ph homeostasis of the circadian sporulation rhythm in clock mutants of Neurospora crassa

The influence of environmental (extracellular) pH on the sporulation rhythm in Neurospora crassa was investigated for wild-type (frq(+)) and the mutan ts chr, frq(1), frq(7), and frq(8). In all mutants, including wild type, th e growth rate was found to be influenced strongly by extracellular pH in th e range 4-9. On the other hand, for the same pH range, the period length of the sporulation rhythm is little influenced in wild type, chr, and frq(1). A loss of PH homeostasis of the period, however, was observed in the mutan ts frq(7) and frq(8), Which also are known to have lost temperature compens ation. Concerning the influence of extracellular pH on growth rates, a clea r correspondence between growth rates and the concentration of available H2 PO4- ion has been found, indicating that the uptake of H2PO4- may be a limi ting factor for growth under our experimental conditions. The loss of pH co mpensation in the frq(7) and frq(8) mutants may be related to less easily d egradable FRQ(7,8) proteins when compared with wild-type FRQ. Results from recent model considerations and experimental results predict that, with inc reasing extra- and intracellular pH, the FRQ(7) protein degradation increas es and should lead to shorter period lengths.