Physiologia Plantarum

Joudi, Mehdi; Ahmadi, Ali; Mohamadi, Valiollah; Abbasi, Alireza; Vergauwen, Rudy; Mohammadi, Hamid; Van den Ende, Wim

doi: 10.1111/j.1399-3054.2011.01517.xpmid: 21895669

Remobilization of stored carbohydrates in the stem of wheat plants is an important contributor to grain filling under drought stress (DS) conditions. A massive screening on Iranian wheat cultivars was performed based on stem dry weight changes under well‐watered and DS conditions. Two cultivars, Shole and Crossed Falat Hamun (CFH), with different fructan accumulation and remobilization behavior were selected for further studies. Water‐soluble carbohydrates (WSCs) and fructan metabolizing enzymes were studied both in the stem penultimate and in sucrose (Suc) treated, excised leaves. Under drought, CFH produced higher grain yields than Shole (412 vs 220 g m−2). Also, grain yield loss under drought was more limited in CFH than in Shole (17 vs 54%). Under drought, CFH accumulated more graminan‐type fructo‐oligosaccharides than Shole. After anthesis, fructan 6‐exohydrolase (6‐FEH; EC 3.2.1.154) activities increased more prominently than fructan 1‐exohydrolase (EC 3.2.1.153) activities during carbon remobilization. Interestingly, CFH showed higher 6‐FEH activities in the penultimate than Shole. The field experiment results suggest that the combined higher remobilization efficiency and high 6‐FEH activities in stems of wheat could contribute to grain yield under terminal drought. Similar to the penultimate, fructan metabolism differed strongly in Suc‐treated detached leaves of selected cultivars. This suggests that variation in the stem fructan among wheat cultivars grown in the field could be traced by leaf blade induction experiments.

Ogawa, Saori; Mitsuya, Shiro

doi: 10.1111/j.1399-3054.2011.01516.xpmid: 21895670

Methionine (Met) is biosynthesized by the activated methyl cycle and S‐methylmethionine (SMM) cycle in one‐carbon (C1) metabolism in plants. It is converted to S‐adenosylmethionine (SAM) which serves as a precursor for many metabolites including glycinebetaine, methylated polyols, polyamines and ethylene which accumulate in plants in response to salinity. We have investigated how the Met biosynthetic pathway is regulated under saline conditions at the transcriptional level in Arabidopsis thaliana plants. Within Met biosynthesis‐related genes, the expression of homocysteine methyltransferase (HMT) and methionine methyltransferase (MMT) genes in SMM cycle had altered toward increasing Met production by the presence of NaCl. We have determined the salinity tolerance of an Arabidopsis mmt mutant with an insertional mutation in the single copy of the AtMMT gene. Although the mmt mutant showed comparable germination and shoot growth with wild type under normal conditions, NaCl treatment caused severe repression of germination rate and shoot growth in the mmt mutant compared with in the wild type. These results indicate that the utilization of SMM is important for the salinity tolerance of Arabidopsis plants at the germination and early growth stages.

Wang, Wei‐Qing; Cheng, Hong‐Yan; Møller, Ian M.; Song, Song‐Quan

doi: 10.1111/j.1399-3054.2011.01518.xpmid: 21910735

Mitochondrial repair is of fundamental importance for seed germination. When mature orthodox seeds are imbibed and germinated, they lose their desiccation tolerance in parallel. To gain a better understanding of this process, we studied the recovery of mitochondrial structure and function in pea (Pisum sativum cv. Jizhuang) seeds with different tolerance to desiccation. Mitochondria were isolated and purified from the embryo axes of control and imbibed–dehydrated pea seeds after (re‐)imbibition for various times. Recovery of mitochondrial structure and function occurred both in control and imbibed–dehydrated seed embryo axes, but at different rates and to different maximum levels. The integrity of the outer mitochondrial membrane reached 96% in all treatments. However, only the seeds imbibed for 12 h and then dehydrated recovered the integrity of the inner mitochondrial membrane (IMM) and State 3 (respiratory state in which substrate and ADP are present) respiration (with NADH and succinate as substrate) to the control level after re‐imbibition. With increasing imbibition time, the degree to which each parameter recovered decreased in parallel with the decrease in desiccation tolerance. The tolerance of imbibed seeds to desiccation increased and decreased when imbibed in CaCl2 and methylviologen solution, respectively, and the recovery of the IMM integrity similarly improved and weakened in these two treatments, respectively. Survival of seeds after imbibition–dehydration linearly increased with the increase in ability to recover the integrity of IMM and State 3 respiration, which indicates that recovery of mitochondrial structure and function during germination has an important role in seed desiccation tolerance.

Nilsson, Lena; Lundmark, Maria; Jensen, Poul E.; Nielsen, Tom H.

doi: 10.1111/j.1399-3054.2011.01520.xpmid: 21910737

The transcription factor PHR1 (PHOSPHATE STARVATION RESPONSE 1; encoded by gene At4g28610) is central for adaptation to phosphate deficiency in Arabidopsis (Arabidopsis thaliana). A rapid turnover of phosphate pools in the leaves is essential for energy transfer and metabolism within photosynthesis, and consequently, we hypothesized that PHR1 is needed for adaptation to high‐light stress during P deficiency. We analyzed three Arabidopsis plant lines: wild‐type, a transgenic PHR1 overexpressor line and a knockout mutant, phr1. The plants were grown under phosphate‐limiting and sufficient conditions and exposed to different light conditions. Photosynthetic activity and light stress of the leaves were characterized by analyzing accumulation of carbohydrates, chlorophyll fluorescence, immunoblot detection of photosystem subunits and anthocyanin accumulation. Compared to the wild‐type and the overexpressor line, the phr1 mutant has decreased levels of phosphate, anthocyanins and carbohydrates during combined P deficiency and light stress. The stressed mutant also has strongly decreased photosystem II (PSII) quantum efficiency, and shows degradation of the core units of PSII demonstrating extensive irreversible photodamage. We conclude that PHR1 is needed for the metabolic balance, for retaining Pi levels and for inducing anthocyanin production, and during P deficiency PHR1 is vital for adaptations to avoid permanent damage to photosystems during high‐light conditions.

