DISTRIBUTION OF CHROMOSOMES IN POLLEN GRAINS IN CERTAIN TRIPLOID AND HYPERTRIPLOID NARCISSUS PLANTS'

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1 DISTRIBUTION OF CHROMOSOMES IN POLLEN GRAINS IN CERTAIN TRIPLOID AND HYPERTRIPLOID NARCISSUS PLANTS' Seijin NAGAO Botanical Institute, Department of Science, Kyoto Imp. Univ. (Rec. Aug. 27, 1934) It has been ascertained in many plants which are in the condition of a triploid or of species hybrids that univalent or extra chromosomes are assorted at random in the reduction division, it giving rise to variable numbers of chromosomes in gamates and, consequently, in the zygotes which are products of union of these gametes. In pentaploid Tnticum hybrids, for example, it has been shown that both miscrospores and megaspores may have any chromosome number from 14 to 21, and that the F2 plants may carry any number of chromosomes from 28 to 42. In these cases, while all the expected numbers are observed, the frequencies in which these numbers occur are found to deviate from expected frequencies owing to the competition exhibited between gametes with different chromosome numbers and to the loss of certain univalent chromosomes in the course of micro- or megasporogenesis (Watkins, 1924, 1930; Kihara, 1924; Kihara, Wakakuwa, Yamamoto, 1933, etc.). In the present paper some results obtained on the frequencies of occurrence of various chromosome numbers in the pollen grains in some tri- and hypertriploid Narcissus species are reported. Chromosome numbers were counted in metaphase in polar view of the first nuclear division in fresh pollen grains mounted with aceto-carmine solution. CHROMOSOME NUMBERS IN POLLEN GRAINS Narcissus poeticus (triploid: 3x= 21) Only pollen grains which were normal in appearance and full in contents were observed, though many shrivelled, empty grains were also found as is usually the case in triploid plants. The results obtained are shown in Table i. From the results of the previous investigation (Nagao, 1929) it may be expected that in this species the chromosome number in pollen grains varies from 7 to 14, the frequency of occurrence being equal in both extreme 1) The results of this investigation were published with figures in Japanese in " Shokubutsu oyobi Dobutsu " (Botany and Zoology) 2, No. 6, 1934.

2 2 THE JAPANESE JOURNAL OF GENETICS, VOL. XI, NO. 1, APRIL, 1935 Table I Narcissus ftoeticus cases of 7 and 14 chromosomes as inferable from the random assortment of chromosomes in segregation, but it turned out, as shown in Table i, that the observed frequencies of the pollen grains with 7, 8 and 9 chromosomes are considerably higher, being 4.629, 17.54% and 26.77% respectively, and those of pollen grains with greater numbers lower than those expected. Narcissus tazetta "Yellow Prince" (triploid: 3x= 30) Narcissus tazetta " B 31 " (hypertriploid: 2n = 3 i ) The former variety is an autotriploid plant with 30 chromosomes in the somatic cells and the latter is a hypertriploid having 31 chromosomes as the diploid number, i i chromosomes out of the 31 being those which behave as univalents and the remaining 20 being those forming 10 bivalent chromosomes in the reduction division (Nagao, 1930, 1933). The results obtained in these two varieties are given in Tables 2 and 3. Table 2 Narcissus tazetta "Yellow Prince" The results of observations show that in all these three plants almost all the expected numbers of chromosomes are observed in pollen grains', but that the frequency curves of these numbers are characterized as follows : the frequencies in the classes of smaller chromosome numbers are considerably higher, and those in the classes of larger numbers are correspondingly lower than those expected ; the curves are, therefore, flat as compared with the latter. 1) In "Yellow Prince" and "B31 ", probably owing to the smallness of the number of pollen grains observed, the two largest numbers were not found in each case (see Tables 2 and 3).

3 Nagao-Distribution of Chromosomes in Narcissus 3 Table 3 Narcissus tazetta " 31 DISCUSSION The number of chromosomes distributed in gametic cells may be determined directly by counting them in the course of gametic development as in the present investigation, by which method Belling (1924), Belling and Blakeslee (1924) and Thompson and Cameron (1932) have also determined statistically the distribution of chromosome numbers in pollen grains in triploid Hyacinthus, tetraploid Datura and pentaploid Triticum hybrid respectively. By this method, however, it can not be determined whether the gametes with different chromosome numbers are equally functionable or not (cf. Blakeslee and Buchholz, 1922, 1932). The method of counting the chromosomes in the back cross may also be used, but in case this method is employed some corrections in respect to the fertility of the Fl-plant and the germination power of seeds produced by back cross are needed (cf. Kihara, Wakakuwa, Yamamoto, 1933, Kihara and Nagao, 1933) In his studies of pentaploid Triticaiin bybrids Kihara has inferred from the results he obtained that the ratio between the frequencies of occurrence of 7 and 14 chromosome gametes is possibly 7 : I. It would be interesting to note that is the case of Narcissus poeticus, too, the ratio between the 7 and 14 chromosome gametes is nearly 7:I. I frequently observed one or more small nuclei which lie in the cytoplasm in pollen grains. These small nuclei may be considered as derived from the chromosome or chromosomes which are extruded into the cytoplasm during the process of meiotic division. The number of these small nuclei observed in Narcissus poeticus are given in Table 4. The elimination or loss of extra chromosomes has been thought to be a cause of the difference found between the expected and the observed frequency (Lesley, 1928; Sax, 1928; Watkins, 1930; McClintock and Hill, 1931; Kihara, Wakakuwa, Yamamoto, 1933). Kihara has shown by counting the loss of about 20% univalent chromosomes in pentaploid Triticum hybrids (Kihara, Yamamoto, Hosono, 1931). McClintock and Hill (193 I )

