Epidermal Browning Research Articles

Rates of bark formation on surfaces of saguaro cacti (Carnegiea gigantea)1, 2

Abstract Twenty-one species of tall, long-lived columnar cactus species show extensive bark coverage (epidermal browning) in the Americas. Each species shows more bark coverage on equatorial-facing surfaces than on polar-facing surfaces. In addition, controlled experiments with supplemental UV-B irradiation show the initial stages of bark coverage. These two facts suggest that UV-B irradiation is the cause of sunlight-induced bark coverage. This sunlight-induced bark leads to premature morbidity and mortality. Saguaro cactus (Carnegiea gigantea (Engelm.) Britton & Rose) of southern Arizona is the most researched cactus species with regard to this bark coverage. The current effort focused on bark coverage rates on 12 cactus surfaces at 1.7 m height above ground by comparing logistic curves of relative bark coverage among stem surfaces. Logistic curves have been used to document progress of many diseases in humans. In this study, logistic curves were best fit to data with least squares analysis in all cases...

Sunlight-induced bark formation in long-lived South American columnar cacti

Previous research has shown that sunlight-induced bark formation (epidermal browning) on vertical surfaces of tall, long-lived columnar cactus species leads to premature death of entire plants. The bark cambium that produces bark for cactus species has been shown to involve proliferation of epidermal cells only. The purpose of this research was to understand (1) the characteristics of cuticles, epidermal and hypodermal cells, (2) the process of sunlight-induced bark formation, and (3) changes in hypodermal cells during the bark formation process for many species of long-lived, columnar cacti from South America. A wide diversity of epidermal and hypodermal cells occurred among the species studied. Epidermal depths ranged from 8.7 to 49.7μm and involved one to several epidermal cells while the thickness of hypodermal cell layers ranged from 42.7 to 661μm among the species studied. During bark cambium formation, each epidermal cell underwent at least one anticlinal cell division prior to numerous periclinal cell divisions since lengths of initially produced bark cambium cells were half the lengths of uninjured epidermal cells. Some cactus species exhibited hypodermal cell injuries during bark formation. This study reports: (1) quantitative measurements of cuticles, epidermal and hypodermal layers, (2) the presence of anticlinal cell divisions of epidermal cells to produce the bark cambium, and (3) the destruction of hypodermal cells during bark formation for columnar cactus species of South America. Possibly these results are specific for sunlight-induced bark formation for cactus species while other types of injuries may result in bark production by other means.

Relationships Between Epidermal Browning, Girdling, Damage, and Bird Cavities In a Military Restricted Database of 12,000+ Plants of the KeystoneCarnegiea giganteaIn the Northern Sonoran Desert

An exceptional dataset for over 12,000 Carnegiea gigantea collected by the Arizona Department of Game and Fish over two field seasons on a restricted military reservation was released to the authors for analysis, including a variety of variables for which little empirical evidence exists. Data on epidermal browning, physical damage due to fire, lightning, gunshot or topping, rodent girdling, bird cavities and other variables were assessed using primarily chi-square analysis. The main findings of this study include: (1) Plants with high amounts of epidermal browning were rather evenly distributed across height classes, although the very smallest plants (0–0.9 m) had substantially less epidermal browning. (2) Although past work has shown that epidermal browning is surely a function of solar radiation receipt, other variables (bird cavities, girdling, damage, branching) are statistically linked with browning, raising the possibility that other biotic and abiotic factors may hasten browning. (3) Bird cavities are better predicted by height than branches, likely due to decreased visibility and exposure to thermally tempering winds caused by branches, and improved defensive position and reduced exposure to heating from the surface associated with taller plants.

