The Effect of Lead and Zinc on Plant Growth and Chlorophyll Content of Holcus lanatus L.

Root length of Holcus lanatus L. declined rapidly with increasing lead and zinc concentrations in nutrient solution. In all used Pb and Zn concentrations root growth of genotypes coming from a Pb-Zn mine area, was greater than that of the control, suggesting that these genotypes evolved tolerance to Pb and Zn.
Negative correlation was also observed between chlorophyll content and increased heavy metal concentrations. The greater chlorophyll content found in tolerant genotypes, in different Pb and Zn concentrations, in comparison with the control, could be served to distinguish tolerant and non-tolerant genotypes.     

Rapid Screening for Aluminum Tolerance in Cereals by Use of the Chlorophyll Fluorescence Test

The effects of aluminum on the photosynthetic apparatus were examined in cereals grown in nutrient solutions (pH 4.5) at two Al levels (0 and 148 μM). The chlorophyll fluorescence kinetics results confirmed that the soft wheat ‘BHG’ cultivar has the potential for growth on acid soils while triticale cultivars ‘Niovi’ and ‘Dada’ appeared to be relatively tolerant. The percentage decrease in F_v/F_m of the less tolerant cultivars after Al-treatment indicated a decrease in the efficiency of the primary photochemistry of PS II, while the decrease in the ratio F_V/F_osuggested that exposure of the cultivars ‘Dio’ and ‘Appulo E’ to aluminum caused injury to the thylakoid structure. The percentage fluctuations of the ratio F_v/F_mwere shown to correlate very closely with the assessment of injury as evaluated by the relative top fresh weight. Measurements of chlorophyll fluorescence in vivo could be used to monitor injury caused by “Al-stress”, and thus they may serve as a rapid screening test for Al tolerance.     

稀土对刺槐苗木生理特性影响的研究

稀土对刺槐苗木生理特性影响的研究赵兰勇，梁玉堂（山东农业大学林学院泰安２７１０１８）王九龄（北京林业大学北京１０００８３）关键词稀土，刺槐，光合速率，叶绿素含量，水分利用效率，矿质元素含量近年来，稀土元素在农业上的应用研究越来越受到人们的重视，并且已...     

Footsteps from Insect Larvae Damage Leaf Surfaces and Initiate Rapid Responses

Plant resistance to insect herbivory involves gene expression in response to wounding and the detection of insect elicitors in oral secretions (Kessler and Baldwin, 2002, Ann. Rev. Plant/ Biol. 53: 299–328). However, crawling insect larvae stimulate the synthesis of 4-aminobutyrate within minutes and imprints of larval footsteps can be visualized within seconds through superoxide production or transient increases in chlorophyll fluorescence (Bown et al., 2002, Plant Physiol. 129: 1430–1434). Here cryo-scanning electron microscopy was used to demonstrate that larval feet, which are equipped with a perimeter row of hook-like crochets, damage leaf tissue and result in larval footprints. Staining for cell death shows that areas of wounding correspond to footsteps detected through increased chlorophyll fluorescence. Superoxide production in response to footsteps was inhibited by diphenyleneiodonium, an inhibitor of the plasma membrane NADPH oxidase enzyme. Inhibition of superoxide production, however, did not eliminate the detection of cell death. The results demonstrate that larval footsteps damage leaf tissue, and initiate rapid local responses which are not dependent on herbivory or oral secretions. It is proposed that superoxide production at the wound site prevents opportunistic pathogen infection.     

Growth- and leaf-temperature effects on photosynthesis of sweet orange seedlings infected with Xylella fastidiosa

The effects of growth and leaf temperature on photosynthesis were evaluated in sweet orange seedlings ( Citrus sinensis cv. Pera) infected with Xylella fastidiosa (the bacterium that causes citrus variegated chlorosis, CVC). Measurements of leaf gas exchange and chlorophyll  a fluorescence were taken at leaf temperatures of 25, 30, 35 and 40°C in healthy and infected (without visible symptoms) seedlings submitted to two temperature regimes (25/20 or 35/20°C, day/night), not simultaneously. The CO₂ assimilation rates ( A ) and stomatal conductance ( g _s) were higher in healthy plants in both temperature regimes. Values for A and g _s of infected and healthy plants were higher in the 35/20°C regime, decreasing with leaf temperature increase. In addition, differences between healthy and infected plants were higher at 35/20°C, while no differences in chlorophyll  a fluorescence parameters were observed except for potential quantum efficiency of photosystem II, which was higher in infected plants. Low A values in infected plants were caused by low g _s and probably by biochemical damage to photosynthesis. The high alternative electron sink of infected plants was another effect of reduced A . Both high growth and high leaf temperatures increased differences in A between healthy and infected plants. Therefore this feature may be partially responsible for lower growth and/or productivity of CVC-affected plants in regions with high air temperature.     

