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How plants have adapted or become acclimated to shade conditons.

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Introduction

Noreen Mc Quaid U5400636 TMA 05 Question 2 HOW PLANTS HAVE ADAPTED OR BECOME ACCLIMATED TO SHADE CONDITIONS. Conditions of shade present low average light intensity for plants, along with a difference in the quality of light (in terms of the numbers of quanta of different wavelengths). Shade light contains more far-red and infra-red quanta and fewer quanta in the range 400 - 680nm. Additionally, light quality and quantity can vary enormously and rapidly due to the occurrence of sunflecks, (a valuable source of light, yet potentially damaging.) Adaptation to shade conditions can be determined genetically or be due to acclimation. Obligate shade plants have evolved genetically to exist in permanent shade and cannot acclimate to long-term levels of high light intensity. ...read more.

Middle

They have wide grana with large numbers of stacked thylakoids, and a ratio of up to five times more appressed: non-appressed lamellae than in sun plants. These features represent a higher proportion of photosystem II (PSII) relative to photosystem I (PSI). * Given that PSI becomes relatively more excited than PSII in far-red enriched light, and that there must be equal excitation of both photosystems in order that non-cyclic electron transport may proceed smoothly, these features are significant in facilitating the necessary increased absorption by PSII to maintain equilibrium between both photosystems. With these structural and biochemical adaptations shade plants can efficiently harvest light at low intensities. * Due to these characteristics shade plants become light saturated at lower light fluxes than sun plants. ...read more.

Conclusion

* During energy redistribution heat energy is dissipated. This is important because increased leaf temperature can cause increased water loss and wilting. It has also been shown that shade plants exposed to prolonged sunflecks possess larger root systems than plants that grow in deeper shade. This facilitates the uptake of water. * Photoinhibition and photo-oxidation occur at lower light intensities in shade plants, as illustrated in the diagram in Appendix 2. Contributing factors are that they possess less ability to produce zeaxanthin, which mediates heat dissipation, and contain less protective enzymes e.g. superoxide dimutase (SOD), which destroys ROS by converting it to hydrogen peroxide. Overall shade plants are adapted to possess a greater ability to photosynthesise efficiently at lower light fluxes. Associated with this, exists the increased likelihood of suffering from photoinhibition. They have, however, also developed ways of coping with this risk, presented to them by their environment. ...read more.

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