Isolation and Bicarbonate Transport of Chloroplast Envelope Membranes from Species of Differing Net Photosynthetic Efficiency

Abstract

A three-phase discontinuous sucrose gradient yielded two fractions of chloroplast envelope membranes from spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L., mesophyl and undifferentiated chloroplasts). These species were selected to represent plants with fast photorespiration and slow net photosynthesis, fast photorespiration yet fast net photosynthesis, and slow photorespiration and fast net photosynthesis, respectively. (2).A very few exceptions to this classification exist. Sunflower leaves have the morphology and photorespiratory rates indicative of species with less efficient photosynthesis, yet their photosynthetic rates approach those of the more photosynthetically efficient species (28). Clearly, sunflower has some mechanism to compensate for a fast photorespiration.One site of this greater efficiency in sunflower may reside in the chloroplast envelope membrane, which regulates the uptake of metabolites required for photosynthesis, including CO2 (7,20,21,25). Studies with chloroplasts involving transport and release of permeants in the presence of anions have indicated the presConnecticut Agricultural Experiment Station, ence of specific carriers ("translocators") in the envelope membrane. These translocators facilitate the exchange of phosphate, dicarboxylic acids, and ATP (7,25). A comparison of the biochemical properties of chloroplast envelope membranes from species with different photosynthetic rates might show differences in the permeability properties and help elucidate the operations of translocators. To this end chloroplast envelope membranes from leaves of the less efficient species, spinach and broad bean, have been isolated and partially characterized in several laboratories (4,11,12,19,22). No descriptions of the properties of isolated chloroplast envelope membranes from more efficient species, sunflower or maize, have previously been reported. This report describes the preparation and establishes the purity of isolated chloroplast envelope membranes from sunflower and maize and shows large differences in the activities of Mg2+-dependent nonlatent ATPase among chloroplast envelope membranes of plant species with different rates of net photosynthesis. These activities were compared with differences in the transport of bicarbonate.

Lipid and Fatty Acid Composition of Chloroplast Envelope Membranes from Species with Differing Net Photosynthesis

“…Freshly isolated chloroplast envelopes appear to give higher values for phosphatidylcholine (12) and variations in purity and extent of envelope membranes containing the complete structure (double membrane as opposed to single) may introduce further changes in the phosphatidylcholine content. Lipid compositions in Table I are for chloroplast envelope membranes with a predominantly complete (double membrane) structure (21).…”

“…Complete envelope membranes were removed from intact spinach, sunflower, and maize chloroplasts by osmotic shock and purified on a three phase discontinuous sucrose gradient. Details of the isolation procedure were described previously (21). Complete envelope membrane fractions were pooled and diluted 2-fold with 330 mm sorbitol in 50 mm Tricine at pH 7.6.…”

“…Recently I have also described the isolation of such membranes from plant species with fast rates of net photosynthesis (21). I believe that differences in the biochemical properties of these envelope membranes might be related to variations in chloroplastic permeability and metabolite transport and hence these variations in biochemical properties could effect photosynthetic efficiency (21).…”

“…Recently I have also described the isolation of such membranes from plant species with fast rates of net photosynthesis (21). I believe that differences in the biochemical properties of these envelope membranes might be related to variations in chloroplastic permeability and metabolite transport and hence these variations in biochemical properties could effect photosynthetic efficiency (21).Characterization of these membranes has shown some differences in their transport abilities (18,19,21), enzymic levels (21), and hexosamine contents (22). The lipid compositions were previously determined only with chloroplast envelope membranes from plant species with slow rates of net photosynthesis (4, 12, 17), hence comparative studies are incomplete.…”

“…Characterization of these membranes has shown some differences in their transport abilities (18,19,21), enzymic levels (21), and hexosamine contents (22). The lipid compositions were previously determined only with chloroplast envelope membranes from plant species with slow rates of net photosynthesis (4,12,17), hence comparative studies are incomplete.…”