Conversion of [14C]gibberellin A12-aldehyde to C19- and C20-gibberellins in a cell-free system from immature seed of Phaseolus coccineus L.

ent-Kaurene biosynthesis as a prerequisite for gibberellin (GA) biosynthesis was studied in germinating Hordeum vulgare L., cv Himalaya caryopses and correlated, in time, with the appearance of a-amylase activity. The rate of ent-kaurene biosynthesis was estimated by inhibiting its further metabolism with plant growth retardants (triapenthenol or tetcyclacis) and measuring its accumulation by isotope dilution using combined gas chromatographymass spectrometry. In the inhibitor-treated caryopses, ent-kaurene accumulation began approximately 24 hours after imbibition and proceeded at a rate of about I to 2 picomoles per hour per caryopsis, depending on the batch of seeds. In the absence of inhibitor, ent-kaurene did not accumulate, indicating that it is normally turned over rapidly, presumably to further intermediates of the GA biosynthesis pathway and eventually to GAs. entKaurene accumulation occurred almost exclusively in the shoot, which is, therefore, probably the site of biosynthesis. a-Amylase production began between 30 and 36 hours after imbibition and, thus, correlated well with de novo GA biosynthesis, as estimated from ent-kaurene accumulation. However, inhibition of ent-kaurene oxidation by plant growth retardants did not reduce the aamylase production significantly, although it did reduce shoot elongation. We conclude that ent-kaurene is produced in the shoot and is continuously converted to GA, which is essential for normal shoot elongation, but not for the production of a-amylase in the aleurone layer.Paleg (15) and Yomo (23) discovered independently that GA3 could substitute for the embryo in initiating a-amylase formation in germinating barley grains. This finding and the demonstration by Chrispeels and Varner (4) that isolated aleurone layers produced a-amylase in response to added GA3 led to the well-known hypothesis that GA3 produced in the embryo diffuses to the aleurone tissue where it induces the formation of a-amylase and other hydrolytic enzymes. The induction of a-amylase in the aleurone layer in response to XSupported by grants from the Deutsche Forschungsgemeinschaft. 2Present address: Instand e.V., Johannes-Weyer-Str.

Section: Methodsmentioning

confidence: 99%

ent-Kaurene Biosynthesis in Germinating Barley (Hordeum vulgare L., cv Himalaya) Caryopses and Its Relation to α-Amylase Production

Großelindemann¹,

Je²,

Stöckl³

et al. 1991

“…ent-[l4C]Kaurene (batches of 7.8 and 8.0 MBqlpmol) was prepared from R-2-['4C]mevalonic acid lactone (Amersham; 1.99 MBq/pmol) using a cell-free system from Cucurbita maxima endosperm Turnbull et al, 1985). Prior to incubation, the enzyme preparation was centrifuged at 100,OOOg for 1 h to remove endogenous ent-kaurene bound to membrane fragments.…”

Section: Preparation Of E~~t-['~c]kaurenementioning

confidence: 99%

ent-Kaurene Biosynthesis Is Enhanced by Long Photoperiods in the Long-Day Plants Spinacia oleracea L. and Agrostemma githago L

Zeevaart

Gage

1993

The effect of photoperiod on ent-kaurene biosynthesis was determined in the long-day (LD) plants spinach (Spinacia oleracea 1.) and Agrostemma githago L . Further metabolism of ent-kaurene was blocked by application of the growth retardant tetcyclacis, and ent-kaurene accumulation was measured by isotopic dilution using gas chromatography-selected ion monitoring (CC-SIM) (E.Physiol 96: 1099-1104). In spinach, the rate of ent-kaurene accumulation in shoots grown under LD conditions was 3 times higher than in shoots grown under short-day (SD) conditions. ent-Kaurene also accumulated in fully expanded leaves, but at a lower rate than in shoots (15 and 55 pmol g-' dry weight h-', respectively). In Agrostemma, ent-kaurene accumulated at a rate 2.5 times higher in plants grown under LD conditions than in those grown under SD conditions. In spinach, enhanced ent-kaurene accumulation was detectable after 1 long day, and with exposure to additional long days, the rate of ent-kaurene accumulation increased further.Conversely, when plants were exposed to LD conditions and then returned to SD conditions, the rate of ent-kaurene accumulation decreased. Following tetcyclacis application, ent-kaurene accumulation was observed in all parts of spinach that were analyzed, but there were large quantitative differences between organs of different ages. As the leaves matured, enf-kaurene biosynthesis declined. Petioles accumulated more ent-kaurene than the corresponding leaf blades. It is concluded that stimulation of entkaurene biosynthesis by LD conditions leads to a higher rate of gibberellin biosynthesis, which is essential for stem elongation in rosette plants.There is considerable evidence that the rate of GA biosynthesis in LD rosette plants is higher under LD conditions, when stem elongation and flower formation take place, than during vegetative growth in the rosette stage under SD conditions. For example, the GA content increased severalfold after the transfer of Silene plants from SD to LD conditions

“…GA biosynthesis performed by means of a cell-free system from suspensor (5) and embryo (21) of developing seeds of P. coccineus showed that these tissues contain all the enzymes necessary to convert mevalonic acid to GAs.…”

mentioning

confidence: 99%

Pattern of Variations in Abscisic Acid Content in Suspensors, Embryos, and Integuments of Developing Phaseolus coccineus Seeds

Perata¹,

Picciarelli²,

Alpi³

1990

Free abscisic acid (ABA) content in suspensors, embryos, and integuments was determined during seed development of Phaseolus coccineus. A highly specific and sensitive solid-phase radioimmunoassay based on a monoclonal antibody raised against free (S)-ABA was used for ABA quantification. Very small amounts of ABA were detected in the suspensor during initial stages of development; later two peaks of ABA occurred. Levels of ABA in the embryo and integument show a coincident triphasic distribution: two maxima in ABA content occurred when the embryo was 11 to 12 and 15 to 16 millimeters in length; later, when the embryo was 19 to 20 millimeters long, a further increase was observed. The role of ABA in runner bean seeds is discussed in relation to the development of the different seed tissues.