4 4 THE JAPANESE JOURNAL OF GENETICS, VOL. XI, NO. 1, APRIL, 1935 who explained genetic results they obtained in Zea Mays by the assumption of the loss or elimination of extra chromosomes have estimated the loss to be 30% in amount on the ground of the genetic results. On the basis of the results given in Table 4, the amount of loss, 11.5 /, of extra chromosomes in Narcissus poeticus can be obtained by the following formula : imination of chromosomes= 1 Number of small nuclei El X ioo X No. of pollen grains observed x No. of extra chromosomes If the segregation of 21 chromosomes in the reduction division takes place at random but without loss of chromosomes, the frequencies of occurrence of gametes with different numbers of chromosomes from 7 to 14 may be represented by the formula (o.5 +o.5)7, but if there is such a moderate amount of loss as 11.5 %, the formula would be such, for instance, as (o )7 or ( )7 (Watkins, '930; Kihara, 1932; Kihara, Wakakuwa, Yamamoto, 1933). In Table 5, the observed frequencies in Narcissus poeticus are compared with those which can be obtained from the (o )7 It would be clear from this table that the deviation of the result from expectation found in Narcissus poeticus is due to a moderate amount of loss, I 1.5 %, of extra chromosomes in the microsporogenesis. LITERATURE BILLING, J The distribution of chromosomes in the pollen grains of a triploid hyacinth. Amer. Nat. 53. BLLLING, J. and BLAKESLTE, A. F The distribution of chromosomes in tetraploid Daturas. Amer. Nat. 53.

5 Nagao-Distribution of Chromosomes in Narcissus 5 BuCHHOLZ, J. T, and BLAKESLEE, A. F Studies of the pollen tubes and abortive ovules of the globe mutant of Datura. Science Pollen tube growth in primary and secondary 2n+ I Daturaṣ Amer. Jour. Bot.19. KIHARA, H Cytologische and genetische Studien bei wichtigen Getreidearten mit besonderer Riicksicht auf das Verhalten der Chromosomen and die Sterilitat in den Bastarden. Mem. Coll. Sci. Kyoto Imp. Univ. B Weitre Untersuchungen iiber die pentaploiden Triticzinl-Bastarde. II. Jap. Jour. Bot. 6. KIHARA, H., WAKAKUWA, Sit. and YAMAMOTO, Y Weitere Untersuchungcn iiber die pentaploiden Triticum-Bastarde. III. Jap. Jour. Bot. 6. KIHARA, H. and NAGAO, S Cytogenetics of cereals. (Japanese). Tokyo. KIHARA, H., YAMAMOTO, Y. and HOSONO, S Studies on chromosome numbers of plants. (Japanese). Tokyo. LESLEY, J. W A cytological and genetical study of progenies of triploid tomatoes. Genet. 13. MCCLINTOCK, B, and HILL, H. E The cytological identification of the chromosome associated with r-g linkage group in Zea Mays. Genet. 16. DE Mor,, W. E Die Enstehungsweise anomaler Pollenkorner bei Hyazinthen, Tulpen and Narzisse. Cytologia Naheres iiber das Vorfinden nebst dem experimentellen Hervorrufen mehrchromosomiger and embryosackartiger Pollenkorner bei diploiden and heteroploiden hollandischen Hyazinthenvarietaten. Cytologia 5. NAGAO, S Karyological studies of the narcissus plant. I. SDmatic chromosome numbers of some garden varieties and some meiotic phases of a triploid variety. Mem. Coll. Sci. Kyoto Imp. Univ. B On the meiosis in the polyanthus narcissus, Narcissus tazetta L. Preliminary note. (Karyological studies of the narcissus plant II). Jap. Jour. Genet Number and behavior of chromosomes in the genus Narcissus. Mem. Coll. Sci. Kyoto Imp. Univ. B Distribution of chromosomes in pollen grains in certain triploid and hypertriploid Narcissus plants. (Japanese). Shokubutsu oyobi Dobutsu (Botany and Zoology) 2. SAY, K Chromosome behavior in Tritirurm hybrids. Zeitschr. f. ind. Abst. u. Vererb. Suppl. 2. THOMPSON, W. P. and ARMSTRONG, J. M Studies on the failure of hybrid germ cells to func-.tion in wheat species crosses. Canadian Jour. Research 6. WATKINS, A. E Genetic and cytological studies in wheat I. Jour. Genet The wheat species : a critique. Jour. Genet. 23.