Essay Sample on Investigating Various Aspects of Plant Physiology

Life of living organisms requires the use of energy for gaseous exchange both in plants and animals. As a result, there are various structural adaptations of various plants to the different ecological niches. Both aquatic and terrestrial plants are adapted to the different structural arrangements of the stomata for the process of respiration. Rice and maize plants are adapted to different habitats. Therefore, they are modified to fit in their environment using different stomatal arrangements. For instance, maize leaves are broad, with numerous stomata on the upper surface. Also, rice species being aquatic plants, they have many stomata on the upper surface to help increase the rate of respiration. In fact, plant species that evolve to live in wet biomes usually have more stomata than plants in dry biomes. Therefore, the purpose of the laboratory exercise was to test the stomatal density of rice and maize and ascertain why there is variation in the density of the two plants. Also, the test will determine the null hypothesis that the density of stomata in rice is greater than or equal to that of maize and that the respiratory rate of rice is greater than or equal to that of maize. (Ho: rice maize, Ha maize rice.

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Results

Eight kinds of rice and maize species of different sizes were collected as sample materials. Also required include the isobilateral leaf and the dorsiventral leaf of the two species. Germinating seedlings were then transferred to an environmental chamber controlled and provided with illumination with a photoperiod of 12 hours, a temperature of 280C day, and 260C night. Also, relative humidity of 70% 5% is provided throughout the experiment (Jones 2013). Stomatal impressions were also made on expanded leaves using dental resin. Usually, eight plants per genotype and two measurements per leaf were examined between the midrib and margin.

Transgenic lines were produced, and the primary transformants were checked using genomic DNA, which revealed a total of 21 out of 24 OsEPF1 transgenes positive putative, and OsEPFL9 of which 17 out of 21 were positive (Jones 2013). The result showed the lines were significantly higher, representing many stomata in the upper leaves. Generally, the rice was overexpressed, causing alterations in the stomatal density and size. The relationship between the mean of the stomatal densities and that of the size of the upper and the lower surfaces shows a distribution in untransformed stomata. The two independent plants showed a significant reduction in stomatal density.

Notably, there is always a decrease in stomatal density (SD), especially when plants have a high concentration of CO2. The signals originating from the mature eaves often play an instrumental role in regulating the SD of developing leaves (Jones 2013). Rice and maize plants often adjust their absorption of CO2 and water loss in response to atmospheric CO2. However, in some cases, particular species can decrease their SD to respond to CO2 enrichment. It should be noted that the SD response to CO2 concentrations depends heavily on the leaving age, plant species, and the environmental conditions on which the plant grows. Research has established that some developing leaves have less autonomy in their stomatal development. Understandably, there is always a decrease of between 20% and 30% in concentrations when new leaves’ SD is under CO2 (360ppm), especially when the leaves have been subjected to double CO2 concentration (Jones 2013). This outcome indicates that mature leaves often play a critical role in the SD of new leaves due to their ability to generate systemic signals.

Discussion and Conclusion

Increasing plant yields often depend on the high efficiency of the C4 pathway. Moreover, C4 isoform that is found in PEP carboxylase can sometimes be expressed n high amounts. Notably, modification of C4 PEP carboxylase can be easily achieved compared to the C3 form. Mutants comprising of PEP carboxylase always fail to concentrate the much-needed CO2 (Jones 2013). The CO2 that enters the mesophyll cells originating from the atmosphere can be easily converted to bicarbonate after being catalyzed by carbonic anhydrase. Malate and aspartate are C4 acids that result from the conversion of oxaloacetate. The structure of C4 helps in providing a liquid diffusion pathway that influences the mesophyll cells and their functions. The effective concentration of CO2 depends greatly on the absence of carbonic anhydrase that is embedded in the bundle sheath (Jones 2013). Furthermore, Rubisco in C4 plants always have a high concentration of CO2, and increased nitrogen content is influenced by enhanced catalytic turnover (Jones 2013). Additionally, in C3 and C4 plants, malate, glutamate, and oxaloacetate often experience counter-exchange on the dicarboxylate translocator. Diffusion often limits the existence of inorganic carbon that is needed for photosynthesis.