Predicting morbidity and mortality for a saguaro cactus (Carnegiea gigantea) population1

Scale and bark injuries (a condition called epidermal browning) have been shown to occur on stem surfaces of 21 species of tall, long-lived cactus species throughout the Americas. The amounts of surface injuries are highly correlated with amounts of sunlight exposures. Epidermal browning causes cactus morbidity and mortality of saguaro cacti. For this study, rates of morbidity and mortality of saguaro cacti (Carnegiea gigantea (Engelm.) Britt and Rose) were determined for 1061 plants from 50 desert field plots. From 2002 to 2010, 16.5% of all saguaros died (increased mortality). During the same period, the percentage of cacti with few epidermal injuries decreased from 25 to 9%, with a 16% increase in initial morbidity. Over this same period, about 10% of the population had a rapid increase of epidermal browning (rapid morbidity). Thus, marked increases in morbidity and mortality occurred over the eight-year period. WEKA, a standard machine-learning program, was used to determine the characteristics of saguaros that predispose them to (1) die, (2) initiate morbidity (start of epidermal browning symptoms) and (3) initiate rapid morbidity (a rapid increase in epidermal browning). Decision trees were created using the C4.5 algorithm, a top-down method that repeatedly chooses the question that produces a maximal information gain. Amounts of epidermal browning on north-facing troughs alone predicted cactus mortality with 89.1% accuracy. Initial morbidity was predicted with 80.2% accuracy with data of south-facing troughs and crests only. Rapid morbidity (less than 20% epidermal browning in 2002 and more than 50% by 2010) was predicted with a very large tree with 79.6% accuracy. For example, rapid morbidity is predicted by more than 3.1% epidermal browning on left troughs on south-facing surfaces in 2002 with 80% accuracy. Moreover, rapid morbidity was also predicted if east-facing crests had more than 3.9% epidermal browning in 2002. Overall, decision tree analysis was very effective at predicting changes in mortality and morbidity for the population of 1061 saguaros from 2002 to 2010. Data from trough surfaces were more effective than data from crests for predicting mortality and morbidity.

Cultivar affects browning susceptibility of freshly cut star fruit slices

Consumption of freshly-cut horticultural products has increased in the last few years. The principal restraint to using freshly-cut carambola is its susceptibility to tissue-browning, due to polyphenol oxidase-mediated oxidation of phenolic compounds present in the tissue. The current study investigated the susceptibility to browning of star fruit slices (Averrhoa carambola L.) of seven genotypes (Hart, Golden Star, Taen-ma, Nota-10, Malásia, Arkin, and Fwang Tung). Cultivar susceptibility to browning as measured by luminosity (L*) varied significantly among genotypes. Without catechol 0.05 M, little changes occurred on cut surface of any cultivars during 6 hour at 25°C, 67% RH. Addition of catechol led to rapid browning, which was more intense in cvs. Taen-ma, Fwang Tung, and Golden Star, with reduction in L* value of 28.60%, 27.68%, and 23.29%, respectively. Browning was more intense in the center of the slices, particularly when treated with catechol, indicating highest polyphenol oxidase (PPO) concentration. Epidermal browning, even in absence of catechol, is a limitation to visual acceptability and indicates a necessity for its control during carambola processing. Care must be given to appropriate selection of cultivars for fresh-cut processing, since cultivar varied in browning susceptibility in the presence of catechol.

IDENTIFICATION AND CHARACTERIZATION OF PHYSIOLOGICAL DISORDERS IN CHERIMOYA (Annona cherimolla Mill.) cv CONCHA LISA IN COLD STORAGE

The cherimoya (Annona cherimolla Mill.) is a subtropical fruit that is very susceptible to physiological disorders during refrigeration. To determine the origin of some of these abnormal manifestations, fruits of cherimoya cv. Concha Lisa were harvested in the loca-tion of Quillota, Chile. The harvest index was the epidermal change of color. The fruits were stored for 42 days in cold storage at 5 °C with 90% relative humidity to accelerate any possible manifestation of the disorders. During storage, the fruit was evaluated every seven days. Physical and chemical parameters were evaluated such as soluble solids, acidity, epidermal color and loss of hu-midity. Once the disorders appeared, a histological and descriptive analysis of them was done. It was relevant that the disorders denominated pitting, spot and epidermal browning resulted from storage and each one caused a particular damage to the fruit. Epi-dermal browning is an advanced stage of the spots, but not of pitting.

