Leaf photosynthesis and conductance of selected triticum species at different water potentials.

Leaf gas exchange characteristics of a desert annual (Triticum kotschyi [Boiss.] Bowden) and the wheat cultivar TAM W-101 (Triticum aestivum L. em Thell) were compared over a range of leaf water potentials from -0.50 to -2.9 megapascals. At an ambient [CO(2)] of 330 microliters per liter, T. kotschyi had higher conductance and CO(2) assimilation (A) at a given water potential than T. aestivum. Under well watered conditions, A versus internal CO(2) concentration (C(i)) response curves for both species were similar in shape and magnitude, and the higher A of T. kotschyi at an ambient [CO(2)] of 330 microliters per liter was mostly related to the higher stomatal conductance of T. kotschyi. The higher conductance of T. kotschyi than T. aestivum under well watered conditions was associated with higher C(i) and lower water use efficiency. Under water deficits, however, C(i) at 330 microliters per liter ambient [CO(2)] did not differ significantly between species. T. kotschyi had higher A under water deficits than T. aestivum primarily because its A versus C(i) response curves had higher A at C(i) values above about 150 microliters per liter. The results show that conductance played an important role in the high A of T. kotschyi under well watered conditions, but under water deficits the high A of T. kotschyi was related more to the maintenance of a higher capacity for mesophyll photosynthesis.

Increase in Internode Length of Phaseolus lunatus L. Caused by Inoculation with a Nitrate Reductase-deficient Strain of Rhizobium sp.

Dramatic differences in the height of lima beans (Phaseolus lunatus L.) treated with two different Rhizobium strains were studied. Lima beans were grown in Perlite in the greenhouse or in a minus-N culture solution in the growth chamber. The plants were inoculated with either Rhizobium sp. (lima bean) strain 127E15, which contains the constitutive nitrate reductase activity, or strain 127E14, which lacks that activity. For up to 3 weeks, no growth differences were observed in the plants inoculated with either strain. Five weeks after inoculation, however, those plants inoculated with strain 127E14 were significantly taller and had a larger number of leaves than those inoculated with strain 127E15. The difference in plant height was the result of increased internode elongation caused by inoculation with Rhizobium sp. 127E14. This response was observed with all lima bean cultivars tested, including Henderson, Fordhook, Allgreen, and Early Thorogreen. The growth difference occurred in plants cultured in the greenhouse or in the growth chamber.No differences were observed in fresh weights of nodules, roots, axes, leaves, or flowers. The number of nodules, pods, or flowers also did not differ. Acetylene reduction rates and total N content were equal in plants inoculated with strains 127E14 or 127E15.Inasmuch as only internode length and leaf number differed between Rhizobium treatments, the response appeared to be hormone-mediated. Application of gibberellic acid to the apex of plants inoculated with strain 127E15 caused an increase in plant height similar to that observed in untreated plants inoculated with strain 127E14. Conversely, the height of plants infected with strain 127E14 was decreased by application of gibberellin synthesis inhibitors to the root system. These data suggest that the increased growth caused by inoculation with strain 127E14 could be the result of increased gibberellin synthesis in lima bean nodules infected with that strain. Whether this response was related to the absence of nitrate reductase activity in strain 127E14 is unknown.