Understanding the long-term storage sink.

Similar to short-term starch storage in the chloroplasts of the leaves that serves to buffer growth of organs from carbohydrate shortages due to diurnal patterns of photosynthesis related to daily patterns of light and darkness, trees also have long-term storage capacity to enable them to supply the minimal respiratory needs of tissues during the winter and resume growth in the spring when trees are still leafless. This long-term storage of carbohydrates and some minerals occurs primarily in the phloem and xylem tissue of the branches, trunk and roots. While active phloem tissue has higher concentrations of stored carbohydrates than xylem tissue, the mass of active xylem storage tissue is many times the mass of the active phloem tissue. Thus, xylem tissue comprises the largest storage compartment of temperate deciduous fruit trees. This chapter deals with understanding the long-term storage sink in fruit trees.

Cold Hardiness of Select Apple Cider Cultivars in Canada

There is increasing interest in growing European origin apple cultivars for the production of hard cider in Canada; however, little is known about their winter hardiness. Eleven promising cider cultivars were evaluated for cold hardiness over two consecutive winters and compared with the winter tender cultivar 'Golden Delicious’. Sections of the current season's dormant shoots were frozen in a series of test temperatures ranging from -20°C to -40°C in a programmable freezer. Xylem tissue browning ratings were used to assess injury after thawing. The temperature of incipient damage (TID), the warmest temperature at which 1-yr-old shoot segments begin to show injury, was obtained from tissue browning curves using non-linear regression. TID varied significantly among cultivars and between sampling years. Overall, the cultivars could be classified according to relative winter hardiness as follows: Ashmead’s Kernel, Bramley’s Seedling (very tender) < Calville Blanc d’Hiver, Porter’s Perfection, Bulmer’s Norman (intermediate) < Crimson Crisp, GoldRush, Golden Delicious, Enterprise, Yarlington Mill, Enterprise (hardy) < Golden Russet (hardy). These data indicate nearly a 10oC range in winter hardiness amongst the 11 cultivars studied, depending on the sampling date. Ashmead’s Kernel and Bramley’s Seedling appear to be particularly winter tender, whereas Bulmer's Norman, Porter's Perfection, and Calville Blanc d'Hiver demonstrated less hardiness during three of the four sampling dates. Based upon these findings, it would be prudent to consult long-term climate normals and consider the frequency of extreme weather events for potential susceptibility to winter injury, particularly prior to establishing more injury-prone cultivars.

Artifactual lipid coatings on intervessel pit membranes in dried xylem tissues of some angiosperms

Intervessel pit membranes are recognized as key structures for influencing water flow/embolism resistance. The mechanisms remain largely unclear owing to difficulties in examining them intact in nature. This study investigates ethanol-extractable pit membrane incrustations (PMIs), which were previously reported in certain angiosperms and may affect their water conduction. The presence of PMIs was determined for 40 angiosperms by field-emission scanning electron microscopy (FE-SEM). Candidate components of PMIs were determined by chemical analyses of wood extracts, and their distributions in the xylem were examined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Cryo-TOF-SIMS and cryo-FE-SEM were also performed to clarify the native distribution of PMIs. PMIs were observed in 11 species. Some of them were categorized as fat trees, which are known to store abundant lipids. Tilia japonica sapwood displaying PMIs contained large amounts of lipids, which were distributed in the dried xylem tissue, consistent with the distribution of the PMIs. In the frozen samples of T. japonica, however, the distributions were restricted to the parenchyma. In conclusion, PMIs consist of an artifactual coating of lipids originated from the parenchyma in dried samples at room temperature. Researchers performing surface analyses of plant cell walls should take strong precautions against such self-coating by these intrinsic chemicals.

Mechanisms of xylem hydraulic recovery after drought in Eucalyptus saligna

The mechanisms by which woody plants recover xylem hydraulic capacity after drought stress are not well understood, particularly with regard to the role of embolism refilling. We evaluated the recovery of xylem hydraulic capacity in young Eucalyptus saligna plants exposed to cycles of drought stress and rewatering. Plants were exposed to moderate and severe drought stress treatments, with recovery monitored at time intervals from 24 hrs to 6 months after rewatering. The percentage loss of xylem vessels due to embolism (PLV) was quantified at each time point using micro-computed tomography with stem water potential (Ψx) and whole plant transpiration (Eplant) measured prior to scans. Plants exposed to severe drought stress suffered high levels of embolism (47.38 ± 10.97 % PLV) and almost complete canopy loss. No evidence of embolism refilling was observed at 24 hrs, one week, or three weeks after rewatering despite rapid recovery in Ψx. Recovery of hydraulic capacity was achieved over a 6-month period by growth of new xylem tissue, with canopy leaf area and Eplant recovering over the same period. These findings indicate that E. saligna recovers slowly from severe drought stress, with potential for embolism to persist in the xylem for many months after rainfall.

