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In addition to angiosperms, most plants are able to synthesize chlorophyll (Chl)-generating green tissues in total darkness. In this study, 140 plants of the angiosperm Pachira macrocarpa were divided into five groups. Among them, one group was grown for 2 weeks under natural light conditions, whereas the others were grown in complete darkness (0 μmol m−2 s−1). Dark-grown plants were then treated with 0~6% glucose for another 8 weeks. The budding and greening ratios, ultrastructure of chloroplasts (ChlPs) of newly developed leaves, and green pigment contents of pre-illuminated mature and young leaves, and totally dark-grown newly developed leaves were measured. Results showed that glucose inhibited the budding and promoted the greening of newly developed leaves. Pre-illuminated mature and young leaves were able to synthesize green pigments during the 2 weeks of dark adaption. Dark-grown newly developed leaves contained high levels of green pigments at 2 and 3 weeks after budding. Green pigments of glucose-fed newly developed leaves had increased, whereas they had decreased in control leaves. In addition, ChlPs of dark-grown glucose-fed newly developed leaves contained both giant grana and prolamellar bodies (PLBs), usually found in shade plants and etiolated seedlings, respectively. The higher the glucose concentration was, the greater the numbers of grana, thylakoids, and PLBs. Glucose increased the green pigment contents and grana formation in newly developed leaves in a dark condition, and the mechanisms are discussed.

The siphonous green alga Codium edule P. C. Silva (Bryopsidales, Chlorophyta) has the highest covering ratio among the macroalgae on the coral reef of Nanwan Bay in southern Taiwan, but its population in the subtidal region drastically decreases from July to September each year. The objective of this study was to determine whether the high temperature of summer could be the basis for this population decrease. Chlorophyll fluorescence measurements revealed that when the algae were incubated at 35°C (a temperature that can be reached in southern Taiwan during the summer), their photosynthetic activities were almost completely inhibited after about 8 h. The circadian rhythm of photosynthesis was disrupted at a temperature as low as 32°C. TEM studies showed that 4 h incubation at 35°C induced a decrease in turgidity accompanied by vacuole shrinkage and plasmolysis. The marked disintegrative changes, including damage to organelles, such as chloroplasts and nuclei, occurred after about 8 h, at which time central vacuoles collapsed and the cell interior was then filled with numerous small vesicles. Our results suggested that the rise in seawater temperature during the summer could be one of the major causes of the massive death of C. edule in the field.

To find out how microalgae cope with heat stress, the small vegetative cells of a synchronous Scenedesmus vacuolatus culture were subjected to heat treatment and then cultured under continuous illumination. The heat-treated cells were found first to enter a degenerative intermediate stage with low cellular activities almost right after the start of the cultivation, which was then followed by a revival. The changes in physiological activities and morphology of the treated cells throughout the whole period of regeneration were explored. The variations in cellular DNA content and protein composition were also investigated. Stressed cells at the end of the degeneration stage were completely bleached and were also characterized by condensed but undegraded chromatin, partially disintegrated chloroplasts but with the thylakoid membrane system retained, partially operating mitochondria, intact plasma membranes, and a dramatically changed profile of cellular proteins. All of our data indicate they were still alive but in a different physiological state than the control cells. Recovery started with regeneration of mitochondrial cristae and redispersion of chromatins. These were followed by regreening and resuscitation of chloroplasts, which often started from one part of a thylakoid membrane system and then spread out. This study provided a unicellular model for studying how plant cells react to a period of stress and recover.

Background To find out how algal cells cope with and recover from heat stress, the small vegetative cells of the synchronous Scenedesmus vacuolatus culture were subjected to a heat pretreatment (46.5°C for 1 h) followed by dark recultivation. The changes in physiological activities and morphology of Scenedesmus cells were continuously monitored throughout the course of decline and recovery. Results It was found that the heat treatment, though completely inhibited photosynthesis, did not kill Scenedesmus cells. These cells, during dark recultivation, could make a fast repair and regained the ability of proliferation. We suggest that they entered a ‘stand-by’ state, which was characterized by condensed chromatin, partially functional but morphologically altered chloroplasts, disappeared vacuoles, slightly shrunk protoplast and intact plasma membranes. These stressed cells, on the surface, seemingly were undergoing some kind of disintegration, could readily and quickly return to normal cells upon illumination. Cell death occurred only after a long period of darkness (>48 h). Conclusions Our results suggest that the recovery of algal cells from stress damage may actually proceed in two steps. The middle “stand-by’ stage normally is gone through too rapidly to be detected unless cells are kept in the dark. Electronic supplementary material The online version of this article (doi:10.1186/1999-3110-54-3) contains supplementary material, which is available to authorized users.