Grasses of different C4 subtypes reveal leaf traits related to drought tolerance in their natural habitats: Changes in structure, water potential, and amino acid content.

Three grasses (Poaceae) of different C(4) subtypes, Paspalum dilatatum (NADP-malic enzyme [ME]), Cynodon dactylon (NAD-ME) and Zoysia japonica (phosphoenolpyruvate carboxykinase), occur in natural habitats that differ in annual rainfall. Their leaf characteristics were studied to identify traits related to drought tolerance. Plants were grown in pots, and water deficit was gradually induced by withholding water.

Drought stress increases the production of 5-hydroxynorvaline in two C4 grasses.

Plants produce various compounds in response to water deficit. Here, the presence and identification of a drought-inducible non-protein amino acid in the leaves of two C(4) grasses is first reported. The soluble amino acids extracted from the leaves of three different species were measured by high-performance liquid chromatography of derivatives formed with o-phthaldialdehyde and beta-mercaptoethanol.

The activities of PEP carboxylase and the C4 acid decarboxylases are little changed by drought stress in three C4 grasses of different subtypes.

The C4 photosynthetic pathway involves the assimilation of CO2 by phosphoenolpyruvate carboxylase (PEPC) and the subsequent decarboxylation of C4 acids. The enzymes of the CO2 concentrating mechanism could be affected under water deficit and limit C4 photosynthesis. Three different C4 grasses were submitted to gradually induced drought stress conditions: Paspalum dilatatum (NADP-malic enzyme, NADP-ME), Cynodon dactylon (NAD-malic enzyme, NAD-ME) and Zoysia japonica (PEP carboxykinase, PEPCK).

Rubisco regulation: a role for inhibitors.

In photosynthesis Rubisco catalyses the assimilation of CO(2) by the carboxylation of ribulose-1,5-bisphosphate. However, the catalytic properties of Rubisco are not optimal for current or projected environments and limit the efficiency of photosynthesis. Rubisco activity is highly regulated in response to short-term fluctuations in the environment, although such regulation may not be optimally poised for crop productivity.

Photorespiration in C4 grasses remains slow under drought conditions.

The CO(2)-concentrating mechanism present in C(4) plants decreases the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and, consequently, photorespiratory rates in air. Under drought conditions, the intercellular CO(2) concentration may decrease and cause photorespiration to increase. The C(4) grasses Paspalum dilatatum Poiret, Cynodon dactylon (L.

Photosynthetic responses of three C grasses of different metabolic subtypes to water deficit.

C plants are considered to be less sensitive to drought than C plants because of their CO concentrating mechanism. The C grasses, Paspalum dilatatum Poiret (NADP-ME), Cynodon dactylon (L.) Pers (NAD-ME) and Zoysia japonica Steudel (PEPCK) were compared in their response to water deficit imposed by the addition of polyethylene glycol to the nutrient solution in which they were grown.