The literature on endogenous gibberellins (GAs) of conifers, and on processes correlated with changes in GA-like substances, or processes affected by exogenous application of GAs is reviewed. It is now apparent that GAs mediate or influence many different growth and development processes in conifers, although just how they evoke the observed responses remains obscure.Practically, the use of certain GAs on conifers should allow advances to be made in the areas of tree breeding (i.e. the promotion of early flowering) and enhancement and regularization of seed production. The possible use of GAs to enhance early vegetative growth is feasible for many species. The use of endogenous GA levels, rate of synthesis, or metabolism as screening techniques in progeny testing, while still speculative, appears attractive.

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Soil drenches of 250, 500 or 1000 mg/l of the growth retardants AMO‐1618 or B‐995 effectively reduced dry matter production and stem elongation in young seedlings of Cupressus arizonica Greene. In seedlings treated with AMO‐1618, the acidic, ethyl acetate‐soluble gibberellin‐like substances (GAs), as detected. by bioassay, were reduced to almost undetectable levels. However, the endogenous GA content in seedlings treated with B‐995 were at least 11‐fold greater than in control seedlings and differed as well in chromatographic characteristics, being of a more polar nature than the endogenous GAs of control seedlings. It was concluded that while AMO‐1618 probably acts through interference with GA biosynthesis, B‐995 may act through the interconversion of GAs.

Levels of auxin- and gibberellin (GA)-like substances were analyzed in floral buds, open flowers, and developing fruit of tomatoes (Lycopersicon esculentum Mill) subjected to 38°C for 5 hr. The levels of these substances were lowest at anthesis. The levels of GA-like substances in all analyses were lower than those of auxin-like substances. High temperature treatment decreased the levels of both substances, especially in floral buds and developing fruit.