Cotton (Gossypium hirsutum L.), sorghum (Sorghum bicolor L.), soybean (Glycine max L.), and sunflower (Helianthus annuus L.) plants were exposed during daylight hours to an atmosphere enriched with CO2 to 630 ppm (v:v) (HiCO2) in a glasshouse. Temperature was trolled continuously to produce a daily maximum of 35 C and a minimum of 21 C. Days were cloudless and long, May to August, in Phoenix, Ariz. Average CO2 exchange rate (CER) increased 15% for cotton, 2% for sorghum, 41% for soybean, and 7% for sunflower compared to the CER of these species at 330 ppm CO2 (LoCO2). The increase in CER was not statistically significant for sorghum and sunflower. Measurements of relative growth rate and net assimilation rate showed the growth rate of all species increased during the juvenile stage (10d‐30d) in the enriched atmosphere. and were not higher in the enriched atmosphere after the juvenile stage, but cotton and soybean plants maintained their larger size and greater absolute growth.Final dry weights of cotton and soybean increased 110 and 380%, respectively, in HiCO2 compared to LoCO2. Lint yield of cotton was increased 180% by HiCO2 on a per‐plant basis and 88% on a unit leaf area basis. Became of growth fimitations imposed by terminal flowers, the final size of sorghum and sunflower plants in HiCO2 was not significantly larger than in LoCO2 These results imply that selection for CER will not effectively increase yield of determinate species such as sunflower and sorghum, but may effectively increase yield of indeterminate species such as cotton and soybean, if a sensitive assay for CER can be found.

Techniques are needed for conserving water and shortening the cotton (Gossypium hirsutum L.) fruiting season in irrigated areas. We conducted field tests at Phoenix, Arizona during the summers of 1978 and 1979 to determine the influence of delaying the first irrigation on subsequent growth, fruiting, and yield of cotton grown in an Avondale clay loam (fine‐loamy, hyperthermic, Typic Torrifluvents). In 1978, the first post‐plant irrigation was applied when the first flower bud (square) became visible (E) or 14 days later (L). Two levels of irrigation during the remainder of the season, normal (N) or 0.6 normal (D), were used as subplots. Delaying the first irrigation slowed growth, square production, and leaf area development, and slightly decreased the number of bolls set by any given date. Despite these apparent adverse effects the LN treatment produced heavier bolls, fewer damaged bolls, and the highest yield. Although LN received 13 cm less water than EN, it produced an average of 606 kg more seed cotton per ha. Water deficit during the remainder of the season (D) greatly decreased growth and yield. In 1979, the first post‐plant irrigation was applied at the time of first visible square (E), 7 days later (M), or 16 days later (L). Two plant populations, 94,000 (Hi) and 52,000 (Lo) plants per ha were also variables. The final irrigation was applied 13 August to shorten the season. Despite a 16‐day delay in the first irrigation, one less irrigation, and a short‐season (early termination), L produced about the same yield as E. The low population produced slightly fewer blooms, but retained more and produced slightly higher yields than the high population. Treatment MLo produced the highest yield, and LLo gave the greatest water‐use efficiency. Delaying the first irrigation conserved water and gave satisfactory yields despite early termination in 1979. Although water deficit during the bloom stage hastened cutout, delaying the first irrigation had little effect on earliness. Likewise, low plant population caused no appreciable delay in setting the crop.

A method of plant culture was developed for growing large leaves of glandless cotton on single stems. Chloroplasts isolated from these leaves actively reduced ferricyanide when assayed for the Hill reaction. Hill reaction activity increased 133%o when the 0.5 M sucrose isolation medium was replaced with 10% (w/v) polyethylene glycol, both buffered at pH 7.6. The presence of 2 or 3% (w/v) Automatic irrigation with a nutrient solution kept the soil near field capacity. Controlled greenhouse temperatures were 30 ± 2 C during the day and 19 i 2 C at night.A serial set of primary leaves on each plant was obtained by removing all axillary growth. Each leaf was tagged on the day it was 1 to 2 cm wide. Leaves nearly the same chronological age were selected for the experiments. Potted plants were preconditioned for 24 hr in reduced light intensities (about 800 ft-c), primarily to reduce the size of the starch grains in the chloroplasts. Large grains usually ruptured the chloroplasts during the isolation procedures. Ten hours before analysis, the plant shoots and leaves were drenched with warm water and enclosed in a polyethylene bag in order to increase the leaf water potential to a maximum value (-3 to -5 bars). Just prior to chloroplast isolation, leaves were excised and placed in shaved ice. Water potentials of individual leaves as indicated were measured in a pressure chamber similar to that of Waring and Cleary (15).Chloroplast Isolation. Two-gram samples of deveined leaves were blended four times at high speed at 1 C, each time 4 sec On and 6 sec Off, in 40 ml of isolation medium consisting of 10%-(w 'v) polyethylene glycol and 0.1 M potassium phosphate buffer adjusted to a pH of 7.6. The homogenate was squeezed through nylon parachute cloth with a mean hole size of 43t X 75,. Extracts were centrifuged at 8000g for 3 min. After two washes with 25 ml of the isolation medium, the chloroplasts were stored for short periods in the isolation medium at 1 C. For longer periods the chloroplasts were stored in 10%-glycerol at -23 C.Assay for Hill Reaction. Ferricyanide reduction by illuminated cotton chloroplasts was assayed potentiometrically in a medium containing 0.5 M sucrose, 0.02 M KCl, 0.03 M MgCl2, and 0.02 M tris buffer at pH 7.4. Each assay totaling 6 ml contained initially 0.9 Amole of K3Fe(CN)6, 0.1 ,umole of K4Fe(CN)6.3H2O, and chloroplasts containing 0.1 mg of chlorophyll. The latter was determined according to the method of Arnon (1)

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Water stress was applied to cotton (Gossypium hirsutum L.) chloroplasts and leaves by the following treatments: (i) prepared chloroplasts were. placed in assay media different osmotic potentials; (ii) cut shoots were allowed to transpire under illumination; (iii) whole potted plants were held for 5 days without irrigation; and (iv) cell sap was expressed from individual leaves via the xylem in a pressure bomb. These treatments caused a decrease in ferricyanide reduction when isolated chloroplasts were assayed potentiometrically for the Hill reaction. The above treatments caused (i) 1.7%, (ii) 1.4%, (iii) 1.8%, and (iv) 1.9% decrease of initial activity rcspectively per bar of water potential decline. This decrease in activity, which was nearly linear with the degree of stress, occurred from —3 to —30 bars leaf water potential in treatments ], 3, and 4, and from —15 to —30 bars in treatment 2. These results indicate that water stress in the leaf can directly influence the photochemical activity of the chloroplasts.