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How plants have adapted or become acclimated to shade.

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Introduction

How plants have adapted or become acclimated to shade. Plants which grow in shady conditions have altered structurally and biochemically in order to cope with the low levels of light and harvest it efficiently. Low level light is rich in far-red light and plants have also adapted to make use of this. Shade plants have also had to make adjustments to cope with sudden high levels of light, for example during sunflecks. Whilst some plants show physiological adaptation, many changes are the result of genetic evolution. * Leaves are thinner with a shallow layer of palisade mesophyll cells and a patchy spongy mesophyll with air spaces (fig 1.). ...read more.

Middle

A few plants cope with this by altering the orientation of leaf blades and hence decreasing the amount of light absorbed. * Some shade plants have enlarged root systems to help combat water lost by heat dissipation during sunflecks. * Sunflecks are not far-red enriched and may cause over-excitation of PSII. In the short term, plants may cope by energy redistribution. Light energy is redistributed from PSII to PSI so both photosystems are equally excited. * Prolonged over-excitation of PSII may lead to photoinhibition (reversible damage of photosynthesis). The build up of reactive oxygen species (ROS) causes damage to the protein D1, found within the PSII complex. ...read more.

Conclusion

Shade plants need pools of active enzymes and intermediates readily available to match demand. The enzyme rubisco is maintained at high levels within the chloroplast but is inactivated in the dark and activated in the light. * Enzymes involved in the regeneration of RuBP also function by activation/inactivation in response to the amount of light present and this forms the basis of a 'brake' system which prevents the C3 cycle from running out of its components. This is the ferredoxin-thioredoxin system. Ferredoxin is linked to PSI and is reduced in light, in turn reducing thioredoxin. Thioredoxin then reduces the C3 cycle enzymes. Structurally plants are designed to cope with light at certain intensity but by using finer biochemical controls plants can easily adapt to changes in their light environment and happily grow in a wide range of conditions. Word count 600 ...read more.

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