-
Creeping bentgrass (cv. Penncross) sods were collected from the turfgrass research farm at Rutgers University and transplanted into polyvinyl chloride tubes (30 cm in length, and 10 cm in diameter) filled with soil. Plants were grown in a greenhouse where the day/night temperature averaged at 23/16 °C and 790 μmol m−2 s−1 photosynthetically active radiation (PAR). Plants were cut twice per week to maintain a canopy height of approximately 4 cm and fertilized weekly with full Hoagland's solution[43]. After 40 d of transplanting, plants were moved to growth chambers controlled at 21/19 °C (day/night) and 12-h photoperiod with PAR of a 660 μmol m−2 s−1 at the canopy level.
After being acclimated for one week in growth chambers, plants in each tube were sprayed with 10 ml of 0.5 mM GABA solution or water (untreated control) every other day three times and then subjected to optimal growth temperature (control) (21/19 °C, day/night) and heat stress (35/30 °C, day/night) for 30 d. Each treatment was replicated four times (four containers) in four growth chambers.
Measurements of endogenous GABA and physiological parameters
-
For determination of endogenous GABA content, fresh leaves (0.2 g) were ground into a fine powder in liquid nitrogen, and 400 μM methanol was added. The mixture was vacuum dried. After adding 1 ml of 70 mM lanthanum chloride, samples were shaken for 15 min and centrifuged for 5 min at 13,000 g. The supernatant (0.5 ml) was then mixed with 160 μl of 1 M KOH and shaken for 5 min. The mixture was centrifuged again at 13,000 g to obtain the supernatant for GABA detection. One millilitre of reaction solution contained 0.1 ml of GABA extraction, 150 μl of 4 mM NADP+, 50 μl of GABA transaminase (2 units per ml), and 200 μl of 0.5 M K+ pyrophosphate buffer (pH 8.6). The initial absorbance of the reaction solution was read at 340 nm with a spectrophotometer (Spectronic Instruments, Rochester, NY, USA). Then 50 μl of 20 mM α-ketoglutarate was added into the reaction solution and the final absorbance was recorded at 340 nm[44].
Leaf RWC, OP, and Chl content were measured by using the method of Barrs & Weatherley[45], Blum[46] and Amnon[47], respectively. For photochemical efficiency, leaves were inserted in clips and kept in the dark for 15 min, and then a fluorescence meter (Fim 1500, Dynamax, Houston, TX, USA) was used to record variable fluorescence (Fv) and maximum fluorescence (Fm) to calculate the ratio of Fv/Fm. For determination of Pn, single individual leaves were placed in the leaf chamber with 400 μl L−1 CO2 at a light intensity of 800 μmol photon m−2 connected to the gas exchange analyzer (Li-Cor 6400, Li-Cor, Inc., Lincoln, NE, USA). Leaf Pn was then recorded until the reading became stable. Leaf EL was measured as an indicator of cell membrane stability using a conductivity meter (YSI Model 32, Yellow Spring, OH, USA) according to the procedure previously described by Blum & Ebercon[48].
Ionomic and nitrogen analysis
-
Leaf tissues were dried at 80 °C to a constant weight, ground into a fine powder, and then passed through a 40-mesh screen. For determination of total N, 0.25 g dry ash was placed in a 75 ml digestion tube and then 6 ml H2SO4 was added. After thoroughly mixing on a vortex stirrer, the digestion tube was preheated to 370 °C until all plant tissue was broken up. The digestion tube was removed from the digestion block and 4 ml 30% H2O2 was added. The tube was placed back on the digestion block and heated at 370 °C for 2 h. After removing the tube from the block and fumehood for 10 min, 15 ml deionized water was added. Sample digests can be analyzed for N on the vario Max C/N Analyzer (Elementar, Germany)[49]. The method of Miller[50] was used for determination of ionomics including P, K, Ca, Na, Mg, Mn, Fe, Cu, B, Al, and Zn. Leaf tissues were placed in a muffle furnace over 4 h at 500 °C and once at room temperature, ashed samples were removed from the furnace. Dry ash (0.25g) was dissolved in 10 ml of 1 N HCl solution. After digestion, ash digests were used for determination of mineral composition by using the Varian 730-ES Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) (Agilent Technologies, USA).
Statistical analysis
-
The experiment was based on a split-plot design with temperature as the main plot and exogenous GABA application as the sub-plot. SAS (9.1, SAS Institute, Cary, NC, USA) was used to analyze treatment effects based on the general linear model procedure. Treatment differences were compared and tested using Fisher’s protected least significance test with P < 0.05.
-
About this article
Cite this article
Li Z, Burgess P, Peng Y, Huang B. 2022. Regulation of nutrient accumulation by γ-aminobutyric acid associated with GABA priming-enhanced heat tolerance in creeping bentgrass. Grass Research 2:5 doi: 10.48130/GR-2022-0005
Regulation of nutrient accumulation by γ-aminobutyric acid associated with GABA priming-enhanced heat tolerance in creeping bentgrass
- Received: 23 May 2022
- Accepted: 08 July 2022
- Published online: 26 August 2022
Abstract: γ-Aminobutyric acid (GABA) is known for its positive effects on improving plant stress tolerance, while the association of its role in regulating nutritional availability and GABA priming-enhanced heat tolerance is not well documented. The objective of this study was to determine whether GABA priming may improve heat tolerance in cool-season grass species involving regulation of plant nutrition for macronutrients and micronutrient elements. Plants of creeping bentgrass (Agrostis stolonifera) (cv. 'Penncross') in each pot were treated with 10 mL of water (control) or 0.5 mM GABA (GABA priming) by foliar spray and then subjected to heat stress (35/30 °C, day/night) or optimal growth temperature (control) (21/19 °C, day/night) (non-stress control) for 30 d in growth chambers. GABA-primed plants had significantly higher endogenous GABA content associated with improved heat tolerance compared to non-treated plants, as reflected by higher leaf cell membrane stability, relative water content, osmotic adjustment, chlorophyll content, photochemical efficiency, and net photosynthetic rate. Plants pretreated with GABA exhibited significantly higher content of nitrogen (N), phosphorus (P), calcium (Ca), sodium (Na), and copper (Cu) but lower content of boron (B) and manganese (Mn) in leaves than non-treated plants under heat stress. The enhanced accumulation of N, P, Ca, Na, and Cu and restricted B and Mn accumulation by GABA priming indicate that GABA could modulate mineral nutrient availability in plants, contributing to improved heat tolerance for creeping bentgrass.
-
Key words:
- GABA /
- Nutrients /
- Heat stress /
- Grass