chlorophyll-a and zeatin-riboside

When inoculated onto maize leaves at the onset of senescence, the hemibiotroph Colletotrichum graminicola causes green islands that are surrounded by senescing tissue. Taking advantage of green islands as indicators of sites of the establishment of successful infection and of advanced high-performance liquid chromatography tandem mass spectrometry methodology, we analyzed changes in the patterns and levels of cytokinins (CK) at high spatial and analytical resolution. Twenty individual CK were detected in green islands. Levels of cis-zeatin-9-riboside and cis-zeatin-9-riboside-5'-monophosphate increased drastically, whereas that of the most prominent CK, cis-zeatin-O-glucoside, decreased. The fungus likely performed these conversions because corresponding activities were also detected in in vitro cultures amended with CK. We found no evidence that C. graminicola is able to synthesize CK entirely de novo in minimal medium but, after adding dimethylallyl diphosphate, a precursor of CK biosynthesis occurring in plants, a series of trans-zeatin isoforms (i.e., trans-zeatin-9-riboside-5'-monophosphate, trans-zeatin-9-riboside, and trans-zeatin) was formed. After applying CK onto uninfected leaves, transcripts of marker genes for senescence, photosynthesis, and assimilate distribution were measured by quantitative reverse-transcribed polymerase chain reaction; furthermore, pulse-amplitude modulation chlorophyll fluorometry and single-photon avalanche diode analyses were conducted. These experiments suggested that modulation of CK metabolism at the infection site affects host physiology.

Topics: Chlorophyll; Chromatography, High Pressure Liquid; Colletotrichum; Culture Media; Cytokinins; Gene Expression Regulation, Plant; Hemiterpenes; Host-Pathogen Interactions; Isopentenyladenosine; Organophosphorus Compounds; Photosynthesis; Plant Diseases; Plant Leaves; Purine Nucleotides; Tandem Mass Spectrometry; Zea mays

Stinging nettle (Urtica dioica) is a herbaceous, dioecious perennial that is widely distributed around the world, reproduces both sexually and asexually, and is characterized by rapid growth. This work was aimed at evaluating the effects of plant maturity, shoot reproduction and sex on the growth of leaves and shoots.. Growth rates of apical shoots, together with foliar levels of phytohormones (cytokinins, auxins, absicisic acid, jasmonic acid and salicylic acid) and other indicators of leaf physiology (water contents, photosynthetic pigments, alpha-tocopherol and F(v)/F(m) ratios) were measured in juvenile and mature plants, with a distinction made between reproductive and non-reproductive shoots in both males and females. Vegetative growth rates were not only evaluated in field-grown plants, but also in cuttings obtained from these plants. All measurements were performed during an active vegetative growth phase in autumn, a few months after mature plants reproduced during spring and summer.. Vegetative growth rates in mature plants were drastically reduced compared with juvenile ones (48 % and 78 % for number of leaves and leaf biomass produced per day, respectively), which was associated with a loss of photosynthetic pigments (up to 24 % and 48 % for chlorophylls and carotenoids, respectively) and increases of alpha-tocopherol (up to 2.7-fold), while endogenous levels of phytohormones did not differ between mature and juvenile plants. Reductions in vegetative growth were particularly evident in reproductive shoots of mature plants, and occurred similarly in both males and females.. It is concluded that (a) plant maturity reduces vegetative growth in U. dioica, (b) effects of plant maturity are evident both in reproductive and non-reproductive shoots, but particularly in the former, and (c) these changes occur similarly in both male and female plants.

Topics: Abscisic Acid; alpha-Tocopherol; Chlorophyll; Cyclopentanes; Cytokinins; Indoleacetic Acids; Isopentenyladenosine; Oxylipins; Plant Leaves; Plant Shoots; Reproduction; Salicylic Acid; Urtica dioica; Zeatin

The possible regulation of senescence-initiated remobilization of carbon reserves in rice (Oryza sativa L.) by abscisic acid (ABA) and cytokinins was studied using two rice cultivars with high lodging resistance and slow remobilization. The plants were grown in pots and either well-watered (WW, soil water potential = 0 MPa) or water-stressed (WS, soil water potential = -0.05 MPa) from 9 days after anthesis until they reached maturity. Leaf water potentials of both cultivars markedly decreased at midday as a result of water stress but completely recovered by early morning. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress accelerated starch remobilization in the stems, promoted the re-allocation of pre-fixed (14)C from the stems to grains, shortened the grain-filling period and increased the grain-filling rate. Sucrose phosphate synthase (SPS, EC 2.4.1.14) activity was enhanced by water stress and positively correlated with sucrose accumulation in both the stem and leaves. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the root exudates and leaves. ABA significantly and negatively, while Z+ZR positively, correlated with Pr and Chl of the flag leaves. ABA, not Z+ZR, was positively and significantly correlated with SPS activity and remobilization of pre-stored carbon. Spraying ABA reduced Chl in the flag leaves, and enhanced SPS activity and remobilization of carbon reserves. Spraying kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization is attributed to an elevated ABA level in rice plants subjected to water stress.

Topics: Abscisic Acid; Adenosine; Biological Transport, Active; Carbon; Carbon Radioisotopes; Chlorophyll; Cytokinins; Glucosyltransferases; Isopentenyladenosine; Oryza; Osmotic Pressure; Photosynthesis; Plant Growth Regulators; Plant Leaves; Plant Roots; Plant Structures; Reproduction; Seeds; Starch; Sucrose; Water; Zeatin