Is desiccation tolerance and avoidance reflected in xylem and phloem anatomy of two coexisting arid-zone coniferous trees?

Plants close their stomata during drought to avoid excessive water loss, but species differ in respect to the drought severity at which stomata close. The stomatal closure point is related to xylem anatomy and vulnerability to embolism, but it also has implications for phloem transport and possibly phloem anatomy to allow sugar transport at low water potentials. Desiccation-tolerant plants that close their stomata at severe drought should have smaller xylem conduits and/or fewer and smaller interconduit pits to reduce vulnerability to embolism but more phloem tissue and larger phloem conduits compared with plants that avoid desiccation. These anatomical differences could be expected to increase in response to long-term reduction in precipitation. To test these hypotheses, we used tridimensional synchroton X-ray microtomograph and light microscope imaging of combined xylem and phloem tissues of 2 coniferous species: one-seed juniper (Juniperus monosperma) and piñon pine (Pinus edulis) subjected to precipitation manipulation treatments. These species show different xylem vulnerability to embolism, contrasting desiccation tolerance, and stomatal closure points. Our results support the hypothesis that desiccation tolerant plants require higher phloem transport capacity than desiccation avoiding plants, but this can be gained through various anatomical adaptations in addition to changing conduit or tissue size.

Juniper wood structure under the microscope

The investigations confirm the physicochemical nature of the structure and self-assembly of wood substance and endorse its application in plant species. The characteristic morphological features, ultra-microstructure, and submolecular structure of coniferous wood matrix using junipers as the representative tree were investigated by scanning electron (SEM) and atomic-force microscopy (AFM). Novel results on the specific composition and cell wall structure features of the common juniper (Juniperus Communis L.) were obtained. These data confirm the possibility of considering the wood substance as a nanobiocomposite. The cellulose nanofibrils (20-50 nm) and globular-shaped lignin-carbohydrate structures (diameter of 5-60 nm) form the base of such a nanobiocomposite.

Microspore development of three coniferous species: affinity of nuclei for flavonoids

The nuclear localization of blue-staining flavanols was investigated histochemically throughout microsporogenesis in yellow cypress (Callitropsis nootkatensis (D. Don) Oerst., formerly Cupressus nootkatensis), juniper (Juniperus communis L.) and yew (Taxus baccata L.). During meiotic development, both the cytoplasm and nuclei of microspores of all species contained varying amounts of flavanols; however, the flavanols were largely confined to the nuclei in microspores just released from tetrads. Quantification by HPLC analysis indicated that, in all species, catechin and epicatechin were the dominant nuclear flavanols. At the early free microspore stage, the nuclear flavanols were barely detectable in all species, but they increased fivefold on incubation in the presence of 0.1 mM benzylaminopurine (BA) or zeatin. Histochemical studies revealed that, in addition to non-fluorescing flavanols, microspores contained yellow-fluorescing flavonoids, which yielded a distinct HPLC flavonoid profile for each species. In yellow cypress, the hydrolyzed flavonoids were identified as quercetin, apigenin, kaempferol and luteolin, whereas only quercetin and myricetin were found in microspores of juniper and in anthers of yew. Application of a UV-VIS titration technique revealed that the aglycone quercetin seems to interact more strongly with histone H3 than either glycoside rutin or kaempferol.