Nutrient-Poor Breeding Substrates of Ambrosia Beetles Are Enriched With Biologically Important Elements

Fungus-farming within galleries in the xylem of trees has evolved independently in at least twelve lineages of weevils (Curculionidae: Scolytinae, Platypodinae) and one lineage of ship-timber beetles (Lymexylidae). Jointly these are termed ambrosia beetles because they actively cultivate nutritional “ambrosia fungi” as their main source of food. The beetles are obligately dependent on their ambrosia fungi as they provide them a broad range of essential nutrients ensuring their survival in an extremely nutrient-poor environment. While xylem is rich in carbon (C) and hydrogen (H), various elements essential for fungal and beetle growth, such as nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn) are extremely low in concentration. Currently it remains untested how both ambrosia beetles and their fungi meet their nutritional requirements in this habitat. Here, we aimed to determine for the first time if galleries of ambrosia beetles are generally enriched with elements that are rare in uncolonized xylem tissue and whether these nutrients are translocated to the galleries from the xylem by the fungal associates. To do so, we examined natural galleries of three ambrosia beetle species from three independently evolved farming lineages, Xyleborinus saxesenii (Scolytinae: Xyleborini), Trypodendron lineatum (Scolytinae: Xyloterini) and Elateroides dermestoides (Lymexylidae), that cultivate unrelated ambrosia fungi in the ascomycete orders Ophiostomatales, Microascales, and Saccharomycetales, respectively. Several elements, in particular Ca, N, P, K, Mg, Mn, and S, were present in high concentrations within the beetles’ galleries but available in only very low concentrations in the surrounding xylem. The concentration of elements was generally highest with X. saxesenii, followed by T. lineatum and E. dermestoides, which positively correlates with the degree of sociality and productivity of brood per gallery. We propose that the ambrosia fungal mutualists are translocating essential elements through their hyphae from the xylem to fruiting structures they form on gallery walls. Moreover, the extremely strong enrichment observed suggests recycling of these elements from the feces of the insects, where bacteria and yeasts might play a role.

MACROSCOPIC AND MICROSCOPIC CHARACTERIZATION OF RAW HERBAL DRUG MAMAJJAKA [ENICOSTEMA AXILLARE SUBSP. LITTORALE (BLUME) A. RAYNAL]

Enicostema axillare subsp. littorale (Blume) A. Raynal belonging to the family Gentianaceae, known as Mamajjaka in Ayurveda, is a medicinally important plant used to treat Madhumeha or diabetes mellitus. The plant has high demand in the Indian herbal drug market and is used in various herbal preparations. The present study was conducted to characterize dried herbal samples of E. axillare subsp. littorale botanically. The botanical characterization involved macroscopic and microscopic studies on the herbal samples. Qualitative and quantitative microscopic characters were studied, and digital photographs of transverse sections (T.S.) and powder cell structures were taken. In T.S. of the stem, the vascular region characters such as the appearance of xylem tissue, lumen diameter of xylem vessels, and powder characters of aerial parts such as abundance and size of starch grains, prismatic crystals, presence of stomata, and trichomes were studied. The characters identified in the present study can be used to identify the herbal samples of E. axillare subsp. littorale in fresh as well as in dry forms.

