A model for rhythmic and temperature-independent growth in ‘clock’ mutants of neurospora

The Q 10 for the frequency (number of bands per 24 hours) of the ‘clock’ mutant (strain CL11A) of Neurospora crassa over the range 20–30° C is close to 1.0. By contrast, that for the double mutant, ‘wrist watch’ (strain CL12a), is closer to 2 over this temperature range. Strain CL12a differs from ‘clock’ in other ways as well, including 1) decreased rate of linear extension and band size, 2) greater sensitivity of growth rate to high temperatures and, 3) masking of rhythmic growth below 15° C. The response to temperature of several colonial mutants and standard (‘wild-type’) strains was studied and it is shown that some strains are temperature-independent yet arhythmic. A temperature-compensation model is presented to explain the response of ‘clock’ mutants to temperature and it is concluded that they demonstrate a non-circadian free-running endogenous rhythm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43284/1/11046_2005_Article_BF02049924.pd

Effect of high and low sulfate concentrations on adenosine 5'-phosphosulfate sulfotransferase activity from Lemna minor

The effect of Na2SO4 concentrations from 0 to 17.6 mM in the nutrient solution of Lemna minor L. strain 6580 on adenosine 5′-phosphosulfate sulfotransferase activity was examined. Routinely, the plants were cultivated on 0.88 mA SO42−. The enzyme activity was increased by 50 to 100% after transfer to 0 or 0.0088 mM SO42−. Transfer back to 0.88 mM rapidly decreased the enzyme activity to the initial level. Cultivation on 17.6 mM Na2SO4 redueed extractable adenosine 5′-phosphosulfate sulfotransferase by 50%. The original level was rapidly re-established on 0,88 mM. In control experiments, a decrease in adenosine 5′-phosphosulfate sulfotransferase activity was also induced by K2 SO4, whereas NaCl caused a small increase. This indicates that the observed effects are dependent on the sulfate ion. ATP-sulfurylase activity measured for comparison was only significantly affected by the omission of sulfate, which induced a 20% increase, indicating that this enzyme activity from Lemna minor is less suseeptible to changes in medium sulfate than adenosine 5′-phosphosulfate sulfotransferase. A close relationship between adenosine 5′-phosphosulfate sulfotransferase activity and the content of asparagine, glutamine, non-protein thiols and sulfate in the tissue was detected, indicating a positive control mechanism induced by amides and a negative mechanism induced by thiols and sulfate