Klatt Simone, Hadacek Franz, Hodač Ladislav, Brinkmann Gina, Eilerts Marius, Hojsgaard Diego, Hörandl Elvira
Albrecht-von-Haller-Institute for Plant Sciences, Department of Systematics, Biodiversity and Evolution of Plants (with Herbarium), Georg-August-University of Göttingen , Göttingen, Germany.
Albrecht-von-Haller-Institute for Plant Sciences, Department of Plant Biochemistry, Georg-August-University of Göttingen , Göttingen, Germany.
Front Plant Sci. 2016 Mar 8;7:278. doi: 10.3389/fpls.2016.00278. eCollection 2016.
Meiosis, the key step of sexual reproduction, persists in facultative apomictic plants functional to some extent. However, it still remains unclear how and why proportions of reproductive pathways vary under different environmental stress conditions. We hypothesized that oxidative stress mediates alterations of developmental pathways. In apomictic plants we expected that megasporogenesis, the stage directly after meiosis, would be more affected than later stages of seed development. To simulate moderate stress conditions we subjected clone-mates of facultative apomictic Ranunculus auricomus to 10 h photoperiods, reflecting natural conditions, and extended ones (16.5 h). Reproduction mode was screened directly after megasporogenesis (microscope) and at seed stage (flow cytometric seed screening). Targeted metabolite profiles were performed with HPLC-DAD to explore if and which metabolic reprogramming was caused by the extended photoperiod. Prolonged photoperiods resulted in increased frequencies of sexual vs. aposporous initials directly after meiosis, but did not affect frequencies of sexual vs. asexual seed formation. Changes in secondary metabolite profiles under extended photoperiods affected all classes of compounds, and c. 20% of these changes separated the two treatments. Unexpectedly, the renowned antioxidant phenylpropanoids and flavonoids added more to clone-mate variation than to treatment differentiation. Among others, chlorophyll degradation products, non-assigned phenolic compounds and more lipophilic metabolites also contributed to the dissimilarity of the metabolic profiles of plants that had been exposed to the two different photoperiods. The hypothesis of moderate light stress effects was supported by increased proportions of sexual megaspore development at the expense of aposporous initial formation. The lack of effects at the seed stage confirms the basic assumption that only meiosis and sporogenesis would be sensitive to light stress. The concomitant change of secondary metabolite profiles, as a systemic response at this early developmental stage, supports the notion that oxidative stress could have affected megasporogenesis by causing the observed metabolic reprogramming. Hypotheses of genotype-specific responses to prolonged photoperiods are rejected.
减数分裂是有性生殖的关键步骤，在兼性无融合生殖植物中仍在一定程度上发挥作用。然而，在不同环境胁迫条件下，生殖途径的比例如何以及为何会发生变化仍不清楚。我们推测氧化应激介导了发育途径的改变。在无融合生殖植物中，我们预期减数分裂后的直接阶段——大孢子发生，会比种子发育的后期阶段受到更大影响。为了模拟适度胁迫条件，我们将兼性无融合生殖的金毛茛克隆体置于反映自然条件的10小时光周期以及延长的光周期（16.5小时）下。在大孢子发生后（通过显微镜）和种子阶段（流式细胞术种子筛选）直接筛选生殖模式。使用高效液相色谱 - 二极管阵列检测器（HPLC - DAD）进行靶向代谢物谱分析，以探究延长的光周期是否以及导致了何种代谢重编程。延长的光周期导致减数分裂后有性与无孢子初始细胞的频率增加，但不影响有性与无性种子形成的频率。延长光周期下次生代谢物谱的变化影响了所有类别的化合物，其中约20%的变化区分了两种处理。出乎意料的是，著名的抗氧化剂苯丙烷类化合物和黄酮类化合物对克隆体间差异的贡献比对处理差异的贡献更大。此外，叶绿素降解产物、未分类的酚类化合物和更多亲脂性代谢物也导致了暴露于两种不同光周期的植物代谢谱的差异。适度光胁迫效应的假设得到了支持，即有性大孢子发育比例增加，以无孢子初始细胞形成为代价。在种子阶段缺乏影响证实了基本假设，即只有减数分裂和孢子发生对光胁迫敏感。次生代谢物谱的伴随变化，作为这个早期发育阶段的一种系统反应，支持了氧化应激可能通过引起观察到的代谢重编程影响大孢子发生的观点。关于对延长光周期的基因型特异性反应的假设被否定。
