To determine the effects of rootstock choice on the scion response to drought stress, we compared the vegetative growth, biomass accumulation, gas exchange, and water-use efficiency (WUE) of ‘Gale Gala’ apple (Malus domestica Borkh.) trees grafted onto nine wild Chinese Malus rootstocks. Compared with the well-watered control, drought treatment limited growth, as manifested by smaller increments in plant height (PH), trunk diameter (TD), total fresh biomass (TB), total dry biomass (TDB), total leaf area (LA), and relative growth rate (RGR). The extent of this effect differed among rootstocks. Stress conditions led to increases in the root/shoot ratio (RSR), leaf thickness (LT), water-holding capacity (WHC), carbon isotope composition (δ13C), and WUE. Decreases were noted in stomatal density (SD), leaf relative water content (RWC), chlorophyll content (Chl), net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs), again varying by rootstock. Those that are generally considered more drought-tolerant, e.g., M. sieversii, M. prunifolia, and M. toringoides, had smaller declines in PH, TD, TB, TDB, LA, RGR, SD, RWC, Chl, PN, E, and gs and proportionally greater increases in RSR, LT, WHC, δ13C, and WUE compared with the droughtsensitive M. hupehensis and
M. sieboldii. These results suggest that moisture stress has a significant dwarfing effect in the latter two species. Based on WUE calculations, trees on drought-tolerant rootstocks showed higher tolerance when stressed, whereas those on drought-sensitive rootstocks were less tolerant, as indicated by their lower WUE values., B. H. Liu ... [et al.]., and Obsahuje bibliografii
Tolerance of photosystem 2 (PS2) to high temperature in apple (Malus domestica Borkh. cv. Cortland) leaves and peel was investigated by chlorophyll a fluorescence (OJIP) transient after exposure to 25 (control), 40, 42, 44, and 46 °C in the dark for 30 min. The positive L-step was more pronounced in a peel than in leaves when exposed to 44 °C. Heat-induced K-step became less pronounced in leaves than in peel when exposed to 42 °C or higher temperature. Leaves had negative L-and K-steps relative to the peel. The decrease of oxygen-evolving complex (OEC) by heat stress was higher in the peel than in the leaves. OJIP transient from the 46 °C treated peel could not reach the maximum fluorescence (Fm). The striking thermoeffect was the big decrease in the relative variable fluorescence at 30 ms (VI), especially in the leaves. Compared with the peel, the leaves had less decreased maximum PS2 quantum efficiency (Fv/Fm), photochemical rate constant (KP), Fm and performance index (PI) on absorption basis (PIabs) and less increased minimum fluorescence (F0) and non-photochemical rate constant (KN), but more increased reduction of end acceptors at PS1 electron acceptor side per cross section (RE0/CS0) and per reaction center (RE0/RC0), quantum yield of electron transport from QA - to the end acceptors (ϕ R0) and total PI (PIabs,total) when exposed to 44 °C. In conclusion, PS2 is more thermally labile than PS1. The reduction of PS2 activity by heat stress primarily results from an inactivation of OEC. PS2 was more tolerant to high temperature in the leaves than in the peel. and L.-S. Cheng, L. Chen.