Using tobacco plants that had been transformed with the cDNA for glycerol-3-phosphate acyltransferase, we have demonstrated that chilling tolerance is affected by the levels of unsaturated membrane lipids. In the present study, we examined the effects of the transformation of tobacco plants with cDNA for glycerol-3-phosphate acyltransferase from squash on the unsaturation of fatty acids in thylakoid membrane lipids and the response of photosynthesis to various temperatures. Of the four major lipid classes isolated from the thylakoid membranes, phosphatidylglycerol showed the most conspicuous decrease in the level of unsaturation in the transformed plants. The isolated thylakoid membranes from wild-type and transgenic plants did not significantly differ from each other in terms of the sensitivity of photosystem II to high and low temperatures and also to photoinhibition. However, leaves of the transformed plants were more sensitive to photoinhibition than those of wild-type plants. Moreover, the recovery of photosynthesis from photoinhibition in leaves of wild-type plants was faster than that in leaves of the transgenic tobacco plants. These results suggest that unsaturation of fatty acids of phosphatidylglycerol in thylakoid membranes stabilizes the photosynthetic machinery against low-temperature photoinhibition by accelerating the recovery of the photosystem II protein complex.The sensitivity of higher plants to chilling is closely correlated with the degree of unsaturation of the fatty acids in the thylakoid membranes of their chloroplasts (1-4). We have demonstrated that both the unsaturation of thylakoid membrane lipids and chilling sensitivity are significantly affected upon transformation of tobacco plants with cDNAs for glycerol-3-phosphate acyltransferases from squash andArabidopsis (5). In particular, the extent of unsaturation of phosphatidylglycerol (PG) was most effectively modified, and this change appears responsible for modification of the ability to tolerate low temperatures.Photosynthesis at low temperature is impeded when plants are exposed to light (6). This phenomenon is known as low-temperature photoinhibition. The main target for photoinhibition is the photosystem (PS) II protein complex (7). Impairment of electron transport is caused by irreversible damage to the Dl protein, which is one of the heterodimeric polypeptides of the PS II reaction center complex (8, 9).Using a cyanobacterial transformation system (10-13), we have demonstrated that a decrease in the unsaturation of membrane lipids by mutation of fatty-acid desaturases enhances the sensitivity to chilling of cyanobacterial cells. This phenomenon is explained by the depression of photoinhibition in vivo as a result of the unsaturation of membrane lipids. This inference was confirmed in another cyanobacterial system in The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fac...

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In the present study, we investigated changes in chlorophyll fluorescence, photosynthetic parameters and fruit yields, as well as fruit phytochemical accumulation of strawberry (Fragaria ananassa Duch.) that had been cultivated in a greenhouse under different combinations of light intensity and temperature. In plants grown with low light (LL) photosystem II chlorophyll fluorescence was found to increase as compared with those grown under high light (HL). When strawberry plants were grown with temperature higher than 5°C in addition to LL, they showed decrease in non-photochemical quenching (NPQ), photochemical quenching (qP), as well as chlorophyll fluorescence decrease ratio (RFd) when compared with other combinations of light and temperature. Moreover, fruit yield of strawberry was closely correlated with chlorophyll fluorescence-related parameters such as NPQ, qP, and RFd, but not with the maximum efficiency of PS II (Fv/Fm). Although plant groups grown under different combinations of light and temperature showed almost comparable levels of photosynthesis rates (Pr) when irradiated with low-intensity light, they displayed clear differences when measured with higher irradiances. Plants grown under HL with temperature above 10°C showed the highest Pr, in contrast to the plants grown under LL with temperature above 5°C. When the stomatal conductance and the transpiration rate were measured, plants of each treatment showed clear differences even when analyzed with lower irradiances. We also found that fruit production during winter season was more strongly influenced by growth temperature than light intensity. We suggest that fruit productivity of strawberry is closely associated with chlorophyll fluorescence and photosynthesis-related parameters during cultivation under different regimes of temperature and light.

The cis -unsaturated molecular species of phosphatidylglycerol (PG) in chloroplasts have been implicated in the chilling sensitivity of plants. Homozygous lines of transgenic tobacco ( Nicotiana tabacum ) that overexpressed the cDNA for glycerol-3-phosphate acyltransferase, a key enzyme in the determination of the extent of cis -unsaturation of PG, were established from a chilling-sensitive squash ( Cucurbita moschata ). In transgenic plants, the proportion of saturated plus trans -monounsaturated molecular species of PG increased from 24 to 65%. However, this change did not affect the architecture of the chloroplasts. Chilling stress decreased the growth and biomass production of young seedlings of transgenic plants more severely than those of wild-type plants, and this observation suggests that the changes in the proportion of cis -unsaturated PG affected not only leaves but also developing plants. Chilling stress also damaged inflorescences. In particular, the abscission of flower buds and inflorescence meristems from transgenic plants occurred more frequently than that from wild-type plants. Thus, it is likely that decreases in the proportion of cis -unsaturated PG enhanced the sensitivity to chilling of reproductive organs.

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Irreversible photoinhibition of photosystem II (PSII) occurred when Synechocystis sp. PCC 6803 cells were exposed to very strong light for a prolonged period. When wild-type cells were illuminated at 20 degrees C for 2 h with light at an intensity of 2,500 micromol photons m(-2) s(-1), the oxygen-evolving activity of PSII was almost entirely and irreversibly lost, whereas the photochemical reaction center in PSII was inactivated only reversibly. The extent of irreversible photoinhibition was enhanced at lower temperatures and by the genetically engineered rigidification of membrane lipids. Western and Northern blotting demonstrated that, after cells had undergone irreversible photoinhibition, the precursor to D1 protein in PSII was synthesized but not processed properly. These observations may suggest that exposure of Synechocystis cells to strong light results in the irreversible photoinhibition of the oxygen-evolving activity of PSII via impairment of the processing of pre-D1 and that this effect of strong light is enhanced by the rigidification of membrane lipids.