Ecophysiology of the saguaro cactus (Carnegiea gigantea) in the Saguaro National Monument: relationship to symptoms of decline

The purpose of this study was to examine physiological correlates to the phenomenon of epidermal browning and saguaro decline in Saguaro National Monument. Gas exchange characteristics, surface temperatures, and the extent of epidermal browning in tissues of both healthy and declining saguaro cacti (Carnegiea gigantea) at different solar orientations were examined in eight long-term monitoring plots in the Rincon Mountain District of the Saguaro National Monument near Tucson, Arizona during both wet and dry seasons and years.Daily maximum surface temperatures were greatest on west-oriented tissues, as predicted by a simple model. However, south- and south-west-oriented tissues showed the highest browning indices, suggesting that browning may be more related to cumulative thermal loading than to extreme late afternoon temperature events. During the wet season, maximum nocturnal CO2uptake rates and total nocturnal CO2uptake were negatively correlated with browning index. Uptake rates during dry seasons and dry years was minimal, and not related to browning indices. However, healthy tissues of saguaros that also had tissues with high browning indices had wet-season maximum CO2uptake rates as high as saguaros without damaged tissues, suggesting that the browning is not systemic but rather is tissue- and angle-specific. Instantaneous measures of water-use efficiency did not vary significantly or predictably by angle, but rather were greatest during night-time and in tissues when CO2uptake was greatest. We suggest that browning symptoms on cacti are most likely due to natural abiotic stress, and are unrelated to systemic pollution stress or increased UV-B radiation.

Population dynamics and trace metal biogeochemistry of the saguaro cactus (Carnegiea gigantea) in the Sonoran desert

:The purpose of this study was to determine if smelter-derived air pollution in the form of trace metal toxicity could be responsible for either the apparent population decline or the epidermal browning of the saguaro cactus (Carnegiea gigantea) within the Saguaro National Monument (SNM). Population density and distribution measurements, estimates of epidermal browning, and tissue major ion and trace metal analyses were conducted in nine sites across the entire climatic range of Carnegiea as comparisons to patterns observed in SNM. Carnegiea from industrialized sites compared to pristine sites did not have statistically greater browning. DTPA-extractable copper (Cu) was significantly elevated in soils from two sites near copper smelters. However, tissue Cu concentrations were not at levels considered phytotoxic, and neither soil nor tissue Cu was significantly related to browning indices or population density measurements. No element showed any significant correlation to epidermal browning. The fact that tissue chemical indicators of photosynthetic enzyme and photosynthetic activity (N, Mg, and Fe in chlorenchyma) were not significantly related to browning suggests that epidermal browning may begin as a cuticular damage event, rather than from a tissue toxicity event that would damage the photosynthetic process. Densities of Carnegiea were greatest at both districts of SNM, with population densities at other regional sites being significantly lower. Our population analysis suggests that the Carnegiea population in SNM at the time of the establishment of the Monument was unusually dense; no present population had similar densities. Results suggest that trace metal pollution may not be causing premature Carnegiea death in SNM, and that browning may be a natural process that is unrelated to the population decline process.

Epidermal browning of saguaro cacti ( Carnegiea gigantea): Relative health and rates of surficial injuries of a population

Epidermal browning appears to be occurring on virtually all medium and older-aged saguaros [ Carnegiea gigantea (Engelm.) Britt. and Rose] throughout the Sonoran Desert. The purpose of this research was to determine if a population of 253 saguaros could be accurately subdivided with regard to health based upon surficial injuries and to determine rates of injuries (morbidity) and death (mortality) by repeated 2–3 year observations of the sampled population. Surficial injuries such as mean percentage of spines present and of crest and trough areas without visible surface blemishes were determined. Data show that the cactus population can be subdivided accurately into (1) cacti that are healthy, (2) cacti that exhibit a health decline, (3) cactic with poor health (many surficial injuries), and (4) cacti that died during the observation period. The changes in percentages of surficial injuries for cacti that exhibited a health decline (group 2 above) were used to determine rates of morbidity; this group comprised 27–49% of the entire cactus population among the three parameters observed. For one group of saguaros (between 11 and 36% of the population), there was up to a 31% decline in health annually. Mortality rates were only between 3 and 4.5% annually, below some other published estimates. From available evidence it appears that the health of a saguaro population can be determined accurately with a relatively small number (253) of cacti examined over a short (2- or 3-year) period because (a) surficial injuries of individual saguaros were determined, (b) three parameters of injury occurred at relatively similar rates, (c) the percentages of cacti that underwent these changes were relatively large, and (d) the negative changes in health were relatively large.

