The effect of light on chlorophyll loss in senescing leaves of sycamore (Acer pseudoplatanus L.)

Transcriptomic analyses provide new insights into green and purple color pigmentation in Rheum tanguticum medicinal plants

Background

Rheum tanguticum Maxim. ex Balf is a traditional Chinese medicinal plant that is commonly used to treat many ailments. It belongs to the Polygonacae family and grows in northwest and southwest China. At high elevations, the color of the plant's young leaves is purple, which gradually changes to green during the growth cycle. Anthraquinone, which is known for various biological activities, is the main bioactive compound in R. tanguticum. Although a significant amount of research has been done on R. tanguticum in the past, the lack of transcriptome data limits our knowledge of the gene regulatory networks involved in pigmentation and in the metabolism of bioactive compounds in Rheum species.

Methods

To fill this knowledge gap, we generated high-quality RNA-seq data and performed multi-tissue transcriptomic analyses of R. tanguticum.

Results

We found that three chlorophyll degradation enzymes (RtPPH, RtPao and RtRCCR) were highly expressed in purple samples, which suggests that the purple pigmentation is mainly due to the effects of chlorophyll degradation. Overall, these data may aid in drafting the transcriptional network in the regulation and biosynthesis of medicinally active compounds in the future.

Short daily ultraviolet exposure enhances intrinsic water-use efficiency and delays senescence in Micro-Tom tomato plants

Ultraviolet (UV) radiation, unless present at high doses, is recognised as a regulator of plant growth and some specific processes. The present study investigated the influence of short daily UV irradiation (15min/day, 11days) on leaf gas exchange and some biochemical and molecular markers of leaf senescence (such as stomata movements, chlorophyll breakdown, anthocyanin production, senescence-associated genes) in Micro-Tom tomato plants. The UV-induced reduction of g s (stomatal conductance) during the treatment was associated with the modified expression of some genes involved in the control of stomatal movements. We hypothesise a two-step regulation of stomatal closure involving salicylic and abscisic acid hormones. The temporal changes of g s and A net (net photosynthetic CO2 assimilation rate) along with the pigment behaviour, suggest a possible delay of leaf senescence in treated plants, confirmed by the expression levels of genes related to senescence such as SAG113 and DFR . The UV potential to induce a persistent partial inhibition of g s without severely affecting A net led to an increased iWUE (intrinsic water-use efficiency) during the 11-day treatment, suggesting a priming effect of short daily UV radiation towards drought conditions potentially useful in reducing the excess water use in agriculture.

Photo-Oxidative Protection of Chlorophyll a in C-Phycocyanin Aqueous Medium

In this study, potential protection of chlorophyll a from illumination and oxidation-induced decomposition has been examined using C-phycocyanin (C-PC) aqueous medium. Photo-oxidation resistance of chlorophyll a was monitored in various aqueous media using ultraviolet-visible spectroscopy and direct-infusion atmospheric pressure chemical ionization mass spectrometry analysis. The spectroscopy results showed that chlorophyll a in C-PC medium experienced the lowest rate of conversion to its derivatives; thus, it was demonstrated that chlorophyll a was mostly intact in the C-PC medium. Furthermore, the C-PC treated with chlorophyll a showed the lowest concentrations of malondialdehyde, and chlorophyll a in C-PC medium did not cause serious damage to human liver cells in vitro after intensive illumination. Therefore, we propose a new method of protecting chlorophyll a from photodegradation and oxidation using C-PC aqueous medium.

Contributions of day length, temperature and individual variability on the rate and timing of leaf senescence in the common lilac Syringa vulgaris

Deciduous trees prepare for winter by breaking up chlorophyll and other nitrogen-rich compounds, which are resorbed for storage. Timing is important as senescence too early will waste growing season, while senescence too late risks the loss of the leaf resources to frost. While plants of temperate and boreal regions use decreasing day length as a cue of approaching winter, we show that decreasing temperature may also play a role in the variability of leaf senescence. We investigated the timing of autumnal decrease in photosynthetic efficiency and the concentration of chlorophyll and total carotenoids in nine common lilac (Syringa vulgaris L.) trees over two consecutive years. Day length explained a greater proportion of photosynthetic efficiency, but temperature had a significant additional role, which seems to be related to individual differences. Precipitation and cloudiness did not explain photosynthetic efficiency. Photosynthetic efficiency was higher outside the canopy and at high and middle elevations than inside and low elevations of the canopy. Late onset of senescence led to a steeper decline in photosynthetic efficiency than early senescence. The onset of decline in photosynthetic efficiency differed between years, but there was no difference in the steepest rate of change in photosynthetic efficiency with respect to sampling year or location. Contributions of day-length vs temperature to leaf senescence have important consequences for the adaptability and invasibility of deciduous trees in a changing climate, especially at the edge of species distributions.

