Diurnal acid cycle

This leads to problems. As desirable as the reduction of water loss is, it is just as undesirable that the uptake of the CO2 needed for photosynthesis be inhibited. A loophole is provided in the diurnal acid cycle which is widely distributed in the plant kingdom but particularly well developed in succulents, apparently in adaptation to the conditions mentioned. At least up to now no better explanation has been found for the fact that in succulents the diurnal acid cycle has been pushed to the extreme. 

Fig. 218. CO2 fixation occurring twice during the overnight acidification in the diurnal acid cycle (tandem hypothesis).

After our digression into the diurnal acid cycle of the succulents, let us return to the mechanism of water transport in the xylem. We have already pointed out that the root pressure can only be of secondary impor-... 

Malic acid monohydroxysuccinic acid, HOOC-CHOH-CHj- OOH, a dicarboxylic acid found in many plant juices, usually in the L(-i-)-form, m.p. 100°C, b.p. 140°C (d.). The malate ion is formed in the Thcarboxylic acid cycle (see) and in the Glyoxy-late cycle (see). Malate plays an important role in the Diurnal acid rhythm (see) of the Crassulaceae (stonecrop family). 

Modification of the Diurnal Malic Acid Cycle by External Factors... 

Effects of temperature on the diurnal pattern of CO2 exchange in CAM are discussed in Chapter 5. In the following section, effects of temperature on the day/ night acid cycle of CAM will be briefly considered (for detailed phenomenology see Wolf, 1960). 

Gender is not an important determinant of plasma amino acid levels. Females have a tendency toward small changes of their amino acid levels during the menstrual cycle. However these changes are barely distinguishable from the normal diurnal changes and dietary influences. 

Fig. 19. UV chromatograms of the urine of normal subjects showing the effect of the diurnal cycle and the comparison between normal subjects. Run conditions column, 0.45 cm ID X 200 cm 316 stainless steel with 10-/t diameter Bio-Rad AG1-X8 urine samples, 2 ml each temperature, 25°C increasing to 60°C after 15 hours pressure, 1500-2300 psig elution, sodium acetate-acetic acid...

Biochemical studies with isolated rat hepatocytes have largely been concerned with transport mechanisms [15], secretion of bile acids [17-19], or biosynthesis of bile acids [20]. The capacity of cultured hepatocytes to convert tauro- or glyco-chenodeoxycholate to a- and )8-muricholates [19,21] and to produce bile salts (glycine or taurine conjugates) during the dark phase of the diurnal cycle [21] has been established. Demonstrations of other metabolic transformations by hepatocytes are included in the following sections. 

This indicates that PEPC was functioning in the light. However, the apparent operation of CAM was evident only in plants grown on 16 h/8 h light/dark cycle, as reflected by significant diurnal fluctuations of both titratable acidity and malate... 

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