Engineering and characterization of gymnosperm sapwood toward enabling the design of water filtration devices

Naturally-occurring membranes in the xylem tissue of gymnosperm sapwood enable its use as an abundantly-available material to construct filters, with potential to facilitate access to safe drinking water in resource-constrained settings. However, the material’s behavior as a filter is poorly understood, and challenges such as short shelf life have not been addressed. Here, we characterize the operational attributes of xylem filters and show that the material exhibits a highly non-linear dependence of flow resistance on thickness upon drying, and a tendency for self-blocking. We develop guidelines for the design and fabrication of xylem filters, demonstrate gravity-operated filters with shelf life >2 years, and show that the filters can provide >3 log removal of E. coli, MS-2 phage, and rotavirus from synthetic test waters and coliform bacteria from contaminated spring, tap, and ground waters. Through interviews and workshops in India, we use a user-centric approach to design a prototype filtration device with daily- to weekly-replaceable xylem filters, and uncover indicators of social acceptance of xylem as a natural water filter. Our work enhances the understanding of xylem as a filtration material, and opens opportunities for engineering a diverse range of low-cost, biodegradable xylem-based filtration products on a global scale.

Aggressiveness of Spanish isolates of Xylella fastidiosa to almond plants of different cultivars under greenhouse conditions

The aggressiveness of Spanish isolates of X. fastidiosa, representing different sequence types, were studied in almond plants of several cultivars by means of the dynamics of the population levels and symptoms, colonization and spread, and dose-response relationships. Pathogen dynamics in almond plants under greenhouse conditions showed doubling times of 2.1 to 2.5 days during the exponential growth phase, with a maximum population size around 35 dpi. A differential pattern in population dynamics was observed between sap and xylem tissue after the exponential growth, as population levels in the xylem tissue remained stable while viable cells in sap decreased. Population levels were higher in two upwards zones than in downwards zones, with respect to the inoculation area. The first symptoms were observed between 20 and 60 dpi, and disease severity increased over time at doubling times of 30 days, with a maximum observed at 120 dpi. Strains tested showed differences in population levels in the cultivars studied and were able to spread with different intensity from contaminated plant parts to new growing shoots after pruning. Two almond isolates showed a different performance in dose-response relationships when inoculated in Avijor cultivar. While IVIA 5387.2 reached higher population levels but showed high ED50 and MID values, IVIA 5901.2 showed low population levels as well as low ED50 and MID values. This study raises implications for the epidemiology of X. fastidiosa in almond crops, estimating doubling times of the pathogen in planta and of symptoms development, as well as showing differential aggressiveness between strains.

Stem canker caused by Phomopsis spp. induces changes in polyamine levels and chlorophyll fluorescence parameters in pecan leaves

Pecan plants are attacked by the fungus Phomopsis spp. that causes stem canker, a serious and emerging disease in commercial orchards. Stem canker, which has been reported in several countries, negatively affects tree canopy health, eventually leading to production losses. The purpose of this study was to inquire into the physiology of pecan plants under stem canker attack by Phomopsis spp. To this end, pecan plants were inoculated with an isolate of Phomopsis spp. and several parameters, such as polyamines, proline, sugars, starch, chlorophyll fluorescence and canopy temperature were analysed. Under artificial inoculation, a high disease incidence was observed with symptoms similar to those in plants showing stem canker under field conditions. Furthermore, the infected stem showed dead tissue with brown necrotic discolouration in the xylem tissue. The free polyamines putrescine, spermidine, and spermine were detected and their levels decreased as leaves aged in the infected plants with respect to the controls. Chlorophyll fluorescence parameters, such as Sm, ψEO, and QbRC decreased under plant infection and therefore the K-band increased. Canopy temperature and proline content increased in the infected plants with respect to the controls while sugar content decreased. These data suggest that stem canker caused by Phomopsis spp. induces physiological changes that are similar to those observed in plants under drought stress. To our knowledge, this is the first study that documents the physiological and biochemical effects derived from pecan-Phomopsis interaction.

A user manual to measure gas diffusion kinetics in plants: Pneumatron construction, operation and data analysis

The Pneumatron device presented measures gas diffusion kinetics in the xylem of plants. The device provides an easy, low-cost, and powerful tool for research on plant water relations. Here, we describe in detail how to construct and operate this device to estimate xylem vulnerability to embolism, and how to analyse pneumatic data. Simple and more elaborated ways of constructing a Pneumatron are shown, either using wires, a breadboard, or a printed circuit board. The instrument is based on an open-source hardware and software system, which allows users to operate it in an automated or semi-automated way. A step-by-step manual and a troubleshooting section are provided. An excel spreadsheet and an R-script are also presented for fast and easy data analysis. This manual should help new users to avoid common mistakes, especially regarding stable measurements of the minimum and maximum amount of gas that can be discharged from xylem tissue.