The effect of drought stress (DS) on photosynthesis and photosynthesis-related enzyme activities was investigated in F. pringlei (C3), F. floridana (C3-C4), F. brownii (C4-like), and F. trinervia (C4) species. Stomatal closure was observed in all species, probably being the main cause for the decline in photosynthesis in the C3 species under ambient conditions. In vitro ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and stromal fructose 1,6-bisphosphatase (sFBP) activities were sufficient to interpret the net photosynthetic rates (PN), but, from the decreases in PN values under high CO2 (C a = 700 µmol mol- 1) it is concluded that a decrease in the in vivo rate of the RuBPCO reaction may be an additional limiting factor under DS in the C3 species. The observed decline in the photosynthesis capacity of the C3-C4 species is suggested to be associated both to in vivo decreases of RuBPCO activity and of the RuBP regeneration rate. The decline of the maximum PN observed in the C4-like species under DS was probably attributed to a decrease in maximum RuBPCO activity and/or to decrease of enzyme substrate (RuBP or PEP) regeneration rates. In the C4 species, the decline of both in vivo photosynthesis and photosynthetic capacity could be due to in vivo inhibition of the phosphoenolpyruvate carboxylase (PEPC) by a twofold increase of the malate concentration observed in mesophyll cell extracts from DS plants. and M. C. Dias, W. Brüggemann.
The distribution of the carboxylating enzyme nbulose-l,5-bisphosphate carboxylase/oxygenase (RuBPCO) and an enzyme of the photorespiratory pathway (glycine decarboxylase) was determined within the leaf tissue by immunocytochemical techniques in C3, C4 and C3:C4 intermediate species. The specificity of the method for all the materiál was demonstrated by sodium dodecyl sulphate acrylamide gels and Western blotting of crude protein extracts. In the C3 species (wheat) the enzymes were located in chloroplasts (RuBPCO) and mitochondria (glycine decarboxylase) of mesophyll cells, while in the three "classical" C4 standards, i.e. Zea mays ("NADP-ME" type). Panicům maximum ("PCK" type) and P. turgidum ("NAD-ME" type), these were found exclusively in the respective organelles of the bundle sheath. In the intermediate species, RuBPCO was not compartmented as it was located in chloroplasts of mesophyll and bundle sheath cells. Yet glycine decarboxylase was found exclusively in bundle sheath mitochondria. InAristida funiculata, a C4 species with "non-classical" leaf structure, RuBPCO was found in chloroplasts of both the inner and outer bundle sheaths and glycine decarboxylase was located exclusively in mitochondria of the inner bundle sheath cells. It is suggested that A. funiculata may be a C4 species with C3:C4-like intermediate characteristics based on the observed distribution of glycine decarboxylase, although gas-exchange characteristics of this species are required before any reclassification can be considered.
Influence of moderate chilling stress on vascular bundle sheath cell (BSC) and especially mesophyll cell (MC) chloroplasts of mature maize leaves was studied by electron microscopy and stereology. Plants of two inbred lines of maize, differing in their photosynthetic activity, and their F1 hybrids were cultivated during autumn in heated or unheated glasshouse. Generally, chilling temperatures resulted mainly in the decrease in stereological volume density (VD) of both granal and intergranal thylakoids of MC chloroplasts, while the ratio of granal to all thylakoids (granality) was less affected. The VD of peripheral reticulum and plastoglobuli usually increased after cold treatment of plants. The volume of MC chloroplasts usually increased under chilling stress, the shape of the chloroplasts changed only slightly. The ultra-structure of chloroplasts differed between individual genotypes; chilling-stressed hybrid plants showed positive heterosis particularly in the granal thylakoids' VD of MC chloroplasts. and J. Kutík ... [et al.].