Mineral Nutrition of Higher Plants, 2nd edition, H. Marschner. Academic Press, London (1995), 889, (ISBN 0-12-473543-6). Price: 29.95 Pound Sterling

Contents Summary 67 I. Introduction 68 II. Silicon transport in plants: to absorb or not to absorb 69 III. The role of silicon in plants: not just a matter of semantics 71 IV. Silicon and biotic stress: beyond mechanical barriers and defense priming 76 V. Silicon and abiotic stress: a proliferation of proposed mechanisms 78 VI. The apoplastic obstruction hypothesis: a working model 79 VII. Perspectives and conclusions 80 Acknowledgements 81 References 81 SUMMARY: Silicon (Si) is not classified as an essential plant nutrient, and yet numerous reports have shown its beneficial effects in a variety of species and environmental circumstances. This has created much confusion in the scientific community with respect to its biological roles. Here, we link molecular and phenotypic data to better classify Si transport, and critically summarize the current state of understanding of the roles of Si in higher plants. We argue that much of the empirical evidence, in particular that derived from recent functional genomics, is at odds with many of the mechanistic assertions surrounding Si's role. In essence, these data do not support reports that Si affects a wide range of molecular-genetic, biochemical and physiological processes. A major reinterpretation of Si's role is therefore needed, which is critical to guide future studies and inform agricultural practice. We propose a working model, which we term the 'apoplastic obstruction hypothesis', which attempts to unify the various observations on Si's beneficial influences on plant growth and yield. This model argues for a fundamental role of Si as an extracellular prophylactic agent against biotic and abiotic stresses (as opposed to an active cellular agent), with important cascading effects on plant form and function.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.15343

The controversies of silicon's role in plant biology.

Drought and salinity are the main abiotic stresses limiting crop yield and quality worldwide. Improving food production in drought- and salt-prone areas is the key to meet the increasing food demands in near future. It has been widely reported that silicon (Si), a second most abundant element in soil, could reduce drought and salt stress in plants. Here, we reviewed the emerging role of Si in enhancing drought and salt tolerance in plants and highlighted the mechanisms through which Si could alleviate both drought and salt stress in plants. Silicon application increased plant growth, biomass, photosynthetic pigments, straw and grain yield, and quality under either drought or salt stress. Under both salt and drought stress, the key mechanisms evoked are nutrient elements homeostasis, modification of gas exchange attributes, osmotic adjustment, regulating the synthesis of compatible solutes, stimulation of antioxidant enzymes, and gene expression in plants. In addition, Si application decreased Na+ uptake and translocation while increased K+ uptake and translocation under salt stress. However, these mechanisms vary with plant species, genotype, growth conditions, duration of stress imposed, and so on. This review article highlights the potential for improving plant resistance to drought and salt stress by Si application and provides a theoretical basis for application of Si in saline soils and arid and semiarid regions worldwide. This review article also highlights the future research needs about the role of Si under drought stress and in saline soils.

Mechanisms of silicon-mediated alleviation of drought and salt stress in plants: a review.

Light emitting diodes (LEDs) applied to microalgal production

Silicon (Si) can improve drought tolerance in plants, but the mechanism is still not fully understood. Previous research has been concentrating on Si’s role in leaf water maintenance in Si accumulators, while little information is available on its role in water uptake and in less Si-accumulating plants. Here, we investigated the effects of Si on root water uptake and its role in decreasing oxidative damage in relation to root hydraulic conductance in tomato (Solanum lycopersicum ‘Zhongza No.9’) under water stress. Tomato seedlings were subjected to water stress induced by 10% (w/v) polyethylene glycol-6000 in the absence or presence of 2.5 mM added silicate. The results showed that Si addition ameliorated the inhibition in tomato growth and photosynthesis, and improved water status under water stress. The root hydraulic conductance of tomato plants was decreased under water stress, and it was significantly increased by added Si. There was no significant contribution of osmotic adjustment in Si-enhanced root water uptake under water stress. The transcriptions of plasma membrane aquaporin genes were not obviously changed by Si under water stress. Water stress increased the production of reactive oxygen species and induced oxidative damage, while added Si reversed these. In addition, Si addition increased the activities of superoxide dismutase and catalase and the levels of ascorbic acid and glutathione in the roots under stress. It is concluded that Si enhances the water stress tolerance via enhancing root hydraulic conductance and water uptake in tomato plants. Si-mediated decrease in membrane oxidative damage may have contributed to the enhanced root hydraulic conductance.