Trichome density and its protective potential against ultraviolet-B radiation damage during leaf development

Trichome density and the capacity of leaf hairs to protect underlying tissues against ultraviolet-B radiation damage were assessed during leaf development in three tree species. In all cases, trichome density and the relative quantities of ultraviolet radiation absorbing phenolic constituents (expressed on a leaf area basis) declined considerably with leaf age. In addition, the percent leaf dry mass invested in trichome decreased significantly. Reductions were greater on the adaxial leaf surface, leading to an almost glabrous upper epidermis in mature leaves. Internal (i.e., leaf total minus trichome) phenolics showed no significant changes with leaf age in Eriobotrya japonica and Cydonia oblonga. In Olea europaea, however, the concentration of internal phenolics was doubled in mature leaves. Ultraviolet-B radiation resulted in a reduction of photosystem II photochemical efficiency and extensive epidermal browning only in young, dehaired leaves. No such effects were observed in young, dehaired leaves in the absence of ultraviolet-B radiation or in normal young or mature ultraviolet-B-irradiated leaves. It is suggested that the dense trichomes often covering young leaves may, in addition to other functions, protect transiently the underlying cells against ultraviolet-B radiation damage during the time period required for the maturation of internal avoidance and (or) repairing mechanisms. Key words: Cydonia oblonga, Eriobotrya japonica, Olea europaea, leaf development, leaf hairs, phenolics, ultraviolet-B radiation damage.

Allelopathic and Water Conserving Functions of Leaf Epicuticular Exudates in the Mediterranean Shrub Dittrichia viscosa

The possible ecophysiological roles of the water soluble, epicuticular material accumulated on the leaves of Dittrichia viscosa (L.) W.Greuter (syn. Inula viscosa (L.) Aiton) (Asteraceae), were investigated in laboratory experiments. It was found that: (a) the material reduced cuticular transpiration; (b) it had a strong absorbance in the ultraviolet, apparently offering the leaves an ultraviolet-B radiation screen; (c) removal of this material, however, and exposure of the leaves to visible light supplemented with ultraviolet-B radiation had no effects on photosystem II photochemical efficiency or stomatal functions and caused no epidermal browning; and (d) the material was strongly inhibitory against germination of lettuce seeds and caused considerable decrease in the radicle length of Phlomis fruticosa L., a species often occupying the same habitat as D. viscosa. We infer from the above that D. viscosa leaves may be resistant to ultraviolet-B radiation damage and, accordingly, the water conservation and allelopathic functions of the epicuticular material may predominate over its potential to protect against ultraviolet-B radiation.

Epidermal browning of saguaro cacti ( Carnegiea gigantea): physiological effects, rates of browning and relation to sun/shade conditions

There has been increased morbidity of saguaro cacti ( Carnegiea gigantea) in some portions of the Sonoran Desert. Injury to individual cacti is characterized by accumulations of epicuticular waxes that obstruct stomata and lead to eventual browning of surfaces. The purpose of this research was to determine physiological effects of obstructed stomata, rates of epidermal browning, and the relationship between epidermal browning and sun/shade conditions of stem surfaces. Nocturnal acid accumulation was positively correlated with visible stomatal density and negatively correlated with characteristics of epidermal browning. Numbers of chloroplasts per cell were higher for green cacti compared with yellow or browning stems. Over a two-year period, thickness of the green chlorenchyma decreased 1.8 mm while the thickness of internal discoloration increased 2.7 mm. Rib crest scaling and barking increased markedly along with a deterioration of spines and areoles over the period. Cacti with sun-exposed south-facing surfaces had 19% greater internal discoloration than cacti at least partially shaded by vegetation. On average, sun-exposed cacti had 20% more surface injuries on crests and trought on south-facing surfaces compared with similar surfaces of shaded saguaros. Results reported herein support the hypothesis that morbidity of some saguaros is occurring at a measurable rate and is related to sun exposure.

