Kaempferol Glycosides and Enzymes of Flavonol Biosynthesis in Leaves of a Soybean Strain with Low Photosynthetic Rates

Abstract

Soybean (Glycine max L.) strains which accumulate kaempferol 3-(2G-glucosylgentiobioside) in their leaves fix CO2 at rates significantly lower than those lacking this compound (Buttery, Buzzell 1976 Crop Sci 16: 547-550), and kaempferol aglycone is a well known inhibitor of photosynthesis in vitro. However, since neither kaempferol nor any of its glycosides could be detected in mesophyll cells isolated from mature soybean leaves we suspect that kaempferol 3420-glucosylgentiobioside) has no direct inhibitory effect on photosynthesis. The most rapid stage of flavonoid accumulation, and the highest level of activity for several enzymes of phenolic biosynthesis, occurs in leaflets 2.5 to 3 centimeters long. Mesophyll cells isolated from these leaflets contain about 70% of the whole leaf activity for shikimate dehydrogenase, 24% of the 4-coumarate:CoA ligase activity, 35% of the activity for chalcone-flavanone isomerase, but no demonstrable activity for phenylalanine ammonialyase. Our results suggest a highly tissue-specific pattern of secondary phenolic metabolism in soybean leaves.

Acifluorfen-Induced Isoflavonoids and Enzymes of Their Biosynthesis in Mature Soybean Leaves

“…Soybean leaves normally accumulate appreciable levels of kaempferol and quercetin glycosides (5) but no flavonoids ofany class were detected in isolated soybean mesophyll cells (7). Flavonoids appear to be restricted to the epidermis of pea leaves (1 1), and presumably of soybean leaves (7), where they may function as UV screens and as preformed defensive compounds (18).…”

“…Flavonoids appear to be restricted to the epidermis of pea leaves (1 1), and presumably of soybean leaves (7), where they may function as UV screens and as preformed defensive compounds (18). A number of isoflavonoids (isoflavone aglycones, isoflavone glucosides, pterocarpans, and coumestans) can be induced to accumulate in soybeans by host-pathogen interactions (10,12,14,20,21) herbicide Acifluorfen (15).…”

“…For ease of quantitation, the isoflavone glucosides and kaempferol glycosides (7) in the aqueous fraction were converted to their aglycones by hydrolysis in 1 N H2SO4 for 1 h at 100°C. These aglycones were extracted from the hydrolysate with 2 x 50 ml of ethyl acetate.…”

“…Cells were isolated from leaves cut into 1 to 2 mm strips by the enzymic technique previously described (7,8) modified by gently agitating the strips with a and by adding 0.1 % (w/v) methylcellulose and 0.1 % (w/v) BSA to the isolating medium. These modifications reduced the time required for cell isolation from 2 h to 15 min.…”

“…Molar absorptivities used for quantitation were 10,500 for daidzein and formononetin (19), 10,000 for the glyceollins (1), and 7,200 for glyceofuran (12; modified from 280 nm). Kaempferol was quantitated by the isocratic HPLC system previously described (7).…”