/pdf/silicon-enhances-water-stress-tolerance-by-improving-root-55km1t98bv.pdf

Silicon Enhances Water Stress Tolerance by Improving Root Hydraulic Conductance in Solanum lycopersicum L.

We investigated the effects of light quality during night interruption (NI) on morphogenesis, flowering, and the transcription of photoreceptor genes in the geranium Pelargonium × hortorum L.H. Bailey ‘Ringo 2000 Violet’ (day neutral plant, DNP). Plants were grown in an environment-controlled chamber under a constant light intensity of 180 μmol·m-2·s-1 PPF. The light was supplied by white (W) light emitting diodes (LEDs) to create long day (LD, 16 h light/8 h dark), short day (SD, 10 h light/14 h dark), or SD with a 4 h night interruption (NI) conditions. The NI was provided by green (NI-G), blue (NI-B), red (NI-R), far-red (NI-Fr), or white (NI-W) LEDs at a significantly reduced intensity of 10 μmol·m-2 ·s-1 PPF (only 5.5% of the intensity of the main light source). Plant height was greatest under NI-Fr. The percent flowering was not affected by light quality during NI, and all plants flowered under all treatments. Among NI treatments, days to visible flower buds (DVB) increased under NI-Fr. All photoreceptor genes except phyB and FTL were highly expressed under normal LD conditions. Under the NI treatment with different qualities of light, these photoreceptor genes were expressed at even higher levels, except under NI-B, as compared to SD. These results suggest that morphogenesis, flowering, and the expression of transcription factor genes are affected by light quality during NI. Light quality during NI in the DNP geranium has more pronounced effects on morphogenesis than on flowering.

Light quality during night interruption affects morphogenesis and flowering in geranium

We investigated the effects of light quality during night interruption (NI) on morphogenesis, flowering, and the transcription of photoreceptor genes in Petunia hybrida Hort. ‘Easy Wave Pink’ (a qualitative long-day plant, LDP). Plants were grown in a closed-type plant factory under a constant light intensity of 180 μmol·m-2·s-1 PPF provided by white (W) light emitting diodes (LEDs) under long day (LD, 16 h light/8 h dark), short day (SD, 10 h light/14 h dark), or SD conditions with a 4 h NI using green (NI-G), blue (NI-B), red (NI-R), far-red (NI-Fr), or white (NI-W) LEDs at an intensity of 10 μmol·m-2·s-1 PPF. Shoot length was greatest under NI-Fr. Flowering was observed under LD, NI-G, NI-Fr, and NI-W. The expression of photoreceptor genes was induced by NI. Specifically, phyA, phyB, and cry1 were more highly expressed under NI-G, NI-B, and NI-R compared to LD and SD. These results suggest that morphogenesis, flowering, and transcriptional factors are strongly affected by light quality during NI.

Light quality during night interruption affects morphogenesis and flowering in Petunia hybrida, a qualitative long-day plant

The effects of the quality and intensity of night interruption light (NIL) on the flowering and morphogenesis of kalanchoe (Kalanchoe blossfeldiana) ‘Lipstick’ and ‘Spain’ were investigated. Plants were raised in a closed-type plant factory under 250 μmol·m−2·s−1 PPFD white light emitting diodes (LEDs) with additional light treatments. These treatments were designated long day (LD, 16 h light, 8 h dark), short day (SD, 8 h light, 16 h dark), and SD with a 4 h night interruption (NI). The NIL was constructed from 10 μmol·m−2·s−1 or 20 μmol·m−2·s−1 PPFD blue (NI-B), red (NI-R), white (NI-W), or blue and white (NI-BW) LEDs. In ‘Spain’, the SPAD value, area and thickness of leaves and plant height increased in the NI treatment as compared to the SD treatment. In ‘Lipstick’, most morphogenetic characteristics in the NI treatment showed no significant difference to those in the SD treatment. For both cultivars, plants in SD were significantly shorter than those in other treatments. The flowering of Kalanchoe ‘Lipstick’ was not affected by the NIL quality, while Kalanchoe ‘Spain’ flowered when grown in SD and 10 μmol·m−2·s−1 PPFD NI-B. These results suggest that the NIL quality and intensity affect the morphogenesis and flowering of kalanchoe, and that different cultivars are affected differently. There is a need to further assess the effects of the NIL quality and intensity on the morphogenesis and flowering of short-day plants for practical NIL applications.

