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Adventitious root formation can be inhibited in stem cuttings of Pisum sativum L. (pea), an easy-to-root species, if the apical and lateral buds are removed. Application of exogenous auxin to the apical stump can replace the rooting stimulus produced by the buds. Root number was reduced by 50 to 100% in the decapitated and disbudded cuttings supplied with an apical source of auxin if photosynthesis was inhibited by 50 to 100% by any of several treatments. The extent to which rooting was reduced was roughly proportional to the extent to which photosynthesis was reduced. Basipetal transport of radioactivity from apically applied ¹⁴C-IAA, as well as basal carbohydrate content, was also consistently reduced under conditions where photosynthesis was inhibited. It appears the reduction in rooting due to a reduction in photosynthesis must take at least two factors into consideration, the transport of auxin from the apex to the base of the cutting and the basal carbohydrate content. The environmental conditions during the stock plant growth are important to the rooting of cuttings. In the present investigation, when pea and Rhododendron stock plants were subjected to low light or to a period of darkness, the rooting of cuttings taken from these plants was significantly promoted. For pea, the promotive effect of darkness was significantly greater when the entire plant was placed in the dark compared to a localized darkening of the stem segment from which roots emerge after excision. The timing of the light and dark periods during stock plant growth also greatly influenced rooting, the greatest promotion was observed when the dark period was given immediately after emergence of the stock plant. This suggests that the root promoting effect of darkness can be destroyed by a brief period of light early in the development of the stock plant. The basal carbohydrate concentration during the first week of rooting was similar in cuttings taken from stock plants receiving light throughout the growth period and those receiving a dark period of 4 days, regardless of whether the dark period was given immediately after emergence or after an exposure to light. This suggests carbohydrates do not play a major role in the promotion of rooting due to a dark treatment on the stock plant. / Graduation date: 1985

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