Effect of abscisic acid on the transport of assimilates in barley

Abstract

The effect of abscisic acid (ABA) on assimilate transport in barley was investigated in two parallel experiments. First, the effect upon [(14)C]sucrose transport from the flag leaf to the ear of a single ABA application made at different stages of growth of the fruits was investigated; the effect was measured 24 h after treatment. Second, the effect of a single application of ABA made at the same stages of growth as above on grain weight of the mature plant was investigated. In both types of experiments ABA was applied once to the ear of different plants as an aqueous solution (10(-3)-10(-5) M), one to five weeks after anthesis. [(14)C] sucrose was applied by means of agar blocks. Parallel to these experiments, the endogenous content of ABA was investigated in the developing grains. When ears were treated with ABA two or four weeks after anthesis, an increase of up to 70% in the (14)C-transport from the flag leaf to the ear was observed within a 24-h period after treatment (short duration experiments). At these growth stages the endogenous concentrations of ABA were low. In sharp contrast, ABA, especially in a concentration of 10(-3) M, decreased (14)C-import from the flag leaf when applied three weeks after anthesis. At this stage the endogenous ABA content had reached its maximum. Long duration experiments with a single application of ABA to the car two weeks after anthesis resulted in a marked increase of weight per thousand kernels. ABA applications made earlier or later than two weeks after anthesis either reduced the grain weight or had no effect. It is concluded that ABA is involved in the regulation of assimilate transport from the leaves to the grains, possibly by influencing the unloading of sieve tubes in the ears. Promotion or inhibition of assimilate import by exogenously applied ABA may depend on the developmental stage of the grains and on the endogenous ABA level.

Hormonal Changes in the Grains of Rice Subjected to Water Stress during Grain Filling

“…Similar results were also reported on wheat (Dewdney and McWha, 1979;Bai et al, 1989), barley (Tietz et al, 1981) and soybean (Glycine max L. Merr; Ackerson, 1985).…”

Abscisic Acid and Its Relationship to Seed Filling in Soybeans

“…ABA enhanced sugar content in roots of intact bean plants, possibly by stimulating sugar transport from the shoot to the root (11). In some cases, applications of ABA to ears of wheat (7) and barley (22) have stimulated 14C assimilate transfer from the flag leaf to the ear. However, King and Patrick (12) saw no stimulation of 14C transport to wheat ears after injection of ABA into the grains.…”

Reserve Carbohydrate in Maize Stem

“…Although the photosynthate requirements for kernels are small at the stage of kernel fertilization and early growth, competition by other sinks might decrease the amount of photosynthate available to kernels or interact with other whole plant regulatory mechanisms (24) such that fertility and kernel survival are decreased. This hypothesis is supported by studies showing that, at the initial stages after anthesis, environmental conditions such as water deficit (4) and cloudiness (20) decrease fertility and grain set while supplemental light ( 19) increases grain set.…”

“…5) suggests that development of export capacity did not determine actual net export rates. Perhaps the relative uptake activities by storage cells and phloem (9), whole plant regulatory controls such as hormones (24), or availability of sugar at phloem loading sites limited the net export rates.…”