biologia plantarum

Biologia plantarum 2016, 60:148-154 | DOI: 10.1007/s10535-015-0575-1

Effects of chilling and high temperatures on photosynthesis and chlorophyll fluorescence in leaves of watermelon seedlings

W. Hou^1,2, A. H. Sun³, H. L. Chen⁴, F. S. Yang^1,*, J. L. Pan², M. Y. Guan²

¹ College of Agronomy, Hainan University, Haikou, P.R. China

² Haikou Meteorological Station, Haikou Meteorological Bureau, Haikou, P.R. China

³ Rubber Research Institute, Chinese Academy of Tropical Agriculture Sciences, Danzhou, P.R. China

⁴ Institute of Meteorological Sciences, Haikou, P.R. China

The effects of chilling (CT, day/night temperatures of 12/10 °C, an irradiance of 250 μmol m^-2 s^-1), chilling combined with a low irradiance (CL, 12/10 °C, 80 μmol m^-2 s^-1), and a high temperature (HT, 42/40 °C, 250 μmol m^-2 s^-1) on chlorophyll content, chlorophyll fluorescence, and gas exchange were studied in two watermelon cultivars, ZJ8424 and YS01, differing in their resistance. The chlorophyll content, net photosynthetic rate (P_N), stomatal conductance (g_s), and transpiration rate (E) decreased substantially, whereas the intercellular CO₂ concentration (c_i) increased when the two watermelon cultivars were grown under these stresses. The photosynthetic parameters showed greater changes at chilling than at the high temperature, and the CL caused a more pronounced inhibition in PN compared with the CT. After 2 d exposure to the CT, YS01 had higher P_N, g_s, and E, but a lower ci compared with ZJ8424. The maximum efficiency of photosystem (PS) II photochemistry (F_v/F_m), effective quantum yield of PS II photochemistry (Φ_PSII), photochemical quenching (qP), and electron transport rate (ETR) decreased under the CT and CL but showed only a slight drop under the HT. All these stresses significantly increased non-photochemical quenching (NPQ). The CT brought more damage to the photosynthetic apparatus of leaves compared with the CL. In addition, after returning to normal conditions (25/15 °C, 250 μmol m^-2 s^-1) for 3 d, the photosynthetic parameters recovered to pre-stress levels in HT treated seedlings but not in CT treated seedlings. In conclusion, the low irradiance could help to alleviate the extent of photoinhibition of PS II photochemistry caused by chilling and cv. ZJ8424 was more sensitive to the extreme temperatures than cv. YS01.

Keywords: chlorophyll content; Citrullus lanatus; irradiance; stomatal conductance; transpiration rate

Subjects: chilling; chlorophyll a fluorescence; chlorophyll content; temperature - high; temperature - low; irradiance; net photosynthetic rate; transpiration rate; stomatal conductance; watermelon

Species: Citrullus lanatus

Received: April 13, 2015; Revised: July 19, 2015; Accepted: August 5, 2015; Published: January 1, 2016Show citation