Structural deviations in secondary phloem of young shoots of Spiraea beauverdiana near magma volcanoes

We performed a comparative analysis of the internal structure of the secondary phloem of one, two and three-year-old stems of Spiraea beauverdiana growing in extreme conditions of solfataric fields of Golovnin Volcano caldera and Mendeleyev Volcano and in normal conditions. The combination of environmental factors in conditions of solfataric activity, such as high temperatures in the soil and in the near-surface air, as well as saturation with gases toxic to plants, rare elements accumulating in the nearby substrate, and lack of soil moisture, interfere with normal phellogen and cambium activity. Deviations from the normal structure involve changes in the following parameters of the internal structure of a year-old stem of S. beauverdiana. Secondary phloem parameters in the studied habitats are normal, except for the length of the segments of sieve tubes, the height of single-row rays, the length of parenchymal girder; these are shorter in S. beauverdiana stems from volcanos. At two and three years of age in volcanic conditions we see reduction in the width of the secondary phloem (both conductive and non-conductive) and the diameter of the segments of sieve tubes. In samples from Golovnin Volcano we see reduction in tangential diameter, while in the samples from Mendeleyev Volcano it’s the radial diameter. We also see reduction in the height of multiple-row rays. At that age we see changes in the structure of the radial parenchyma; namely, we find no double-row rays in samples from Golovnin Volcano caldera. One of the signs of impact of volcanic activity on the bark structure is development of non-specific anomalies in the internal structure of the S. beauverdiana bark, namely, in the outer bark, or in deeper levels, such as the secondary phloem. That causes sclerification and dilatation of parenchyma, and multiple layers in some tissues.

Seasonal changes in cambium activity from active to dormant stage affect the formation of secondary xylem in Pinus tabulaeformis Carr

Understanding the changing patterns of vascular cambium during seasonal cycles is crucial to reveal the mechanisms that control cambium activity and wood formation, but this area has been underexplored, especially in conifers. Here, we quantified the changing cellular morphology patterns of cambial zones during the active, transition and dormant stages. With the help of toluidine blue and periodic acid Schiff staining to visualize cell walls and identify their constituents, we observed decreasing cambial cell layers, thickening of newly formed xylem cell walls and increased polysaccharide granules in phloem from June to the following March over the course of our collecting period. Pectin immunofluorescence showed that dormant stage cambium can produce highly abundant de-esterified homogalacturonan and (1–4)-β-D-galactan epitopes, while active cambium can strong accumulate high methylesterified homogalacturonan. Calcofluor white staining and confocal Raman spectroscopy analysis revealed regular changes in the chemical composition of cell walls, such as relative lower cellulose deposition in transition stage in vascular cambium, and higher lignin accumulation was found in dormant stage in secondary xylem. Moreover, RT-qPCR analysis suggested that various IAA (Aux/IAA protein), CesA, CslA and HDZ genes, as well as NAC, PME3 and PME4, may be involved in cambium activities and secondary xylem formation. Taken together, these findings provide new information about cambium activity and cell differentiation in the formation, structure, and chemistry in conifers during the active–dormant transition.

Xylogenesis, photosynthesis and respiration of Scots pine trees growing in Eastern Siberia (Russia)

Key message The relationships between cambium activity, cell wall biomass accumulation and photosynthesis/ respiration in Scots pine trees, growing in Eastern Siberia (Russia), change during the season in dependence on combination of summer-weather conditions. The wood formation in tree trunks depends on photosynthesis and respiration and the each of the processes are under the effect of external factors. Each factor effects the growth in combination with other factors and the change in any of these factors leads to strengthen or to weaken of the growth processes in tree. We investigated the formation of xylem and phloem cells by cambium, cell wall biomass accumulation in Scots pine trees, growing in Eastern Siberia (Russia), in dependence on the productivity of photosynthesis and energy cost in separate seasonal periods in the years with opposite summer-weather conditions. The cores extracted throughout 10-day from the stems of 10 trees during the seasons were used to determine the number of cells with different development degree and their morphological parameters. Cambium activity and cell wall biomass accumulated on the separate stages of annual ring wood formation and their connections with the photosynthetic productivity of crown and the level of stem respiration photosynthesis were assessed. The activity of cambial cell division into xylem or phloem sides in separate periods depended on the combination of temperature/precipitation and on the connection with photosynthesis and respiration. The dynamics of biomass accumulation was bimodal with the maximums in June (earlywood development) and mainly in August (development of thick-wall late tracheids), what was due to the combination of optimal temperature and the moisture in the stem tissues. The variation in the external factors changed the balance between the incoming of photoassimilates and the energy cost causing a competition for photosynthesis products and, as a consequence, photoassimilates were used not only for cell-wall biomass synthesis and but also for their reservation of spare substances in the form of starch. The data is useful to understanding of internal processes of wood annual ring formation in pine trees.

