KAEMPFEROL GLYCOSIDES AND ENZYMES OF FLAVONOL BIOSYNTHESIS IN LEAVES OF A SOYBEAN STRAIN WITH LOW PHOTOSYNTHETIC RATES

Soybean strains which accumulate kaempferol 3-(2G-glucosylgentiobioside) in their leaves fix CO2 at rates significantly lower than those lacking this compound, 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 it is probable that kaempferol 3-(2G-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 2.5-3 cm 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. A highly tissue-specific pattern of secondary phenolic metabolism in soybean leaves is suggested.