Heat stress is one of the main abiotic stresses that limit plant growth. The effects of high temperature on oxidative damage, PSII activity and D1 protein turnover were studied in three wheat varieties with different heat susceptibility (CS, YN949 and AK58). The results showed that heat stress induced lower lipid peroxidation in AK58 and YN949 than CS, which was related to different changes of SOD, CAT, POD and H 2 O 2 . Similarly, AK58 and YN949 performed better PSII photochemical efficiency (F v /F m , ΦPSII and ETR) under high temperature, which was attributed to rapid synthesis and degradation of D1 protein. Moreover, higher expression of D1 protein turnover-related genes ( PsbA , STN8 , PBCP , Deg1 , Deg2 , Deg5 , Deg8 , FtsH1/5 and FtsH2/8 ) and SOD activity in AK58 and YN949 under normal conditions also established a basis for acclimatizing high temperatures, thereby alleviating PSII photoinhibition and reducing oxidative damage when exposed to heat stress.

To investigate the effect of exogenous progesterone on the activities of lipid peroxidation and antioxidant enzymes,the seedlings of maize (Zea may cv. Zhuyu 309) were pretreated with 10 -9 mol/L, 10 -7 mol/L,10 -5 mol/L,10 -3 mol/L of progesterone under the high temperature stress. The activities of superoxide dismutase ( SOD) ,catalase ( CAT) ,peroxidase ( POD) ,CAT and POD isozymes,and the ma-londialdehyde ( MDA) content,membrane permeability and chlorophyll fluorescence parameters of maize leaves were assayed. The results showed that,CAT activity of 10 -9 mol/L progesterone pretreatment was 2. 4 times higher than the high temperature treatment,and the activities of SOD and POD of 10 -7 mol/L progesterone pretreatment were 1. 1 times and 1. 2 times higher than the high temperature treatment,re-spectively. In addition,the relative electric conductivity of 10 -9 mol/L and 10 -7 mol/L progesterone pre-treatment decreased to 70% and 65% of the high temperature treatment,respectively; Malondialdehyde contents were also reduced to 69% or 74% of the high temperature treatment,respectively. The expression levels of POD and CAT isozymes of 10 -7 mol/L progesterone treatment elevated,as well as oxygen release rate and chlorophyll fluorescence paraments. This study showed that the pretreatment with 10 -9 mol/L and 10 -7 mol/L progesterone increased the activities of antioxidant enzymes,and decreased the MDA content and the electrolyte leakage rate under high temperature stress,thus to protect the photosynthesis in maize leaves.

Drought usually induces plant growth inhibition and oxidative damage. This report showed the protections of hydrogen sulfide (H2S) against drought-induced damage in wheat, which was manifested in the better growth, higher relative water content (RWC), lower thiobarbituric acid-reactive substances (TBARS), and hydrogen peroxide (H2O2) as well as the increased activities of superoxide dismutase (SOD) and catalase (CAT). Drought often causes photosystem II (PS II) damage, which was observed in the decreased potential photochemical efficiency (F v/F m), actual photochemical efficiency (ΦPS II), photochemical quenching (qP), electron transfer rate (ETR), and increased non-photochemical quenching (qN), however, these effects could be alleviated by NaHS (H2S donor). D1 protein in PS II reaction center is the most sensitive target of PS II damage. Compared to water treatment, a higher level of transcription but less D1 protein and phosphorylated D1 protein was detected in wheat leaves when exposed to NaHS under drought stress, which may result from the higher expression of STN8 (catalyze D1 protein phosphorylation) and D1 protein degradation-related gene (Deg1, Deg5, Deg8, FtsH2, and FtsH5). These results suggested that H2S alleviated drought-induced PS II damage owing to fast D1 protein turnover rather than D1 protein content.

干旱胁迫会抑制小麦种子的萌发及生长,20％聚乙二醇(PEG-6000)模拟干旱胁迫的同时施以不同浓度的外源葡萄糖处理小麦种子,探讨外源葡萄糖对干旱胁迫下小麦种子萌发及幼苗生长的影响.14 h光照/10 h黑暗的光周期培养条件下,较低浓度的葡萄糖(0.02 mmol/L和0.05 mmol/L)促进了干旱胁迫下小麦种子的萌发及幼苗生长,但较高浓度的葡萄糖(0.1 mmol/L,0.2 mmol/L及0.5 mmol/L)加强了干旱胁迫对小麦种子萌发及幼苗生长的抑制效应;而在黑暗条件下培养,葡萄糖的上述调节作用消失.以上结果说明葡萄糖对干旱胁迫下小麦种子萌发及幼苗生长的调节作用具有浓度效应,并且依赖于光.

microRNA是一种非编码蛋白质的小分子RNA,参与了植物生长发育及环境胁迫响应的调控,主要通过对靶基因的负调控去影响生物学过程.基于前人对拟南芥全基因组microRNAs及其靶基因的预测,我们找到了靶向15个缺铁响应基因的22个microRNAs(miR158a、miR164c、miR172a、miR1887、miR2111ab、miR3933、miR395ade、miR414、miR828、miR831、miR837-3P、miR837-5P、miR854abcd、miR857、miR861-5P、miR864-5P).对这些microRNAs的启动子进行分析,发现分别有17、10和4个microRNAs启动子中包含缺铁响应元件IDE1、生长素响应元件和乙烯响应元件.进一步通过Poly(T) adaptor RT-PCR方法对这22个microRNAs在缺铁条件下的表达变化做了检测,结果显示,除miR158a和miR837-5P外的20个microRNAs在缺铁条件下的表达变化都有显著差异,且具有时间依赖性.这20个microRNAs可作为缺铁响应的候选microRNAs.