The investigation dealt with starch accumulation in four species of Cuscuta {CiLsciita cnmpcvtri.s, (.. indecora, C. phmiflorit and (.. refh'xn), a leafy mistletoe {Driulrophthne falcatn] and a chloropbyll-lackiog root parasite {Orobanche acgypti(fca}. The highest content of .starcti occurred In O. acgypliaca, witb a maximum of 45 per cent of dry weigbt. Starch in Cuscuta filaments and mistletoe leaves showed a maximum of about 10 per cent of dry weight. The starch content varied along the length of the Cuscula vine, with a maximum in the apical region. Orobanche hati a higher starcli content when it was still submerged than it was fully developed. Cuscuta vines did not show any marked diurnal alteration in tbe starch content. The content of etbanol-soluble carbohydrate was only a tenth of the starch in Orobancbe, but was relatively bigber in tbe other parasites. Tbe neutral sugars in Cnscuta filaments were sucrose and glucose, whereas fructose was also present in mistletoe and Orobanche. Raffinose and stachyose were absent or present only ill traces in parasite tissue. Starcli granules from Cuscuta and Orobanche bad .\l)P(i/UI)P(i-starcb synthetase activity and homogenates starch phospborylase activity. Tbe former enzyme appeared to be responsible for synthesis of starch and the latter for utilization. Tbe four different species of Cuscnta, growing on alfalfa, had more or less the same activity of starcb syntbetase and also of i)hospborylase activity. Hosts infected by Cuscuta bad significantly less starch per plant tlian tbe controls. A characteristic feature of invasion by Cuscuta and Orobanche was increased phos-|»borylase activity in the bost tissues. The protein content of the tissues of Cuscuta and Orobanche was of a lower level tban that of tbe bost shoot system or foliage, indicating that tbe parasite differed from the host in having a Iiigher carbon (of starch) to nitrogen (of protein) ratio.;i. '> Fhysiol. Plant., 21, l')'iS [525] Phyaiol. riant.. 21,1968

No abstract

Field experiments were conducted at the village Kasiadihi, Dhenkanal district, Orissa, India during wet seasons 2001, 2002 and 2003 under non water-stressed conditions (0–25 cm standing water) to assess variability in N uptake and utilization by medium and late duration rice varieties. The N rates were 0, 40, 80 and 120 kg N/ha applied as urea in four equal splits at transplanting, active tiller initiation, panicle initiation and flowering stages. The grain yield response was up to 80 kg N/ha. The optimum grain yield attainable by the efficient medium duration varieties was 4·5 t/ha. The N efficient late duration varieties produced optimum grain yield of 5·8 t/ha. The relationship for total dry matter and grain yield production between N fertilized (40, 80 and 120 kg N/ha) and non-fertilized treatments were all significant, suggesting cultivar selection under optimum N fertilized conditions. The difference in optimum yield of the medium and late duration varieties was due to the differences in the amount of N uptake and its use efficiency by the plant for grain production. There was a curvilinear relationship between grain yield and N use efficiency for grain production. The relationship between N use efficiency for grain production and N contents of leaf, stem and grain at maturity was quadratic. The optimum plant N use efficiency of medium duration varieties was 49 kg grain/kg N uptake, achieved with leaf, stem and grain N contents of 10, 8 and 14 g/kg, respectively, at maturity. For late duration varieties, the optimum plant N use efficiency was 68 kg grain/kg N uptake and it was maintained with leaf and stem N content of 4·0 g/kg each and grain N content of 9·0 g/kg at maturity. The N content in plant organs could be the selection guide used to obtain efficient rice varieties.

1. In kidney, but not in rat whole brain and liver, guanine-deaminase activity was localized almost exclusively in the 15 OOOg supernatant fraction of iso-osmotic sucrose homogenates. However, as in brain and liver, the enzymic activity recovered in the supernatant was higher than that in the whole homogenate. The particulate fractions of kidney, especially the heavy mitochondria, brought about powerful inhibition of the supernatant guanine-deaminase activity. 2. In spleen, as in kidney, guanine-deaminase activity was localized in the 15 OOOg supernatant fraction of iso-osmotic sucrose homogenates. However, the particulate fractions did not inhibit the activity of the supernatant. 3. Guanine-deaminase activity in rat brain was absent from the cerebellum and present only in the cerebral hemispheres. The inhibitor of guanine deaminase was located exclusively in the cerebellum, where it was associated with the particles sedimenting at 5000g from sucrose homogenates. 4. Homogenates of cerebral hemispheres, the separated cortex or the remaining portion ofthe hemispheres had significantly higher guaninedeaminase activity than homogenates of whole brain. The enzymic activity of the suboellular particulate fractions was nearly the same. 5. Guanine deaminase was purified from the 15 OOOg supernatant of sucrose homogenates of whole brain. The enzyme separated as two distinct fractions, A and B, on DEAE-cellulose columns. 6. The guanine-deaminase activity of the light-mitochondrial fraction of whole brain was fully exposed and solubilized by treatment with Triton X-100, and partially purified. 7. Tested in the form of crude preparations, the inhibitor from kidney did not act on the brain and liver supernatant enzymes and the inhibitor from cerebellum did not act on kidney enzyme, but the inhibitor from liver acted on both brain and kidney enzyme. 8. The inhibitor of guanine deaminase was purified from the heavy mitochondria of whole brain and liver and the 5000g residue of cerebellum, isolated from iso-osmotic homogenates. The inhibitor appeared to be protein in nature and was heat-labile. The inhibition of the enzyme was non-competitive. 9. Kinetic, immunochemical and electrophoretic studies with the preparations purified from brain revealed that the enzyme from light mitochondria was distinct from enzyme B from the supernatant. A distinction between the two forms of supernatant enzyme was less certain. 10. Guanine deaminase isolated fromlight mitochondria ofbrain did not react with 8-azaguanine or with the inhibitor isolated from heavy mitochondria.

Leaf senescence in the rice (Oryza sativa) cultivars FR13A and IR42 under submergence was assessed in terms of changes in total chlorophyll, soluble amino acids and protein concentrations and peroxidase activity in crude extracts. The objective was to determine whether delay in leaf senescence was related to the submergence tolerance of a rice cultivar. Submergence induced senescence and its extent was notably dierent in the two cultivars. Results indicated a reduction in chlorophyll and protein concentrations in leaves during submergence but an increase in amino acid concentration and peroxidase activity. These relative changes were more pronounced in submergence intolerant IR42 than in tolerant FR13A even at four days after complete submergence. When plants were desubmerged and returned to standard irrigated conditions after 10 days of complete submergence the rate of recovery was dierent for the two cultivars. FR13A showed a greater protein and chlorophyll restoring ability compared with the intolerant IR42. The dierences observed between the responses of FR13A and IR42 to submergence were likely to be due to dierences in proteolysis. Senescence of leaves due to submergence was similar to the senescence of non-submerged excised leaves. Results demonstrate that, in the two cultivars studied, leaf senescence is an important biochemical mechanism in plants under submergence and its slower development in tolerant cultivars is, in part, responsible for submergence tolerance.