Surficial injuries of several long-lived columnar cacti of the Sonoran Desert, Mexico

The giant cactus, Carnegiea gigantea (Engelm.) Britt. & Rose, of the Sonoran Desert of North America, is experiencing an epidermal browning of stem surfaces in which sheeting of epicuticular waxes leads to scaling and barking (epidermal browning). The purpose of this study was to determine the degree that four species of long-lived columnar cacti, namely, Stenocereus thurberi (Engelm.) Britt. & Rose, Lophocereus schottii (Engelm.) Britt. & Rose, Pachycereus pringlei (S. Wats.) Britt. & Rose and C. gigantea exhibit epidermal browning at a site in Sonora, Mexico where all four species occur. Estimates of scaling and barking of crests and troughs were made on stems and branches closest to 180° azimuth. All four species showed from 27 to 75% scaling and barking on crests. However, only C. gigantea exhibited scaling and barking on more than 40% of trough areas. The degree of scaling and barking of trough surfaces was correlated positively with degree of sheeting of epicuticular waxes, and negatively with number of visible stomata. These results show that symptoms of epidermal browning are not specific to C. gigantea but are present on all four cactus species observed.

Epidermal browning of saguaro cacti ( Carnegiea gigantea): Surface and internal characteristics associated with browning

In some locations of Saguaro National Monument near Tucson, Arizona, there has been a decline in saguaro cacti ( Carnegiea gigantea (Engelm.) Britt. and Rose). Injury to individual cacti is frequently characterized by epidermal browning and premature senescence. On green cactus surfaces, most epicuticular waxes flake off and stomata are not obscurred. As cactus surfaces become more yellow in color (less green), epicuticular waxes no longer flake off and the build up or sheeting of waxes obscures stomata. This sheeting eventually leads to visible scaling and barking. Epicuticular wax sheeting, scaling and barking of troughs were negatively correlated with depth of green chlorenchyma but were positively correlated with depth of discoloration of internal parenchyma. These results suggest that the first step in epidermal browning is an excessive accumulation of epicuticular waxes. Sheeting of epicuticular waxes results in scaling and barking of crests followed by these same events on troughs. Areoles deteriorate as crest scaling and barking occur. These events are well-correlated with trunk color and the depths of both the green chlorenchyma and discoloration of the internal parenchyma.

Leaf hairs of Olea europeae protect underlying tissues against ultraviolet-B radiation damage

The photochemical efficiency of photosystem II, as measured by chlorophyll fluorescence induction, was not affected in de-haired olive leaves kept in the dark or intact leaves irradiated with a moderate (3.75 W m −2) ultraviolet-B (UV-B) intensity. In de-haired, UV-B-irradiated leaves, however, the ratio of variable to maximum ( F v/ F m) chlorophyll fluorescence declined significantly and irreversibly. Reduction in F v/ F m was associated with an increase in instantaneous ( F 0) and a decrease in maximum ( F m) fluorescence, indicating perturbation by the UV-B exposure of more than one photosynthetic site. Extensive epidermal browning in dehaired, UV-B irradiated leaves was also observed, indicating possible damage to cell membranes. The results strengthen the hypothesis that leaf hairs protect the underlying tissues against UV-B radiation damage.

Epidermal browning of saguaro cacti ( Carnegiea gigantea): is it new or related to direction?

Browning of epidermal surfaces of saguaro cacti ( Carnegiea gigantea) is associated with premature death of the species in the northern Sonoran Desert. Analyses of authentic historical photographs of mature saguaros from 1903 to 1987 demonstrated a significant (1) loss of spines, (2) decrease in apparently healthy crests, and (3) increased trough barking over the period. All three of these changes occurred to saguaros of over 115 years of age at a projected rate of 4–5% per decade. Analyses of epidermal characteristics of saguaros at the Saguaro National Monument were performed to determine if epidermal browning was related to compass direction. Results show that both scaling and barking of crests and troughs and loss of spines, all symptoms of epidermal browning, were 10 times higher on southern exposures (between 140 and 220°) compared with northern exposures (between 320 and 40°). The two troughs of a crest were evaluated separately. The results demonstrated that injury to one trough of a crest could be as much as four times greater than that of the second trough.