Certain plants are frost tender due to cellular damage from ice crystal formation
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Peer-reviewed literature and historical sources support that certain plants are frost tender and experience tissue collapse or damage due to ice crystal formation and freeze-dehydration.
In this review we focus on photosynthetic behavior of overwintering evergreens with an emphasis on both the acclimative responses of photosynthesis to cold and the winter behavior of photosynthesis in conifers. Photosynthetic acclimation is discussed in terms of the requirement for a balance between the energy absorbed through largely temperature-insensitive photochemical processes and the energy used for temperature-sensitive biochemical processes and growth. Cold acclimation transforms the xanthophyll-mediated nonphotochemical antenna quenching of absorbed light from a short-term dynamic response to a long-term sustained quenching for the whole winter period. This acclimative response helps protect the evergreen foliage from photooxidative damage during the winter when photosynthesis is restricted or prevented by low temperatures. Although the molecular mechanisms behind the sustained winter excitation quenching are largely unknown, it does involve major alterations in the organization and composition of the photosystem II antenna. In addition, photosystem I may play an important role in overwintering evergreens not only by quenching absorbed light photochemically via its support of cyclic electron transport at low temperatures, but also by nonphotochemical quenching of absorbed light irrespective of temperature. The possible role of photosystem II reaction centers in nonphotochemical quenching of absorbed energy in overwintering evergreens is also discussed. Processes like chlororespiration and cyclic electron transport may also be important for maintaining the functional integrity of the photosynthetic apparatus of overwintering evergreens both during periods of thawing in winter and during recovery from winter stress in spring. We suggest that the photosynthetic acclimation responses of overwintering evergreens represent specific evolutionary adaptations for plant species that invest in the long-term maintenance of leaf structure in cold climatic zones as exemplified by the boreal forests of the Northern Hemisphere.
This report provides a brief review of key findings related to frost resistance in alpine woody plant species, summarizes data on their frost resistance, highlights the importance of freeze avoidance mechanisms, and indicates areas of future research. Freezing temperatures are possible throughout the whole growing period in the alpine life zone. Frost severity, comprised of both intensity and duration, becomes greater with increasing elevation and, there is also a greater probability, that small statured woody plants, may be insulated by snow cover. Several frost survival mechanisms have evolved in woody alpine plants in response to these environmental conditions. Examples of tolerance to extracellular freezing and freeze dehydration, life cycles that allow species to escape frost, and freeze avoidance mechanisms can all be found. Despite their specific adaption to the alpine environment, frost damage can occur in spring, while all alpine woody plants have a low risk of frost damage in winter. Experimental evidence indicates that premature deacclimation in Pinus cembra in the spring, and a limited ability of many species of alpine woody shrubs to rapidly reacclimate when they lose snow cover, resulting in reduced levels of frost resistance in the spring, may be particularly critical under the projected changes in climate. In this review, frost resistance and specific frost survival mechanisms of different organs (leaves, stems, vegetative and reproductive over-wintering buds, flowers, and fruits) and tissues are compared. The seasonal dynamics of frost resistance of leaves of trees, as opposed to woody shrubs, is also discussed. The ability of some tissues and organs to avoid freezing by supercooling, as visualized by high resolution infrared thermography, are also provided. Collectively, the report provides a review of the complex and diverse ways that woody plants survive in the frost dominated environment of the alpine life zone.
Sub-zero temperatures put plants at risk of damage associated with the formation of ice crystals in the apoplast. Some freeze-tolerant plants mitigate this risk by expressing ice-binding proteins (IBPs), that adsorb to ice crystals and modify their growth. IBPs are found across several biological kingdoms, with their ice-binding activity and function uniquely suited to the lifestyle they have evolved to protect, be it in fishes, insects or plants. While IBPs from freeze-avoidant species significantly depress the freezing point, plant IBPs typically have a reduced ability to lower the freezing temperature. Nevertheless, they have a superior ability to inhibit the recrystallization of formed ice. This latter activity prevents ice crystals from growing larger at temperatures close to melting. Attempts to engineer frost-hardy plants by the controlled transfer of IBPs from freeze-avoiding fish and insects have been largely unsuccessful. In contrast, the expression of recombinant IBP sequences from freeze-tolerant plants significantly reduced electrolyte leakage and enhanced freezing survival in freeze-sensitive plants. These promising results have spurred additional investigations into plant IBP localization and post-translational modifications, as well as a re-evaluation of IBPs as part of the anti-stress and anti-pathogen axis of freeze-tolerant plants. Here we present an overview of plant freezing stress and adaptation mechanisms and discuss the potential utility of IBPs for the generation of freeze-tolerant crops.
