Specificity and reversibility of the rapid stomatal response to abscisic acid

The effects of the bacterial phytotoxin, syringomycin, on stomata were investigated using detached leaves of Xanthium strumarium and isolated epidermes of Vicia faba. Syringomycin is known to cause K+ efflux in fungal and higher plant cells. Doses of syringomycin as low as 0.3 unit per square centimeter (about 0.88 pmole per square centimeter) resulted in measurable stomatal closure when applied through the transpiration stream of detached leaves; higher doses produced larger reductions in stomatal conductance. Stomatal apertures of isolated epidermes were also reduced by low concentrations (3.2 units per milliliter; 10-8 molar) of syringomycin. The effects of syringomycin were similar to those of ABA. Both compounds closed stomata at a similar rate and at similar concentrations. In addition, neither compound significantly affected the relationship between photosynthesis and intercellular CO2 based on data taken after stomatal conductance had stabilized following the treatment. It is possible that synngomycin and ABA activate the same K+ export system in guard cells, and syringomycin may be a valuable tool for studying the molecular basis of ABA effects on guard cells.

Section: Discussionmentioning

confidence: 99%

Syringomycin, a Bacterial Phytotoxin, Closes Stomata

Mott

Takemoto²

1989

“…It has been suggested that hormonal regulation may be involved in chilling resistance (6,9,15). ABA may aid plants in preserving better water balance (4,7) and in tolerating more chilling stress (8,10). The following reports on water relations and the metabolism of the ABA in corn leaves after mefluidide treatment before, during, and after chilling.…”

mentioning

confidence: 99%

Relationship between Mefluidide Treatment and Abscisic Acid Metabolism in Chilled Corn Leaves

Chenglie

Li²,

Brenner³

1986

resistance (6, 9, 15). ABA may aid plants in preserving better water balance (4, 7) and in tolerating more chilling stress (8,10). The following reports on water relations and the metabolism of the ABA in corn leaves after mefluidide treatment before, during, and after chilling. MATERIALS AND METHODSSeeds of 'A632 x C103YU', a single cross corn hybrid (Zea mays L.), were sown into a soil/sand/peat (3:2:2, v/v) medium in 1 5-cm diameter pots. Seedlings were thinned to two per pot. Pots were kept in a growth chamber with a regime of 12-h photoperiod, 400-450 E m-2 s-' PAR, and 26°C D/N3 temperature. When plants had 3 to 4 true leaves, they were sprayed with analytic grade mefluidide at concentrations of 10 and 20 ppm (mg/L). The mefluidide was first dissolved in 2 to 3 ml of acetone, and then quickly diluted with distilled H20 to an appropriate volume and a few drops of Tween 20 surfactant added. Foliar spray was stopped when leaf tips showed droplets.Twenty-four h after treatment, plants were transferred from Water Relations. Leaf water potentials (WP), using the first true leaf, were measured with a pressure chamber. Seven measurements from each of 6 plants for each treatment were made at each sampling date. Leaf osmotic potentials were measured with a vapor pressure osmometer. Discs were punched from the 3rd true leaf. Leaf sap was pressed from the disc and collected with a filter-paper disc which was then placed in an osmometer. OP was calculated according to OP = iCRT, where i = isosmotic coefficient, C = leaf sap concentration, R = gas coefficient, and T = absolute temperature. Seven OP measurements from each of 6 plants were made for each treatment at each sampling date. RWC was calculated according to RWC = (fresh weight -dry weight/(turgid weight -dry weight). Turgid weight was obtained by placing the cut end of the first true leaf in a beaker containing water. The beaker was enclosed in a humid-atmosphere chamber for 12 h at either 26C or 4C ambient temperatures, corresponding to the plant-grown temperatures. Submerged ends of leaves were blotted rapidly before weighing. Leaves were dried in an oven at 1 20°C for about 48 h and dry weights determined. RESULTS ABA Content. Endogenous free ABA in controls and mefluidide-treated plants before, during and after chilling is shown in Figure 1. During the first 24 h period after mefluidide treatment at 26°C, control plants had a constant ABA content of 28, ng/g 699 www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

“…Since exogenous application of ABA is known to close stomata (5,9,11), the increased endogenous ABA level that occurs during dehydration may represent an important regulatory mechanism for closing stomata, thereby restricting transpirational water loss (14). Despite this important role for ABA in regulating stomatal aperture, there is little evidence to suggest how its synthesis is triggered or controlled.…”

mentioning

confidence: 99%

Abscisic Acid Accumulation in Cotton Leaves in Response to Dehydration at High Pressure

Ackerson¹,

Radin²

1983

Pressure-volume techniques were utilized to examine the control of abscisic acid (ABA) accumulation in dehydrated cotton (Gossypium hirsutum L. cv Tamcot SP 37) leaves. Leaves were rapidly dehydrated in a pressure chamber to a balance pressure coincident with the loss of cellular turgor, and then the pressure was either maintained at that level or released. Rapid accumulation of ABA began within two hours after the balance pressure was achieved, whether or not the high pressure potential of the cells was maintained by the externally imposed pressure. The results show that loss of pressure per se does not trigger ABA accumulation in dehydrated leaves. Rather, the stimulus may be related to cellular shrinkage and relaxation of the elastic wall.