced. as follows: ' ? 01 In this case, adjxent s200.es are not sister spores. The case of rascher appears to me to be the strongest but I wish it were better analyscd from a genetic poi t of view. It seems to me that the geneticists have assumed that the genie activity of the nucleus takes place from the Vesting nucleus4 without, as you point out, the necessary evidence. I d0nt think our apparent evidence at the resent time is very decisive. The geneticists have considered the Vesting -nucleusTr as the actively functioning organ bar so long, based on differentiation, dedifferentiation ancl wound responses (in plants) that they hxve not been alert to the evidence when it did ap,,ear axa have not pointed it out as such but have taken it for granted, You don-t mention the paper of 3erril and Ruskins in the American Naturalist 7O.(May-June) 1936, entitled "The Resting nucleus? You may have/ seen it ana found it not to your point, 4 About publishing the pap:-:r - d short parer pointing out the need of decisive evideace is not out of order. A question for a title is quite appropriate under the circumstances. There should be some response to such a question. in the Am. Nat.? iTould you publish It is an a:,,ropriate glace for such an article. I was gleased to learn you Were to make a trip home. I hope it will be successful. Uiss Clark tells me you are expecting another Fl - or should'nt I know? I111 try to get up and see you after your return - sometime tow,ard the end of August. Last summer was so difficult I had no tize off all summer and was even three weeks late getting to my neIv job. Xy best to you and Zvelyn. Sincerely,