Leaf Disc Assay Research Articles

Site of Monoterpene Biosynthesis in Majorana hortensis Leaves

Excised epidermis of Majorana hortensis Moench (sweet marjoram) leaves incorporates label from [U-(14)C]sucrose into monoterpenes as efficiently as do leaf discs, while mesophyll tissue has only a very limited capacity to synthesize monoterpenes from exogenous sucrose. These results strongly suggest that epidermal cells, presumably the epidermal oil glands, are the primary site of monoterpene biosynthesis in marjoram. Using a leaf disc assay, it was demonstrated that label from [U-(14)C]sucrose is incorporated into monoterpenes most efficiently in very young leaves.

The biological activity of fluorogibberellins

The biological activities of gibberellin A9 (GA9), gibberellin A12 (GA12) and monofluoro-analogues (F-GA9 and F-GA12), substituted in the 1 β-methyl group, were compared in the barley endosperm, cucumber hypocotyl, lettuce hypocotyl, 'Meteor' dwarf pea, dwarf-5 maize and Rumex leaf disc assays. In most cases the fluorosubstituted compounds had a potency similar to, or less than, the relevant unmodified gibberellin but, in the lettuce assay, F-GA9 was approximately 5 times more active than GA9 up to a dose rate of 10(-1) μg.A 27-30% mixture of fluorogibberellin A3 (F-GA3) in GA3 had a lower activity than 100% GA3 in the barley endosperm, lettuce hypocotyl and dwarf maize assays. This suggested that pure F-GA3 may be a competitive inhibitor of GA3 action. The findings are discussed in the context of the structure/activity relationships of the gibberellins.

Investigation on Photorespiration With a Sensitive 14C-Assay

A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed (14)CO(2) in light in a rapid stream of CO(2)-free air at 30 degrees to 35 degrees . In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the (14)CO(2) output in the dark. In maize, photorespiration is only 2% of that in tobacco.The importance of open leaf stomata, rapid flow rates of CO(2)-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the (14)CO(2) evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by alpha-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35 degrees the quantity of (14)CO(2) released in the assay may represent only 33% of the gross (14)CO(2) evolved in the light, the remainder being recycled within the tissue.It was concluded that maize does not evolve appreciable quantities of CO(2) in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO(2) uptake at the normal concentrations of CO(2) found in air and at higher light intensities.