H2

Light

Light stress is not always a consequence of too much light; competition for light in the shade of a tree canopy is likewise stressful and can lead to complex morphological and physiological changes. One characteristic of shade leaves is a large leaf area but a low leaf weight. This feature increases the light-harvesting area, and also shades competing neighbouring plants. The genus Cecropia is particularly successful in adapting to light conditions in forming enour-mous leaves. Cecropia trees also live in symbiosis with the ants that colonise the hollow stems. The ants chase damaging insects and provide the host with nitrogen and phosphate, nutrients which are limiting factors in tropical forests. La Carbonnera Reserve near Merida, Venezuela. Photo E.-D. Schulze

Recommended Literature

• Dekker JP, Boekema EJ (2004) Supramolecular organization of thylakoid membrane proteins in green plants. Biochim Biophys Acta (Bio-energetics) in press

• Huner NPA, Oquist G, Sarhan F (1998) Energy balance and acclimation to light and cold. Trends Plant Sci 3:224-230

• Long SR, Humphries S (1994) Photoinhibition of photosynthesis in nature. Annu Rev Plant Physiol Plant Mol Biol 45:633-662

• Liittge U (1997) Physiological ecology of tropical plants. Springer, Berlin Heidelberg New York

• Pessarakli M (1997) Handbook of photosynthesis. Marcel Dekker, New York

• Wada M, Suetsugu N (2004) Plant organelle positioning. Curr Op Plant Biol 7:626-631

Sunlight, by far the dominating energy source for all life on earth, varies from place to place, time of day to time of day, and season to season, in intensity and also in spectral composition (UV light will be discussed in a separate chapter). As primary producers, plants need to adapt to different light environments. Too little light means a negative energy balance, i.e. gain from photosynthesis does not cover energy require-

Rosette leaf

Natural position

Return to vertical position

Return to vertical position

Bud leaf

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