The Effect of Ringbarking
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Plant Transport Investigation Name: Date:
Aim: To use evidence from ringbarking and defoliation of a shoot and from the use of radioactive tracers to learn something about the movement of nutrients within a plant.
The Effect of Ringbarking.
Wood taken from the central part of the stem of a tree or woody shrub. Fig 1 A shows part of a transverse section through a woody twig from the outside of the stem to the centre.
Identify the 3 regions of the stem.
In the centre is a region of unspecialised parenchyma cells – the pith. Then there is a mass of tissue –the wood. Finally towards the outside is the bark. Large numbers of xylem vessels are visible in the wood, and rays of parenchyma cells run outwards through the wood along radia from the centre of the stem. Like wood, the bark contains several recognisable types of cell. There may be cork cells towards the outside and a mixture of parenchyma cells and fibres within.
The bark also contain specialised cells producing compounds which appear to protect the stem from attack or from wound damage. Latex is such a compound; rubber is made from the milky latex of the bark of the rubber tree, Hevea brasiliensis. Quinine is prepared from the bark of a South American tree, Cinnamon is the ground bark of the tree Cinnamomum, which grows in SE Asia. The bark of wattles contain much tannin which combines with and coagulates protein and is used in tanning hides to make leather.
The phloem of woody stems is found near the inside of the bark. It consists of non woody, living cells.
Here we are considering the implications of experiments in which the bark has been removed from the stem- a technique known as ‘ringbarking’. Ringbarking usually removes the phloem, cork cells parenchyma cells and fibres.
Part A: Ringing and Translocation
During the period 1920-25 an American plant physiologist O.F. Curtis carried out a number of experiments involving the removal of bark. Shoots still attached to the plant were treated in one of 4 ways.
Fig 2
1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. Control: no treatment
2. Ringed treatment: A 1cm long ring of bark was removed in the 5th internode from the shoot apex.
3. Defoliated: Leaves were removed from the nodes above the 5th internode. 4. Ringed and defoliated: Bark was removed in the 5th internode and leaves above the ring were removed.
The overall length of these shoots was measured and the amount the shoots had grown was calculated. See Table 1 below
Average Growth (mm) Days after Control Ringed Defoliated Ringed & Treatment Defoliated 3 94 71 36 14 5 164 130 80 16 9 341 218 270 20
1. Cut and past the table into an Excel sheet and use Excel to construct a line graph of these results with time on the horizontal axis and average growth on the vertical axis. Label the graph appropriatly and re insert into this report below the table.
In interpreting these results you have to take into account the the potential for photosynthesis to produce new organic compounds( Glucose) necessary for growth and the plants ability to move this around the plant body. Both the processes of transpiration and translocation are implicated.
2. What effect does ringing have on the growth? Suggest why
3. What effect does defoliation have on the growth? Suggest why?
4. Suggest why growth increased so much between 5-9 days?
5. What effect does both ringing and defoliation have on growth? Part B : The Pathway of Mineral Nutrients in Stems
In the years since Curtis’s work new techniques have been developed. As a result, our understanding of the movement of materials in plants has advanced considerably.
One technique of particular significance is the use of radioactive tracers to follow the movement of compounds throughout the plant.
The Radioactive isotope carbon -14 14 C was added to leaves as the carbon in carbon dioxide. Many of the important nutrients taken up by the roots also have useful radioactive isotopes. eg there is a radioactive isotope of potassium with an atomic weight of 42 42K and one for phosphorus 32P. Both have been used to trace the movement of nutrients from the roots to the rest of the plant.
In a typical experiment of this type Eucalyptus seedlings grown in sand to which nutrients were added regularly until the plants were about 50 cm high. The sand was then gently washed away from the roots and the plants fixed with their roots suspended in well aerated solutions containing all the nutrients the plant needs for growth. Radioactive potassium 42K+ was added to this solution.
After 90 minutes the plants were removed from solution and the tracer in the plant measured as follows.
The shoot was cut up into pieces in such a way that the amount of tracer in the bark and the wood in the lowest six internodes could be determined separately. The pieces of plant material were then dried on an aluminium metal tray about 5cm in diameter and put under a Geiger counter.
The results are shown in Table 2 below, one for control plants and the other for plants ringbarked in the 3rd internode.
Average number of counts Internode Control plant Ringed plant number Wood Bark Wood Bark 6 70 30 75 35 5 90 50 85 50 4 115 60 110 65 3 125 65 Ring Ring 2 135 65 150 75 1 180 80 200 90
Table 2: Radioactive counts using wood and bark pieces after application of readioactive 42K+ to seedling roots
6. What effect did ringing have on movement through the stem? Why do you think so? 7. Which conducting ( vascular) tissue seems to be more involved in transport from the roots; the phloem or the Xylem? Why do you think so?
8. Can you draw any conclusions about radial ( horizontal)movement of ions in the stem? Explain
9. In what part of the stem could radial transport of nutients occur?
Part C: Uptake and Transport by Leaves
The presence of radioactive compounds in a leaf can be detected by leaving the leaf on a photographic film for some time;the developing the film. The resulting print – an autoradiograph- darkens where radioactive compounds were present.
Fig 3 is an autoradiograph of two leaves.
The leaves had latex solution put on nthe leaf to form the leatters B S ( blocked stomata). The leaf on the left was the exposed to radioactive carbon dioxide which formed radioactive carbohydrate as a a result of photosynthesis.
The leaf on the right was from a plant which had had radioactive phosphate solution supplied to its roots.
Examine the distribution of the darkened areas in each leaf.
10. Which parts of each leaf appear to contain most radioactive carbohydrates?
11. Which parts appear to contain the most radio active phosphate?
12. Would the reason be the same for each leaf? Explain.