A B S T R A C T The fatty acid composition of sunflower (Helianthus annuusL

The diurnal pattern of nitrate uptake by Capsicum annuum L. cv. California Wonder in a constant environment is described by a Fourier harmonic, with the maximum uptake in the middle of the photoperiod and the minimum in the middle of the dark period. Comparison of the uptake pattern with that of nitrate reductase (EC 1.6.6.1.) activity suggests against a direct control of one process by the other. This was confirmed by the observation that the pattern of nitrate reductase activity was not altered by restricting nitrate uptake to one hour per day. Translocation of (15)N from the roots is much greater in the lightperiod than in the dark period. Reduction of (15)N in the leaves occurs in the lightperiod but very little is reduced in the dark period. Amino acid levels showed marked daily fluctuations but in the roots neither amino acids, sucrose, fructose, glucose nor malate showed fluctuations. The amino acid composition of roots and leaves differed: glutamine+glutamate were relatively more important in leaves than in roots whereas alanine was a more important constituent of roots than of leaves.

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Expanding leaves of Capsicuin frutescens L. cv. California Wonder, Cucumis melo L. cv. Hales Best, and Citrus sinensis L. Osbeck cv. Washington Navel showed a marked diurnal periodicity in the incorporation of "C from photosynthetically fixed "CO2 into amino acids. Incorporation was virtually nil at the beginning of the photoperiod, reached a maximum in the 6th to 7th hour and decreased during the latter part of the photoperiod. In Capsicum frutescens this was apparently a reflection of the availability of reduced nitrogen controlled by the activity of nitrate reductase in the leaves. This also controlled the periodicity of the incorporation of "C into fraction I protein. Possible control mechanisms and the relation of nitrogen metabolism to the periodicity of leaf expansion growth are discussed.Despite the extensive literature on carbon metabolism in photosynthesis in higher plants, there is little information on variations in the flow of carbon to photosynthetic products with respect to the time of day. Before the influence of environmental factors on photosynthetic carbon metabolism can be studied, it seems necessary to establish the basic patterns of diurnal variations in metabolism. Filippova (8) Cary (7).The experimental material was in all cases intact expanding leaves, and in any one experiment the leaves used were of the same insertion number. Comparable leaves of Capsicumit fruScientific and Inidlustrial Research Organization, Griffith, tescens and Cucumis melo were selected on the basis of laminar area and leaf plastochron index using an arbitrary leaf length value of 10 mm (17, 18) and 20 mm for the respective species. In the experiments reported, leaf 2 of Capsicum frutescens has an LPI' of about 5.0 and an area of 10 cm2, and leaf 3 an LPI of 8.0 and an area of 10 cm2. The values for Cucumis melo were LPI of 1.40 and area 38 cm2. LPI values were not estimated for the flush of Citrus sinensis, but halfexpanded leaves were used with a leaf area of close to 17 cm2."CO2 Presentation and Isolation of Labeled Compounds. The experimental plants were moved from the greenhouse to a controlled temperature and light environment on the afternoon preceding the experimental day. The day length of the experimental day was the same as the current natural day, but the incident light intensity and temperature (25 ± 1.5 C) were constant. In early experiments the lighting was provided by fluorescent lamps, but later experiments used a combination of metal arc and tungsten lamps. Light intensity during each experiment was measured with an ISCO spectroradiometer and is quoted in the "Results" section for the waveband 400 to 700 nm.Trace amounts of "'CO2 were used to supplement air, and, assuming the CO, concentration to be 300 Mul/liter, the level of radioactivity provided was 20 ptc in 10 ,umoles of CO2. In an experiment where the CO2 concentration was doubled to an assumed 600 ,tl/liter the pattern of variation in photosynthetic products was no different from that in normal CO2 levels.Leaves were presented w...

Inflorescence leaves improve fruit set on sweet orange trees. We sought an explanation for this effect in terms of carbon demand by developing fruit versus potential supply from adjacent leaves. Our assessment was based upon measurements of fruit growth, leaf photosynthesis and 14C distribution patterns in plants grown under controlled conditions. Leafy inflorescences had sufficient foliar surface (1.24 dm2) and photosynthetic capacity (CO2 10.1 mg · dm‐2· h‐1) to support early development of fruits on the same shoot, and to make a substantial contribution towards subsequent growth. 14C‐assimilates derived from new leaves were distributed towards adjacent fruit which showed strong competition for labelled substrate. By contrast, fruit borne on leafless inflorescences had to obtain all their assimilates from older leaves whose photosynthetic capacity (CO2 3.5–4.6 mg · dm‐2· h‐1) and individual area (0.2 dm2) were generally insufficient to wholly sustain fruit growth, so that a large number of old‐leaves were needed; these fruit would be more susceptible to competition from other sinks.