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1.
Metabolic acclimation-a key to enhancing photosynthesis in changing environments?
Herrmann, HA, Schwartz, JM, Johnson, GN
Journal of experimental botany. 2019;(12):3043-3056
Abstract
Plants adjust their photosynthetic capacity in response to their environment in a way that optimizes their yield and fitness. There is growing evidence that this acclimation is a response to changes in the leaf metabolome, but the extent to which these are linked and how this is optimized remain poorly understood. Using as an example the metabolic perturbations occurring in response to cold, we define the different stages required for acclimation, discuss the evidence for a metabolic temperature sensor, and suggest further work towards designing climate-smart crops. In particular, we discuss how constraint-based and kinetic metabolic modelling approaches can be used to generate targeted hypotheses about relevant pathways, and argue that a stronger integration of experimental and in silico studies will help us to understand the tightly regulated interplay of carbon partitioning and resource allocation required for photosynthetic acclimation to different environmental conditions.
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2.
Nitric oxide in plants: pro- or anti-senescence.
Bruand, C, Meilhoc, E
Journal of experimental botany. 2019;(17):4419-4427
Abstract
Senescence is a regulated process of tissue degeneration that can affect any plant organ and consists of the degradation and remobilization of molecules to other growing tissues. Senescent organs display changes at the microscopic level as well as modifications to internal cellular structure and differential gene expression. A large number of factors influencing senescence have been described including age, nutrient supply, and environmental interactions. Internal factors such as phytohormones also affect the timing of leaf senescence. A link between the senescence process and the production of nitric oxide (NO) in senescing tissues has been known for many years. Remarkably, this link can be either a positive or a negative correlation depending upon the organ. NO can be both a signaling or a toxic molecule and is known to have multiple roles in plants; this review considers the duality of NO roles in the senescence process of two different plant organs, namely the leaves and root nodules.
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3.
Roles of potential plant hormones and transcription factors in controlling leaf senescence and drought tolerance.
Jan, S, Abbas, N, Ashraf, M, Ahmad, P
Protoplasma. 2019;(2):313-329
Abstract
Plant leaves offer an exclusive windowpane to uncover the changes in organs, tissues, and cells as they advance towards the process of senescence and death. Drought-induced leaf senescence is an intricate process with remarkably coordinated phases of onset, progression, and completion implicated in an extensive reprogramming of gene expression. Advancing leaf senescence remobilizes nutrients to younger leaves thereby contributing to plant fitness. However, numerous mysteries remain unraveled concerning leaf senescence. We are not still able to correlate leaf senescence and drought stress to endogenous and exogenous environments. Furthermore, we need to decipher how molecular mechanisms of the leaf senescence and levels of drought tolerance are advanced and how is the involvement of SAGs in drought tolerance and plant fitness. This review provides the perspicacity indispensable for facilitating our coordinated point of view pertaining to leaf senescence together with inferences on progression of whole plant aging. The main segments discussed in the review include coordination between hormonal signaling, leaf senescence, drought tolerance, and crosstalk between hormones in leaf senescence regulation.
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4.
On the minimum leaf conductance: its role in models of plant water use, and ecological and environmental controls.
Duursma, RA, Blackman, CJ, Lopéz, R, Martin-StPaul, NK, Cochard, H, Medlyn, BE
The New phytologist. 2019;(2):693-705
Abstract
Contents Summary 693 I. Introduction 693 II. Comparison of various definitions and measurement techniques of minimum conductance 694 III. Cuticular conductance 695 IV. Contribution of stomata 696 V. Environmental and ecological variation in minimum conductance 696 VI. Use of minimum conductance in models 698 VII. Conclusions 703 Acknowledgements 703 References 703 SUMMARY When the rate of photosynthesis is greatly diminished, such as during severe drought, extreme temperature or low light, it seems advantageous for plants to close stomata and completely halt water loss. However, water loss continues through the cuticle and incompletely closed stomata, together constituting the leaf minimum conductance (gmin ). In this review, we critically evaluate the sources of variation in gmin , quantitatively compare various methods for its estimation, and illustrate the role of gmin in models of leaf gas exchange. A literature compilation of gmin as measured by the weight loss of detached leaves is presented, which shows much variation in this trait, which is not clearly related to species groups, climate of origin or leaf type. Much evidence points to the idea that gmin is highly responsive to the growing conditions of the plant, including soil water availability, temperature and air humidity - as we further demonstrate with two case studies. We pay special attention to the role of the minimum conductance in the Ball-Berry model of stomatal conductance, and caution against the usual regression-based method for its estimation. The synthesis presented here provides guidelines for the use of gmin in ecosystem models, and points to clear research gaps for this drought tolerance trait.
