Carl S. Pike

Effects of acclimation to low temperature and to water stress on photosynthesis and on physical and chemical properties of lipids from thylakoids of cucumber and cotton

Abstract The effects of growth at low temperature and under water stress on the physical and chemical properties of lipids of thylakoids from leaves of cucumber ( Cucumis sativis L. cv. Beit Alpha MR) and cotton ( Gossypium hirsutum L. cv. glandless Stoneville 213) were examined. The phospholipid transition temperature (measured by fluorescence polarization) was not different in cold-grown, water-stressed, or warm-grown control plants. These treatments also had no effect on the critical temperatures for chilling injury to photosynthetic oxygen evolution or for heat-induced increase in chlorophyll fluorescence. The molecular species compositions of cucumber and cotton thylakoid phosphatidylglycerols were compared to those of other chilling-sensitive plants and to those of plants able to acclimate. The acclimation treatments caused no changes in the phosphatidylglycerol molecular species of cucumber. However, in cold-grown cotton there was a marked decrease in the content of molecular species with high melting points. Collectively the results suggest that changes in phosphatidylglycerol molecular species composition are not always indicative of a critical process required for chilling resistance.

Zinc toxicity in corn as a result of a geochemical anomaly

SummaryCorn grown on zinc-rich soil (adjacent to an abandoned zinc mine) showed severe chlorosis and stunting. Soil zinc content was positively correlated with leaf zinc content, but not correlated with leaf iron content. Soil zinc was negatively correlated, and soil iron positively correlated, with chlorophyll content. Excess zinc may interfere with iron metabolism in the plant, but does not appear to affect the iron supply to the leaf.

Nitrate reductase: A model system for the investigation of enzyme induction in eukaryotes

Plant nitrate reductase is an easily studied enzyme whose induction by various signals can be explored in inquiry‐based undergraduate laboratories. Barley, mustard, and radish seedlings are grown for 3–7 days with different light conditions and nitrogen nutrition. The enzyme activity of crude extracts is assayed in a colorimetric procedure. The protocols can be used in student independent research projects.