Syed Sabhi Ahmad

Physiological and biochemical changes associated with flower development and senescence in Dianthus chinensis L

Flowers of Dianthus chinensis growing in Kashmir University Botanic Garden (KUBG) were selected for the present study. Flower development and senescence was divided into six stages (I–VI), categorized as (I) tight bud stage, (II) mature bud stage, (III) paint brush stage, (IV) fully open/bloom stage, (V) partially senescent stage and (VI) senescent stage. Various physiological and biochemical changes associated with flower development and senescence were recorded. Fresh and dry mass, water content and flower diameter showed a continuous increase from bud to bloom, i.e., from stage I–IV and a significant decrease from stage V to VI. Scanning electron microscopic studies showed a clear degeneration of the cellular integrity and architecture with the onset of senescence in Dianthus chinensis. Soluble proteins, α-amino acids and sugar fractions increased with flower opening and showed a decrease as the senescence progressed. SDS-PAGE of the petal tissues revealed a decrease in both high and low molecular weight proteins. The present study suggests that the protein degradation is the key factor in regulating the process of flower senescence in this flower.

Sugar Signaling in Plant Growth and Development

Sugars are the primary energy sources produced by green plants via the life-sustaining process of photosynthesis. The metabolic role of sugars as energy compounds and essential metabolites in living organisms has long been recognized. However, genetic and molecular (mutational) studies during the last decade have highlighted the role of sugars as signaling molecules in controlling diverse aspects of plant growth and development. The review focuses on specific signaling roles of various sugars particularly hexoses (glucose and fructose), sucrose, trehalose, and small glycans. Moreover, the sugar-specific regulations of various genes and the diverse signaling cascades involved have been discussed. The role of hexokinase–kinase-dependent and hexokinase-independent signals (like G proteins) in sugar signal transduction pathways has also been documented. The evidences generated from the analyses of sugar-insensitive mutants and hormone-insensitive mutants have also demonstrated a complex interplay of factors regulating the common signaling capabilities of sugar/hormone interactions. Characterization of sugar-signaling mutants in Arabidopsis has unraveled a complex signaling network that links sugar responses to two plant stress hormones, abscisic acid and ethylene, in opposite ways. Similar cross talk between sugar and other plant hormones in their signaling capabilities has been discussed.

Is the biochemical mechanism of petal senescence similar within a genus? A case study of Dianthus.

Physiological and biochemical changes were documented during various stages (I-VI) of flower development and senescence in Dianthus barbatus L. and Dianthus chinensis L. A comparison between various biochemical parameters revealed that different biomolecules show different trends during senescence in these two species. Although floral diameter, fresh mass, dry mass and water content showed a positive relationship with flower opening and a sharp decline with senescence in both species; soluble proteins, α-amino acids and phenols showed a significant increase towards opening and a decrease towards senescence in D. chinensis but a reverse trend was observed in D. barbatus. Specific protease activity in D. chinensis showed a decrease towards flower opening and an increase towards senescence, but in D. barbatus, specific protease activity increased continuously from bud formation to senescence. Total sugars increased with flower opening and decreased as senescence progressed in both species. Reducing sugars increased as the flowers of D. chinensis opened and declined towards senescence, but in D. barbatus, reducing sugars remained almost constant from flower opening to senescence. To summarize, the various physiological and biochemical changes that execute senescence vary within a genus.

Regulatory role of phenols in flower development and senescence in the genus Iris

The mechanism of flower development and senescence involves a lot of biochemical and molecular changes. These changes are governed by various external (temperature, light and humidity) and internal factors, viz., protein turnover, protease activity, antioxidant activity, phenols and plant growth regulators. The role of proteins, growth regulators, changes in various antioxidant enzymes and protease activity has been studied to a great extent; however the contribution of phenols in flower development and senescence is still elusive. Generally, flower senescence is thought to be associated with a decrease in the total phenolic content, but the present study on various species of the genus Iris revealed that total phenolic content showed diverging trends, varying from species to species within the same genus. The total phenolic content has been shown to decrease during senescence in Iris versicolor and Iris japonica, but an increase in total phenolic content was registered in Iris germanica, Iris kashmiriana and Iris ensata. Fresh mass, dry mass and water content was shown to increase towards flower anthesis (stages I–IV) and a significant decrease was observed at V and VI stages of flower senescence in all the species of Iris under study. The ascorbate peroxidase activity during the various stages of flower development and senescence indicated that phenols have a more contributory role than just being free radical scavengers in regulating flower senescence of various species of the genus Iris.

