Fatty acids as model systems for the action of Ricinus leaf extract on higher plant chloroplasts and algae

Effects of nanoanatase on the photosynthetic improvement of chloroplast damaged by linolenic acid

To further evaluate the photosynthetic effects of nanoanatase, the improvement of spinach chloroplast photosynthesis damaged by linolenic acid was investigated in the present paper. Several results showed that after the addition of nanoanatase to the linolenic acid-treated chloroplast, the light absorption increased by linolenic acid could be decreased, but the excitation energy distribution from photosystem (PS) I to PS II was promoted, and the decrease of PS II fluorescence yield caused by linolenic acid was reduced and the inhibition of oxygen evolution caused by linolenic acid of several concentrations was decreased. It was considered that nanoanatase could combine with linolenic acid and decrease the damage of linolenic acid on the structure and function of chloroplast.

Nano-anatase relieves the inhibition of electron transport caused by linolenic acid in chloroplasts of spinach

Linolenic acid is an inhibitor of electron transport in chloroplasts of higher plants. It has obvious effects on the structure and function of chloroplasts. In the present paper, we investigated the nano-anatase relieving the inhibition of photoreduction activity and oxygen evolution caused by linolenic acid in spinach chloroplasts. The results showed that linolenic acid in various concentrations could obviously reduce the whole chain electron transport and the photoreduction activity of two photosystems, especially on the oxidative reside and reduce reside of photosystem II (PS II). After adding nano-anatase to chloroplasts treated by linolenic acid, the whole chain electron transport rate, the photoreduction activity of two photosystems, and the oxygen evolution rate were increased significantly, indicating that nano-anatase could obviously decrease the inhibition of linolenic acid on the electron transport, photoreduction activity, and oxygen evolution of spinach chloroplasts.

Cytotoxic effects of free fatty acids on phytoplankton algae and cyanobacteria

Some free fatty acids are toxic to phytoplankton, and the toxic effects are multiple. However, precisely how they kill phytoplankton is debatable. Here we show that fatty acids result in damage to plasma membranes, which might account for their lethal effects on phytoplankton. In this study, we used two chlorophytes (Chlorella vulgaris Beij. and Monoraphidium contortum (Thur.) Kom.-Legn.) and a cyanobacterium (Anabaena P-9) as test organisms. When these organisms were treated with deleterious concentrations of fatty acids, a remarkable elevation of extracellular potassium (K+) was detected in the culture medium; this indicates that leakage of intracellular K+ occurred as a result of damage to the plasma membranes. Exposure to unsaturated fatty acids resulted in higher levels of leaked K+ than did exposure to saturated ones, and levels of leakage displayed a positive correlation with the susceptibility of the growth of organisms to fatty acids. Stressed phytoplankton cells also exhibited cell lysis followed by free release of phycobilins. The sequence of cytotoxic effects elucidated here suggests that fatty acids primarily affect the plasma membranes, leading to a change in membrane permeability and dissociation of phycobilins from the thylakoids. Severe damage to the plasma membranes would give rise to a disruption of the stressed cells.

Phospholipase A2 induced effects on the structural organization and physical properties of pea chloroplast membranes

Phospholipase A2 (PLA2)-induced effects on the membrane organization, fluidity properties and surface charge density of pea chloroplasts were investigated. It was observed that lipolytic treatment with PLA2 altered the chloroplast structure having as a result a swelling of thylakoids and a total destruction of normal granal structure. In spite of this, the thylakoid membranes remained in close contact. At the same time, a slight decrease of surface charge density was registered, thus explaining the adhesion of swelled membranes. Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured during PLA2 treatment. A pronounced decrease of DPH fluorescence polarization was found, indicating that phospholipase treatment resulted in considerable disordering and/or fluidization of the thylakoid membranes. The increased fluidity could be attributed to the destabilizing effect of the products of enzymatic hydrolysis of the phospholipids (free fatty acids, lysophospholipids) on the bilayer structure of thylakoids membranes.

Interaction of linolenic acid with bound quinone molecules in Photosystem II. Time-resolved optical and electron spin resonance studies

Time-resolved spectroscopic techniques, including optical flash photolysis and electron spin resonance spectroscopy, have been utilized to monitor electron-transport activity in Photosystem II subchloroplast particles. These studies have indicated that in the presence of 100 microM linolenic acid (1) a high initial fluorescence yield (Fi) is observed upon steady-state illumination of the dark-adapted sample; (2) flash-induced absorption transients (t greater than 10 mus) in the region of 820 nm, attributed to P-680+, are first slowed, then abolished; and (3) electron spin resonance Signal IIs and Signal IIf (Z+) are not detectable. Upon reversal of linolenic acid inhibition by washing with bovine serum albumin, optical and electron spin resonance transients originating from the photooxidation of P-680 are restored. Similarly, the variable component of fluorescence is recovered with an accompanying restoration of Signal IIs and Signal IIf. The data indicate that linolenic acid affects two inhibition sites in Photosystem II: one located between pheophytin and QA on the reducing side, and the other between electron donor Z and P-680 on the oxidizing side. Since both sites are associated with bound quinone molecules, we suggest that linolenic acid interacts at the level of quinone binding proteins in Photosystem II.

