Search

According to a common hypothesis, some of the epidermal structural features in the leaves of tracheid- bearing plants “offset” low specific conductivity of vesselless wood. The data concerning this issue is contradictory, which can be explained by the fact that leaf water relations depend not only on the epidermis structure, but also on the structure of other leaf tissues. In the current study we aimed to evaluate the diversity of water transport systems in the leaves of tracheid-bearing woody plants in the temperate rainforest of south-central Chile. For this purpose, we collected leaves of four Podocarpaceae and two Winteraceae species in natural habitats, examined their leaf anatomy using light and transmission electron microscopy, measured the quantitative characters and analyzed the data using principal component analysis. Leaves of the studied species differ in the mesophyll and xylem anatomy. Four species have features that accelerate water transport through the leaf tissues via the apoplast (Prumnopitys andina), accessory transfusion tissue (Podocarpus saligna) and a network of veins (Drimys species). On the contrary, the leaves of Saxegothaea conspicua and Podocarpus nubigena accumulate water in water-storage tissue (hydrenchyma), but their ecology suggest that hydrenchyma is not an adaptation to environmental conditions. The obtained data indicate the existence of different ways of water delivery to the photosynthetic tissue in the leaves of vesselless plants. In the case of insufficient water supply through the tracheids, hydrenchyma is likely to maintain hydration of the leaves.

As future climates continue to change, precipitation deficits are expected to become more severe across tropical ecosystems. As a result, it is important that we identify plant physiological traits that act as adaptations to drought, and determine whether these traits act synergistically or independently of each other. In this study, we assessed the role of three leaf-level putative adaptations to drought: crassulacean acid metabolism (CAM), the turgor loss point (TLPΨ) and water storage hydrenchyma tissue. Using the genus Clusia as a model, we were able to explore the extent to which these leaf physiological traits co-vary, and also how they contribute to species' distributions across a precipitation gradient in Central and South America. We found that CAM is independent of the TLPΨ and hydrenchyma depth in Clusia. In addition, we provide evidence that constitutive CAM is an adaptation to year-long water deficits, whereas facultative CAM appears to be more important for surviving acute dry seasons. Finally, we find that the other leaf traits tested did not correlate with environmental precipitation, suggesting that the reduced transpirational rates associated with CAM obviate the need to adapt the TLPΨ and hydrenchyma depth in this genus. By identifying physiological traits more common in drier environments, it is possible to understand the ways in which tropical trees have adapted to deal with drought. By analysing a genus from Central and South America, we were able to test if it is more beneficial to prevent or tolerate water loss. Our results show that preventing water loss has a greater benefit to living in drier niches, which has implications for the ways in which future climates will affect tropical flora. [ABSTRACT FROM AUTHOR]

Main conclusion: Leaf surfaces of Dracaena draco are wettable and can absorb water. The thick, basal leaf part could act as a water reservoir that changes in volume with plant hydration. Rosettes of leaves of Dracaena draco play an important role in directing fog water through leaf axils into the stem tissues, where it can be stored for further use. However, how water is intercepted and collected by the leaves remains unclear, especially since leaf blade surfaces are considered hydrophobic. Based on the observations of D. draco individuals growing in Spain and in glasshouse conditions in Poland, we hypothesised that their long leaves (~ 70 cm) are able to absorb water along the whole leaf blade, but leaf age affects this process. We used water droplet contact angle measurements, anatomical analyses of leaf cross sections along the age gradient and dye tracer experiments to test this hypothesis. The data showed that the leaf surfaces of D. draco are wettable. In general, the mature leaves of the rosette are more wettable than the young ones. Water can be absorbed both through the adaxial and abaxial surfaces. The hydrenchyma is not uniformly distributed along the leaf, it is especially abundant towards the leaf base where it forms a massive water reservoir, which changes in volume depending on plant water status. The results of these studies shed light on the role of rosettes in water absorption by D. draco, and broaden our understanding of the functioning of this vulnerable species. [ABSTRACT FROM AUTHOR]

