Effects of SO(2) on Stomatal Metabolism in Pisum sativum L.

Pea (Pisum sativum L. cv ;Little Marvel') plants were exposed to SO(2) for short term (3 hours) and long term (2 days) at 0.2 and at 0.5 microliter per liter (ppm) levels. The effect of this treatment on the activity of phosphoenolpyruvate carboxylase, NAD- and NADP-malate dehydrogenases, and alanine aminotransferase from epidermis and whole leaves was investigated. Short-term exposure to SO(2) at 0.2 or 0.5 ppm decreased the activity of the carboxylase and the dehydrogenases in the epidermis. In contrast, the activity of the same three enzymes increased in whole leaves with either short- or long-term exposure to SO(2). Alanine aminotransferase in epidermis or whole leaves was not much affected by short-term exposure, but the epidermal activity was decreased and whole leaf activity was increased with long-term exposure. SO(2) exposure which was initiated prior to illumination decreased the free thiol content of both epidermis and of whole leaf. Net photosynthesis was reversibly inhibited by long-term exposure to SO(2) at 0.5 ppm. No effect of 0.5 ppm SO(2) on stomatal conductance was detectable after 3 hours. Stomatal conductance appeared to decrease after longer exposure times (2 days) at 0.5 ppm.

Chloroplast alkaline fructose 1,6-bisphosphatase exists in a membrane-bound form.

An alkaline fructose 1,6-bisphosphatase activity associated with soybean (Glycine max cv Beeson) chloroplasts appears to be membrane-bound. The pH optimum of the membrane-associated activity corresponds to that found for activity associated with the stroma. Illumination of washed thylakoids results in an increase in alkaline fructose 1,6-bisphosphatase activity in the absence of any added stromal factors. Exposure to pH 8.0 results in a partial release of enzyme activity from the membrane. The activation status of the enzyme does not appear to alter its association with the membrane.

Ribosome-thylakoid association in peas: influence of anoxia.

Isolated pea chloroplast thylakoids ordinarily have ribosomes attached which survive sequential washes. Extensive in vivo loss of these thylakoidbound ribosomes occurred if the pea plants were placed in the dark without O(2) for 2 or more hours. This loss was indicated from measurements of both the total thylakoid-bound RNA levels, and the capacity for amino acid incorporation into proteins on the addition of soluble enzymes for protein synthesis. Stroma ribosome profiles lost any indication of polysome structure due to the same anoxic treatment in vivo. The return of ribosomes to the thylakoids when plants were placed in the light in air occurred over an 8-hour time course. This return was prevented by lincomycin, spectinomycin, and chloramphenicol, indicating a requirement for protein synthesis steps in the stroma at some point in the reassociation process.