| Phenotypic plasticity refers to the ability of the same genotype to produce different phenotypes in response to different environments.In particular,the maternal environment may affect the performances of the offsprings,resulting in transgenerational plasticity.Previous studies of theoretical models have shown that both within-and trans-generational plasticity may help organisms cope with environmental changes and accelerate the process of adaptation.Currently,there are much more case studies for within-generational plasticity than for transgenerational plasticity.In this paper,the widespread annual herb Thlaspi arvense（pennycress）was used as the material to investigate the within-and trans-generational plasticity under cadmium stress.Specifically,T.arvense were grown for two consecutive generations under stress and control conditions,respectively,with reciprocal transplantation for the second generation.The multi-level responses from morphology,physiology,and gene expression,were examined to infer how the cadmium stress experienced by parents may affect themselves and their offsprings.The results are as follows:1.At the morphological and physiological level,a range of traits in T.arvense can respond plastically to cadmium stress.Specifically,under stress conditions,a few functional trais were significangly decreased,including plant height,biomass,number of seeds,and photosynthetic capacity.The flowering time was significantly delayed.The plasticity may reflect the damage or restriction of the stress on the plant.However,there are also some traits may represent the active adjustments to stress.For example,under stress conditions,although the number of seeds decreased,the seeds became larger,and the antioxidant system were activated（for example,the concentration of GSH and the activity of SOD enzyme increased）.These changes may help T.arvense cope with stress.2.Among the plastic traits observed in the first generation,at least part of them can be found in the second generation（i.e.transgenerational plasticity）.In the reciprocal transplant experiment,some traits were significantly affected by the maternal environment.For examples,the plant height,the seed size,and SOD enzyme activity showed similar changes to the stressed mother plants although there was no cadmium stress in their immediate environments.Other traits,i.e.biomass,flowering time,GSH concentration,and photosynthetic capacity,were not affected by maternal environmental stress,resulting in no obvious transgenerational plasticity.3.At the level of gene expression,there were 5138 genes whose expression levels were significantly changed in response to cadmium stress.At least some of the genes may be related to enhancing stress tolerance,including the physical defense genes such as cellulose synthase,the Pectin methylesterase inhibitor genes involved in antioxidant stress such as glutathione S-transferase,superoxide dismutase,and peroxidase,etc.In the second generation of reciprocal transplantation,even if there was no environmental stress,the expression levels of some of the differentially expressed genes（641,ca.12.5%）still showed significant differences.Among them,the cellulose synthase gene,pectin methylesterase inhibitor gene,and glutathione synthesis-related genes were still significantly up-regulated under control conditions,indicating that the stress experienced by the parents produced transgenerational plasticity in the second generation.Taken together,these data suggested that cadmium stress can induce significant phenotypic plasticity of T.arvense at multi-levels,and at least some of them can be found in the second generation.As most seeds fall in soils around mother plants in field,the stress experienced by mother could be used as a reliable signal for the environmental quality of offsprings.Thus,these multi-level within-and transgenerational plasticity may be adaptive for T.arvense under cadmium stress. |
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