Correlations between Calcium Oxalate Crystals and Photosynthetic Activities in Palisade Cells of Shadeadapted Peperomia glabella

Each photosynthetic palisade cell in the leaves of shade-adapted Peperomia glabella contains a druse calcium oxalate crystal which we hypothesize is involved in dispersing light to the chloroplasts. The effect of light intensity on druse size, number and position, relative to growth and phototsynthesis was determined. Peperomia glabella grew best at 50-100 mu E m(-2) s(-1), and at 300-400 mu E m(-2) s(-1) had smaller leaves with considerable yellowing. Plants grown under lower light had well developed chloroplasts while at 300-400 mu E m(-2) s(-1) the chloroplasts accumulated plastoglobuli and showed thylakoid swelling. Chlorophyll content, chlorophyll a/b, and photosynthetic rate decreased with increasing light intensity. Druse crystals were produced in palisade cells under all light conditions but crystal diameter changed, being greatest at 100 mu E m(-2) s(-1) and decreasing with higher light. The position of the crystals also changed with light intensity. Under 50 and 100 mu E m(-2) s(-1) the crystals were predominantly located at the bottom or middle of cells while at 300 and 400 mu E m(-2) s(-1) they were at the top of cells. The data indicate an adaptive role of calcium oxalate crystals in photosynthesis in Peperomia.