ARE PHYTOCHROME-MEDIATED EFFECTS ON LEAF GROWTH, CARBON PARTITIONING AND EXTRACTABLE SUCROSE-PHOSPHATE SYNTHASE ACTIVITY THE MERE CONSEQUENCE OF STEM-GROWTH RESPONSES IN LIGHT-GROWN MUSTARD

Growth, carbohydrate pools and extractable sucrose-phosphate synthase (SPS) activity were studied in the leaves of light-grown mustard seedl ings exposed to red or far-red end-of-day light pulses. Over a single dark period far-red, compared to red light (a) had no effect on leaf a mounts of reducing sugars, sucrose, starch, and hemicellulose, (b) red uced cellulose accumulation in the leaves, and (c) caused a rapid prom otion of extractable activity for SPS (lag > 0.5 h, < 1 h), Within a p lant, one leaf of the first pair was covered while the other leaf and the rest of the shoot were exposed to end-of-day far-red, The leaf exp osed to far-red showed (a) lower rates of extension growth, (b) reduce d accumulation of dry matter and structural carbohydrates, and (c) hig her activities of SPS, than the leaf covered during the far-red pulse, despite the fact that both leaves were attached to the same internode , We conclude that phytochrome-mediated effects on leaf growth, carbon partitioning and extractable SPS activity are not the mere consequenc e of changes in internode growth and carbon demand,