PHOTOSYNTHESIS AND METABOLIC CHANGES IN LEAVES OF RAPESEED GROWN UNDER LONG-TERM SULFATE DEPRIVATION

The effect of prolonged sulfur (S) deficiency on photosynthesis and S- containing compounds in leaves of rapeseed (Brassica napus L.) plants, grown in nutrient solution, was studied under greenhouse conditions. The rate of photosynthetic activity and stomatal conductance of water and CO2 in treated plants decreased significantly after 3 months of tr eatment. The total chlorophyll content decreased after one month of S deprivation, after which it remained constant. The total S content and both the water-soluble and non-protein soluble S fractions in the lea ves showed a marked decrease. Whereas, the total protein soluble S rem ained unaffected during the period of observation. In the treated plan ts, the content of two major S compounds, e.g., cysteine and glutathio ne, were as a result of deprivation, although in the control it showed a trend to increase. Sulfur deficiency also decreased appreciably the activity of ATP sulfurylase. After the three-month period of S depriv ation, this enzymatic activity was about four times lower than that in the control plants. The data reported in this paper suggested that pl ants grown under S deficiency were capable of adjusting their S metabo lism to maintain a sufficient protein and glutathione synthesis by low ering their photosynthetic activity.