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Root restriction may be of importance for productivity in both forestry and agriculture. To study the physiological effects of root restriction in European alder (Alnus glutinosa Gaertn.), seedlings were grown in aerated liquid culture under one of four root. volumes to induce the following levels of root restriction: 1.5, 6, 16 and 500 ml. Root restriction for 96 days reduced shoot elongation, plant dry weight, leaf area and chlorophyll, levels and increased leaf area/root dry weight ratio and correlative bud inhibition in seedlings. The initial reduction in root/shoot ratios of severely restricted seedlings was followed by a reduction in leaf water potential, the development of internal water deficits in the upper shoots, a reduction in stomatal opening and transpiration rates and, eventually, stomatal closure. Severe prolonged root restriction (1.5 ml root volume) resulted in a decline in seedling vigour and ultimately. senescence as determined by increased electrical impedance ratios, followed by visible leaf senescence and later, by whole plant senescence. Of the severely restricted seedlings, 40%. were dead after 96 days of restriction. The results suggest that imbalanced root/shoot ratios caused the development of internal water stress and the consequent reduction in stomatal aperture, culminating in leaf and whole plant senescence. [ABSTRACT FROM AUTHOR]

Indol-3yl-acetic acid (IAA) present in the rooting solution for 1-4 days appreciably decreased the number of roots subsequently formed in pea stem cuttings. Removal of the lowest 10 mm of the cutting base after IAA treatment abolished the inhibitory effect of IAA almost completely. The number of roots formed from the remaining part of the base internode after excision of the basal centimeter of the internode 4 days after the cuttings were taken was similar to that of the control. It is concluded that the first root primordia, which develop near the cut surface, have an inhibitory influence on development of further roots. The inhibitory effect of IAA may be explained as a strengthening of this dominance phenomenon. Addition of charcoal to the rooting solution delayed the appearance of roots but increased the number of roots developed during a standard rooting period. Adsorption of stimulatory and inhibitory compounds at the surface of the cutting base is believed to be the reason for these results as no evidence of accumulation of inhibitory compounds in the solution was obtained. Charcoal reversed the inhibitory effect of IAA if added after the IAA treatment. This reversal was almost complete if the IAA treatment lasted for one day only but decreased drastically if the IAA treatment was extended over 4 days. [ABSTRACT FROM AUTHOR]

Removing apical portions of current growth coppice shoots from field-grown, low-pruned stumps of mulberry (Morus alba L. cv. Shin-ichinose) caused sprouting of one or more upper main buds, almost concurrently with that of accessory buds. However, removal of the new sprouts, including those from accessory buds, slightly enhanced the sprouting of buds immediately below them, and did not affect buds lower down. In contrast, mature leaves inhibited the buds in their axils. Budless, leafy nodes on the upper part of pruned shoots tended to swell after treatment, perhaps due to the accumulation of substances translocated from the roots and possibly from the remaining leaves. Lateral buds at different positions along the shoot differed in their sprouting ability with buds lower on the shoot being more inhibited. This inhibition gradient dissappeared when all coppice shoots on one stump were pruned to the same bud position, suggesting inhibition from neighboring, actively growing shoots. These results demonstrate that acropetal influences are important in bud dominance relationships. [ABSTRACT FROM AUTHOR]

Plants of Pisum sativum var. arvense Poir. cv. Dun were grown with two equal shoots kept in different light conditions. In these plants a darkened shoot was inhibited and it eventually withered and died; it elongated and became etiolated only when the shoot in the stronger light was removed. A similar result was obtained in simulated ecological conditions, when the shoot in the inferior light was merely shaded: this shoot was severely inhibited, though it did survive. The inhibition of the shaded shoot was more pronounced when the plants were stressed by the removal of large parts of their cotyledonary reserves. These results demonstrate an integration of responses to the light environment with the correlative inhibition between shoots of the same plant. This integration enables the plant to use its developmental resources optimally in heterogeneous environments, rather than merely growing where conditions are 'appropriate'. [ABSTRACT FROM AUTHOR]

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node of Phaseolus vulgaris (L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth. Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral buds. [ABSTRACT FROM AUTHOR]