Plants have evolved a multitude of adaptations to survive extreme conditions. Succulent plants have the capacity to tolerate periodically dry environments, due to their ability to retain water in a specialized tissue, termed hydrenchyma. Cell wall polysaccharides are important components of water storage in hydrenchyma cells. However, the role of the cell wall and its polysaccharide composition in relation to drought resistance of succulent plants are unknown. We investigate the drought response of leaf‐succulent Aloe (Asphodelaceae) species using a combination of histological microscopy, quantification of water content, and comprehensive microarray polymer profiling. We observed a previously unreported mode of polysaccharide and cell wall structural dynamics triggered by water shortage. Microscopical analysis of the hydrenchyma cell walls revealed highly regular folding patterns indicative of predetermined cell wall mechanics in the remobilization of stored water and the possible role of homogalacturonan in this process. The in situ distribution of mannans in distinct intracellular compartments during drought, for storage, and apparent upregulation of pectins, imparting flexibility to the cell wall, facilitate elaborate cell wall folding during drought stress. We conclude that cell wall polysaccharide composition plays an important role in water storage and drought response in Aloe. This paper highlights the significance of structured cell wall folding in the drought‐stressed hydrenchyma tissue of Aloe helenae and Aloe vera. Dynamic changes in cell wall polysaccharide composition, especially mannan polymers, reveal a potential mechanism for plant leaf succulence. [ABSTRACT FROM AUTHOR]

• First report of a C4 leaf-succulent grass (Poaceae). • Reports of leaf succulence in C3 grasses reviewed. • First report of a C4 grass that is capable of undergoing CAM photosynthesis. Leaf succulence is considered an adaptation to drought and salt stress, and it is often correlated with CAM photosynthesis. Although grasses often grow in arid and salty environments, leaf succulence (in the form of hydrenchyma) has only previously been reported in one C 3 grass. Leaf succulence is reported here for the first time in the Southeast Asian C 4 grass Spinifex littoreus, according to anatomical, water content, saturated water content, and mesophyll succulence indices. Because succulence and CAM are highly correlated, diel leaf acidity and photosynthetic parameters were measured to determine whether CAM occurs in S. littoreus in different coastal regions of Taiwan. In situ diel acidity fluctuations and nighttime stomatal closure indicate CAM-cycling in this grass. This rare form of intermediacy (C 4 /CAM-cycling) has only previously been reported in Portulaca. The results of this study comprise the first report of any grass with CAM photosynthesis of any kind. Spinifex littoreus may provide an important model, in addition to Portulaca, for studying the regulation and evolutionary history of C 4 and CAM photosynthesis, and the finding of CAM biochemistry in a grass might also prove to be of special value for experimental breeding programs for improving drought and salt tolerance in cereal crops. [ABSTRACT FROM AUTHOR]

Abstract: Leaf succulence is common among drought-adapted plants, including many tropical and subtropical epiphytic species. A prominent anatomical feature of many such succulent leaves is a clear, water-storing tissue often referred to as “hydrenchyma” (water-storage parenchyma). Functionally, hydrenchyma appears to store water for use by the leaf during drought. Although this has been confirmed in several laboratory studies, field studies linking the amount of hydrenchyma in plants with availability of water in their environment are lacking. In this study, the relative amount of leaf hydrenchyma in one of the most widely distributed epiphytes in Taiwan, Pyrrosia lanceolata, was measured in plants growing along a gradient of annual mean precipitation from 2048 to 3688mm. In addition, because Pyrrosia lanceolata is a Crassulacean acid metabolism (CAM) plant, the amount of CAM activity was also examined in plants along the gradient. At each of seven sites along the precipitation gradient, leaves were collected, and, using thin mid-leaf slices, the relative areas of the leaf cross-sections occupied by hydrenchyma were determined. CAM, measured as diel changes in leaf acidity, was measured in plants from each site in the field, after 3 days of water-saturation in the greenhouse, and also after 14 days without water in the greenhouse. Regressions of relative hydrenchyma with ten environmental variables in the dry season revealed that the amount of hydrenchyma was significantly and positively correlated with monthly mean number of rainless days, monthly mean number of days with daily mean temperature over 30°C, and monthly mean temperature. During the wet season, relative hydrenchyma area correlated only with the amount of cloud cover, and the correlation was negative. All plants at all sites exhibited CAM acid fluctuations in the field, under water-saturated conditions, and after desiccation. The largest nocturnal acid accumulations were found when plants were well-hydrated in the field and in the greenhouse, although evidence of drought-induced elevations of CAM was found at the drier sites. The results of this study indicate that the amount of leaf hydrenchyma was greatest in areas with warmer, drier environments. Also, drought-induced elevation of CAM activity occurred in plants from drier sites. This may help to explain the wide range of environments inhabited by this epiphytic fern in Taiwan. [Copyright &y& Elsevier]