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5.
The occurrence of red and yellow autumn leaves explained by regional differences in insolation and temperature.
Renner, SS, Zohner, CM
The New phytologist. 2019;(4):1464-1471
Abstract
Red or yellow autumn leaves have long fascinated biologists, but their geographical concentration in trees in Eastern North America (ENA) has defied evolutionary explanations. In this review, anthocyanins and xanthophylls are discussed in relation to their occurrence in different regions of the Northern Hemisphere, phylogenetic distribution and photoprotective function during the breakdown of chlorophylls. Pigments in senescing leaves that intercept incident light and dissipate the absorbed energy extend the time available for nutrient resorption. Experiments with Arabidopsis have revealed greatest anthocyanin photoprotective function at low temperatures and high light intensities, and high-resolution solar irradiation maps reveal that ENA and Asia receive higher irradiation than does Europe. In addition, ENA experiences higher temperature fluctuations in autumn, resulting in cold snaps during leaf senescence. Under common garden conditions, chlorophyll degradation occurs earlier in ENA species than in their European and East Asian relatives. In combination, strong solar irradiation, temperature fluctuations and, on average, 3-wk shorter vegetation periods of ENA species favour investment in pigments to extend the time for nutrient resorption before abscission, explaining the higher frequency of coloured species in ENA compared to Europe. We end by outlining research that could test this new explanation of bright New England autumns.
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6.
Membrane Dynamics and Multiple Functions of Oil Bodies in Seeds and Leaves.
Shimada, TL, Hayashi, M, Hara-Nishimura, I
Plant physiology. 2018;(1):199-207
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Abstract
Oil bodies have multiple functions: oleosin-mediated freezing tolerance of seeds, direct interaction with glyoxysomes for lipid degradation in seedlings, and antifungal compound production in leaves.
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7.
Reactive oxygen species and redox regulation in mesophyll and bundle sheath cells of C4 plants.
Turkan, I, Uzilday, B, Dietz, KJ, Bräutigam, A, Ozgur, R
Journal of experimental botany. 2018;(14):3321-3331
Abstract
Redox regulation, antioxidant defence, and reactive oxygen species (ROS) signalling are critical in performing and tuning metabolic activities. However, our concepts have mostly been developed for C3 plants since Arabidopsis thaliana has been the major model for research. Efforts to convert C3 plants to C4 to increase yield (such as IRRI's C4 Rice Project) entail a better understanding of these processes in C4 plants. Various photosynthetic enzymes that take part in light reactions and carbon reactions are regulated via redox components, such as thioredoxins as redox transmitters and peroxiredoxins. Hence, understanding redox regulation in the mesophyll and bundle sheath chloroplasts of C4 plants is of paramount importance: it appears impossible to utilize efficient C4 photosynthesis without understanding its exact redox needs and the regulation mechanisms used during light reactions. In this review, we discuss current knowledge on redox regulation in C3 and C4 plants, with special emphasis on the mesophyll and bundle sheath differences that are found in C4. In these two cell types in C4 plants, linear and cyclic electron transport in the chloroplasts operate differentially when compared to C3 chloroplasts, changing the redox needs of the cell. Therefore, our focus is on photosynthetic light reactions, ROS production dynamics, antioxidant defence, and thiol-based redox regulation, with the aim of providing an overview of our current knowledge.
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8.
Olive tree (Olea europaea L.) leaf as a waste by-product of table olive and olive oil industry: a review.
