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Morphological organization is the expression of optimality of living state. This is also reflected in leaf structure. Leaf anatomy is organized for the optimal use of light and coordination of processes connected with photosynthesis. The optimum photosynthetic performance of leaves is linked to the location and concentration of different enzymes related to photosynthetic process within the leaves. Spatial distribution of photosynthetic and respiratory activities within spinach (Spinacia oleracea L.) leaves has been investigated using non-freezing vibrational microtomy. Sun and shade leaves were cut into 7 cross-sections and distribution of enzymes and oxygen uptake by mitochondria were studied.  The maximum activity of chloroplastic enzymes performing photosynthetic CO₂ fixation was in the middle of the palisade mesophyll, where the photon flux density is not necessarily the greatest. This profile was sharper in sun than in shade leaves. The similar profiles were revealed for the enzymes participating in photorespiratory processes. Most mitochondrial enzymes, except photorespiratory glycine decarboxylase, revealed the opposite profile, being twice as active towards the bottom of leaf. Mitochondria isolated from different leaf sections differed in their rates of oxidation of respiratory substrates (succinate, malate) and photorespiratory substrate (glycine). Differences in mitochondria in their response to different substrates and in loading by different enzymes indicate their involvement to carrying out of different functions at different levels of leaf depth. The distribution of enzymes within the leaf provides for optimal coordination between different metabolic processes (photosynthesis, mitochondrial respiration, photorespiration).
 

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