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a Dep. of Botany and Microbiology, Univ. of Oklahoma, Norman, OK 73019
b USDA-ARS, Corvallis, OR 97331
* Corresponding author (huang{at}aesop.rutgers.edu)
Heat stress injury may involve inhibition of cytokinin biosynthesis in roots. The objective of this study was to examine whether application of a synthetic cytokinin, zeatin riboside (ZR), to the root zone would enhance tolerance of creeping bentgrass (Agrostis palustris L.) to high soil temperature or in combination with high air temperature. Grasses were exposed to three air and soil temperature regimes for 56 d in growth chambers: (i) optimum air and soil temperature (control), 20/20°C; (ii) optimum air but high soil temperature (20/35°C); and (iii) high air and soil temperatures (35/35°C). Four concentrations (0.01, 0.1, 1, and 10 µmol) of ZR or water (control) were injected into the 05 cm root zone on the day before heat stress (0 d) and 14 d after. Turf visual quality, canopy net photosynthetic rate (Pn), leaf photochemical efficiency (Fv/Fm), and vertical shoot extension rate decreased, whereas root mortality and root electrolyte leakage increased at 20/35 and 35/35°C, and to a greater extent at 35/35°C. Applications of 1 and 10 µmol ZR mitigated heat stress injury to shoots and roots during most of the experimental period, with 10 µmol ZR being more effective when applied at either 0 or 14 d of heat stress. Application of 0.1 µmol ZR was less effective than 1 and 10 µmol ZR. Application of 0.01 µmol ZR had no effects on shoot and root responses to high soil temperature alone or combined with high air temperature. Endogenous cytokinin content in both shoots and roots increased with the application of 1 and 10 µmol ZR. These results demonstrated that applying ZR at 1 or 10 µmol concentration to the root zone could alleviate heat stress injury of creeping bentgrass.
Abbreviations: Fv/Fm, photochemical efficiency LSD, least significance difference Pn, net photosynthetic rate VSER, vertical shoot extension rate ZR, zeatin riboside
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