Şahin, S, Bilgin, M
Journal of the science of food and agriculture. 2018;(4):1271-1279
Abstract
Research into finding new uses for by-products of table olive and olive oil industry are of great value not only to the economy but also to the environment where olives are grown and to the human health. Since leaves represent around 10% of the total weight of olives arriving at the mill, it is worth obtaining high added-value compounds from those materials for the preparation of dietary supplements, nutraceuticals, functional food ingredients or cosmeceuticals. In this review article, olive tree (Olea europaea L.) leaf is reviewed as being a potential inexpensive, renewable and abundant source of biophenols. The importance of this agricultural and industrial waste is emphasised by means of describing its availability, nutritional and therapeutic effects and studies conducted on this field. © 2017 Society of Chemical Industry.
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9.
Functional Genomics and Genetic Control of Compound Leaf Development in Medicago truncatula: An Overview.
Chen, R
Methods in molecular biology (Clifton, N.J.). 2018;:197-203
Abstract
Diverse forms of leaves are present in nature. However, the regulatory mechanisms that underpin the development of diverse leaf forms remain enigmatic. The initiation of leaf primordia from the periphery of shoot apical meristem (SAM) requires downregulation of the class 1 knotted-like homeobox KNOXI proteins. In plants with simple leaves, this downregulation is permanent, consistent with leaves being determinant organs. In most of plants with compound leaves, the KNOXI proteins are reactivated in developing leaf primordia, and this reactivation is required for the development of compound leaves in these plants. Surprisingly, in Medicago truncatula and pea (Pisum sativum) that belong to the so-called inverted repeat-lacking clade (IRLC) of legume plants, the KNOXI proteins are not reactivated in leaf primordia and therefore not likely involved in the development of compound leaves in these plants. Instead, the legume FLORICAULA/LEAFY orthologues, UNIFOLIATA (UNI) and SINGLE LEAFLET1 (SGL1), are required for the initiation and development of lateral leaflet primordia in pea and M. truncatula plants, respectively. On the other hand, PALMATE-LIKE PENTAFOLIATA1 (PALM1) encoding a novel Cys(2)His(2) zinc finger transcription factor is required to suppress a morphogenetic activity at the leaf margin by negatively regulating SGL1 gene expression, and FUSED COMPOUND LEAF1 (FCL1) encoding a class M KNOX protein is required for the development of the leaf proximo-distal axis and organ boundary separation in M. truncatula. Thus, these recent studies have shown that SGL1/UNI, FCL1, and PALM1 provide a genetic framework for our understanding of compound leaf development in the legume plants.
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10.
Stevia Leaf to Stevia Sweetener: Exploring Its Science, Benefits, and Future Potential.
Samuel, P, Ayoob, KT, Magnuson, BA, Wölwer-Rieck, U, Jeppesen, PB, Rogers, PJ, Rowland, I, Mathews, R
The Journal of nutrition. 2018;(7):1186S-1205S
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Abstract
Steviol glycoside sweeteners are extracted and purified from the Stevia rebaudiana Bertoni plant, a member of the Asteraceae (Compositae) family that is native to South America, where it has been used for its sweet properties for hundreds of years. With continued increasing rates of obesity, diabetes, and other related comorbidities, in conjunction with global public policies calling for reductions in sugar intake as a means to help curb these issues, low- and no-calorie sweeteners (LNCSs, also known as high-potency sweeteners) such as stevia are gaining interest among consumers and food manufacturers. This appeal is related to stevia being plant-based, zero calorie and with a sweet taste that is 50-350 times sweeter than sugar, making it an excellent choice for use in sugar- and calorie-reduced food and beverage products. Despite the fact that the safety of stevia has been affirmed by several food regulatory and safety authorities around the world, insufficient education about stevia's safety and benefits, including continuing concern with regard to the safety of LNCSs in general, deters health professionals and consumers from recommending or using stevia. Therefore, the aim of this review and the stevia symposium that preceded this review at the ASN's annual conference in 2017 was to examine, in a comprehensive manner, the state of the science for stevia, its safety and potential health benefits, and future research and application. Topics covered included metabolism, safety and acceptable intake, dietary exposure, impact on blood glucose and insulin concentrations, energy intake and weight management, blood pressure, dental caries, naturality and processing, taste and sensory properties, regulatory status, consumer insights, and market trends. Data for stevia are limited in the case of energy intake and weight management as well as for the gut microbiome; therefore, the broader literature on LNCSs was reviewed at the symposium and therefore is also included in this review.