Grafting of Cucumis sativus onto Cucurbita ficifolia leads to improved plant growth, increased light utilization and reduced accumulation of reactive oxygen species in chilled plants

The effects of chilling at 14 and 7A degrees C on plant growth, CO2 assimilation, light allocation, photosynthetic electron flux and antioxidant metabolism were examined in cucumber (Cucumis sativus L. cv. Jinyan No. 4, CS) plants with figleaf gourd (Cucurbita ficifolia Bouch,, CF) and cucumber as rootstocks, respectively. Growth inhibition by chilling at 7A degrees C was characterized by irreversible inhibition of CO2 assimilation in grafted plants with cucumber as rootstock and scion (CS/CS) but this effect was significantly alleviated by grafting onto CF roots (CS/CF). Chilled CS/CF plants exhibited a higher photosynthetic activity and lower proportion of energy dissipation than chilled CS/CS plants. Chilling resulted in a greater decrease in the electron flux in photosystem (PS) II (J (PSII)) than the rate of energy dissipation either via light-dependent (J (NPQ)) or via constitutive thermal dissipation and fluorescence (J (f,D)) in CS/CS plants. In parallel with the reduction in J (PSII), electron flux to oxygenation (J (o)) and carboxylation by Rubisco (J (c)) all decreased significantly whilst alternative electron flux in PS II (J (a)) increased, especially in CS/CS plants. Moreover, CS/CF plants exhibited higher activity of antioxidant enzymes, lower antioxidant content and less membrane peroxidation relative to CS/CS plants after chilling.