Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

Development of the Stem Tuber in Kohlrabi

I. W. SELMAN and S. KULASEGARAM
Journal of Experimental Botany
Vol. 18, No. 56 (August 1967), pp. 471-490
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23686976
Page Count: 23
  • Download ($42.00)
  • Cite this Item
Development of the Stem Tuber in Kohlrabi
Preview not available

Abstract

Stem swelling in kohlrabi (KR) normally occurred between the third and fifth node and followed initiation of meristematic activity in pith parenchyma cells; this usually began about 7 weeks after germination and was associated with the death of parenchyma cells in the centre of the pith lower down the stem. Cell division began just above this region, at about the third node and zones of dividing cells extended upwards and laterally, giving rise to more centres of active division. Carbohydrate analyses showed that fructose, glucose, starch, and an unidentified sugar accumulated in the stem. Melezitose appeared in the stem and raffinose in the leaves only after visible bulbing had occurred. Sucrose content fluctuated in both leaves and stems and in the latter was positively correlated with hours of sunshine on the day before sampling. The contents of gibberellin-like substances in the leaves of KR were compared at two stages of development with those of marrowstem kale (MSK). Gibberellins were present in both acidic and neutral fractions in KR tissues and the amounts were similar to those in MSK. Stem swelling in KR could not be attributed to a gross deficiency of gibberellins. Inter- and intra-varietal approach-grafts were made with KR and MSK plants. With KR as 'scion' partner, stem elongation of the scion was not greatly affected by the nature of the stock, but stem swelling was much reduced on MSK stocks. Stem swelling in MSK scions was greater on KR stocks than on MSK. Retention of stock leaves and buds above the union tended to inhibit elongation of the scion partner and also inhibited stem swelling in KR scions on MSK stocks. Application of gibberellic acid to leaves of MSK stocks from which the terminal bud had been removed, increased both stem elongation and swelling in KR scions. KR scions top-grafted on defoliated MSK stocks showed vigorous stem elongation without swelling. MSK scions top-grafted on KR stocks showed reduced stem elongation with abnormal stem thickening. It is suggested that high auxin levels may prevent bulbing in KR and that gibberellin-like substances may facilitate both stem elongation and bulbing when auxin levels are low. Applying gibberellic acid (GA3) or indole-3-acetic acid (IAA) alone or in combination, to young intact plants of KR increased stem height and checked stem swelling. Application of benzyladenine (BA) at 10-4 M accelerated swelling and checked stem elongation. GA3 applied with BA (10-4 M) increased both stem height and girth, both with or without added IAA. It was concluded that the requisite conditions for stem swelling included the presence of a kinin2 and a low level of auxin. High levels of auxin prevented stem swelling, whether applied as IAA to young intact plants or as natural auxins from leaves and buds of MSK plants grafted to KR scions. Although applied gibberellins usually tended to prevent swelling, native gibberellins appeared to play a minor role in controlling its initiation which probably occurs when the auxin/kinin ratio in the plant reaches a critical low level.

Page Thumbnails

  • Thumbnail: Page 
[471]
    [471]
  • Thumbnail: Page 
472
    472
  • Thumbnail: Page 
473
    473
  • Thumbnail: Page 
474
    474
  • Thumbnail: Page 
475
    475
  • Thumbnail: Page 
476
    476
  • Thumbnail: Page 
477
    477
  • Thumbnail: Page 
478
    478
  • Thumbnail: Page 
479
    479
  • Thumbnail: Page 
480
    480
  • Thumbnail: Page 
481
    481
  • Thumbnail: Page 
482
    482
  • Thumbnail: Page 
483
    483
  • Thumbnail: Page 
484
    484
  • Thumbnail: Page 
485
    485
  • Thumbnail: Page 
486
    486
  • Thumbnail: Page 
487
    487
  • Thumbnail: Page 
488
    488
  • Thumbnail: Page 
[unnumbered]
    [unnumbered]
  • Thumbnail: Page 
[unnumbered]
    [unnumbered]
  • Thumbnail: Page 
[unnumbered]
    [unnumbered]
  • Thumbnail: Page 
489
    489
  • Thumbnail: Page 
490
    490