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Chlorophyll Accumulation (chlorophyll + accumulation)
Selected AbstractsPhotoactive Protochlorophyllide Regeneration in Cotyledons and Leaves from Higher Plants,,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2000Benoît Schoefs ABSTRACT Chlorophyll accumulation during greening implies the continuous transformation of photoactive protochlorophyllide (Pchlide) to chlorophyllide. Since this reaction is a light-dependent step, the study of regeneration of photoactive Pchlide under a continuous illumination is difficult. Therefore this process is best studied on etiolated plants during a period of darkness following the initial photoreduction of photoactive Pchlide. In this study, the regeneration process has been studied using spinach cotyledons, as well as barley and bean leaves, illuminated by a single saturating flash. The regeneration was characterized using 77 K fluorescence emission and excitation spectra and high-performance liquid chromatography. The fluorescence data indicated that the same spectral forms of photoactive Pchlide are regenerated by different pathways: (1) photoactive Pchlide regeneration starts immediately after the photoreduction through the formation of a nonphotoactive Pchlide form, emitting fluorescence at approximately 651 nm. This form is similar to the large aggregate of photoactive Pchlide present before the illumination, but it contains oxidized form of nicotinamide adenine dinucleotide phosphate, instead of the reduced form (NADPH), in the ternary complexes; and (2) after the dislocation of the large aggregates of chlorophyllide,light-dependent NADPH:Pchlide a photooxidoreductase,NADPH ternary complexes, the regeneration occurs at the expense of the several nonphotoactive Pchlide spectral forms present before the illumination. [source] Molecular control of ethylene production by cyanide in Arabidopsis thalianaPHYSIOLOGIA PLANTARUM, Issue 2 2000Jennifer McMahon Smith Although cyanide has long been recognized as a co-product of ethylene synthesis, little attention has been given to its potential physiological and molecular roles. In the present work, the long-term effects of cyanide on growth and development were observed in Arabidopsis thaliana. Two days after a single 20-min application of cyanide, plants demonstrated visible signs of stress. Long-term detrimental effects on growth and photosynthetic capabilities were noted, including low chlorophyll accumulation and stunted growth. Because of the relationship between cyanide and ethylene production, we chose to evaluate the results of cyanide treatment on genes encoding proteins involved in ethylene synthesis. We have found that only the 1-aminocyclopropane-1-carboxylic acid (ACC) synthase gene, ACS6, is rapidly activated in response to cyanide treatment, while other ACS genes were unaffected. This same gene has previously been shown to be transcriptionally activated in response to touch and other environmental stimuli. Cyanide was capable of activating ACS6 transcription within 10 min of treatment, and the amount of transcript correlated positively with the cyanide dosage. Due to the toxic nature of cyanide, plant in vivo concentrations are generally maintained lower than 10 ,M, but can increase under certain stresses. In the present work, we observed that physiologically relevant concentrations as low as 1 ,M HCN, considered metabolically ,safe', were capable of initiating ACS6 transcription. ACS6 transcripts were not substantially reduced as a result of multiple cyanide treatments, which is in contrast with the effects of mechanical stimulation on transcription. Our results suggest a relationship between cyanide production during ethylene synthesis and the molecular control of ethylene synthesis. This work corresponds with earlier experiments that have demonstrated that ethylene and cyanide can elicit some similar physiological responses. It is possible that cyanide may play an active role in ethylene regulation under conditions where rapid cyanide accumulation occurs. Since cyanide can rapidly activate ethylene synthesis, it is possible that it is involved in the positive-feedback regulation of ethylene that occurs in some plant tissues. [source] On the mechanism of rejuvenation of ageing detached bean leaves by low-concentration stressorsPLANT BIOLOGY, Issue 2 2009P. Nyitrai Abstract The effect of low concentrations of some stress-inducing compounds of different toxicity and chemical nature, such as Cd and Pb salts or DCMU, was investigated on the senescence of chloroplasts in detached primary leaves of bean (Phaseolus vulgaris L.). After 1 week of senescence followed by root development from the petiole, these agents stimulated chlorophyll accumulation and photosynthetic activity (14CO2 fixation) as compared to the control, thus inducing rejuvenation. Low-concentration stressors increased the level of active cytokinins in roots and leaves during the treatment, as monitored by the Amaranthus betacyanin bioassay and high-pressure liquid chromatography. The lithium ion, an inhibitor of the PIP2 -IP3/DAG signal transduction pathway, abolished the stimulating effect of stressors, both in roots (retarding cytokinin synthesis) and consequently also in leaves (reducing cytokinin-dependent chlorophyll accumulation). This suggests the involvement of the PIP2 -IP3/DAG signal transduction pathway in generation of these consecutive organ-specific responses. [source] A role for ethylene in the phytochrome-mediated control of vegetative developmentTHE PLANT JOURNAL, Issue 6 2006Eloise Foo Summary Members of the phytochrome family of photoreceptors play key roles in vegetative plant development, including the regulation of stem elongation, leaf development and chlorophyll accumulation. Hormones have been implicated in the control of these processes in de-etiolating seedlings. However, the mechanisms by which the phytochromes regulate vegetative development in more mature plants are less well understood. Pea (Pisum sativum) mutant plants lacking phytochromes A and B, the two phytochromes present in this species, develop severe defects later in development, including short, thick, distorted internodes and reduced leaf expansion, chlorophyll content and CAB gene transcript level. Studies presented here indicate that many of these defects in phyA phyB mutant plants appear to be due to elevated ethylene production, and suggest that an important role of the phytochromes in pea is to restrict ethylene production to a level that does not inhibit vegetative growth. Mutant phyA phyB plants produce significantly more ethylene than WT plants, and application of an ethylene biosynthesis inhibitor rescued many aspects of the phyA phyB mutant phenotype. This deregulation of ethylene production in phy-deficient plants appears likely to be due, at least in part, to the elevated transcript levels of key ethylene-biosynthesis genes. The phytochrome A photoreceptor appears to play a prominent role in the regulation of ethylene production, as phyA, but not phyB, single-mutant plants also exhibit a phenotype consistent with elevated ethylene production. Potential interactions between ethylene and secondary plant hormones in the control of the phy-deficient mutant phenotype were explored, revealing that ethylene may inhibit stem elongation in part by reducing gibberellin levels. [source] | ||||||||||