PLANT TROPISMS

A Demonstration Web Page by John Foster

This web page has been designed as part of an MSc. in Biological Computation at The University of York.

Its purpose is to demonstrate the potential use of the WWW as a means of displaying time-lapse video sequences of plant tropisms for educational and research interests.

The sequences were captured directly to a computer using Microsoft Video For Windows and a Creative Labs Video Blaster SE video card.

These sequences are in .AVI format, suitable for viewing with Microsoft Windows Media Player.

You may e-mail your comments to drf1@york.ac.uk

TROPISMS

Tropisms are plant responses in which the direction of movement is strongly related to the direction of some environmental factor.
Gravitropism and phototropism are the two principle responses and thus the majority of work done has been on these. Gravitropism (also known as geotropism) is the response in which the direction of growth is determined by the effects of gravity on the plant. Phototropism is a response to a gradient of light intensity. Most typically these responses result from differential growth rates of cells within or between organs (see Hart1990). Being a growth process means such movements are relatively slow and therefore ideally observed using time lapse photography.

Standard time lapse photography is expensive (cost of film), limiting the number of frames taken and therefore the 'smoothness' of the image playback. Also it is not 'real time'. There is the added delay waiting for film to be developed before knowing whether the results are usable. Of course if there were problems (and there often are eg. bad lighting) then that film was wasted.

An alternative is to use Video and a V.C.R. This however suffers from poor image quality and as the images are stored on tape until filming is complete, it does not allow real time intervention.

Capturing direct to a computer is potentially ideal. Good images are attainable, with the benefit of being able to preview them before capture to make any necessary adjustments. Image data is held in binary bitmap format allowing immediate use of image processing tools before compression for storage. The stored image is then in a format which is easily and cheaply reproduced, edited and communicated. Well, potentially.

• SUNFLOWER SHOOT GRAVITROPISM (278 KBytes)
  

  180 frames filmed over 5 hours at 0.01 f.p.s. Replay at 3 f.p.s. Duration 1 minute.

  Click on this to see it grow into this

  Shoots generally show negative gravitropism. This is typically demonstrated by taking a young vertically growing shoot and reorienting it horizontally. The shoot will then curve until it is once again growing vertically. This shows us that the shoot wasn’t just growing in a straight line that ‘happened to be’ vertical but rather that it’s direction of growth was quite specific with respect to the direction of gravitational force.

  The gravitropic response is usually first observed in the apical region of the shoot. Rapid curving at the tip progresses as a standing wave along the whole stem. The rate of curvature is not necessarily constant along the stem and the issue is confused further by subsequent straightening of curved areas known as autotropism, which corrects the ‘overshoot’ of the vertical direction of growth.

• CRESS ROOT GRAVITROPISM (89 KBytes)
  

  180 frames filmed over 7 hours at 0.007 f.p.s. Replay at 5 f.p.s. Duration 36 seconds.

  Click on this to see it grow into this

  The gravitropic response of main roots is generally positive (orthogravitropic ie.downwards). The major difference from the response of shoots is that the area of response is confined to the region of cell elongation, just behind the root tip. This presumably is because growing in soil the rest of the root isn’t free to move in the way a shoot growing in air can.

  When reoriented horizontally the tip gradually curves around until it is once again growing vertically down. The interesting point here is that the root does not simply produce a right-angled change of shape which may have been expected as the root grows from just a single region. Instead it continues to grow in all the intermediate directions before finally achieving the ‘intended’ one and thereby produces a smooth, curved shape.

• CRESS SHOOT PHOTOTROPISM (230 KBytes)
  

  180 frames filmed over 4 hours at 0.013 f.p.s. Playback at 5 f.p.s. Duration 36 seconds.

  Click on this to see it grow into this

  Here the shoot has been grown in unidirectional light from the right. Again there is a rapid curving response in the apical region which moves down the stem. Autotropic straightening of the upper stem in the later stages of the sequence makes the shoot appear to stop curving or even curve backwards, but close examination of the lower stem shows there is still an ongoing response towards the light source.

  Additional files may be downloaded direct from the File Archive These are similar to the above examples, but are compressed using WinZip V6.0 to reduce the transfer times.
  There is also a copy of the MSc. project report (compressed as above) and an abstract of this report for a quick preview.Read Abstract
  

References:

For a general work on plant tropisms see

Hart, J.W. (1990) Plant Tropisms: and other growth movements.
Unwin Hyman Ltd. (London) ISBN 0-04-445370-1

For more specific information on the study of Phototropism see

Firn, R.D. (1986) Phototropism. Cited in: Photomorphogenesis in Plants. Editors R.E.Kendrick and G.H.M.Kronenberg
Martinus Nijhoff Publishers (Dordrecht) ISBN 90-247-3317-0