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Nuclear volume changes in southeastern tree species before spring growth

Nuclear volume changes in southeastern tree species before spring growth

Rudiation Botany, 1965, Vol. 5, pp. 61 to 66. Pergamon Press Ltd. Printed in Great Britain. NUCLEAR VOLUME CHANGES IN SOUTHEASTERN SPECIES BEFORE SP...

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Rudiation Botany, 1965, Vol. 5, pp. 61 to 66. Pergamon Press Ltd. Printed in Great Britain.







Radiation Ecology Section, Health Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee (Received 17 August 1964) Abstract-The nuclear volume of shoot apex cells of most of 14 local tree species at Oak Ridge, Tennessee, increased before spring growth. Between January and March Pinus strobus and P. taeda showed the greatest increase in nuclear volumes from 63 1~8 f 38.49 SE to 1113~8 + 43.12 and from 638~s f 26.67 to 1026~3 + 23.41 respectively. The nuclei ofcoraurflotida showed no response to approach of spring activity, remaining unchanged from 99pa+2.85 to 100~~ + 5.79, while four species of Acer showed increases (45-199p’ in January to 83-264~~ in March).

R&mme--Le volume nucltaire des cellules apicales parmi 14 especes locales d’arbres d’Oak Ridge, Tennessee, s’accroit avant la periode de croissance printanitre. Entre janvier et mars, Pinus strobus et P. taeda ont montre le laximum d’accroissement du volume nucltaire allant de -I 631$, 38.49 ES a 1113~8 + 43.12 et de 638~~ k 26.67 a 10.26~8 + 23.41 respectivement. Les noyaux de Cornur jlorida ne montrent pas de modification a l’approche de l’activite printaniere allant de 99ps+ 2.85 a lOO$+ 5.79. Par contre, quatre esptces d’Acer ont montrt des accroissements (45-199pa en janvier a 83-264~~ en mars). Kernvolumen von Sprossscheitelzellen bei den meisten von 14 lokalen Baumarten in Oak Ridge/Tennessee nahm vor dem Frtihjabrswacbstum zu. Zwischen Januar und Mara zeigten Pinus strobus und P. taeda die stlrkste Zunabme des Kernvolumens u. zw. von 63 1~~ + 38,49 SE auf 1113pa + 43,12 bzw. von 638~~ f 26.67 auf 1026t?+ 23,41. Die Kerne von Comusflorida liessen bingegen bei Herannahen der Friibjabrsaktivitat keine derartige Reaktionerkennen, sie blieben unverindert bei 99pa + 2,85 bzw. lOOpa f 5,79. 4 Arten von Acer zeigten Zunahmen von 45-19gpa im Januar auf 83-264~~ im M&s. Zusammenfassung-Das

between sensitivity and average chromosome volume, nuclear volume/somatic chromosome number.(r*sl For example Acer rubrum, a polyploid species, has a nuclear volume 2 to 4 times larger than the other maples studied in this report, and on that basis would appear to be more radiosensitive. However, by considering the chromosome complement (chromosome number) the predicted degree of sensitivity is reduced to within the range of the other maples. While the interphase nuclear volumes and


between radiosensitivity and volume of the interphase cell nucleus of vegetative shoot apices has facilitated prediction of the sensitivity of vegetation to damage from ionizing radiation.tlO~lll It is generally accepted that diploid species are more radiosensitive and that polyploidy or increasing chromosome numbers in diploids increase tolerance to ionizing radiation. A correlation has been demonstrated, which is not so strongly affected by polyploidy, THE


*Research Corporation.

sponsored by the U.S. Atomic


Commission 61

under contract


the Union





some chromosome volumes of numerous herbaceous annuals and perennials have been cataloguedW*s-‘) woody species have been [email protected]). One purpose of this report is to add to the small number of trees previously reported. A second and primary purpose is to study early seasonal changes in nuclear and chromosome volumes which might affect the tolerance of the tree species to ionizing radiation. Dormant meristematic nuclei are reported to be approximately 40 per cent smaller than the nuclei of active meristematic cells.(9) If this generalization is true for all species it is important that any prediction of radiosensitivity be defined in terms of time which would include seasonal variations in nuclear and chromosome volumes. MATERIALS



Vegetative shoots were collected during the secondweek of each month from sexually mature trees. The shoots, collected at random from terminal positions in exposed locations, ranged from 5 to 10 in number. For each subsequent sampling period shoots were collected from the sametree. Prior to killing, the apices were carefully dissected from the shoot and fixed in a Nawaschin type fixative, Craf III.t4) The tissue was dehydrated-infiltrated with a standard tertiary-butyl alcohol series,embedded in Paraplast, and cut into serial sections 8-10 p thick. The larger apices(P&U) were difficult to section. However, the difficulty was corrected by soaking 2 hr in a dilute detergent solution prior to cutting. The longitudinal sectionswere stained with Safranin 0, counterstained with Fast Green, and made into permanent slides. From the slidesnumerous micrometric measurements were made of the interphase nuclei in the “tunica and corpus” tiers of angiosperms,and apical initial and central mother cell zones of gymnosperms.Three shoot apicesof each species were used in determining the mean interphase diameter. An average of 48 nuclear measurements were made per species.From the mean diameter the nuclear volume was calculated. Average chromosomevolumes were determined by dividing the calculated nuclear volume by the somatic chromosome number as listed by [email protected])The nuclei measured were uniformally spherical except in pines whose


diameters taken at right angles varied as much as 7 per cent within a nucleus. RESULTS

An analysis of variance comparing the mean diameters showed a significant change between sampling periods (P
suggested that in white pine seedlings,Pinus strobus, increasesin nuclear size are associated with onset of active growth. Table 1 summarizes the volumetric changes in interphase nuclei and chromosomesfor 14 tree speciesduring the first quarter of 1964. It is clear that there is a progressive increase in nuclear volume with approach of spring activity, but before the period of active growth of new shoots. The increasesin nuclear volumes also mean that the sensitivity of the plant is increasing before [email protected])


