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Phloem transport was monitored using a continuous stream of 11CO2‐labelled air administered to one leaf while gamma detectors measured 11C activity at intervals along the stem. The effect of gentle, non‐injurious mechanical perturbation on phloem transport was tested in cotton (Gossypium hirsutum L. cv. Stoneville 213). Mechanical stimuli such as shaking, localized vibration and gentle massage were applied while the plants were at isotope equilibrium. Localized phloem blockages were observed within 1–2 min of the stimuli. The blockages lasted from 6–55 min and full recovery of transport required 20–175 min. The effect of preconditioning to mechanical perturbation on phloem transport was tested in bush beans (Phaseolus vulgaris L. cv. Cherokee Bush). Preconditioning of a bean seedling to gentle stem massage resulted in a shorter blockage response and quicker transport recovery period when the seedling was massaged during a 11C tracer experiment compared to a control seedling. These results indicate that measurements of phloem transport on recently disturbed plants will probably show depressed phloem transport velocities. Measurements should be made after at least a 24‐h disturbance‐free recovery period. [ABSTRACT FROM AUTHOR]

Trifolium subterraneum (cv. Dinninup) responds to enriched atmospheric CO2 in a manner similar to that described by Madsen (1968 and 1976) for tomato. In immature leaves, the total chlorophyll content per unit dry weight and the chlorophyll a:b ratio are significantly lower in plants grown at 0.10 vol% CO2. Although fully expanded mature leaves partially overcome the deficit in chlorophyll content, the chlorophyll a:b ratio remains substantially lower in these high CO2 grown plants. The large amount of starch accumulated as irregularly shaped grains appears to disrupt normal chloroplast structure in clover plants grown in enriched atmospheric CO2. These results indicate the chlorotic appearance of leaves from high CO2 grown clover plants is due to a decrease in chlorophyll content per dry weight possibly resulting from large starch grains and starch accumulation altering normal chloroplast structure and function. [ABSTRACT FROM AUTHOR]

Alaska pea plants (Pisum sativum L.) were grown at 0.10 vol% and 0.035 Vol% CO2 to determine the effects of high CO2 concentration upon plant growth and apical dominance. The results showed that a 0.10 vol% CO2 atmosphere significantly increased the rate of lateral branch, flower bud, flower and fruit development over an environment with 0.035 vol% CO2. At plant maturity, however, there were no significant differences in the number of branches or fruits produced at the different CO2 levels. Thus, no evidence was obtained for the loss of apical dominance at the CO2 concentrations tested. Root dry weight was significantly greater in plants grown at 0.10 vol% CO2 than in those grown at 0.035 vol% CO2 and leaf dry weight was significantly lower. However, no significant differences were found in total plant dry weight production at plant maturity. [ABSTRACT FROM AUTHOR]