[Effects of exogenous abscisic acid (ABA) on the photosynthesis and chlorophyll fluorescence parameters of Tripterygium wilfordii seedlings exposed to low temperature].

Taking one year-old Tripterygium wilfordii cutting seedlings as test materials, this paper studied the effects of foliar spraying 0, 5, 10, 15, 20, and 25 mg x L(-1) of abscisic acid (ABA) on the leaf photosynthesis and chlorophyll fluorescence characteristics of the seedlings under low temperature stress. Spraying 20 mg x L(-1) of ABA increased the cold- resistance of the seedlings significantly, manifesting in the slowing down of the decrease amplitudes of leaf net photosynthetic rate (P(n)), transpiration rate (T(r)), stomatal conductance (g(s)), and intercellular CO2 concentration (C(i)) and the increase of photosynthetic capacity. After 6 days exposure to low temperature, the initial fluorescence (F(o)) decreased with increasing concentration of applied ABA, the maximum fluorescence (F(m)) and maximal photochemical yield (F(v)/F(m)) increased, the actual photochemical efficiency of system II (phi(PSII)) and photochemical quenching coefficient (q(P)) increased after an initial decrease, and the non-photochemical quenching coefficient (q(N)) showed a 'decreasing-increasing-decreasing' trend. The P(n), g(s), q(P), F(m), and F(v)/F(m) reached their peak values at 20 mg x L(-1) of ABA. In all treatments, with the increase of photosynthetically active radiation (PAR), the relative electron transport rate (rETR) increased first and decreased then, reached the peak when the PAR was 395 micromol x m(-2) x s(-1), and the peak value of the rETR in treatments 25 and 20 mg x L(-1) of ABA was 17.1% and 5.2% higher than that of the control, respectively. The light response curves of the psi(PSII) decreased with increasing PAR, whereas those of q(N) performed in adverse.