Concerning the improved C3 and C4 metabolic networks, the research has compared the optimal biomass synthesis with the CO2 fixation. Being that the biomass synthesis is the function; the maximum flux becomes 3.6 and 4.6 mmol/hr for C3 and C4, respectively (Jones 2013). Additionally, for the optimization of the fixation of CO2, maximum flux can be recorded at 200.89 mmol/hr and 387.5 mmol/hr for C3 and C4, respectively. Therefore, the result shows that C4 networks display greater biomass fluxes as well as higher CO2 fixation compared to C3 networks in the experiment. It is worth noting that the two genome scales for the metabolic networks are used to explain the real scenario as well as being compared for a proper understanding of both the differences and similarities of C3 and C4 plants in the experiment.

Based on the impact of enzyme Knockouts on the CO2 biomass and fixation, a knockout for the enzyme indicates that the corresponding reaction would be erased, thereby resulting in the actual change in the optimum flux and the CO2 fixation during the experiment. The objective results based on the simulation can be classified as reduced= (0,1), unchanged=1, and no objective=0 (Jones 2013). The impact of deleting one corresponding reaction on the maximum flux of biomass on the two networks shows that over 80% reaction had no impact on the maximum biomass for the two networks during the knockout; hence, less than 20% may result into zero biomass, and both networks portray robustness in the reaction.

In the upper surface of the leaves of rice, there was decreased CO2 concentration compared to the lower leaves. The results indicated that there was a substantial difference between low D treatments and ambient in the lamina area. Moreover, in the maize plant, the stomatal density and stomatal index had significantly lower abaxial surfaces (Jones 2013). It should be noted that the stomatal density and index often decrease with declining light intensity. Further, shading the lower mature leaves of rice substantially reduced the SD and the stomatal index in the new leaves. Notably, the results indicate that the changes in irradiance that often triggers signals are always transmitted from mature leaves to new ones, and this ultimately regulates stomatal development (Jones 2013). Moreover, in both the mature leaves of maize and rice, it is indicated in the results that there is no independence of light regime on the effect of CO2 concentration on the stomatal development of developing leaves.

More imperatively, the stomata control the circulation of gasses in and out of both rice and maize leaves; thereby, making CO2 available for photosynthesis, and regulating the loss of water through the process of transpiration. And the stomatal density varies between different types of plant species as well as on the top surface and underside surface of the leaf. About 50% of the rice plant may be experiencing drought-related loss of yield (Jones 2013). Therefore, because of factors including climate change, increased human population and the scarcity of water, it is imperative to reduce plant water while maintaining the process of photosynthesis for both rice and maize, and at higher concentrations of CO2. Based on the results of the experiment, overexpression of OsEPFI in rice caused arrested stomata development that triggered the reduction of stomata density, index, and sizes (Jones 2013). Both in maize and rice, such phenotypic changes occur at the leaf surface, leading to increased drought resistance through the reduction of water loss.

More significantly, shading the mature leaves of rice resulted in reduced epidermal cell density of unshaded developing leaves. Also, there was a similar result in maize where the mature leaves that had been shaded brought a great reduction of epidermal cell density of the unshaded new leaves (Jones 2013). It is further indicated that there was limited sensitivity of epidermal cell density of the upper developing leaves of maize and rice to the increased CO2 on their lower mature leaves. Notably, the results demonstrate that there is no relation to the changes of epidermal cell density to the overriding changes in the production of carbohydrates. Conversely, in the experiments, it was deduced that the epidermal density of the upper leaves was sensitive to CO2 concentration (Jones 2013). This suggests that the differentiation of stomatal density is regulated by distinct physiological mechanisms. Stomatal density depicts no change in response to the increased CO2 concentration in the upper and lower leaves of maize and rice. However, it is worth noting that the inconsistencies in the report are a result of differences that punctuate growth light intensity.

Understandably, it is due to the difficulty in studying the processes of roots the same way as that of shoots. Therefore, current advances in methodology should be in a position to enable a better understanding of physiological mechanisms and processes coordinating shoot and root functions. The report observed the key role of a gene in the regulation of the development of leaf stomata. Also, in the report is how the gene overexpression influences the root aerenchyma tissue development. Typically, rice plants showed effects on stomatal density, conductance, size drought tolerance, and use efficiency of leaf water. However, the report has shown the formation of oxygen-independent aerenchyma in the tips of the root, which resulted from the growth of waterlogged conditions that are deficient in oxygen supply where rice is grown as opposed to maize. Although the mechanism is not yet known, the data brought important implications that are used for mechanisms of the transport of oxygen from shoot to root. Additionally, it helps to signal a deficiency of oxygen in the root tissue.

Reference

Jones, H.G., 2013. Plants and microclimate: a quantitative approach to environmental plant physiology. Cambridge university press.

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