Low temperature stress significantly threatens crop productivity and economic sustainability. Plants counter this by deploying advanced molecular mechanisms to perceive and respond to cold stress. Transmembrane proteins initiate these responses, triggering a series of events involving secondary messengers such as calcium ions (Ca<sup>2+</sup>), reactive oxygen species (ROS), and inositol phosphates. Of these, calcium signaling is paramount, activating downstream phosphorylation cascades and the transcription of cold-responsive genes, including cold-regulated (COR) genes. This review focuses on how plants manage freeze-induced damage through dual strategies: cold tolerance and cold avoidance. Tolerance mechanisms involve acclimatization to decreasing temperatures, fostering gradual accumulation of cold resistance. In contrast, avoidance mechanisms rely on cryoprotectant molecules like potassium ions (K<sup>+</sup>), proline, glycerol, and antifreeze proteins (AFPs). Cryoprotectants modulate intracellular solute concentration, lower the freezing point, inhibit ice formation, and preserve plasma membrane fluidity. Additionally, these molecules demonstrate antioxidant activity, scavenging ROS, preventing protein denaturation, and subsequently mitigating cellular damage. By forming extensive hydrogen bonds with water molecules, cryoprotectants also limit intercellular water movement, minimizing extracellular ice crystal formation, and cell dehydration. The deployment of cryoprotectants is a key adaptive strategy that bolsters plant resilience to cold stress and promotes survival in freezing environments. However, the specific physiological and molecular mechanisms underlying these protective effects remain insufficiently understood. Therefore, this review underscores the need for further research to elucidate these mechanisms and assess their potential impact on crop productivity and sustainability, contributing to the progressive discourse in plant biology and environmental science.
Freezing and high temperature thresholds of photosystem 2 (PS2), ice formation and frost and heat damage were measured in leaves of evergreen subalpine plants under conditions of naturally low (winter) to high (summer) PS2 efficiencies (F V /F M ). The temperature‐dependent change in basic Chl fluorescence (F 0 ) (T‐F 0 ) technique that is usually used to assess the high temperature threshold of PS2 in a new approach was applied to test freezing temperature thresholds of PS2. T‐F 0 curves (+5 °C to −10 °C at 2 K h −1 ) revealed a significant, sudden increase in F 0 on extracellular ice formation (−4.0 or −5.5 °C). The rise in F 0 was recorded 0.3–0.6 K below ice nucleation (10–20 min later) and was produced by freeze dehydration of cells. The rise in F 0 was not caused by frost damage, as during winter LT 50 was lower than −27 °C and not by formation of ice on the leaf surface. Hence, F 0 measurements during freezing are a useful tool to distinguish between surface ice and extracellular ice inside the leaf tissue which cannot be differentiated by other ice‐detecting methods. PS2 efficiency significantly affected the shape of the high temperature T‐F 0 curves (20–65 °C at 1 K min −1 ). Under F V /F M >0.6, two F 0 maxima were recorded. The fast rise phase to the first F 0 maximum corresponded with tissue heat damage (LT 50 : 46.9–54.3 °C). The second F 0 maximum occurred at leaf temperatures between 55 and 60 °C. Under F V /F M <0.2 only, the second F 0 maximum was detectable. Lack of awareness of the missing F 0 maximum would lead to an overestimation of the PS2 high temperature threshold by >10 K; hence, under low F V /F M , it cannot be determined by the T‐F 0 technique.
Low temperature is a critical environmental stress factor that restricts crop growth and geographical distribution, significantly impacting crop quality and yield. When plants are exposed to low temperatures, a series of changes occur in their external morphology and internal physiological and biochemical metabolism. This article comprehensively reviews the alterations and regulatory mechanisms of physiological and biochemical indices, such as membrane system stability, redox system, fatty acid content, photosynthesis, and osmoregulatory substances, in response to low-temperature stress in plants. Furthermore, we summarize recent research on signal transduction and regulatory pathways, phytohormones, epigenetic modifications, and other molecular mechanisms mediating the response to low temperatures in higher plants. In addition, we outline cultivation practices to improve plant cold resistance and highlight the cold-related genes used in molecular breeding. Last, we discuss future research directions, potential application prospects of plant cold resistance breeding, and recent significant breakthroughs in the research and application of cold resistance mechanisms.
