The Influence of Leaf Age on C4 Photosynthesis and the Accumulation of Inorganic Carbon in Flaveria trinervia, a C4 Dicot 1

AUTOR(ES)

Moore, Brandon d.

RESUMO

Characteristics of C4 photosynthesis were examined in young, mid-age, and mature leaves of Flaveria trinervia (an NADP-malic enzyme-type C4 dicot). The turnover of [4-14C] (malate plus aspartate) following a pulse with 14CO2 was similar in leaves of different ages (apparent half-time of 18-25 seconds). However, the rate of 14CO2 incorporation in mid-age leaves was about 1.5-fold higher than in young leaves, and about 2.5-fold higher than in mature leaves. The rate of 14CO2 fixation was proportional to the total active pool of malate plus aspartate but was not correlated with the total photosynthetically derived inorganic carbon pool. The leaf's ability to concentrate inorganic carbon photosynthetically declined during leaf expansion, from 29 down to 7 nanomoles per milligram chlorophyll. Similarly, the active aspartate pool also declined during leaf expansion, from about 123 down to 20 nanomoles per milligram chlorophyll. Enhanced metabolism of aspartate to CO2 and pyruvate in young leaves is suggested to facilitate the maintenance of high CO2 levels in bundle sheath cells which are thought to have a higher conductance to CO2.

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