Photosynthesis, respiration, and chlorophylls in presenescent, regreened, and senescent leaves of forest herb Smyrnium perfoliatum L. (Apiaceae)

Smyrnium perfoliatum L. (Apiaceae), an endangered forest herb with only one main locality in South-West Slovakia (Devínska Kobyla in the Little Carpathian Mountains), is capable to recover chlorophylls at the end of the growing season. This regreening only within bracts was observed during two weeks before achieving the so-called “point of no return” that leads to the last stage of ontogenesis — leaf senescence. The effect not only of endogenous cytokinins on chlorophyll content and carbon dioxide exchange (photosynthesis, mitochondrial respiration, and photorespiration) is discussed but also of other factors such as strong irradiance, high temperature or drought stress on studied parameters was considered.