Results

Effects of light，oxygen，and substrates on RuBPCase and Bchl.RuBPCase is a major soluble cytoplasmic enzyme characteristic of photosynthetic growth and was chosen for study.Further，Bchl levels were used as a measure of photosynthetic development，since the level of Bchl is a measure of intracellular membrane content and composition［16］.Four different growth conditions were used to study the effects of light and O2on RuBPCase and Bchl.①In the high-light conditions，R.sphaeroides cells were photosynthetically grown under near-saturating high intensity light（10 W/m2）.②In the dark conditions，the cells were grown under high light intensity and were shifted to the dark for 1 h.③ In the lowlight conditions，cells were photosynthetically grown under low-intensity light（3 W/m2）.④ In partial O2，the cells were aerobically cultured on a shaker.Because cells growing under these different growth conditions had different growth rates，an effort was made to harvest the cells at comparable cell densities（from 110 to 125 Klett units）unless otherwise noted.After the cells were harvested，the RuBPCase activity and Bchl content were determined.Both RuBPCase and Bchl were affected by light and O2（see Table 2）.The shift of cells from high-intensity light to the dark resulted in a 25%reduction in RuBPCase activity，but only a 10%reduction in the level of Bchl，after 1 h.Under steady-state low-intensity light，the RuBPCase activity was approximately 50%of its high-light level，whereas the level of Bchl was approximately 80%greater than its high-light level，as expected.The partially aerobically grown cells had negligible RuBPCase activity，whereas the Bchl content，although low，was detectable.At 110 to 125 Klett units on a rotary shaker the cells were beginning to go through a low-O2 phase followed by the induction of the photosynthetic apparatus（see below）.

Table 2　Effects of light and O2 on the Bchl content and RuBPCase activity of R.sphaeroidesⓐ

ⓐCells were grown on Sistrom medium containing 0.4%butyrate and 0.1%sodium bicarbonate.
ⓑ HL，high-intensity light（10 W/m2）；D，shift from high-intensity light to dark for 1 h；LL，low-intensity light（3 W/m2）；O2，partially aerobic growth.(https://www.daowen.com)

The cellular levels of RuBPCase and Bchl were also compared among the cells growing on the different substrates，namely，butyrate，malate，and succinate（see Table 3）.The cells were grown at high light and harvested during the late log phase（between 200 and 220 Klett units）.Under these conditions the cells are undergoing severe shading；however，such conditions are useful in seeing maximal RuBPCase levels.The levels of Bchl showed only slight，but reproducible，differences on the different substrates，whereas the RuBPCase activity showed a marked decrease when the cells were grown on malate（20-fold）and succinate（8-fold）relative to butyrate-grown cells.The relative order of RuBPCase levels（see Table 3）is the reverse of the relative growth rates.(https://www.daowen.com)

Table 3　Effects of carbon substrates on Bchl content and RuBPCase activity of R.sphaeroides