An omni-directional fibre optic microprobe was used to measure the quantity and quality of light within the leaves of six succulents having epidermal windows, three species having a subterranean growth habit (Haworthia truncata, Lithops olivacea, and Opthalmophyllum longum) and three growing above ground (Peperomia dolabriformis, P. graveolens, and the sprawling vine Senecio rowleyanus). Although light levels at most locations inside the leaves of all species were high, near those incident on the window surfaces, light levels inside the leaves of the two species of Peperomia often greatly exceeded incident light levels, indicating considerable light scattering and focusing by the leaf tissue. The spectral quality of light inside the leaves of all taxa reflected the absorption properties of chlorophyll, with most of the photons in the green wavelengths. Light quality and quantity inside the leaves did not correlate with the growth habit of the plants, the size of the window (as a proportion of the total leaf area), or location inside the leaf, although light levels generally declined and wavelengths increased deeper in the leaves. Application of reflective tape to the windows reduced internal light levels in L. olivacea and S. rowleyanus, although reductions were not always statistically significant. Although light levels throughout the leaves of P. graveolens were substantially and significantly reduced as a result of the application of reflective tape to its windows, the light levels even at the basal chlorenchyma on the abaxial side of the leaf remained high. In all species investigated, the levels of near-infrared radiation inside the leaves were surprisingly high, yet also declined deeper inside the succulent leaves. This near-infrared radiation may add to the heat load of these plants. Furthermore, application of reflective tape to the windows also reduced the amount of near-infrared radiation inside the leaves of the three succulents examined. These results led to a novel, testable hypothesis that may help to explain previous findings that application of reflective tape to the windows of the leaves of these succulents did not effect a reduction in photosynthetic activity. [ABSTRACT FROM PUBLISHER]

• Drought promotes changes in water status and photosynthesis of tank-bromeliads. • Tank bromeliads exhibited decreased Stomatal conductance during the dry season. • More succulent tank-bromeliads kept their stomata open during the dry season. • Seasonal drought promotes photo-inhibition in tank-bromeliads from Campo Rupestre. • Drought determines convergent physiological response in CAM and C 3 tank-bromeliads. The Campo Rupestre (CR) harbors a diversified flora including both C 3 and CAM tank-bromeliads growing side by side. This scenario facilitates the investigation of whether different species of tank-bromeliads possess convergent physiological responses to drought with regard to their different water-use strategies. To determine the drought response of tank-bromeliads we evaluated seasonal variation in titratable acidity, stomatal conductance (g s), chlorophyll fluorescence, leaf water content (LWC), and pigment content of the CAM species Aechmea nudicaulis and Neoregelia bahiana and the C 3 species Vriesea minarum. A decrease in g s was observed in the dry season for plants of both types of photosynthetic pathways, which accompanied a reduction in LWC and a decrease in tissue acidity for the CAM species. Vriesea minarum presented a thinner hydrenchyma and stronger stomatal restriction in the dry season compared to the CAM species. Irrespective of photosynthetic pathway, drought led to a decrease in total chlorophyll and the Chl a :Chl b ratio and an increase in carotenoid content, but these changes were not sufficient to prevent photoinhibition. These results indicate that water and light stress during the dry season promoted a convergence of responses in gas-exchange and PSII damage in the studied co-occurring C 3 and CAM tank-bromeliads of CR. [ABSTRACT FROM AUTHOR]

• Relationships between leaf succulence and CAM was evaluated in 10 Sansevieria species. • CAM correlated negatively with leaf thickness and leaf hydrenchyma/chlorenchyma ratio. • CAM correlated negatively with leaf water content, if based on fresh but not dry mass. • CAM was not correlated with "mesophyll succulence" or leaf chlorophyll concentration. • CAM and succulence arose multiple times in the genus Sansevieria. Relationships between different measures of succulence and Crassulacean acid metabolism (CAM; defined here as nocturnal increases in tissue acidity) were investigated in leaves of ten species of Sansevieria under greenhouse conditions. CAM was found in seven of the ten species investigated, and CAM correlated negatively with leaf thickness and leaf hydrenchyma/chlorenchyma ratio. Similarly, CAM correlated negatively with leaf water content, but only when expressed on a fresh mass basis. CAM was not correlated with "mesophyll succulence", but weakly with leaf chlorophyll concentration. These results indicate that CAM is associated more with "all-cell succulence" and not with the amount of leaf hydrenchyma in the genus Sansevieria. The findings of this study emphasize the importance of defining the nature of "leaf succulence" in studies of photosynthetic pathways and leaf morphology. Evidence is also provided that CAM and succulence arose multiple times in the genus Sansevieria. [ABSTRACT FROM AUTHOR]