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(i) The initial elongation rate of excised coleoptile sections is shown to increase with increasing concentration of indoleacetic acid (IAA). In supra-optimal concentrations (1 X 1O-3M) this initial phase is followed by shrinkage of the sections accompanied by loss of water and solid matter; the latter is quantitatively recoverable in the solution. The respiratory rate drops rapidly while the sections elongate in 1 X 10-3M IAA.

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Studies of 14C distribution in P. sativum cv. Greenfeast over 24 h indicate that 60-80% of 14C incorporated by the single leaf, on a plant pruned to leave one leaf and one pod, moves to the growing ovules at all developmental stages. Approximately 40% of the total activity was found in the ovules within 5 h after exposure of the leaf to 14CO2. As the pod temperature increases there is an increase in 14C uptake by the ovules, from 2% of the total 14C assimilated by the leaf at 10°C to 28% at 30°C, within 2.5 h of 14C application. These results are discussed in relation to possible mechanisms of nutrient uptake by the pod. However, it is impossible at this stage to decide whether the transport of photosynthate into the developing fruit and its seeds is controlled simply by the metabolic sink status of the developing system or if, in addition, there is a 'remote' effect on the transport system itself.

No abstract