Enzymes of nitrogen mobilization in detached leaves of Lolium temulentum during senescence

During the senescence of Lolium temulentum leaf sections in the dark, asparagine and glutamine accumulated as the level of soluble protein declined. During the first 3–4 days after detachment, when the rate of protein loss was maximal, a four-fold increase in acid protease activity (EC 3.4.4.?) occurred. Subsequently this activity was replaced by proteases with a higher pH optimum. There was also a pronounced and continued activation of glutamate dehydrogenase (EC 1.4.1.2) during senescence. Glutamate pyruvate transaminase (EC 2.6.1.2), benzoylarginine-p-nitroanilide hydrolase (EC 3.4.?.?) and leucyl-p-nitroanilide hydrolase (EC 3.4.1.1) declined from high initial activities after 3–4 days. Glutamate oxaloacetate transaminase (GOT, EC 2.6.1.1) was fairly stable although a marked increase occurred in the activity of one of two major GOT isoenzymes over the first two days. Glutamine synthetase (EC 6.3.1.2) was highly active in non-senescent leaves but fell sharply during the first three days of senescence. Little asparagine synthetase (EC 6.3.1.1) was detected. The role of these enzymes in the nitrogen metabolism of senescent detached leaves is discussed.     

Invasion of naturally senescing root cortices of cereal and grass seedlings byMicrodochium bolleyi

Summary In glasshouse experiments, invasion of wheat and grass (Dactylis glomerata) seedling roots byMicrodochium bolleyi was strongly correlated with the pattern and rate of natural senescence of the root cortex. The fungus did not enhance cortical senescence and did not damage roots except in a few instances when it invaded and killed their tips.M. bolleyi behaved as a weak parasite, largely restricted to invasion of naturally senescing cortices of cereal and grass roots.     

Role of adiponectin as a modulator of testicular function during aging in mice

The mechanisms by which testicular functions decline with aging remain largely speculative. Our recent finding showed the importance of adiponectin in the regulation of testicular functions, whereas its concentration declines during male infertility. Thus, the aim of present study was to explore the potential role of adiponectin during aging. The changes in adiponectin, adiponectin-receptors, and insulin receptor proteins expression in the testis were evaluated and compared with the testicular parameters, mass, and testosterone level in the mice from early post-natal to late senescence period. Further, the current study has examined the effect of exogenous adiponectin treatment on testicular functions in aged mice. The results showed a significant decline in adiponectin/adiponectin-receptors expression simultaneously with a significant decline in testicular mass, insulin receptor expression and testosterone synthesis in the testis of aged mice. Exogenous treatment of adiponectin to aged mice resulted in marked improvements in testicular mass, histological features (cells proliferation), insulin receptor expression, testicular glucose uptake, anti-oxidative enzymes activity and testosterone synthesis as compared with the control. Based on these findings, it may be concluded that a marked decline in adiponectin synthesis and action results in decreased insulin sensitivity (development of insulin resistance) and increased oxidative stress which consequently suppresses testicular functions during aging. This study further showed that treatment with adiponectin ameliorates reduced testicular functions by enhanced expression of insulin receptor in the testis of senescent mice. It is thus hypothesized that systemic adiponectin treatment could be a promising therapeutic strategy for improvement of testosterone production and sperm counts during aging.     

Cytokinin oxidase/dehydrogenase in Pisum sativum plants during vegetative development. Influence of UV-B irradiation and high temperature on enzymatic activity

Cytokinin oxidase/dehydrogenase (EC 1.5.99.12) specific activity was determined in leaves and roots of two P. sativum cultivars (cv. Scinado and cv. Manuela) during vegetative development and the effect of UV-B irradiation or elevated temperature was assessed. The measurement of CKX activity during development showed localisation of this enzyme to roots. The reduction in CKX activity in leaves after UV-B irradiation and the increased levels of the enzyme in high temperature-treated plants suggests that the enzymes from the CKX gene family have a different expression during stress responses provoked by different factors and probably are tissue specific. Differences regarding cytokinin oxidase/dehydrogenase activity stress response were observed between the two pea cultivars.     

