Ontogenetic interactions between photosynthesis and symbiotic nitrogen fixation in pigeonpea

Total nodule nitrogenase activity (TNA, μmols ethylene plant^-1 h^-1) in pigeonpea (Cajanus cajari) increased with plant growth to reach maximum at flowering (75 days after sowing), decreasing thereafter until maturity (120 days after sowing). However, specific nodule nitrogenase activity (SNA, μmols ethylene g^-1 nodule fresh wt h^-1) reached its maximum earlier (45 days after sowing). The rate of photosynthesis and shoot and nodule respiration followed a similar pattern to TNA. However, higest rates of root respiration were observed at flowering and again immediately before final harvest. ¹⁴CO₂ feeding studies showed that assimilates produced in leaves before flowering were retained in the vegetative parts. Assimilates produced after flowering were exported to the reproductive structure at the expense of the nodules. It is suggested that the decreased availability of photosynthate to nodules decreased nitrogen fixation.     

Cytotaxonomic study in the order Falconiformes (Aves)

Karyotypes of six species of birds of the order Falconiformes are presented. The chromosomes of three of these, Neophron percnopterus, Butastur teesa (family Accipitridae) and Falco chicquera (family Falconidae) are described for the first time. The systematic position of these birds are discussed in relation to the karyological characters of other diurnal birds of prey.     

Ontogenetic Changes in the Level of Ureides and Enzymes of their Metabolism in Various Plant Parts of Pigeonpea (Cajanus cajan)

Levels of allantoin and allantoic acid in shoots, roots, nodulesand leaves of pigeonpea plant, in general, followed the patternof acetylene reduction in nodules, increasing progressivelyfrom 15 days after sowing (DAS) and attaining peaks at 75 DASand 60 DAS, respectively, except in shoots where their contentsevinced maximum values at pod-setting (90 DAS). Activity ofGS in nodules and shoots reached a maximum at 60 DAS and 75DAS, respectively. However, in leaves and roots, the enzymeshowed a biphasic behaviour with peaks at days 60 and 105 inleaves and at days 75 and 105 in roots. GDH activity in nodulespeaked at 60 DAS, whereas, in leaves and roots, the maximumactivity was observed at flowering (75 DAS). Uricase was presentonly in nodules with peak activity at flowering. Allantoinaseactivity again peaked at flowering, where nodules had maximumactivity followed by leaves, roots and shoots. Urease couldbe detected in all the organs with maximum activity at 60 DASin leaves followed by roots and nodules. Except uricase, allthe enzymes reported above were also present in reproductivestructures. Compared to GS, GDH was more active both in flowerbuds and developing pods. Seeds, compared to podwalls, containedhigher activities of GDH, allantoinase and urease at day 105.Only allantoin could be detected in seeds and podwalls at day105. Key words: Cajanus cajan, Allantoin, Allantoic acid, Nitrogenase, Glutamine synthetase, Glutamate dehydrogenase, Uricase, Allantoinase, Urease, Development     

Stem Cell Factor Regulates the Melanocyte Cytoskeleton

Stem cell factor is a growth factor for normal human melanocytes, that acts through the tyrosine kinase receptor c-kit. We have previously demonstrated that stem cell factor increases melanocyte adhesion and migration on fibronectin, and regulates integrin protein expression. In this report, we have characterized the effect of stem cell factor on the organization of the actin cytoskeleton in human melanocytes attached to fibronectin, and have examined the effect of stem cell factor on the phosphorylation of the focal contact protein paxillin and on the expression of the focal contact proteins talin, paxillin, vinculin, and α-actinin. Paxillin is a vinculin-binding protein that is a substrate of focal adhesion kinase, a nonreceptor tyrosine kinase, and in its phosphorylated form is believed to stabilize focal contacts. We show that stem cell factor induces a rapid increase in actin stress fiber formation in melanocytes, which can be abrogated by genistein, a tyrosine kinase inhibitor, and that stem cell factor induces phosphorylation of paxillin on tyrosine residues. In contrast, stem cell factor did not regulate expression of any of the four focal contact proteins tested. These findings have implications for the models describing the mechanisms of action of stem cell factor on melanocyte adhesion and migration, and suggest that reorganization of the cytoskeleton is a primary effect of stem cell factor on human melanocytes.     

Partitioning of Carbon and Nitrogen During Growth and Development of Pigeonpea (Cajanus cajan L.)

Budgets for C and N were computed for pigeonpea (Cajanus cajanL.) at 15 d intervals, for the entire life cycle. Maximum Cand N in dry matter was observed at 90 d after sowing. Of theplants total respiratory loss during the vegetative phase, shoots,roots and nodules accounted for 65%, 23% and 12%, respectively.During the reproductive phases, the respiratory burden of theroots increased, while that of shoots and nodules decreased.Total respiratory loss as a proportion of net photosynthateremained more or less constant until ‘flowering and pod-setting’but increased heavily during seed filling, losing nearly 75%of the photosynthate in respiration. The efficiency of nitrogenfixation, in relation to respiratory output of the whole plantand nodulated roots, decreased during the period 60–90d after sowing, while that of nodules decreased from day 45onwards. Photosynthate supply to nodules and nodulated rootsincreased up to 75 d and 90 d after sowing, respectively. During45–90 d, nodules were fixing a constant proportion ofN per unit of C translocated (0.2 mg N mg^–1 C). Nodulatedroots, on an average, fixed 0.07 mg N mg^–1 C translocatedin the vegetative phase and this value decreased considerablyduring the subsequent phases. The crop produced during its lifecycle 50.4 g of glucose equivalents and yielded 3.8 g seed drymatter and 0.8 g seed protein giving an average of 13.2 g g^–1seed dry matter and 62.8 g g^–1 seed protein. Selectioncriteria for the improvement of C, N economy in pigeonpea havebeen suggested. Key words: Cajanus cajan, Carbon, Nitrogen, Dry weight, Plant parts, Growth, Development, Models     

Partitioning and Utilization of Carbon and Nitrogen for Dry Matter and Protein Production in Chickpea (Cicer arietinum L.)

The partitioning of N and utilization of C in various processesin chickpea (Cicer arielinum L.) was studied at 10 d intervalsfrom 35 to 135 d after sowing (DAS). Dry matter, C and N contentof the plant increased throughout the study period. The maximumamounts of C and N were fixed during the flowering and earlyfruiting phase (75–115 DAS) and the minimum during theseed filling phase (115–135 DAS). Efficiency of nitrogenfixation in relation to net C utilization and respiratory outputof the whole plant, nodules and nodulated root, varied widely,but was maximum during 75–115 DAS. The crop experiencedsevere respiratory losses, particularly during the vegetativephase, when 83% of the total fixed C was lost in respiration.The crop produced 54·6 g of glucose units, 2·36g of seed dry matter and 495 mg of seed protein. Possible reasonsfor the poor efficiency of chickpea, in terms of photosynthateutilization for dry matter and protein production are discussed. Key words: Cicer arietinum, C, N, economy