lllinois 61 801Crafting studies involving Williams 82 (normally nodulating) and N O D l -3 (hypernodulating) soybean (Glycine max [LI Merr.) lines and Lablab purpureus were used to evaluate the effect of shoot and root on nodulation control and plant growth. A single-or doublewedge graft technique, with superimposed partia1 defoliation, was used to separate signal control from a photosynthate supply effect.Crafting of hypernodulated soybean shoots to roots of Williams 82 or L. purpureus resulted i n increased nodule numbers. Crafting of two shoots to one root enhanced root growth in both soybean genotypes, whereas the nodule number was a function of shoot genotype but not of the photosynthetic area. In double-shoot, single-root-grafted plants, removing trifoliolate leaves from either Williams 82 or NOD1-3 shoots decreased root and shoot dry matter, attributable to decreased photosynthetic source. Concurrently, Williams 82 shoot defoliation increased the nodule number, whereas N O D I -3 shoot defoliation decreased the nodule number on both soybean and L. purpureus roots. It was concluded that (a) soybean leaves are the dominant site of autoregulatory signal production, which controls the nodule number; (b) soybean and L. purpureus have a common, translocatable, autoregulatory control signal; (c) seedling vegetative growth and nodule number are independently controlled; and (d) two signals, inhibitor and promoter, may be involved i n controlling legume nodule numbers.

No abstract

Gibberellin A4/7 (GA4/7) was applied twice weekly to 2‐year‐old Pinus sylvestris (L.) seedlings in each of two years, starting close to budbreak and ending after shoot elongation, but before cambial activity ceased. In 1988, the GA4/7 was injected into the 1987 terminal shoot (0, 0.2 or 2 mg seedling−1 application−1), while in 1990 it was applied as a soil drench (0, 10 or 50 mg seedling−1 application−1). In the 1988 experiment, GA4/7 treatment promoted diameter growth, and tended to increase both longitudinal growth and the indole‐3‐acetic acid (IAA) level in the 1988 terminal. In the 1990 experiment, GA4/7 treatment increased tracheid production, longitudinal growth, and the cambial region IAA concentration in the 1990 terminal, but did not affect its pith diameter, needle number, needle dry weight, or needle IAA level. Tracheid production in the previous‐year's terminal was also promoted in both experiments. The 50 mg GA4/7 soil drench markedly elevated the concentrations of GA4, GA7 and GA9 in the needles and cambial region of the 1990 terminal, while the 10 mg treatment raised the GA4 level in the cambial region, providing evidence that GA4 and GA7 applied to the roots reaches the shoot system. The results support the hypothesis that the exogenous GA4/7‐induced stimulation of tracheid production in the terminal shoot of intact plants is mediated through an increase in the IAA level in the cambial region. However, per se activity of GA4, GA7 or their metabolites cannot be ruled out.