Photosynthetic, biochemical, and ultra-structural changes in the chloroplasts of two ginkgo (Ginkgo bilobaL.) cultivars during leaf development

SummaryChanges in chlorophyll fluorescence, leaf biochemistry, and ultra-structure were studied in 10-year-old female ginkgo trees (Ginkgo biloba L.) cvs. Dafozhi and Qixingguo, from April to October in Jiangdu, Jiangsu Province, P. R. China. The maximum quantum efficiency (Fv / Fm)of PS II and the potential photosynthetic capacity (Fv / Fo) of PS II peaked in June and July, then declined. Changes in the concentrations of chlorophyll a and total chlorophyll followed these patterns, whereas changes in the concentrations of chlorophyll b andtotal carotenoids were less dramatic or had no clear trend. Changes in electron transport activities (PS II, PS I, and the whole chain) followed the same pattern as total chlorophyll content, with increases up until June, then a decline. Changes in the biochemistry of photosynthesis were associated with changes in the ultra-structure of the chloroplasts. Initially, the chloroplasts had tightly-stacked thylakoids with distinctive starch grains. However, as the leaves senesced, the chloroplast membranes began to degrade, the thylakoids became disorganised, and there was a large increase in the number of osmiophilic granules. Overall, there were only small differences in chlorophyll fluorescence and leaf biochemistry between the two cultivars. These results show that ginkgo leaves reached their full photosynthetic capacity in June, when they were fully expanded. Photosynthetic capacity declined as the leaves began to senesce in September, with the decline possibly being accelerated by lower temperatures and water deficits at this time of year. Senescence may be the result of active adaptation by leaves to changes in the external environment.