Lu, Hongxia; Wan, Qi; Wang, Huahua; Na, Xiaofan; Wang, Xiaomin; Bi, Yurong

doi: 10.1111/j.1399-3054.2011.01521.xpmid: 21916896

Narciclasine (NCS) is a plant growth inhibitor isolated from the secreted mucilage of Narcissus tazetta bulbs. It is a commonly used anticancer agent in animal systems. In this study, we provide evidence to show that NCS also acts as an agent in inducing programmed cell death (PCD) in tobacco Bright Yellow‐2 (TBY‐2) cell cultures. NCS treatment induces typical PCD‐associated morphological and biochemical changes, namely cell shrinkage, chromatin condensation and nuclear DNA degradation. To investigate possible signaling events, we analyzed the production of reactive oxygen species (ROS) and the function of mitochondria during PCD induced by NCS. A biphasic behavior burst of hydrogen peroxide (H2O2) was detected in TBY‐2 cells treated with NCS, and mitochondrial transmembrane potential (MTP) loss occurred after a slight increase. Pre‐incubation with antioxidant catalase (CAT) and N‐acetyl‐l‐cysteine (NAC) not only significantly decreased the H2O2 production but also effectively retarded the decrease of MTP and reduced the percentage of cells undergoing PCD after NCS treatment. In conclusion, our results suggest that NCS induces PCD in plant cells; the oxidative stress (accumulation of H2O2) and the MTP loss play important roles during NCS‐induced PCD.

Acosta‐Muñiz, Carlos H.; Escobar‐Tovar, Lina; Valdes‐Rodríguez, Silvia; Fernández‐Pavia, Silvia; Arias‐Saucedo, Luis J.; de la Cruz Espindola Barquera, Maria; Gómez Lim, Miguel Á.

doi: 10.1111/j.1399-3054.2011.01522.xpmid: 21916897

Huang, Shan‐Shan; Chen, Juan; Dong, Xue‐Jun; Patton, Janet; Pei, Zhen‐Ming; Zheng, Hai‐Lei

doi: 10.1111/j.1399-3054.2011.01523.xpmid: 21919914

As a second messenger, the free cytosolic calcium ion (Ca2+) plays important roles in many biochemical and physiological processes including photosynthesis in plants. In this study, we investigated morphological changes, chlorophyll accumulation and chloroplast development during early photomorphogenesis in etiolated seedlings of both Arabidopsis thaliana wild type (WT) and those with the antisense of CAS, a calcium sensor (CASas). Seedlings were grown at high, medium and low Ca2+ concentrations to identify the roles of Ca2+ and CAS in de‐etiolation and chloroplast development. The results demonstrated that Ca2+ and CAS are correlated with de‐etiolation of A. thaliana after light exposure. High Ca2+ significantly increased chlorophyll content and improved chloroplast development in both A. thaliana WT and CASas etiolated seedlings during de‐etiolation. The analysis by western blot and real‐time fluorescent quantitative polymerase chain reaction indicated that the expression levels of CAS mRNA and protein were upregulated by white light and external Ca2+ significantly. Etiolated CASas plants showed much lower chlorophyll content and delay of chloroplast development as compared with WT plants, indicating that CAS functions in de‐etiolation. All together, we concluded that the de‐etiolation in A. thaliana was promoted by the high Ca2+ concentration and CAS expression to a certain extent.

Peeva, Violeta N.; Tóth, Szilvia Z.; Cornic, Gabriel; Ducruet, Jean‐Marc

doi: 10.1111/j.1399-3054.2011.01519.xpmid: 21910736

Cyclic electron flow around photosystem I drives additional proton pumping into the thylakoid lumen, which enhances the protective non‐photochemical quenching and increases ATP synthesis. It involves several pathways activated independently. In whole barley leaves, P700 oxidation under far‐red illumination and subsequent P700+ dark reduction kinetics provide a major probe of the activation of cyclic pathways. Two ‘intermediate’ and ‘slow’ exponential reduction phases are always observed and they become faster after high light illumination, but dark inactivation of the Benson–Calvin cycle causes the emergence of both a transient in the P700 oxidation and a ‘fast’ phase in the P700+ reduction. We investigate here the afterglow (AG) thermoluminescence emission as another tool to detect the activation of cyclic electron pathways from stroma reductants to the acceptor side of photosystem II. This transfer is activated by warming, yielding an AG band at about 45°C. However, treatments that accelerate the ‘intermediate’ and ‘slow’ P700+ reduction phases (brief anoxia, hexose infiltration, fast dehydration of excised leaves) also produced a downshift of this AG band. This pathway ascribable to NADPH dehydrogenase (NDH) would be triggered by a deficit in ATP, while the ‘fast’ reduction phase corresponding to the ferredoxin plastoquinone reductase pathway is triggered by an overreduction of the photosystem I acceptor pool and is undetected in thermoluminescence. Contrastingly, slow dehydration of unwatered plants did not cause faster reduction of P700+ nor temperature downshift of the AG band, that is no induction of the NDH pathway, whereas an increased intensity of the AG band indicated a strong NADPH + ATP assimilatory potential.