A reproducible method of Agrobacterium-mediated transformation was developed for Cicer arietinum (chickpea). Initial explants consisted of longitudinal slices from embryonic axes of imbibed, mature seed. The plasmid contained a bi-functional fusion gene conferring both beta-glucuronidase and neomycin phosphotransferase activities, under the control of a 35S35SAMV promoter. Using a series of tissue culture media for co-cultivation, shoot initiation and rooting, we recovered transgenic plants from approximately 1.3% of the sliced embryo axes. The addition of a shoot elongation medium to the protocol improved the success rate to 3.1% but increased the time in tissue culture. Inheritance of the gus gene was followed through four generations, both through expression and Southern hybridization assays, and showed the expected Mendelian inheritance pattern.

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Sunflower (Helianthus annuus L.) leaf discs were exposed to (14)CO2 or (14)CO2 followed by (12)CO2 at 21% O2 and three different CO2 concentrations. After intervals of up to 15 min, the specific activity of some photosynthetic intermediates was determined. At all CO2 concentrations, the specific activity of 3-phosphoglyceric acid (3-PGA) increased most rapidly and after 15 min of (14)CO2 feeding was 92% (967 ppm CO2), 87% (400 ppm CO2) and 53% (115 ppm CO2) of CO2 supplied to the assimilation chamber. The specific activity of glycine, serine and the photorespiratory CO2 was similar at all CO2 concentrations, in aggreement with their proposed close metabolic relationship in the glycolate pathway. However, the kinetics of serine and glycine labelling suggested that serine was not totally derived from glycine. Because the specific activity of these glycolate-pathway intermediates was very differnet from that of 3-PGA at all CO2 concentrations, not all of the carbon traversing this pathway came directly from the Calvin cycle. The non-equilibration of the 3-PGA with the feeding gas reflects the recycling of C from the glycolate pathway into the photosynthetic reduction cycle. Measurements of the rates of CO2 evolution in the light and estimates of the C flux through the glycolate pathway suggest that the photorespiratory activity was high and similar at 115 ppm CO2 and 400 ppm CO2 but inhibited at 967 ppm CO2.

The effects of position and age of leaves on CO2 exchange rate (CER) are described for a single-cross corn (Zea mays L.) hybrid ('Harrow 691') grown at 10-h and 20-h photoperiods. The effect of leaf age is also described for barren plants grown at a 10-h photoperiod.CER of newly matured leaves increased from leaf 3 to leaf 6 (10 h) or 8 (20 h). The rates were not significantly different for leaves 6 to 13, but were lower for leaf 14, at 10 h; while the rate for leaf 10 was lower than for leaf 8 but not different from that for leaves 11–15, at 20 h.CER declined with leaf age, but the rate of decline was reduced after pollination at both 10 h and 20 h. The stomatal resistance changed little for a period of 4 to 5 weeks following silking. The decline in CER of all leaves studied for barren plants was smooth, with the rate being unaffected in the postsilking period; in these plants changes in stomatal resistance closely reflected the decrease in photosynthetic rates.The results emphasize that the CER of newly matured leaves was lower for leaves produced in the early stages of ontogeny than for those maturing later, and that the pattern of decline with age in photosynthetic activity varied considerably amongst those leaves that would have been contributing assimilates to the developing ear.

Pisum sativum L. cv. Trapper plants were inoculated and grown in a controlled environment on N-free nutrient solution. After 4 weeks N was supplied to treatment plants as NH4NO3, KNO3, or NH.C1 and rates of C2H2 reduction, root + nodule respiration, and leaf photosynthesis were determined 1 week later. The increase in respiration per unit of C2H2 reduction was not affected by either the fonn of N added or the light conditions during growth, although the basal respiation rate with no C2H2 reduction increased with iradiance level. The mean regression coefficient from plots of respiration versus C2H2 reduction was 0.23 + 0.04 (P . ; .01) mg of CO2 (jmol of C2H2 reduced)-1 which was very similar to the value for the coefficient of respiration associated with nitrogenase activity estimated by subtracting growth and maintenance respiration. Since the rate of N accumulation in N-free nutrient conditions was proportional to the rate of C2H2 reduction, it appears that the method gives a true estimate of the energy requirements for N fixation which for these conditions was equivalent to 17 grams of carbohydrate consumed per gram of N fixed.Because of recent evidence that symbiotic N fixation can be limited by energy supply from the host plant (8, 11,12,20) there is increasing interest in the efficiency of energy use by the N-fixing reactions (6,15,19). Although the theoretical energy requirements for N fixation and nitrate reduction are similarly high (5,8,15), the difficulties in estimating the in vivo energy consumption (1, 3, 5, 15) have prevented any critical examination of the relative efficiency of energy use by the two processes.In a previous report (13), it was suggested that an extension of the two-component respiration model (14,22) to include a fixation component could provide the basis for estimating the respiration directly related to the fixation process. After comparing the effects of several treatments on the rates of both root + nodule respiration and C2H2 reduction (13); it was concluded that addition of NH4NO3 to nodulated plants decreased the respiration associated with nitrogenase activity while causing little difference in growth and maintenance components as compared to N-free treated plants of similar age. A comparison of the changes in respiration and C2H2 reduction under these conditions should be useful in assessing the energy requirements of N fixation. However, difficulties with parallel changes in other respiration components, high variability within a single symbiotic system, and the indirect nature of the C2H2 reduction assay could decrease the utility of this method. Therefore before the method can be applied to comparison of different symbiont genotypes, these possible problems must be examined and minimized. Measuring System. All measurements were made in the laboratory gas exchange system described previously (13). Rates of C2H2 reduction were determined from gas chromatographic analysis of C2H4 10, 20, and 30 min after the injection of C2H2 to a final concentration of 0.02 at...