Morphoanatomy of three Indigofera species (Leguminosae-Papilionoideae) in Java, Indonesia

Fugarasti H, Muzzazinah, Ramli M. 2020. Morphoanatomy of three Indigofera species (Leguminosae-Papilionoideae) in Java Indonesia. Biodiversitas 21: 5531-5538. This study aimed to explore the morphological and detailed anatomical features of the stems, leaves, and roots from three Indonesian Indigofera species. Morphological-anatomical studies of three Indonesian Indigofera species were carried out using embedded microscopic preparations. The anatomical characters of the specimens were observed using a compound optical microscope with magnification 40x, 100x, and 400x. The observation showed the anatomical cross-section of I. tinctoria stem was rectangular, I. suffruticosa was hexagonal, and I. arrecta was rounded. The tissue structures of Indigofera species, from the outside layer, were the epidermis, thin cortex, secondary phloem (narrow or wide), thick secondary xylem, and conspicuous pith in the middle. Whilst, the corner of I. suffruticosa stem contained thick collenchyma. The vascular bundles were the open collateral. The leaves of Indigofera species are made up of the upper epidermis, mesophyll (palisade parenchyma, spongy parenchyma), and the lower epidermis. The vascular bundles were located in the middle, with five or six segments of the xylem elements and small groups of phloem elements, all in the parallel lines. The primary stele type of the roots is actinostele, cambium activity pushed him aside. The vascular bundle of the roots consisted of a dense and tight secondary xylem composed of thick-walled circular vessels (mostly tightly arranged). Data about the morphoanatomy structure of three Indonesian Indigofera species could complement the novelty of the morpho-anatomy information records obtained by previous researchers.

A novel pathway controlling cambium initiation and - activity via cytokinin biosynthesis in Arabidopsis

Plant secondary growth, also referred to as wood formation, includes the production of secondary xylem, which is derived from meristematic cambium cells embedded in vascular tissues. Despite the importance of secondary xylem in plant growth and wood formation, the molecular mechanism of secondary growth is not yet well understood. Here we identified an important role for the Arabidopsis thaliana (Arabidopsis) AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED 15 (AHL15) gene, encoding for a putative transcriptional regulator, in controlling vascular cambium activity and secondary xylem formation. Secondary xylem development was significantly reduced in inflorescence stems of the Arabidopsis ahl15 loss-of-function mutant, whereas AHL15 overexpression led to extensive secondary xylem formation. AHL15 expression under a vascular meristem-specific promoter also enhanced the amount of interfascicular secondary xylem. Moreover, AHL15 appeared to be required for the enhanced secondary xylem formation in the Arabidopsis double loss-of-function mutant of the SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1) and FRUITFULL (FUL) genes. A well-known central regulator of cambial activity is the plant hormone cytokinin. We showed that the expression of two cytokinin biosynthesis genes (ISOPENTENYL TRANSERASE (IPT) 3 and 7) is decreased in ahl15 loss-of-function mutant stems, whereas the secondary xylem deficiency in these mutant stems can be resorted by cambium-specific expression of the Agrobacterium tumefaciens IPT gene, indicating that AHL15 acts through the cytokinin pathway. These findings support a model whereby AHL15 acts as a central factor inducing vascular cambium activity downstream of SOC1 and FUL and upstream of IPT3, IPT7 and LOG4, LOG5 governing the rate of secondary xylem formation in Arabidopsis inflorescence stems.

Cytokinin-promoted secondary growth and nutrient storage in the perennial stem zone of Arabis alpina

Perennial plants maintain their life span through several growth seasons. Arabis alpina serves as model Brassicaceae species to study perennial traits. A. alpina lateral stems have a proximal vegetative zone with a dormant bud zone, and a distal senescing seed-producing inflorescence zone. We addressed the questions of how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage, and which signals affect the zonation. We found that the vegetative zone exhibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and sequestration of storage compounds. The inflorescence zone with only primary growth, termed annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application, cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis cytokinin-related genes represented enriched gene ontology terms and were expressed at higher level in PZ than AZ. Thus, A. alpina uses primarily the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth.HighlightArabis alpina stems have a perennial zone with secondary growth, where cambium and derivatives store high-molecular weight compounds independent of vernalization. Cytokinins are signals for the perennial secondary growth zone.