The proteolytic degradation in vitro of the NADPH-protochlorophyllide oxidoreductase of barley (Hordeum vulgare L.)

A cell-free membrane system has been developed from isolated barley etioplasts which displays a highly selective decrease of the NADPH-protochlorophyllide oxidoreductase in vitro which is indistinguishable from that observed previously in the intact plant. The rapid breakdown of the enzyme protein in vitro is caused by a membrane-bound proteolytic activity. The protease is essentially independent of pH in the physiological pH range of 6 to 8.5. The optimum temperature for the reaction is approximately 40 degrees C. In the presence of excessive protochlorophyllide the enzyme is no longer degraded or inactivated during illumination of dark-grown plants. In the isolated membrane fraction protochlorophyllide also enhances the stability of the enzyme, a similar effect is exerted by NADPH but not by NADH. The results suggest that the inactivation of the NADPH-protochlorophyllide oxidoreductase is influenced by the interaction of the enzyme with protochlorophyllide and NADPH. In the absence of these two components the enzyme becomes susceptible to proteolytic degradation.     

Retrograde signaling by the plastidial metabolite MEcPP regulates expression of nuclear stress-response genes

Plastid-derived signals are known to coordinate expression of nuclear genes encoding plastid-localized proteins in a process termed retrograde signaling. To date, the identity of retrograde-signaling molecules has remained elusive. Here, we show that methylerythritol cyclodiphosphate (MEcPP), a precursor of isoprenoids produced by the plastidial methylerythritol phosphate (MEP) pathway, elicits the expression of selected stress-responsive nuclear-encoded plastidial proteins. Genetic and pharmacological manipulations of the individual MEP pathway metabolite levels demonstrate the high specificity of MEcPP as an inducer of these targeted stress-responsive genes. We further demonstrate that abiotic stresses elevate MEcPP levels, eliciting the expression of the aforementioned genes. We propose that the MEP pathway, in addition to producing isoprenoids, functions as a stress sensor and a coordinator of expression of targeted stress-responsive nuclear genes via modulation of the levels of MEcPP, a specific and critical retrograde-signaling metabolite.     

Sublethal effects of Beauveria bassiana on life table parameters of two–spotted spider mite,Tetranychus urticae (Acari: Tetranychidae)

Effects of the entomopathogenic fungus Beauveria bassiana were studied on life table parameters of two-spotted spider mite, Tetranychus urticae feeding on bean and cucumber under laboratory conditions. The developmental periods for all immature stages were not affected by fungal infection on each host plant but the duration of larval stage was significantly longer on bean. The female and male longevity, oviposition period and fecundity were significantly lower on fungus-treated mites but were not different between two host plants. Significant reductions were found on the intrinsic rate of increase (r _m ), the net reproductive rate (R ₀), the finite rate of increase (λ), the mean generation time (T _c ) and the population doubling time (D _t ) as a result of mycosis. Only the mean generation time (T _c ) was influenced considering the effect of host plant, which was shorter on cucumber.     

锈褐原花蝽在不同温度下的发育与积温必需条件

阿月浑子树木虱Agonoscena pistaciae Burckhardt and Lauterer （半翅目: 木虱总科）是伊朗园林树木阿月浑子树上常见的最具破坏性的害虫,其捕食性天敌锈褐原花蝽Anthocoris minki pistaciae Wagner在伊朗阿月浑子树种植区为该害虫的生防因子。本研究在17.5~35℃的8个恒温以及相对湿度55%±5%,光照周期16L∶8D的控制条件下,在A. pistaciae若虫上饲养这种捕食性花蝽的同时,调查温度对其发育的影响。结果表明：这种捕食性花蝽在17.5~32℃下可成功发育;然而在35℃下,卵不能孵化,且只有10%的若虫进入成虫阶段。30℃下从卵至成虫羽化的发育历期最短。据测算估计,这种捕食性花蝽的卵、若虫发育以及整个发育（卵至成虫）的积温分别为77,200和263度·日;卵、若虫和整个发育的低温度阈值分别为8.53, 9.2 和9.47℃。这些结果为建立阿月浑子树木虱的综合防治计划提供了宝贵的信息。     

Chlorophyll synthesis in green leaves and isolated chloroplasts of barley (Hordeum vulgare)

The photoreduction of protochlorophyllide was studied in leaves and isolated chloroplasts of barley. Leaves of plants which had been preilluminated for varying lengths of time were incubated with [¹⁴C]-δ- aminolevulinic acid for 2 h in the dark. The subsequent photoreduction of [¹⁴C]-protochlorophyllide was analyzed by high performance liquid chromatography of pigments extracted from illuminated leaves and plastids. The plastids used in this study were isolated in the dark from leaves at the end of the 2 h labelling period. Three major results were obtained:

• 1

  The extent of protochlorophyllide reduction in vivo was rapidly reduced as a function of the preillumination period. In 24 h preilluminated plants only a small fraction of the radioactively labelled protochlorophyllide was reduced during the subsequent light period.
• 2

  The amount of NADPH-protochlorophyllide oxidoreductase (EC 1.6.99.-) present in plastids of fully-green plants was drastically reduced relative to levels in plastids of dark-grown plants as estimated by the methods of immunoblotting of plastid proteins and immunogold labelling of ultrathin sections of the leaf tissue.
• 3

  In etiolated plants light seemed to affect the reduction of protochlorophyllide directly through the excitation of protochlorophyllide. In fully green plants, however, light also affected chlorophyll formation indirectly by the supply of NADPH via photosynthetic electron transport.