A guideline for leaf senescence analyses: from quantification to physiological and molecular investigations

Leaf senescence is not a chaotic breakdown but a dynamic process following a precise timetable. It enables plants to economize with their resources and control their own viability and integrity. The onset as well as the progression of leaf senescence are co-ordinated by a complex genetic network that continuously integrates developmental and environmental signals such as biotic and abiotic stresses. Therefore, studying senescence requires an integrative and multi-scale analysis of the dynamic changes occurring in plant physiology and metabolism. In addition to providing an automated and standardized method to quantify leaf senescence at the macroscopic scale, we also propose an analytic framework to investigate senescence at physiological, biochemical, and molecular levels throughout the plant life cycle. We have developed protocols and suggested methods for studying different key processes involved in senescence, including photosynthetic capacities, membrane degradation, redox status, and genetic regulation. All methods presented in this review were conducted on Arabidopsis thaliana Columbia-0 and results are compared with senescence-related mutants. This guideline includes experimental design, protocols, recommendations, and the automated tools for leaf senescence analyses that could also be applied to other species.

Disruption of Chlorella vulgaris cells for the release of biodiesel-producing lipids: a comparison of grinding, ultrasonication, bead milling, enzymatic lysis, and microwaves

A comparative evaluation of different cell disruption methods for the release of lipids from marine Chlorella vulgaris cells was investigated. The cell growth of C. vulgaris was observed. Lipid concentrations from different disruption methods were determined, and the fatty acid composition of the extracted lipids was analyzed. The results showed that average productivity of C. vulgaris biomass was 208 mg L⁻¹ day⁻¹. The lipid concentrations of C. vulgaris were 5%, 6%, 29%, 15%, 10%, 7%, 22%, 24%, and 18% when using grinding with quartz sand under wet condition, grinding with quartz sand under dehydrated condition, grinding in liquid nitrogen, ultrasonication, bead milling, enzymatic lysis by snailase, enzymatic lysis by lysozyme, enzymatic lysis by cellulose, and microwaves, respectively. The shortest disruption time was 2 min by grinding in liquid nitrogen. The unsaturated and saturated fatty acid contents of C. vulgaris were 71.76% and 28.24%, respectively. The extracted lipids displayed a suitable fatty acid profile for biodiesel [C16:0 (~23%), C16:1 (~23%), and C18:1 (~45%)]. Overall, grinding in liquid nitrogen was identified as the most effective method in terms of disruption efficiency and time.

THE DEGRADATION OF CHLOROPHYLL - A BIOLOGICAL ENIGMA

Some 10⁹ tonnes of chlorophyll are destroyed each year on land and in the oceans. The fate of these chlorophylls is, however, largely unknown. This review describes the developmental stages at which chlorophyll breakdown occurs in aquatic and terrestrial biological systems, and the destruction arising from herbivory, disease, pollution and other physical hazards. At the cellular level, an attempt is made to separate the breakdown of chlorophyll during senescence from the many other events associated with cell destruction and death. A consideration of the more important chemical and biophysical properties of chlorophylls and their derivatives is provided, together with data on their spectral properties. The biosynthetic and biodegradative pathways of chlorophyll metabolism are, so far as is possible, described with some predictions as to the likely fate of the missing tonnes. Two types of degradation are recognized; the first involves up to five defined enzymes concerned with the early stages, the second covers the less well defined enzymic and non-enzymic destruction of the macrocyclic structure. These degradative reactions are compared with the reactions implicated in the breakdown of other porphyrins including haems in plants and animals. A brief description is given of the occurrence of breakdown products of chlorophyll in past biomass, including those of geological significance and those in a more recent archaeological context. Finally, the economic significance of chlorophyll breakdown is considered in the context of agriculture and horticulture, veterinary and medical sciences, food colouring and cosmetic industries, and the multi-million-dollar attraction of autumn leaf fall to tourism. Contents Summary 256 I. Introduction 256 II. Chlorophylls: global production and destruction 259 III. Chlorophylls: nomenclature and chemical characteristics 260 IV. Chlorophyll metabolism 268 V. Chlorophyll degradation during senescence 274 VI. Other degradative conditions 278 VII. Breakdown products in past biomass 287 VIII. Pathways of degradation 289 IX. Economic importance 291 Acknowledgements 294 References 294.