浅析测定植物抗旱性方法的应用

本文介绍了干旱对植物伤害及表现,根据国内外相关文献资料对叶绿素荧光法和电阻抗图谱法两种测定植物抗旱性方法进行概述。     

Induction of Drought Tolerance in Maize (Zea mays L.) due to Exogenous Application of Trehalose: Growth,Photosynthesis, Water Relations and Oxidative Defence Mechanism

The present investigation was conducted to assess the ameliorative effects of foliar‐applied trehalose on growth, photosynthetic attributes, water relation parameters and oxidative defence mechanism in two maize cultivars under field water deficit conditions. Various components of the experiment comprised two maize cultivars (EV‐1098 and Agaiti‐2002), two water‐stress levels (irrigation after 2 weeks and irrigation after 3 weeks during the entire period of growth), and two levels of trehalose (0 and 30 mm ) and four replicates of each treatment. Water stress significantly reduced the plant biomass production, photosynthetic attributes and water relation parameters in both maize cultivars. In contrast, water stress considerably increased the leaf malondialdehyde (MDA) contents, the activities of antioxidant enzymes such as peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT), and the levels of non‐enzymatic compounds such as ascorbic acid and tocopherols. In contrast, water stress caused a marked reduction in leaf phenolic contents. Foliar‐applied trehalose significantly increased plant biomass production, and improved some key photosynthetic attributes and plant–water relation parameters. The ameliorative effect of exogenously applied trehalose was also observed on the activities of some key antioxidant enzymes (POD and CAT) and non‐enzymatic compounds (tocopherols and phenolics). Overall, exogenously applied trehalose considerably improved drought tolerance of maize plants by up‐regulating photosynthetic and water relation attributes as well as antioxidant defence mechanism.     

自然低温胁迫下3种桉树的叶绿素荧光特性研究

对临安市3种桉树幼苗叶片叶绿素荧光特性进行研究,结果表明,自然低温下,各桉树表现出不同的适应性,总的来说,邓桉>柳桉>巨桉;自然低温(日最低气温-3.6℃)对柳桉和巨桉造成较大损害,而邓桉可通过维持相对较高的光化学效率,以及利用不断增加的qN来进行耗散,具有较强的抵抗低温胁迫伤害的能力。     

Evaluating the role of seed priming in improving drought tolerance of pigmented and non‐pigmented rice

This study was conducted to evaluate the influence of seed priming on drought tolerance of pigmented and non‐pigmented rice. Seeds of pigmented (cv. Heug Jinju Byeo) and non‐pigmented (cv. Anjoong) rice were soaked in water (hydropriming) or solution of CaCl₂ (osmopriming). Seeds were sown in soil‐filled pots retained at 70 (well‐watered) and 35% (drought) water‐holding capacity. Drought stress caused erratic and poor stand establishment and decreased the growth of both rice types. More decrease in plant height and leaf area under drought stress was noted in pigmented rice, whereas decrease in root length and seedling dry weight, under drought, was more obvious in non‐pigmented rice. Pigmented rice maintained more tissue water and photosynthesis and had more polyphenols, flavonoids and antioxidant activity than non‐pigmented rice. Seed priming was effective in improving stand establishment, growth, polyphenols, flavonoids and antioxidant activity; however, extent of improvement was more in pigmented rice under drought. In conclusion, drought caused erratic germination and suppressed plant growth in both rice types. However, pigmented rice had better drought tolerance owing to uniform emergence, and better physiological and morphological plasticity. Seed priming was quite helpful in improving the performance of both rice types under drought and well‐watered conditions.     

OsHemA gene,encoding glutamyl-tRNA reductase(GluTR) is essential for chlorophyll biosynthesis in rice(Oryza sativa)

Chlorophyll(Chl) biosynthesis is essential for photosynthesis and plant growth. Glutamyl-tRNA reductase(GluTR) catalyzes glutamyl-tRNA into glutamate-1-semialdehyde(GSA) and initiates the chlorophyll biosynthesis. Even though the main role of GluTR has been established, the effects caused by natural variations in its corresponding gene remain largely unknown. Here, we characterized a spontaneous mutant in paddy field with Chl biosynthesis deficiency, designated as cbd1. With intact thylakoid lamellar structure, the cbd1 plant showed light green leaves and reduced Chl and carotenoids(Cars) content significantly compared to the wild type. By map-based gene cloning, the mutation was restricted within a 57-kb region on chromosome 10, in which an mPingA miniature inverted-repeat transposable element(MITE) inserted in the promoter region of OsHemA gene. Both leaf color and the pigment contents in cbd1 were recovered in a complementation test, confirming OsHemA was responsible for the mutant phenotype. OsHemA was uniquely predicted to encode GluTR and its expression level was dramatically repressed in cbd1. Transient transformation in protoplasts demonstrated that GluTR localized in chloroplasts and a signal peptide exists in its N-terminus. A majority of Chl biosynthesis genes, except for POR and CHLG, were down-regulated synchronously by the repression of OsHemA, suggesting that an attenuation occurred in the Chl biosynthesis pathway. Interestingly, we found major agronomic traits involved in rice yield were statistically unaffected, except for the number of full grains per panicle was increased in cbd1. Collectively, OsHemA plays an essential role in Chl biosynthesis in rice and its weak allele can adjust leaf color and Chls content without compromise to rice yield.