Photosynthetic alterations of pea leaves infected systemically by pea enation mosaic virus: A coordinated decrease in efficiencies of CO2 assimilation and photosystem II photochemistry

We have investigated photosynthetic changes of fully expanded pea leaves infected systemically by pea enation mosaic virus (PEMV) that often attacks legumes particularly in northern temperate regions. A typical compatible virus–host interaction was monitored during 40 post-inoculation days (dpi). An initial PEMV-induced decrease in photosynthetic CO₂ assimilation was detected at 15 dpi, when the virus appeared in the measured leaves. This decrease was not induced by stomata closure and corresponded with a decrease in the efficiency of photosystem II photochemistry (Φ_PSII). Despite of a slight impairment of oxygen evolution at this stage, PSII function was not primarily responsible for the decrease in Φ_PSII. Chlorophyll fluorescence imaging revealed that Φ_PSII started to decrease from the leaf tip to the base. More pronounced symptoms of PEMV disease appeared at later stages, when a typical mosaic and enations appeared in the infected leaves and oxidative damage of cell membranes was detected. From 30 dpi, a degradation of photosynthetic pigments accelerated, stomata were closing and corresponding pronounced decline in CO₂ assimilation was observed. A concomitant photoprotective responses, i.e. an increase in non-photochemical quenching and accumulation of de-epoxidized xanthophylls, were also detected. Interestingly, alternative electron sinks in chloroplasts were not stimulated by PEMV infection, which is in contradiction to earlier reports dealing with virus-induced plant stresses. The presented results show that the PEMV-induced alterations in mature pea leaves accelerated leaf senescence during which a decrease in Φ_PSII took place in coordinated manner with an inhibition of CO₂ assimilation.     

Heat-induced hormesis in longevity as correlated response to thermal-stress selection in Drosophila buzzatii

Hormesis in longevity is a widespread phenomenon across the animal kingdom. It takes place when longevity is improved as an indirect effect of mild stress. We explored some possible evolutionary trajectories of hormesis in longevity in artificially selected lines of Drosophila buzzatii. The lines were bi-directionally selected for either knockdown resistance to heat stress (K⁻, K⁺) or chill-coma recovery (CCR⁻, CCR⁺, with the + and – signs indicating selection for decreased and increased tolerance, respectively). All K and CCR lines successfully diverged due to thermal-stress selection. The heat-inducible hormesis in longevity was substantial in both K⁻ and CCR⁻ females, whereas no hormesis was apparent for females in CCR⁺, K⁺ and control lines. Among-line differences in longevity of non-heat-treated females disappeared after a heat-hardening treatment. Hormesis effects on the demographic senescence rate were sex-specific and consistently higher in the shorter-lived than in the longer-lived lines. Hormesis is an adaptive response, as its magnitude can evolutionary increase with stress-sensitivity.     

Nucleic acids from leaves of a yellowing and a non-yellowing variety of Festuca pratensis Huds.

High molecular weight ribosomal RNA components and their pattern of loss on ageing of excised leaf sections were the same in the non-yellowing mutant and the normal genotype of Festuca pratensis even though the mutant showed retarded chlorophyll loss. Thus it appears that the genetic lesion does not extend to changes in the ribosomal RNA components of chloroplasts or cytoplasm.     

Nitrogen redistribution during grain growth in wheat (Triticum aestivum L.)

The activity of a range of endo- and exopeptidase enzymes have been measured in the glumes, flag leaf and stem during the period of grain development in wheat. The enzymes show a sequential pattern of appearance with activity peaks occurring at a number of intervals from anthesis until just prior to the cessation of grain growth. Of the enzymes studied only the haemoglobin- and casein-degrading activity and alanylglycine-dipeptidase activity increased during the period of rapid protein loss, while aminopeptidase, carboxypeptidase and leucyltyrosine dipeptidase reached maximum activity prior to this period.