Wheat Sources and Sinks

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Wheat sources and sinks experiment report


Most research on grain yield in relationship to the source or sink has been inconclusive in most experiments (Schnyder, 233-245). It is not well established the yield is influenced more by the sinks or the source. The majority of these studies reported results on grain mass as a mean without consideration of other factors (Paul et al, 1383-1400). In this experiment, the effect of sinks and sources on the grain yield is investigated. The wheat plant is used, and the mass of the grain in the control and the treated groups are compared; keeping other factors constant by keeping the plants in the greenhouse for the entire experimental period. The experiment aims to establish whether the sources or the sinks have more effect on the grain mass. It also investigates the intensity of the effect of these two factors on the grain mass. The translocation of carbohydrates between sinks and sources is the determining factor of the grain yield. Individual group results are compared against the class results. The used SE is the same across the data.

Materials and Method

The wheat plants were sown in a population of 10 seeds per pot; after a couple weeks the seedling population was thinned out to 5 per pot. At 9 weeks, just a week postanthesis, the plants were subjected to treatments as follows: Each group was provided with 10-15 plants contained in 2 or 3 pots. 10 plants were selected a stem to be experimented on was identified and marked on the ten plants. The sizes of the stems were chosen in respect the ear and size and development to achieve uniformity. The stems were marked from 1 to 12 and a different treatment carried on each of them. The stem identified as 1 was the control and no treatment done. On the second stem, the flag leaf was excised (Fl1).

The second uppermost leaf was exercised on the second stem as well as flag 2 on stem 3. On stem 4, the fl1 and fl2 were covered with aluminum foil and the foil pricked 12 times to allow limited air flow and prevent infection. The ear was enclosed in aluminum foil and the foil pricked on stem 5. On stem 6, the aluminum foil was used to cover the ear and both the FL1 and FL2 excised. On stem 7, half of the ear was excised and on stem 8, the ear was excised at the level of the flag leaf. Both the FL1, FL2 and the ear were covered for stem 9. For stem 10, all tillers were cut except one. Two more stems 11 and 12 were treated. In stem 11, the FL1 leaf was shaded and in 12, both the FL1/FL2.

After the treatment, a detailed tagging of each plant was made using a pencil. The plants were kept in the glass-house for the whole experiment time. On ripening, the grains were carefully harvested taking care not to drop any. The harvested grains were labeled according to the stems and pots they were harvested from. The FL1 and FL2 were also harvested and labeled. The grains and the FL1, FL2 were weighed and recorded accordingly. The masses were measured against the control. The table below shows the data results.

Result-analysis and discussion

Wheat Sources and SinksTable 1: Results of the grain and FL1 and FL2 masses

From the results, the cutting of all the tillers registered the highest grain mass of 61.12g. The cutting of all the other tillers except one, seems to have reduced the sinks. This means that the sucrose made in the process of photosynthesis was consumed by the few remaining sinks including only one tiller. It is arguably true that the reduced tiller number availed more sucrose for the grain to consume hence the yield. Of note, the same stem number 10, registered the lowest mass of the FL1 and FL2 (117g) The leaves being the main surface area for photosynthesis, are sources of sucrose. The translocation of the sucrose made through photosynthesis was not impaired by the cutting off of the tillers; it somehow facilitated its movement to the grain since the sink number had been reduced.

The treatment of stem 2 by covering excising FL1 significantly affected the grain (33.1g) yield compared to the control (40.44). The FL1and FL2 mass for this treatment was the highest (208.00g). This implies that the FL1 has a role in the development of the grain. Being the closest to the grain ear, the sucrose produced by the fl1 has excellent translocation to the grain. This explains the low grain mass. As for the FL1 and FL2, it is not clear that the high mass is due to the FL1 or the Fl2. The covering of FL1/FL2 on stem 4 did not have a huge impact on the grain mass (38.95g) compared to the control (40.00g). Although light is a required condition for phototsynthesis, reducning the surface area exposure to sunlight does not significantly affect the process due to the prick hoels on the foil and the act of phototropism. The FL1/FL2 mass of stem four wighed lower (152g) than the control (167.00g).

The grain mass as well as the FL1/FL2 masses were the lowest on stem 5 (86.00g). The treatment of covering the ear by pricked aluminum foil negatively impacted the grain yield. The lower leaf mass cannot be explained by this experiment. The stem number 7 has the lowest grain mass, but a fairly high leaf mass compared to the control. Excising half the ear led to low grain yield. Since the leaves were not treated, the mass was as expected. It is higher than the control leaf mass because the ear size was reduced and therefore the amount of sucrose consumed by the ear was reduced.

According to the results, the FL1 leaf has the highest strength in affecting the grain yield. The excision of both the FL1/FL2 leaves does not show the expected results. The grain mass form stem 3 should be lower than the grain mass in stem 2. Nonetheless, it is appreciable that the FL1 leaf has a higher role in providing the grain with carbohydrates. The shading of the leaves FL1 and FL2 leaves yielded a lower grain mass compared to the control. The mass of the leaves increased compared to the control. This is because the shading affects the translocation of sucrose from the source to the grain. The carbohydrates after manufacture via photosynthesis, is then locally consumed by the shaded leaf leading to increase in its size and sugar content measured as higher mass in this experiment.


Sources and sinks in wheat plants affect the grain yield if other factors are kept constant i.e. in a glass-house. The first leaf a.k.a the flag leaf, has the highest influence on the grain yield as confirmed by a significant decrease in yield mass in the stems whose flag leaves are treated. The second leaf from the uppermost most part of a grass plant also affects the carbohydrate content the grain gets but not as much as the flag leaf. The reduction of sinks e.g. the number of tillers increases the grain yield significant while decreasing the source, i.e. leaves, negatively impacts the grain yield (Schnyder, 233-245). The translocation of carbohydrates synthesized by the sources to the sinks is influenced by the various treatments affecting either the sources or the sinks (Paul et al, 1383-1400).

Works cited

Paul, Matthew J., and Christine H. Foyer. «Sink regulation of photosynthesis.» Journal of experimental botany 52.360 (2001): 1383-1400.

Schnyder, Hans. «The role of carbohydrate storage and redistribution in the source‐sink relations of wheat and barley during grain filling—a review.»New Phytologist 123.2 (1993): 233-245.