Flowering and Morphogenesis of Kalanchoe in Response to Quality and Intensity of Night Interruption Light.

The rose is one the most commercially grown and costly ornamental plants because of its aesthetic beauty and aroma. A large number of pests attack its buds, flowers, leaves, and stem at every growing stage due to its high sugar content. The most common pest on roses are aphids which are considered to be the major cause for product loss. Aphid infestations lead to major changes in rose plants, such as large and irregular holes in petals, intact leaves and devouring tissues. It is hypothesized that different cut rose cultivars would have different levels of sensitivity or resistance to aphids, since different levels of infestation are observed in commercially cut rose production greenhouses. The present work compared four cut rose cultivars which were bred in Korea and were either resistant or sensitive to aphid infestation at different flower developmental stages. An integrative study was conducted using comprehensive proteome analyses. Proteins related to ubiquitin metabolism and the stress response were differentially expressed due to aphid infestation. The regulations and possible functions of identified proteins are presented in detail. The differential expressions of the identified proteins were validated by immunoblotting and blue native page. In addition, total sugar and carbohydrate content were also observed.

https://www.mdpi.com/2227-7382/6/2/25/pdf

Proteomic Analysis of Aphid-Resistant and -Sensitive Rose (Rosa Hybrida) Cultivars at Two Developmental Stages.

Studies were conducted to develop an efficient cutting propagation method for domestic cut roses (Rosa hybrida Hort.). Three experiments were conducted in controlled environment growth chambers to investigate the effect of node position where the cuttings were taken, and number of leaflets left on each cutting, and light intensity on rooting and growth of the sapling. Domestic cut rose cultivars used in the first experiment for the effect of node position were standard type ‘Pink Song’ and ‘Gouni’, and spray type ‘Little Sun’ and ‘May.’ In the second experiment for the effect of number of leaflets left, standard type ‘Pink Song’, ‘Orange Beauty’ and ‘Gummack’, and spray type ‘May’ were used. In the third experiment for the effect of light intensity, standard type ‘Red Sun’ and ‘Gouni’, and spray type ‘Little Sun’ and ‘May’ were used. Cuttings were taken from third node positions each with a five leaflet. Each cutting had either 1, 3, or 5 leaflets by removing the rest of leaflets among five leaflets. Three light intensities used were 90, 180, and 270 μmol·m−2·s−1. Node position only affected rooting percent. However, number of roots, root length and weight, and length of new shoot were not significantly affected by the node position. In ‘Pink Song’, ‘Little Sun’, and ‘Gouni’, the greatest rooting percent was observed in the 1–2th (top), whereas in ‘May’ it was observed 4–5th (middle) and 7–8th (bottom). Number of leaflets left on each cutting affected number of roots, root length and root weight, but not the length of new shoot and rooting percent. In ‘Gummack’, treatment with three leaflets left resulted in the greatest number of roots, length of the longest root, root weight, length of new shoot, and percent rooting. Also, similar results were observed in ‘Pink Song’, ‘May’, and ‘Orange Beauty’, except in length of new shoot. Optimum light intensity for rooting was 270 μmol·m−2·s−1 for ‘Red Sun’, ‘Little Sun’, and ‘May’. In these three cultivars, rooting percent of the cuttings increased with increasing light intensity. In ‘Gouni’, however, the optimum light intensity for rooting was 180 μmol·m−2·s−1.

Yoo Gyeong Park

Papers

Light quality during night interruption affects morphogenesis and flowering in geranium

Light quality during night interruption affects morphogenesis and flowering in Petunia hybrida, a qualitative long-day plant

Flowering and Morphogenesis of Kalanchoe in Response to Quality and Intensity of Night Interruption Light.

Proteomic Analysis of Aphid-Resistant and -Sensitive Rose (Rosa Hybrida) Cultivars at Two Developmental Stages.

Effects of Node Position, Number of Leaflets Left, and Light Intensity during Cutting Propagation on Rooting and Subsequent Growth of Domestic Roses