Effects of chemical and environmental stress on cytochrome P-450 activity and phospholipid composition of midgut microsomal fraction in southern armyworm S̲p̲o̲ḏo̲p̲ṯe̲ṟa̲ e̲ṟi̲ḏa̲ṉi̲a̲ Cramer (noctuidae)

Date Issued
December 1, 1980
Author(s)
Nikbakht, Kave Noghrei
Advisor(s)
Lena B. Brattsten
Additional Advisor(s)
Robert H. Feinberd
Leaf Huang
Permanent URI
Abstract
The objective of this project was to study the effects of the temperature and two chemical inducers, namely pentamethylbenzene and phenobarbital on cytochrome P-450 activity and phospholipid composition of midgut microsomal fraction in southern armyworm Spodoptera eridania Cramer. We were also interested to know how the inductive properties of these chemicals might be modified in relation to the changes in the temperature. Finally, an analysis of fatty acyl composition of midgut microsomal phospholipids was performed at two temperatures (15 C and 30 °C). Low temperature (15 °c) caused a significant induction of both microsomal phospholipids and cytochrome P-450 activity. The inductive effect of the low temperature in microsomal phospholipids was through decreasing PE/PC ratio as the rate of PC induction was much higher than PE induction. From quantitative analysis of microsomal phospholipids, it turned out that the major phospholipid is phosphatidylcholine followed by phosphatidylethanolamine. The other microsomal phospholipids included phosphatidylserine and phosphatidylinositol. Both chemical inducers caused a substantial induction of microsomal phospholipids and cytochrome P-450 activity at 15 °C but pentamethylbenzene turned out to be a stronger inducer than phenobarbital. At 30 'C, however, the induction caused by pentamethylbenzene was not as strong as its induction at 15 'C and that of phenobarbital totally disappeared. It was concluded that the shift in the temperature had somehow modified the inductive properties of these chemicals. We also found out that the induction of microsomal phospholipids by pentamethylbenzene was through increasing the PE/PC ratio.

The induction of cytochrome P-450 activity which occurred along with the proliferation of the microsomal membranes was considered as a defensive adaptation mechanism developed by armyworms upon their exposure to the toxic foreign compounds. Fatty acyl analysis of microsomal phospholipids showed that at 15 c, the concentration of myristic, palmitic, stearic and palmitoleic acid decreases, whereas concentrations of two unsaturated fatty acids, namely oleic and linoleic increases at that temperature.

Since membrane fluidity affects the properties of a number of membrane-bound enzymes as well as transport proteins, this tendency toward higher levels of unsaturation at the low temperature presumably had some adaptive values for armyworms in order to cope with the external stress imposed on them.

Degree
Master of Science
File(s)
Thumbnail Image
Name

Thesis80N552.pdf

Size

2.81 MB

Format

Unknown

Checksum (MD5)

c4aa408672085e28951fcbc4e07d003f