Malic acid temperature effects

Addition of salts, adds and bases tend to make the laevo-rotary acid more dextro-rotary. With rising temperature, the pure add and also the solutions become more laevo-rotary. These changes cannot be due to dectrolytic dissociation, because the effect of hydrochloric acid is quite marked up to rdatively high concentrations and it would take relatively little acid to force back the dissociation of malic acid to a negligible value. Another reason is that we get a similar change with the concentration with malic ester in alcoholic solution. 

It must be mentioned that the discussion of temperature effects is complicated by the fact that CAM is modified both by direct temperatures and to a great extent by temperature pretreatment. In general, it is well known that low night temperatures favor nocturnal acid accumulation (for example DeVries, 1884 Richards, 1915). Below 5° and above 30° C, nocturnal malic acid synthesis is inhibited. 

Wood (1952) showed the enhancing effect of CO2 concentration up to 10% on dark malic acid synthesis to be temperature-dependent. There was greater stimulation at 6° C compared with 19° C. 

There is overwhelming evidence that high night temperatures inhibit malic acid accumulation in CAM plants, whereas low night temperatures have the opposite effect (see reviews of Wolf, 1960 Ranson and Thomas, 1960 see Chap. 4.3.1). Because malic acid is the end product of the metabolic pathway of dark CO2 fixation, it is reasonable to predict that CO2 exchange during the night would also be affected by temperature. 

Brandon (1967) concluded from in vitro experiments that the thermal properties of the carboxylating and decarboxylating enzymes (PEP carboxylase, malic enzyme, see Chap.4.2.3.2) are such that lower temperatures would favor CO2 consumption (i.e., malic acid synthesis) higher temperatures, however, would increase CO2 production by malic acid decarboxylation. Hence, the thermal properties of the enzymic proteins could account partly for the observed temperature effects. 

Vickery, H. B. The effect of temperature on the behaviour of malic acid and starch in leaves of Bryophyllum calycinum cultured in darkness. Plant Physiol. 29,385-392 (1954 a)... 

Varga et al. measured surface tension at room temperature of aqueous solutions of oxalic, malonic, succinic, glutaric, adipic, maleic, malic, citric, and c/s-pinonic acid [96]. Surface tension decreased with increasing hydrophobic chain length. c -Pinonic acid was found to decrease the surface tension effectively over a wider range of concentrations than the other organics. 

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