45+ 45+_ 199+ 94+ 49+ 58& 99+

60 53 80 105 60 43 52 55 40 40 40

1.43 2.13 9.46 3.42 1.88 2.82 2.85




45 45 40 40 40 40



52 85 45 40 60 65

63 1 f 38.49 638 + 26.67 599 + 24.88 357 f 10.42 -



69k 69+_ 254+ 92+ 85+ 79+ 91+

148+ 1.39t 2.59t 10.81t 3.44 2.85t 3.45-f 2.08


693 + 23.34 830 + 23.89t 792 + 28.03t 599 f 32.81 475 + 38.04-f 493k21.78


Nuclear Volume (12 zk SE)

45 50 40 40 12 40 50


40 41 50 40 60



2.63t 2.467 6.24 2.507 1.13t 4.987 5.79



82i 83+_ 264& 132f 1195 106+ loo+


763f 11.81t 1113*43.12? 1026+23.41-t 784521.44t 735 + 19.877 517 f 26.68


volumes calculatedfrom mean diameters tree s~cciesJ Jirst quarter 1964




of interphare


1. Summary

* (nuclear volume/somatic chromosome number). t P

lkga camzfensis (24) Pinus strobus (24) Pinus taeda (24) Pinus echinata (24) Pinus virginiana (24) Junifierus virginiana (22) Liriodendron tulipifera (38) Liquidambar s&racijlua (30) Acer saccharum (26) Acer rubrum (78) Acer saccharinurn (52) Acer negundo (26) Aesculus octandra (40)

Species and Somatic Chromosome Number (1)




1.50 f 0.0476 1.73 +_0.0819 2.55kO.1212 1.81 f 0.0657 1.88kO.0721 1.45 f 0.0705 4.50 + 0.1295

2.82 + 0.1278

2.30 2.65 3.26 1.77 3.27 1.98 4.14

+ 0.0463 +- 0.0996 + 0.1385 f 0.0661 f 0.1096 f 0.0862 * 0.0945

3.89 + 0.1526

28.88 + 0.9725 34.58 f 0.9954 33.00 + 1.1679 24.96 f 1.3670 19.79& 1.5850 22.41 f 0.9900

26.29 + 1.6037 26.58+ 1.1112 24.96 + 1.0366 14.87 + 0.4341 -


Average Chromosome (@f SE)



and interjhase

2.73 f 0.0876 3.19 + 0.0946 3.38 + 0.0800 2.54 + 0.0480 4.58 +- 0.0435 2.65kO.1245 4.54 f 0.2631

4.00 + 0.0763

0.4920 1.7966 0.9754 0.8933 0.8279 1.2127

March 31.79* 46.37 + 42.75 f 32.67 f 30.62 f 23.50+





the sensitivity is further changed by the mitotic cycle. Initial spring activity of interphase nuclei in shoot apices is thus earlier in eastern Tennessee than would be anticipated from any external evidence, and much earlier than reported for Pinus strobus seedlings on Long Island. Information of this nature would prove valuable in interpreting plant irradiations using outdoor field sources of radiation, which may have varying effectiveness according to season. The data of the 14 tree species presented in this report are of special interest because the seasonal changes apparently started early in winter. Continuing changes are being followed through the growing season. Reliable predictions of community radiosensitivity can be made only if larger numbers of local species are studied through time for many species of a region.

4. 5.




9. REFERENCES 1. DARLINGTON C. D. and WYLIE A. P. (1955) Chromosome Atlas of Flowering Plants. Allen and Unwin, London. p. 5 19. 2. EVANS H. J. and SPARROW A. H. (1961) Nuclear factors affecting radiosensitivity. II. Dependence on nuclear and chromosome structure and organization. Brookhaven Symp. Biol. 14, 101-127. 3. NIRULA S. (1963) Studies on some nuclear factors controlling radiation sensitivity and the induced

10. 11.


mutation rate in eu- and para-sorghum species. Radiation Botany 3,351-361. SASSJ. E. (1958) Botanical Microtechnique. The Iowa State College Press, Ames. p. 228. SPARROW A. H., CUANY R. L., Mncscns J. P. and SCH~URERL. A. (1961) Some factors affecting the responses of plants to acute and chronic radiation exposure. Radiation Botany 1, 10-34. SPARROW A. H. and EVANS H. J. (1961) Nuclear factors affecting radiosensitivity. I. The influence of nuclear size and structure, chromosome complement, and DNA content. Brookhaven Symp. Biol. 14,761OO. SPARROW A. H., SCHAIRER L. A. and SPARROW R. C. (1963) Relationship between nuclear volumes, chromosome numbers, and relative radiosensitivity. Science 141, 163-166. SPARROW A. H., SCHAIRERL. A., SPARROW R.C. and CAMPBELL W. F. (1963) The radiosensitivity of gymnosperms. I. The effect of dormancy on the response of Pinus strobes seedlings to acute gamma irradiation. Radiation Botany 3,169-173. SPARROW A.H., SPARROW R.C., TOM~SON K.H. and SCHAIRER L. A. in Proceedings of tech&al meeting on the use of induced mutations in plant breeding. Rome, May 25 to June 1, 1964. Supplement to Radiation Botany (in press). SPARROW A. H. and WOODWELL G. M. (1962) Prediction of the sensitivity of plants to chronic gamma irradiation. Radiation Botany 2,9-26. WOODWELL G. M. and SPARROW A. H. (1963) Predicted and observed effects of chronic gamma radiation on a near-climax forest ecosystem. Radiation Botany 3,231-237.