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Two dry bean (Phaseolus vulgaris L.) cultivars were grown in controlled‐environment chambers under standard light [390 μ Einsteins m‐2 sec‐1 (400 to 700 nm) = approx. 22,000 lux] and shaded light [55 μ Einsteins m‐2 sec‐1 (400 to 700 nm) = approx. 3,200 lux] intensities. Experimental observations included measurement of gas exchange and photosynthetic and respiratory enzyme activity along with examination of plant morphology, leaf anatomy, and chloroplast ultrastructure.Shading reduced leaf number, area, and thickness. Photosynthesis/unit area of shaded leaves was decreased by an average of 38%. Transpiration was not significantly affected. Increased intracellular resistance of the shaded leaves was more important in reducing CO2 uptake than was the increase in stomatal resistance. The increase in mesophyll resistance was reflected both in the biochemical reactions of the leaf (activity of all measured enzymes being reduced by 70%) and in the ultrastructure of the leaf chloroplasts (reduced quantities of starch in spite of extensive grana).

1. The incorporation of (14)CO(2) and dl-[2-(14)C]mevalonic acid into various terpenoids in developing chloroplasts in a number of seedlings has been studied. 2. beta-Carotene and phytol (from chlorophyll) tend to be heavily labelled from (14)CO(2), whereas sterols and beta-amyrin are only slightly labelled; with dl-[2-(14)C]mevalonic acid the situation is reversed. 3. The incorporation of (14)CO(2) into terpenoids is dependent on the stage of chloroplast development, whereas that of mevalonic acid is independent of chloroplast development. 4. The uptake of (14)CO(2) into beta-carotene and phytol in mature chloroplasts is very low in monocotyledons but somewhat greater in dicotyledons. 5. The results are discussed in relation to the view that terpenoid biosynthesis in developing chloroplasts is regulated by a combination of enzyme segregation and specific membrane permeability.

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The variation in rate of apparent photosynthesis (PR) with leaf age in three populations of orchardgrass, grown in two different temperature environments, was investigated using a Warburg manometric technique. Fully expanded leaves maintained a high PR for 15 to 20 days but the rate rapidly declined thereafter. PR (oxygen evolution) per unit leaf area closely paralleled the synthesis and degradation of the chlorophyll pigments; PR per unit chlorophyll changed very little throughout the life of the leaf. These results were confirmed by the pattern of assimilation of C14O2 by leaves of different ages. The Portuguese ecotype had a significantly higher photosynthetic rate at 21 C than the cultivars ‘S.143’ and ‘Boone’ in both growth environments. Plants grown at 21 C day/13 C night temperatures had a significantly higher rate at 21 C than plants grown at 29 day/21 night temperatures, but when measured at 29 C plants grown in the higher temperature regime had a significantly higher rate of PR. The relative pattern of change of PR with leaf age was unaffected by the temperature at which the plants were grown.