How does the salinity of water affect the germination of mung been seeds as measured by the number of seeds that successfully germinate?

Graph 2 showing the effect changing the salinity of water added to ten ungerminated Vigna radiate (mung bean) seeds has on the seeds ability to successfully germinate as determined by the mean number of seeds with the visible presence of a radicle seven days after the solution was added to the seeds

Comment on the graph

As we had no radicles present at 0.3 0.4 and 0.5 the standard deviation is zero and therfore it is reliable, however it is not the expected trend, indicating that there were other factors which effect the germination at the aforementioned salinities. The calculated standard deviation and error bars for the other two of my results (0.0 and 0.2) varied in size. As at 0, the error bar is very large (1SD is 2) this indicates that the values recorded for this percentage was less valid and some other factor may have been affecting the results. This error bar also overlaps the 1 other data point at 0.2, indicates that this first decrease may not be a clear trend due to this overlap. The line of best fit is not accurate and it does not passes through all of the error bars and point. This indicates that the trend indicated by the line is inaccurate and more likely to be less extreme.

Conclusion:

In my experiment I investigated whether changing the salinity of water effected the germination capabilities of mung beans, originially this was going to be indicated by the visible presence of a radicle, 10 days after being exposed to the solution, however these results were inconclusive so we also indluded our data from the fourth day which measured how many seeds testas had begun to crack. Both of these results indicate that the salinity of water significantly affects the ability for mung been seeds to germinate. As our research question investigates the effect of salinity on germination my conclusion shall be primarily concerned with my results for the visible presence of a radicle as that was what our research question was in relation to.

As we increased the salinity of the water the indicators of successful germination decreased. This is shown by the overall negative trend of our data as at 0, 6 seeds had successfully germinated while at 0.5 no seeds had germinated. As we had no radicles present at 0.3 0.4 and 0.5 the standard deviation is zero and therfore it is reliable, however it is not the expected trend, indicating that there were other factors which effect the germination at the aforementioned salinities. The calculated standard deviation and error bars for the other two of my results (0.0 and 0.2) varied in size. As at 0, the error bar is very large (1SD is 2) this indicates that the values recorded for this percentage was less valid and some other factor may have been affecting the results. This error bar also overlaps the 1 other data point at 0.2, indicates that this first decrease may not be a clear trend due to this overlap. The line of best fit is not accurate and it does not passes through all of the error bars and point. This indicates that the trend indicated by the line is inaccurate and more likely to be less extreme. In otherwords it is more likely that salinity has a more gradual effect on the inhibition of germination than the trend seen in our results.

We were able to do a total of 5 repeats for each concentration which meant we were able to ensure greater reliability of our results. However there were still some anomilies which would have caused our error bars to increase. Though there are no single outliers the results for our 0 salinity trial had a large range of results from 4 to 9. Although some level of variation is expected due to seeds being biological in nature, this level of range is unprecidented and indicates that this trial in particular was effected by other factors.

The data we collected was insufficient as we only had 8 out of 25 petri dishes have seeds with visible radicles. This led to the inclusion of the data from day four, as the testa cracking is an indicator of the start of germination. This data presented a clearer trend, though still negative it is less extreme, however it also has anomilies, such as recording zero seeds with cracked testas in one trial of the 0 salinity solution, this would have greatly decreased the mean and would have also increased the error bar seen in this graph, as discussed above, this adds to the theory that the 0 salinity results were greatly effected. Another anomily exists in the 0.4 salinity where we recorded 6 seeds with cracked testas, this would have increased the mean therefore it is this result which caused the slight mean increase at 0.4, which does not follow our otherwise negative trend. However the exclusion of this data point would not have effected our graph as the mean would still be 3 seeds.

Our results are explained by the science behind plant germination, and the factors which effect this process. For germination to occur the seed must have the correct abiotic conditions to begin. These conditions include:

1. Water – to metabolically activate the cells within the seed
2. Oxygen – to enable aerobic respiration
3. Warmth – for optimal enzyme function

If these three factors are present then germination can begin. The first step of germination is the absorption of water, this causes gibberellic acid to be produced and as the seed absorbs water and swells the testa will begin to crack. Gibberellic acid in tern causes the synthesis of amylase, which breaks down the starch contained within the cotyledon into maltose. The maltose can then be hydrolysed to glucose for respiration of polymerised to form cellulose, necessary for plant walls. The starch contained within the cotyledon sustains the seed until the plumule reaches light and the radicle can absorb water, and photosynthesis can begin. Though important this is a very vulnerable stage in the plants life and can be negatively affected by abiotic factors.

The solutions we were adding to our seeds with the exception of 0.0 contained water and dissolved NaCl. When dissolved in water the ions in the salt dissociate resulting in the ions Na+ and Cl- to be present in the water.  Although plants require Na+, in excess this mineral can begin to have toxic effects on the plant that affects it capacity to germinate. Excess salt can cause “reduced cell turgor and depressed rates of [radicle] … elongation... Furthermore, high intracellular concentrations of both Na+ and Cl- can inhibit the metabolism of dividing and expanding cells, retarding germination and even leading to seed death.” The reduced cell turgor is explained though osmosis, “as osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration”. Therefore when we placed our seeds in high salt solutions there was a high concentration of salt in the area surrounding the seed, which would cause movement of water out of the seed, and thus water, which is necessary for germination would not be absorbed in the needed quantities, inhibiting germination. At zero salt concentrations this would not have affected the seed, and it would have been able to absorb water, and thus would be able to begin germination.

Our results are supported by multiple experiments, including this one conducted primarily by the Department of Agronomy in Zabol University, Iran. This particular study took many measurements investigating the effect of salinity on germination, including investigating the effect salinity had on radicle length. As you can see, though it would appear our results are more extreme, their results to reflect our negative trend.

Their justification of their results also reflects my own justification, namely that “salinity … leads reduction in water absorbance so cell division and differentiation reduce and [causing the] reduction of … radicle length”.

It is important to understand the factor which effect seed germination as germination is the first stage in a plants life cycle, and without plants to convert carbon dioxide into oxygen life would not be sustainable on earth, plants also play a hugely important role in the agriculture and food industry.  

Evaluation:

Bibliography

1. http://www.amjbot.org/content/88/1/62.abstract
2. http://www.academia.edu/2359325/Impact_of_Salinity_on_Seed_Germination_and_Early_Seedling_Growth_of_Three_Sorghum_Sorghum_biolor_L._Moench_Cultivars