IDENTIFICATION OF ENDOGENOUS GIBBERELLINS, AND METABOLISM OF TRITIATED AND DEUTERATED GA(4), GA(9) AND GA(20), IN SCOTS PINE (PINUS-SYLVESTRIS) SHOOTS

The application of gibberellin A(4/7) (GA(4/7)) to the stem of previou s-year (1-year-old) terminal shoots of Scots pine (Pinus sylvestris) s eedlings has been observed to stimulate cambial growth locally, as wel l as at a distance in the distal current-year terminal shoot, but the distribution and metabolic fate of the applied GA(4/7), as well as the pathway of endogenous GA biosynthesis in this species, has not been i nvestigated. As a first step, we analysed for endogenous GAs and monit ored the transport and metabolism of labelled GAs 4, 9 and 20. Endogen ous GAs from the elongating current-year terminal shoot of 2-year-old seedlings were purified by column chromatography and high-performance liquid chromatography and analysed by combined gas chromatography-mass spectrometry (GC-MS). GAs 1, 3, 4, 9, 12 and 20 were identified in th e stem, and GAs 1, 3 and 4 in the needles, by full-scan mass spectrome try (GAs 1, 3, 4, 9 and 12) or selected-ion monitoring (GA(20)) and Ko vats retention index. Tritiated and deuterated GA(4), GA(9) or GA(20) were applied around the circumference at the midpoint of the previous- year terminal shoot, and metabolites were extracted from the elongatin g current-year terminal shoot, the application point, and the 1-year-o ld needles and the cambial region above and below the application poin t. After purification, detection by liquid scintillation spectrometry and analysis by GC-MS, it was evident that, for each applied GA, unmet abolised [H-2(2)]GA and [H-3]radioactivity were present in every seedl ing part analysed. Most of the radioactivity was retained at the appli cation point when [H-3]GA(9) and [H-3]GA(20) were applied, whereas the largest percentage of radioactivity derived from [H-3]GA(4) was recov ered in the current-year terminal shoot. It was also found that [H-2(2 )]GA(9) was converted to [H-2(2)]GA(20) and to both [H-2(2)]GA(4) and [H-2(2)]GA(t), [H-2(2)]GA(4) was metabolised to [H-2(2)]GA(t), and [H- 2(2)]GA(20) was converted to [H-2(2)]GA(29). The data indicate that fo r Pinus sylvestris shoots (1) GAs applied laterally to the outside of the vascular system of previous-year shoots not only are absorbed and translocated extensively throughout the previous-year and current-year shoots, but also are readily metabolised, (2) the GA metabolic pathwa ys found are closely related to the endogenous GAs identified, and (3) GA(9) metabolism follows two distinctly different routes: in one, GA( 9) is converted to GA(1) through GA(4), and in the other it is convert ed to GA(20), which is then metabolised to GA(29). The results suggest that the late 13-hydroxylation pathway is an important route for GA b iosynthesis in shoots of Pinus sylvestris, and that the stimulation of cambial growth in Scots pine by exogenous GA(4/7) may be due to its c onversion to GA(t), rather than to it being active per se.