How and why of flower senescence: understanding from models to ornamentals

Flower senescence involves an ordered set of coordinated and tightly regulated developmental events which bear the hallmark of programmed cell death. Flowers are ideal for senescence studies as the tissue is relatively homogenous and chemical manipulation can be applied without substantial wounding. The onset of flower senescence is triggered by a number of factors which initiate a series of physiological events, orchestrated by plant growth regulators. Ethylene is a clear regulator of petal senescence in some species (ethylene sensitive) while as in others (ethylene insensitive) it has little or no role to play. In ethylene insensitive flowers, abscisic acid has been shown as being the key factor regulating flower senescence. The turnover of various hormones in different flower parts may activate degeneration processes that lead the flower to wilting or death. In some species petals wilt prior to abscission and as such efficient remobilization of nutrients takes place while as in others the petals abscise when they are still turgid without complete nutrient recycling. Based on this diversity of mechanisms employed in initiation and execution of flower senescence in various flower systems, a strong need is felt to identify suitable model systems to study petal senescence in various groups of flowers. A shift from identifying good models to ornamentals is in vogue for understanding flower senescence in ornamentals which will provide biochemical and molecular insights for extending their vase life using modern biotechnological approaches.

Ethylene Signaling in Plants: Introspection

Ethylene is the simplest unsaturated hydrocarbon gas produced in most plants that regulates a number of biochemical processes. Ethylene regulates a wide array of developmental processes, but its precise role in the regulation of these processes is still not clear. Ethylene’s role as a signal molecule depends on the cell response to its changing concentrations and the processing of this information in the form of physiological responses in the target cell. Ethylene is perceived by a family of ER-membrane-bound receptors encoded by the ethylene response 1 (ETR1) gene, and these receptors transduce the ethylene signal. Other ethylene receptors such as ERS1, ERS2, EIN4, ETR1, and ETR2 act as negative regulators via constitutive triple response 1 (CTR1) gene. The CTR1 is presumed to show similarities with Raf, a mitogen-activated protein kinase kinase kinase (MAPKKK) and thus is thought to function like Raf, in a typical MAPK cascade. It has been demonstrated that CTR1 binds ER membrane via ETR1 or by a direct association with ERS1 and ETR2 during ethylene signaling. Ethylene is thought to regulate several aspects of plant growth involving associations with other plant hormones primarily auxins and gibberellins.

Physiological and biochemical aspects of flower development and senescence in Nicotiana plumbaginifolia Viv.

Abstract Healthy buds of Nicotiana plumbaginifolia growing in the Kashmir University Botanic Garden were selected for the present study. Flower development and senescence was divided into seven stages, viz., tight bud stage (I), mature bud stage (II), pencil stage (III), partially open stage (IV), open stage (V), partially senescent stage (VI) and senescent stage (VII). Various physiological and biochemical changes were recorded at each stage of flower development and senescence. Floral diameter, fresh mass, dry mass and water content showed an increase up to flower opening (stage V) and thereafter a significant decrease was recorded as the flower development progressed towards senescence through stages VI and VII. An increase in α-amino acids, total phenols and sugars was registered towards anthesis (stage V) and a decrease in these parameters was recorded with senescence. Protease activity showed a significant increase towards senescence with a concomitant decrease in soluble proteins. Based on the quantitative analysis of various biochemical parameters, the flower opening in N. plumbaginifolia seems to be accompanied by an increase in the water content, soluble proteins, α‑amino acids and phenols. A decrease in these parameters, besides an increase in protease activity induces senescence in the beautiful flowers of N. plumbaginifolia. Understanding flower senescence may help in improving the postharvest performance of this beautiful ornamental flower to make it a potential material for the floriculture industry.

Senescence: Regulation and Signalling

Senescence is a multifaceted, genetically regulated programme, in which cascade of physiological and biochemical changes occur which bring about the deprivation of macromolecules and the recycling of their components to different parts of the plant. Senescence culminates in death of the plant organ as it necessitates cell viability and is often reversible until the late stages of development. The environmental stress factors such as drought, water logging, high or low solar radiation, extreme temperatures, ozone and other air pollutants, and excessive soil salinity, besides inadequate mineral nutrition in soil, negatively influence the senescence. These stress factors disturb the endogenously regulated system of the plant tissue which may result in promoting the process of the senescence. Despite the initiation by environmental factors, the process of senescence is coordinated through a common signalling network by endogenous and exogenous signals involving the signalling molecules ethylene, abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA).