Jatropha curcas, one of the most important energy plant resources, is vulnerable to chilling. To evaluate the effects of chilling on photosynthesis of J. curcas and intraspecific differences in chilling tolerance, seedlings of twelve populations were treated with the temperature of 4-6°C for five consecutive nights with normal environmental temperature during the day. Night chilling treatment decreased light-saturated photosynthetic rate (Pmax) significantly for all populations. Stomatal limitation could not explain the decreased Pmax because intracellular CO2 concentration was not significantly reduced by night chilling in all populations (with only one exception). The decreased soluble-protein content, which may be related to the increased malondialdehyde (MDA) content, contributed to the decreased Pmax. The increased MDA content indicated that oxidative stress occurred after night chilling, which was associated with the larger decrease in Pmax compared with the decrease in actual photochemical efficiency of photosystem II, and the slight increase in thermal dissipation of excessive energy. After five-day recovery, MDA (with two exceptions) and Pmax still did not recover to the levels as those before night chilling treatment for all populations, indicating that J. curcas was vulnerable to chilling. Chilling tolerance was significantly different among populations. Populations originating from high elevations had greater chilling-tolerant abilities than populations originating from low elevations, showing a local adaptation to environmental temperatures of origins. Our study shed light on the possibility to find or breed chilling-tolerant genotypes of J. curcas. and Y.-L. Zheng ... [et al.].
Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO2 concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant's ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.