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

The action of lipase on chloroplast membranes: II. Polypeptide patterns of bean galactolipase- and phospholipase A2-treated thylakoid membranes

Thylakoid membranes obtained from bean chloroplasts treated with bean galactolipase or phospholipase A2 (from Crotalus terr. terr.) showed marked changes in their polypeptide patterns when separated on SDS-PAGE. The obtained results have been discussed with regard to the relationship between chloroplast lipids and polypeptides originating from chlorophyll-protein complexes of bean thylakoids. A coexistence between galactolipids and the peripheral antennae in PS I complex and LHCP(3) as well as a conspicuous role of phospholipids in PSI and PSII centre chlorophyll-protein complexes has to be underlined.

The action of lipase on chloroplast membranes: II. Polypeptide patterns of bean galactolipase- and phospholipase A2-treated thylakoid membranes

Thylakoid membranes obtained from bean chloroplasts treated with bean galactolipase or phospholipase A2 (from Crotalus terr. terr.) showed marked changes in their polypeptide patterns when separated on SDS-PAGE. The obtained results have been discussed with regard to the relationship between chloroplast lipids and polypeptides originating from chlorophyll-protein complexes of bean thylakoids. A coexistence between galactolipids and the peripheral antennae in PS I complex and LHCP(3) as well as a conspicuous role of phospholipids in PSI and PSII centre chlorophyll-protein complexes has to be underlined.

Transmembrane distribution of phospholipids and their involvement in electron transport, as revealed by phospholipids A2 treatment of spinach thylakoids

Thylakoid membranes were treated with either pancreatic or snake venom phospholipase A2, and the residual phospholipid content of these membranes was determined and compared to the rates of Photosystem II and/or Photosystem I electron transports. The hydrolysis curves of both phosphatidylglycerol and phosphatidylcholine displayed a first, rapid phase which was almost temperature-insensitive, followed by a second, slower phase which depended strongly on the temperature. When pancreatic phospholipase A2 had access either to the outer face or to both faces of the thylakoid membrane, either only part of or all the phospholipids, respectively, could be hydrolysed. These results were interpreted as indicating an asymmetric distribution of phospholipids across the thylakoid membrane, phosphatidylglycerol and phosphatidylcholine being preferentially located in the outer and the inner layer, respectively. When acting on uncoupled thylakoid membranes, phospholipase A2 exerted an inhibitory effect on Photosystem II activity and a stimulatory effect on Photosystem I activity. The involvement of phosphatidylcholine and of phosphatidylglycerol in electron transport activities of Photosystem II and of Photosystem I are discussed with special reference to the role of the external and internal pools of these phospholipids.

Role of lipids in functions of photosynthetic membranes revealed by treatment with lipolytic acyl hydrolase

1. Thylakoid membranes and subchloroplast particles I and II enriched in photosystem I and photosystem II, respectively, were treated with a potato lipolytic acyl hydrolase. 2. In the thylakoid membrane fraction, this treatment inhibited electron flows involving both photosystems and the associated photophosphorylations. However, electron flows involving either photosystem I or photosystem II were still preserved. The treatment of thylakoid membranes by lipolytic acyl hydrolase brought about a temporal convergence of different events such as maximal activity of reduced dichloroindophenol-supported electron flows, complete inhibition of photophosphorylations and electron transport activities through photosystem II + I, onset of the decay N,N,N',N-tetramethyl-rho-phenylenediamine-supported activity of photosystem activity and of the stimulation of photosystem activity (from reduced dichloroindophenol to NADP+ by exogenous plastocyanin. 3. Lipolytic acyl hydrolase catalyzed a limited hydrolysis of each lipid but in a stepwise manner, the galactolipids being attacked before the ionic lipids. The extent of the hydrolysis was not more than 50% for each lipid. Most of the hydrolytic process occurred before any significant change in photochemical activities could be observed. 4. In subchloroplast particles I, a treatment by lipolytic acyl hydrolase did not greatly affect the electron transport whilst lipid hydrolysis was almost complete. 5. In subchloroplast particles II, neither the electron flow activities nor lipid content were significantly altered by lipolytic acyl hydrolase. 6. The sites of lipolytic acyl hydrolase action appeared to be localized between plastoquinones and P700. It is suggested that it is not possible to establish a quantitative and/or temporal correlation between the extent of lipid hydrolysis and the inhibition of photochemical activities. 7. The profile of the hydrolysis of lipids in thylakoid membranes suggests that ionic lipids are less accessible to lipolytic acyl hydrolase than galactolipids.

Ultrastructure, polypeptide composition and photochemical activity of chloroplasts during foliar senescence of a non-yellowing mutant genotype of Festuca pratensis Huds

A study was made of the structure and function of senescent chloroplasts from a non-yellowing (NY) mutant of Festuca pratensis. Electron microscopy suggested that the stroma matrix was destroyed but that thylakoid membranes persisted in a loose, unstacked condition. By contrast, chloroplasts from the normal (Y) genotype lost both stroma and recognizable thylakoid systems. Fraction 1, the major protein of the stroma, disappeared from Y and NY at similar rates during senescence. The activities of photosystems I and II from NY also declined at a similar rate to Y photosystems. Polypeptides of chloroplast membranes were separated by SDS gel electrophoresis into at least 30 components. There was considerable heterogeneity in rates of breakdown of the different protein species of the membranes. Of the five major polypeptide components, two had kinetics of breakdown similar to those of stroma proteins and were lost from NY and Y at about the same rate, whereas the remaining three (one of which was tentatively identified as the apoprotein of the light-harvesting chlorophyll-protein complex) were more stable in NY than in Y. These results are discussed in relation to the mechanism and function of chloroplast disintegration during leaf senescence.