The rapid senescence of the Ipomoea corolla is characterized by the breakdown of protein and nucleic acids. At the onset of wilting the activities of deoxyribonuclease (DNase), ribonuclease (RNase), and /J-glucosidase are increased dramatically, while other hydrolytic activities such as the actions of protease, aminopeptidase, a-glucosidase, phosphatase, esterase, and a-amylase are only slightly changed.Isolated corolla discs show a course of senescence similar to that of the intact organ. When floating on solutions of cycloheximide the activities of DNase, RNase, and |3-glucosidase do not increase. Actinomycin D inhibits the increase in RNase activity. It is concluded that protein synthesis is a prerequisite for the changes in these enzyme activities in the senescing corolla.The function of the lysosomal compartment in the process of senescence is illustrated by electron micrographs showing the autophagic activity of vacuoles. The last phase of senescence is characterized by the breakdown of the tonoplast and complete digestion of the cytoplasmic constituents in the autolysing cells.

Preparations of heterocysts of Anabaena cylindrica Brunswick, N.J.) continuously illuminated with six fluorescent tubes (daylight, 15 w) and gassed with air to a density of 3.0 ,ug Chl/ml. The doubling time based on Chl was approximately 17 hr. Cultures were checked regularly for bacterial contamination by microscopic examination, and occasionally by subculture of 1 ml into 10 ml of culture medium supplemented with 1% glucose and 0.5% peptone. Every 24 hr 7 to 8 liters of the 12 liters of algal suspension were removed and replaced with fresh medium. Filaments concentrated by centrifugation (5 min, 1100g) were resuspended in a small volume of used growth medium and stored on ice for 1 to 3 hr. Harvest, concentration, and resuspension of filaments were accomplished within 30 min.Preparation of Cell-Free Extracts. Immediately prior to use, the concentrated suspension was centrifuged (2 min, 5000g) and resuspended either approximately 100 ug Chl/ml in ice-cold tris buffer (20 mm tris HCl, pH 7.6, containing 0.1 mm EDTA and 10 mm 2-mercaptoethanol), or approximately 250 ,ug Chl/ ml in ice-cold phosphate buffer (40 mm KH}P04-K,HPO4 pH 7.0). The dense suspension was cavitated at setting no. 3 of a Model S-125 Sonifier (Heat Systems, Inc., Melville, N.Y.), which was cooled with a water jacket (12 C). Cavitation for 5 to 11 sec/ml broke most of the vegetative cells and left the major portion of the heterocysts apparently intact. After 1 min/ml of cavitation, virtually all of the vegetative cells and heterocysts were broken. In certain experiments, the phosphate buffer was supplemented with 1.5 mM glucose-6-P and 3 mM MgCl,. Cell-free extracts were obtained by centrifugation for 4 or 5 min at 50OOg or 12,000g.For studies on the time course of solubilization of glucose-6-P dehydrogenase an algal suspension, initial volume 22 ml, was cavitated for 5 sec/ml and then for four successive periods of 3 sec/ml each. After each period of cavitation, a 1-ml aliquot was withdrawn and transferred into a 4-ml centrifuge tube at 0 C. The volume of suspension was then reduced to 12 ml, and cavitation was continued for a total of 1 min/ml. All centrifugations were carried out at 1 to 5 C.Heterocyst Preparations. Twenty-two-milliliter batches of algal suspension containing about 250 ,ug Chl/ml were cavitated for 11 sec/ml, left 10 min at 24 C, diluted with 60 ml of distilled water (2-4 C), and centrifuged for 2 min at 1500g.The pellets were combined and washed three times with 20 ml of growth medium (2-4 C). The final pellet was resuspended in phosphate buffer with supplements (Table IA). In another set of experiments (Table IB)

Heterocysts of Anabaena cylindrica, isolated rapidly in the cold, were found-in contrast to earlier reports-to contain all of the same lipids and lipophilic pigments, and in about the same proportions, as vegetative cells. In broken filaments and in heterocysts damaged during isolation, the membrane lipids and certain pigments (myxoxanthophyll and an unidentified red pigment) break down rapidly. The glycolipids specific to heterocyst-forming blue-green algae are localized in the laminated layer of the heterocyst envelope. A possible role of the laminated layer is discussed.

Chromoplasts of unfolding petals of Tropaeolum majus contain large amounts of filaments (which, in sections, appear as tubules), and unevenshaped, isodiametric to elongated bodies (IBs). These structural elements are the major sites of the chromoplast pigments. They were freed from isolated chromoplasts and subjected to sucrose density gradient centrifugation. At a density of 1.080 g cm(-3) a distinct orange band contained almost exclusively fine filaments of 15-20 nm in diameter as shown after negative staining. Other filaments and most of the IBs were heterogeneous in size, shape, and density and were collected in two fractions of buoyant densities of 1.025 and 1.055 g cm(-3). The three fractions thus obtained comprise 15-33% protein, large amounts of carotenoids and their esters, glyco- and phospholipids, as well as minor amounts of tocopherols. A higher buoyant density of particles is correlated with a higher relative content of protein and glyco- and phospholipids and a lower relative content of carotenoids. The polypeptide pattern, as shown by SDS-polyacrylamide gel electrophoresis, is very similar in all three fractions. There is one main polypeptide, with a MW of about 30,000, accounting for up to 80% of the protein of each fraction.

Nitrogen was supplied in the form of nitrate, nitrite, or ammonium ions to whole cells of Dunaliella tertiolecta, to whole cells and chloroplast preparations of Acetabularia mediterranea, and to spinach chloroplasts, while they were photosynthesizing in 14CO2. The 14C labeling patterns in these experiments provide information on several aspects of the photosynthesis, nitrogen metabolism, and physical properties of these systems. The rates and products of photosynthesis are affected in different ways by different ions, depending on the penetration of each ion, its toxicity, and on the ability of the system under test to synthesize amino acids. Thus the ions that penetrate spinach chloroplasts, while they may inhibit photosynthesis, do not affect the distribution of 14C among photosynthetic products because no amino acids are formed. The large differences in behavior between Acetabularia whole cells and chloroplast preparations from these cells suggest that the membrane structure surrounding cytoplasmic droplets in the latter may be tonoplast rather than plasmalemma in origin.