Wang Q, Little CHA, Moritz T, Oden PC
Identification of endogenous gibberellins, and metabolism of tritiated and deuterated GA(4), GA(9) and GA(20), in Scots pine (Pinus sylvestris) shoots
Physiologia Plantarum: 1996 97:764-771
The application of gibberellin A(4/7) (GA(4/7)) to the stem of previous-year (1-year-old) terminal shoots of Scots pine (Pinus sylvestris) seedlings has been observed to stimulate cambial growth locally, as well 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 investigated. As a first step, we analysed for endogenous GAs and monitored the transport and metabolism of labelled GAs 4, 9 and 20. Endogenous 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 the stem, and GAs 1, 3 and 4 in the needles, by full-scan mass spectrometry (GAs 1, 3, 4, 9 and 12) or selected-ion monitoring (GA(20)) and Kovats 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 elongating current-year terminal shoot, the application point, and the 1-year-old needles and the cambial region above and below the application point. After purification, detection by liquid scintillation spectrometry and analysis by GC-MS, it was evident that, for each applied GA, unmetabolised [H-2(2)]GA and [H-3]radioactivity were present in every seedling part analysed. Most of the radioactivity was retained at the application 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 recovered 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 for 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 pathways 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 converted 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 biosynthesis 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 conversion to GA(t), rather than to it being active per se.
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