The ontogeny of lipid bodies (spherosomes) in plant cells : Ultrastructural evidence

Maturing embryos of 16 oil plants, anise suspension culture cells, and Neurospora crassa cells were prepared for electron microscopy at different stages during massive lipid accumulation. Lipid-rich structures of certain species were best preserved by dehydration of fixed tissues in ethanol without propylene oxide, embedding in Spurr's Medium, and polymerization at room temperature. In all cells examined, spherical lipid bodies (spherosomes) showed a moderately osmiophilic, amorphous matrix and displayed a delimiting half-unit membrane when sectioned medially. Associations with the endoplasmic reticulum (ER) were viewed at any stage during lipid body development but with different frequency in the different plant species. Plastids of fat-storing cells exhibited conspicuously undulate outer and inner envelope membranes that formed multiple contact sites with each other and protuberances into both cytoplasm and stroma. Some species, e.g., Linum, have plastids with tubular structures that connect the inner membrane to the thylakoid system; in addition, in the stroma vesicles fusing with or apparently passing through the envelope were observed. The outer envelope membrane may be associated with ER-like cytoplasmic membrane structures. In addition, lipid bodies of various sizes were found in contact with the plastid envelope. The ultrastructural observations are interpreted to match the published biochemical evidence, indicating that both plastids and ER may be involved in the synthesis of storage lipids and lipid body production.

Photosynthetic apparatus in chilling-sensitive plants : I. Reactivation of hill reaction activity inhibited on the cold and dark storage of detached leaves and intact plants

Chloroplast isolated from the detached leaves of chilling-sensitive plants-Phaseolus vulgaris L., Cucumis sativus L., and Lycopersicon esculentum Mill.-stored in the cold for 2-4 days in the dark exhibit an almost complete loss of Hill reaction activity, which on illumination of leaves is restored to almost the original level. In contrast, illumination of either chloroplast suspensions or homogenates from leaves stored in the cold in the dark does not cause restoration of electron transport. Cold and dark storage of leaves of chilling-sensitive plants affects the electron transport before the site of electron donation by diphenylcarbazide and results in an increased sensitivity of the Hill reaction of isolated chloroplasts to exogenous linolenic acid. Illumination of leaves reverses these processes. When tomato plants are exposed to 0°C in intermittent light, Hill reaction activity is not affected while dark storage either at 0°C or 25°C results in a significant decrease of Hill reaction activity after 2-3 days followed by the restoration of electron transport to the original level after 1 or 2 days of the prolonged dark storage of plants. When tomato plants are stored either at 0°C in intermittent light, at 0°C in dark, or at 25°C in dark the sensitivity of the Hill reaction to exogenous linolenic acid remains increased despite a significant restoration of this activity. In conclusion, both darkness and the detachment of leaves from the plant are more effective than cold treatment in damaging photosystem II whereas both light and intact structure of the cell are required for restoration of Hill reaction activity in chloroplasts following cold and dark storage of detached leaves.

[The effect of phospholipase D on photochemical activity and lipid composition of isolated spinach chloroplasts]

Phospholipase D shows short and longtime effects on photochemical activity of isolated spinach chloroplasts. After very short incubations with Phospholipase D (Pl D) the Ferricyanide reduction and Dichlorphenol-idenophenol reduction are 70% to 90% higher than in control chloroplasts. In uncoupled chloroplasts the reduction rates are about 20% higher than in the controls. After one h of incubation time with Phospholipase D the photochemical activity is inhibited and now shows only 40% of the control activity. The effect of Phospholipase D on uncoupled chloroplasts is somewhat lower. After two h of incubation time the control activity decreases to about 50% whereas the PLD-effected activity is reduced to 10% of the initial rates. Cyclic phosphorylation is inhibited by Phospholipase D, presumably because Phospholipase D exerts an uncoupling effect.

Direct and indirect mechanisms of deaggregation by fatty acids in chlorophyll-countaining systems

The ability of an exogenous long-chain unsaturated fatty acid (linolenic acid) to induce changes in the circular dichroism (C.D.) spectra of chlorophyllous systems of various levels of organization is demonstrated and attributed to its deaggregating influence. In the case of chlorophyll in solution (CCl(4) or CCl(4)-hexane), deaggregation is by direct action on the chromophore. Evidence is also given for an indirect mechanism when chlorophyll is attached to protein (e.g., in HP-700 complexes); in this case, deaggregation results from a conformational change in the protein. Interpretations are given for the differences in C.D. spectra of nonmembranous and membranous chlorophyll-containing systems. (The latter include "digitonin-isolated" system I particles, subchloroplast particles obtained by means of sonication, and specially prepared intact chloroplasts.)

The influence of two naturally occurring factors, from the leaves of Ricinus communis, on the fluorescence induction of higher plant chloroplasts and intact algae

Changes in fluorescence induction, brought about by incubation of chloroplasts (Zea mays) in an aqueous extract of Ricinus leaf, have been divided, on the basis of speed of manifestation, into two categories: "fast" changes and "slow" changes (i.e. those observed after 5 min and 1(1/2) hr of incubation, respectively). The former, which include a large increase in the magnitude of the fast component of variable fluorescence and a retardation of decay from maximum to minimum levels of fluorescence, have been ascribed to inhibition of electron transport at a site beyond that of 3-(p-chlorophenyl)-1,1-dimethylurea (CMU)-i.e., towards system I; these changes result from the action of a fraction of the extract consisting of molecules of small size. The latter changes, which include a marked attenuation of the variable part of fluorescence induction, have been associated with system II and may arise from inhibition of electron flow between water and Q or from decrease in number of functional reaction centers; these changes result from the activity of a proteinaceous fraction of the extract, that simultaneously converts the low temperature steady-state emission spectrum of the chloroplasts into a one-banded one, with maximum at 698 nm.