AbstractThe influence of ice crystal formation in tissues of unhardened and hardened seedlings of Pinus silvestris L. and Picea abies (L.) Karst. was determined. An apparatus for this purpose was constructed.Unhardened seedlings of spruce collapsed completely as a result of ice crystal formation in their shoots, while unhardened seedlings of pine survived ice crystal formation with or without injury to the needles. After a hardening period of 4–5 weeks, seedlings of spruce and pine survived ice formation but injuries occurred in spruce. For pine, on the contrary, the temperature after ice formation had a decisive effect on the extent of the injuries. Observed injuries are discussed in terms of inter‐ and intracellular ice crystal formation.
In frost hardy plants, the lethal intracellular formation of ice crystals has to be prevented during frost periods. Besides the ability for supercooling and pre-frost dehydration of tissues, extracellular ice formation is another strategy to control ice development in tissues. During extracellular ice formation, partially large ice bodies accumulate in intercellular spaces, often at preferred sites which can also be expandable. In this contribution, the physico-chemical processes underlying the water movements towards the sites of extracellular ice formation are studied theoretically, based on observations on the frost hardy horsetail species Equisetum hyemale, with the overall aim to obtain a better understanding of the physical processes involved in extracellular ice formation. In E. hyemale, ice accumulates in the extensive internal canal system. The study focuses on the processes which are triggered in the cellular osmotic-mechanic system by falling, and especially subzero temperatures. It can be shown that when the temperature falls, 1) water flow out of cells is actuated and 2) "stiff-walled" cells lose less water than "soft-walled" cells. Furthermore, 3) cell water loss increases with increasing (= less negative) turgor loss point. These processes are not related to any specific activities of the cell but are solely a consequence of the structure of the cellular osmotic system. On this basis, a directed water flow can be initiated triggered by subzero temperatures. The suggested mechanism may be quite common in frost hardy species with extracellular ice formation.
Abstract Strategies for reducing bacterially induced frost damage to tender plants were examined. Introduction of the competitive bacterium, Erwinia herbicola M232A (not active in ice nucleation) did not lower the temperature at which freeze injury of tomato shoots occurred. Streptomycin was effective in reducing freeze damage of tomato shoots only when mixed with the Pseudomonas syringae suspension prior to plant inoculation. Spectinomycin, another aminoglycoside, was effective in reducing frost damage to tomato plants due to P. syringae. Bacteria present intercellularly (within the plant) may play a significant role in bacterial ice nucleation.
The precise location where ice forms in plants affects the physical constraint it exerts on the different biological compartments (cells, tissues, organs). It is therefore critical to understand where and how ice nucleates to predict the extent of low temperature damage. On one hand, extracellular ice formation can protect living plant cells by lowering their intracellular freezing point through water efflux and an increase in osmolyte concentration. On the other hand, extended freezing-induced dehydration may cause damage and rupture of the plasma membrane. The location and pattern of ice formation in plants are marked by high spatio-temporal variability in relation to the type of plant tissue, its developmental stage, and the nature of the initial ice nucleus. This review focuses on the mechanisms and dynamics of intrinsic ice nucleation and subsequent propagation in perennial plants. We describe the factors that influence ice nucleation, such as the nature of nucleating agents and other biophysical conditions. We also highlight the shortcomings of studies on plant freezing, especially regarding laboratory studies, and emphasize the need to investigate ice nucleation in plants using interdisciplinary approaches. We finally provide a practical workflow to guide new experimenters in this research field.
Plant Breeders Have Worked Long to Improve Hardy Chrysanthemums Efforts Now Rewarded by Variety in Form Color And Blooming Habits Majority Should Be Pinched Back to Encourage Full Bushy Type of Growth By W H YOUNGMAN Last weeks snowstorm demonstrated the importance of hardy chrys anthemums in the perennial border The freezing temperatures that accompanied the snowstorm killed most of the annuals and many of the perennials so that without the chrysanthemums our gardens would be colorless for the remainder of the fall While there are a great many kinds of chrysanthemums ranging from the native wildfloweroxeye daisy and the annuals to the huge Japanese types which are grown by the florists we shall confine this article to a brief discussion of the hardy garden types Plant breeders have been working for many years to improve the chrysanthemums and today we have an infinite variety of forms colors and blooming habits The wellknown Korean group as typified by Mars Ceres Daphne and many others is widely grown and enjoyed They are mostly singles and are comparatively earlyblooming Gen erally speaking they are fairly hardy and freeflowering They are most ly tall growers and should be pinched back to stimulate branching
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