Influence of environmental conditions on the ovarian cycle and serum chemistry of Cyprinus carpio in the Dal lake, Kashmir (India)

SUMMARY 1. The study presents adaptive and acclimatory changes observed in Cyprinus carpio communis L with respect to ovarian cycle and serum levels of electrolytes, calcium, total proteins and albumin as a consequence of wide temperature and sunshine variation in the natural environment of Dal lake in Srinagar, Kashmir (India).
2. The atmospheric temperatures in Srinagar show well-defined seasonal and diurnal variations. During the period of study, the mean monthly average temperature in summer (June-August) was 24°C whereas in winter (December-February) it fell to 3.6°C. The total hours of sunshine during the winter months were about half of those found in summer.
3. Under local thermal and photo conditions the fish was found to spawn once a year compared to biannual spawning in tropical chmates.
4. A significant decrease was found in serum sodium, potassium and chloride concentrations during the months of January and February when the mean minimum atmospheric temperatures reached −2.5°C and −l.2°C respectively.
5. The serum calcium levels showed a marked increase during the period corresponding to ovarian maturity and spawning of fish.
6. A significant rise in total serum protein concentration was induced by decreased environmental temperatures. Serum albumin levels were found to exhibit a sharp fall coinciding with the spawning period.     

Rubisco Activity: Effects of Drought Stress

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activityis modulated in vivo either by reaction with CO₂ and Mg²⁺ tocarbamylate a lysine residue in the catalytic site, or by thebinding of inhibitors within the catalytic site. Binding ofinhibitors blocks either activity or the carbamylation of thelysine residue that is essential for activity. At night, inmany species, 2-carboxyarabinitol-1-phosphate (CA1P) is formedwhich binds tightly to Rubisco, inhibiting catalytic activity.Recent work has shown that tight-binding inhibitors can alsodecrease Rubisco activity in the light and contribute to theregulation of Rubisco activity. Here we determine the influencethat such inhibitors of Rubisco exert on catalytic activityduring drought stress. In tobacco plants, ‘total Rubiscoactivity’, i.e. the activity following pre-incubationwith CO₂ and Mg²⁺, was positively correlated with leaf relativewater content. However, ‘total Rubisco activity’in extracts from leaves with low water potential increased markedlywhen tightly bound inhibitors were removed, thus increasingthe number of catalytic sites available. This suggests thatin tobacco the decrease of Rubisco activity under drought stressis not primarily the result of changes in activation by CO₂and Mg²⁺ but due rather to the presence of tight-binding inhibitors.The amounts of inhibitor present in leaves of droughted tobaccobased on the decrease in Rubisco activity per mg soluble proteinwere usually much greater than the amounts of the known inhibitors(CA1P and ‘daytime inhibitor’) that can be recoveredin acid extracts. Alternative explanations for the differencebetween maximal and total activities are discussed.